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Black_Moons
01-21-2010, 07:45 AM
Hi, Iv read that 0.614*pitch is the recommended thread depth for single point threading.. but is that for 'proper' threadforms or sharply pointed turning tools? What would it be for sharply pointed turning tools if its for proper threadforms?

Glenn Wegman
01-21-2010, 07:54 AM
"Proper" thread form for UN does not use a sharp pointed tool.

That's where it gets a little sticky...

"Proper" thread depth is determined by the pitch diameter measurement, not the minor diameter, or depth from major diameter.

Depth calculations are sometimes handy to get an idea of how deep to cut before you start measuring with wires etc.

Black_Moons
01-21-2010, 07:56 AM
Unfortualy I don't feel like grinding a new tool for every TPI range, so a select few tools will have to do, hence im wondering what kinda range there is beween 'ideal' threadform and pointed..
My tools are not totaly pointed, but likey moreso then the TPI would call for. As less pointed.. doesnt work very well.

Glenn Wegman
01-21-2010, 08:05 AM
This might work for what you want to do.

http://img.photobucket.com/albums/v647/Fighter1/ThreadChart.jpg

Vee-Form tool= sharp V tool

NF or National Form tool= tool with proper tip truncation.

hwingo
01-21-2010, 08:23 AM
This might work for what you want to do.

http://img.photobucket.com/albums/v647/Fighter1/ThreadChart.jpg

Vee-Form tool= sharp V tool

NF or National Form tool= tool with proper tip truncation.

Really nice chart. Where did you find this chart?

Harold

Glenn Wegman
01-21-2010, 08:38 AM
Harold,

I have no idea, it's been in a file folder with some other charts as long as I can remember.......

hornluv
01-21-2010, 08:47 AM
The sharp tool will work, the standards folks just realized that the point won't last long so they built in some wear clearance. As Glen mentioned though, proper fit is determined by pitch diameter. Machinery's Handbook has a mess of charts giving the tolerances for major, minor, and pitch diameter for the standard and some not-so-standard threads.

EVguru
01-21-2010, 09:19 AM
The sharp tool will work, the standards folks just realized that the point won't last long so they built in some wear clearance. As Glen mentioned though, proper fit is determined by pitch diameter. Machinery's Handbook has a mess of charts giving the tolerances for major, minor, and pitch diameter for the standard and some not-so-standard threads.

The standards people realised that a pointed tool gives a smaller core diameter and induces a stress raiser, both of which weaken the threaded item. In many cases this simply doesn't matter because the thread isn't under any great load.

Carld
01-21-2010, 09:30 AM
I have the same chart Glenn and I got it from a machinist years ago. I posted it here several times and was getting ready to repost it when I saw you had already done so.

I use that chart all the time, it's the first chart I go to when starting to cut a thread. I have found that the Depth of Compound Feed--Single Depth--N.F. Tool column is the most accurate depth to go for. If you cut to about .005" less than the listed number and start using the test nut or measuring with wires the final thread will be close to the number in that column.

That chart is the best thing I have found for single point threading. I know I have used it for over 20 years and have found nothing better.

Also, I too got tired of putting the designated flat on the end of each threading tool for each size and just use a sharp V now with a light stoning of the sides and tip.

hwingo
01-21-2010, 09:51 AM
For certain, that's a good chart to have and it will become a part of my library.

Harold

Video Man
01-21-2010, 01:16 PM
Really nice chart. Where did you find this chart?

Harold
I recognize that, it is from the Atlas / Craftsman Lathe Manual. Notice that this is National Form, iirc this is not the Unified thread series which replaced national form in 1948, the specs are a little different...../video_man

Carld
01-21-2010, 02:20 PM
Yes, but it's still a 60* V and if used with care it works. Remember, charts are sometimes a guide not an exact truth.

Glenn Wegman
01-21-2010, 02:51 PM
The sharp V column would be the same for either.

Forrest Addy
01-21-2010, 03:13 PM
It's always nice to do stuff by the numbers but the way I was taught was a little more casual: cut untll it looks like a thread then stop and gage or measure. It's worked for me for - um - 244 years now or it seems like it.

And Glenn's right. The end of the tool is suppose to have a flat on the tip. There are specific standards of course but you can wing that for non-fussy threads. I use 1/5 to 1/6 pitch for the flat width for external threads and 1/10 to 1/16 for internal. This ensures there wll be no crest/root interferance in the assembled thread. Those little comparator loupes ( http://www.measuringmagnifiers.com/ ) work well even if they are a bit expensive. You put the graticule right on the tool and read the tip width right off the scale. Naturally you have to calculate the depth comp.

The flat at the tip of the threading tool will affect the threading depth. The nice three and four digit numbers shown in the charts represents a theoretical calculation. If you cut the threads using the charts data, you have to compensate for the actual tip flat of the tool you are using then adjust the threading depth you cut to. Stop a few thou short of full depth and check/gage. Don't thread right to calculated depth with a fresh tool. You can always take off a little more but so far cutting tool technology hasn't brought us a "puttin'-on" tool.

Carld
01-21-2010, 03:18 PM
Yes, and that's why I cut short and test to finish size.

Black_Moons
01-21-2010, 03:52 PM
Thank you ever so much for the chart. Exactly what I was looking for. *saves*

Its a weee bit hard to test for size when your threading something for say, your lathes T nut.. or your lathes headstock :)
Course I did learn picking up threads, but I also realise picking up a thread could go wrong.

Glenn Wegman
01-21-2010, 04:12 PM
Get some wires!

Glenn Wegman
01-21-2010, 07:41 PM
So here's UN

http://img.photobucket.com/albums/v647/Fighter1/MHChart-1.jpg

Dr. Rob
01-21-2010, 11:30 PM
And for metric M threads (if i recall correctly) it works out to

infeed = 0.865 x P with a sharp vee tool.

(or maybe it was 0.869? pretty close anyway. Somebody might want to check.)

(edit: Yeah, the cosine of 30 degrees is 0.866, so that makes sense.)

Get you in the ballpark anyway.

So really BlackMoons, there is the answer to your original question. 60 degree sharp vee tool = approx 0.866 x pitch, so your 0.614 must be for a truncated vee tool.

.

mf205i
01-22-2010, 01:13 AM
Many years ago I was having a hard time with threading. I insisted on using those theoretical charts some of you are using and all I got was frustration. I was following a thread on PM and it seemed that due to the many variables involved, most folks trying to adhere to them were in a world of hurt. Then some guy told us one of the best pieces of practical advice I have been given. He said to “Just cut it until it looks like a thread’. If you start at the proper nominal diameter and cut it until the threads-crest look correct, all of the other dimensions will be in line. Sounds simple but it works and I haven’t looked at those damn charts in years. So, for this and all of your other words of wisdom, this is an official Thank You to Mr. Forrest Addy.
Mike

beanbag
01-22-2010, 01:28 AM
The way I deal with a "too sharp" cutting tool is as follows.

1) Thread to the proper depth
2) After the compound is fully advanced... For the next step, advance the coupound MORE, like 5 thou, and move the cross slide BACK by 4.3 or whatever mill it was which results in the threading tool being offset sideways, but not any more forwards. (use geometry for a 30 deg triangle)
3) keep doing this until you have the correct flat at the bottom of the threads

Edit:
3) might be easier to watch the flat at the crests

Glenn Wegman
01-22-2010, 05:58 AM
If you cut it to the "proper depth" to start with, and then "widen" it, it is no longer the proper depth!

The pitch diameter is the governing factor on a thread, not the infeed depth, not the root flat, not the major or minor diameter.


I'm not claiming that every thread has to be perfectto the letter of the law. Especially for home shop stuff.

I'm just suggesting that once you understand what makes a thread a thread rather than a spiral groove, threading becomes very easy and the results will be better.

oldtiffie
01-22-2010, 06:16 AM
These are the best graphical practical, non-academic every-day use for every-day US threads for machining etc. that I've seen and use regularly:

http://i200.photobucket.com/albums/aa294/oldtiffie/Screw_threads/Screw-thread_form7.jpg

The main objective is to have sufficient nut-to-bolt contact on the thread 60 degree flanks and not to contact the radius-ed surfaces at the bottom of the threads.

The radii you cut should be equal to or less than the radii shown.

The gaps at the bottom of the threads are not just "stress-reducers" either as they are intended to catch a lot of the grit that forms in threads and so reduces wear, galling and tight spots.

I agree that in an ideal state - which many HSM and jobbing shops are not - thread wires will be fine - but if and only if all of the following criteria are met:
- the cutting tool faces are straight and sharp to a high degree of accuracy;
- the tool cutting angle is precisely 60 degrees;
- the tool nose radius is accurately curved to a radius not exceeding the radius in the specification.
- the axis of the tool is precisely normal to the work/lathe axis.

Those are even more important if using a thread micrometer.

I don't like the "3 wires" or thread micrometers.

You can buy accurately-made standard nuts at specified fits/clearances from McMaster-Carr (US) and they make it so much easier.

I prefer the "screw to fit" (mating part) method.

It is quite feasible to match the "3-wire" method (which is a hang-over from pre-CAD days) quite well if you have a good CAD system and have a good grasp of geometry and are competent in the use of CAD. "Standard" wires or rods are not required. It will work with one, two, or three wires of any size/s and rods in use need not be the same diameter.

It will be quite adequate for many jobbing shops and HSM shops.

If anyone wants it any better - stay with Machinery's Handbook and your set of 3-wires.

Here is the sketch for external threads:
http://i200.photobucket.com/albums/aa294/oldtiffie/Sketches/3-wire1.jpg

Peter.
01-22-2010, 08:56 AM
Really nice chart. Where did you find this chart?

Harold

It looks very much like a page out of my Atlas manual, though I passed it along with the lathe when I sold it so I can no longer check.

Pete.

EDIT: actually I just remembered I made a pdf of the manual, the page is almost identical:

http://peterrimmer.myby.co.uk/files/atlas10fthreadcutting.pdf

Paul Alciatore
01-22-2010, 10:03 AM
The thing about thread depth when single point cutting is it is NOT always the same. The American Standard shows a 0.25P FLAT as the primary form with a round form as optional. These two will be 0.125P different in depth. At 16 TPI, for example, that is a difference of about 0.0075". That will throw off any thread depth table I have ever seen.

When single point cutting threads, you simply must measure the actual thread using some method that is suitable for the job. For coarse work, a nut and a somewhat loose fit will do. For a thread that only has to mate with a single thread of the opposite gender, you can test/measure with that mating thread. If you need both high precision and multiple pieces, then you need a thread mike or the three wire method or whatever.

Again, the sharper the cutting tool is, the quicker it will wear down at the tip. So a sharp tool will need less depth as the tip wears to a rounded tip when making multiple parts.

But the point is, the thread depth thing is only a starting point, not a final, absolute thing. You really need to measure the thread. That being said, in a production situation where multiple pieces are being made, that measurement may not need to be made on every piece. 5, 10, 100, or more pieces can perhaps be made between measurements, depending or many factors like tolerances and allowances and the actual wear experienced on the tool. Start with a low number and increase it until you know when your situation will start producing out of tolerance parts and then back down a bit.

The Fixer
01-22-2010, 10:54 AM
Just want to mention the reason for the thread root not being pointed is that it is a stress point for cracking...... just as a fillet should be used when turning a shaft to a shoulder.

al

Carld
01-22-2010, 11:03 AM
beanbag, when you widen the V in a thread to make a flat on the bottom your narrowing the actual metal V of the thread. The width of the V cut in the shaft is supposed to be the same width as the metal V left on the shaft. In other words they are equal width to each other.

If you want a flat in the bottom of the V grind it on the tool.

oldtiffie
01-22-2010, 03:38 PM
Just want to mention the reason for the thread root not being pointed is that it is a stress point for cracking...... just as a fillet should be used when turning a shaft to a shoulder.

al

I think its more to do with keeping a good strong edge on the end of the tool.

A radius-ed tool end works much better than one with a flat and two relatively sharp corners - and its easier to grind and keep sharpened.

It also makes for easier manufacture of taps and dies - where stress IS a problem.

If we are getting into the realm of "stress-raisers" we are getting into limit state design (of the bolt/thread) where class of finish is a serious concern.

In that case the threaded items will need to be designed by an Engineer for each specific application as we may be looking at reduction of safety factors that have been incorporated in the standards.

beanbag
01-22-2010, 04:30 PM
I don't claim to know which parameters of the thread profile are most important. However, my point was that if you are trying to make a certain thread profile - such as the one that calls for a root flat of 1/4 P, then cutting with a too sharp nose radius tool, and then cutting only sideways and not deeper, is equivalent to cutting with a tool with a small flat ground on the tip.

Carld
01-22-2010, 06:21 PM
No beanbag, it's not the equivalent of having a flat on the threading tool. If you only cut on the left side of a finished thread to put a flat in the bottom of the V all your doing is reducing the width of the V that is the thread and that will cause the nut to have end play and the pitch diameter will change.

It's not a good way to get a flat, just grind or stone a flat the required width on the tip of the threading tool.

Dr. Rob
01-22-2010, 06:28 PM
Geometry being the way it is, I'm with Beanbag.

Its okay Beanbag. I understand.

.

davidh
01-22-2010, 06:45 PM
This might work for what you want to do.

http://img.photobucket.com/albums/v647/Fighter1/ThreadChart.jpg

Vee-Form tool= sharp V tool

NF or National Form tool= tool with proper tip truncation.

i just cut a 5/16 - 20 thread in a stainless shaft using a PERFECT ground 60 degree cobalt tool. i used the v thread as shown in the shaft and the nut turned on like it was suppose to.. no wiggle, no wrench, just great. . . .

thanks for the chart. . . its now in plastic and will always be used as others have said.

davidh

the PERFECT ground tool was ground on my "Oliver of Adrian Ace Grinder" that i really enjoyed using for something important. . . . .

whitis
01-22-2010, 07:24 PM
I just posted a diagram over on another thread that dealt with putting a radius on the end of a cone. The math, however, would also apply to a thread cutting tool with a tip radius. It also can be used in measuring with thread wires or using round rods to measure V shapes.
http://bbs.homeshopmachinist.net/showpost.php?p=512576&postcount=7

A useful exercise might be to calibrate your threading/fishtail gage. This tells you the distance between the V root of the fish tail gage and the opposite side. Use a large thread wire or other precise round rod and a micrometer. reading-radius-radius/sin(theta) is the distance from the V root to the opposite side of the gage. Write that on the gage. Now, you can easily measure the distance between the tip of all your threading tools (where you touch off) and the theoretical point of the tool, immediately before use. Touch off, then back off by this distance. Or ignore that distance and just set the tool against the fishtail gage against the work, remove the fishtail, and advance by the fishtail calibration number determined above. Fish tail gage must be flat between the tool tip and the axis of the work. The imaginary point of the tool is now "touching" the OD of the work. Then, it doesn't matter what the tip radius is as long as it is within the allowed range from a perfect V and where it starts to adversely affect the flanks of the thread for a particular thread size.

Assuming the OD of the work was turned to the correct size, then advance the cross slide by 7/8H from the OD for radial infeed or the compound by 7/8H/cos(29) for a 29 degree modified flank infeed (spread over multiple passes). Leave just a hair and measure with thread wires or thread micrometer for the finishing pass. Don't forget to divide the error by cos(29degrees) for 29 degree modified flank infeed. If you don't have thread measurement tools, then just finish to the calculated dimension and, if possible, cut a mil or two deeper so you err on the side of a loose thread rather than one that won't fit. Compound angle needs to be set accurately if you are going to calculate the modified flank infeed.

Column 5 of the first (atlas) table is 7/8H and Column 8 is 7/8H/cos(29), so both those numbers are already there. H = pitch/tan(30)/2. pitch = 1/TPI.

Diagram of Unified Thread standard threads, shows what H and 7/8H are all about:
http://en.wikipedia.org/wiki/File:ISO_and_UTS_Thread_Dimensions.svg

The radius on the end of the tool both helps the tool last longer and reduces the stress risers. A unified thread with reasonable number of turns engaged for the material strength will break (http://www.practicalmachinist.com/vb/showpost.php?p=1050158&postcount=8) at the thread root before the threads strip. Thus the stress riser is significant.

Carld
01-22-2010, 07:43 PM
Ok, here's a drawing of what happens when you cut on just the left side of a finished thread.

http://i82.photobucket.com/albums/j276/yeathatshim/thread.jpg

You will notice the finished thread V is on the line of the OD of the thread. Then you can see the line to the left of the correct thread V there is a line that has a wide flat at the bottom and a NARROWER V with an OD that is less than the correct OD.

Has this helped you to see what happens when you cut the left side of a finished thread to get a flat on the minor diameter of the thread?

Two things happen, the pitch diameter is wrong and the OD of the thread is undersize. The thread is now worthless.

beanbag
01-22-2010, 09:18 PM
Ok, here's a drawing of what happens when you cut on just the left side of a finished thread.


When using a "too sharp" tool, and advancing the compound in the prescribed amount according to a chart, the thread is NOT FINISHED. This is because a too sharp tool cuts a narrower width than a tool with a radius. The remaining metal part of the thread is still too thick. To FINISH the thread, you'd then have to increment the too sharp tool sideways, so that it's cutting cross section matched that of the tool with the flat on it.

Edit: according to the chart posted by glenn, you can take your too sharp tool (V form) and continue advancing the compound in. Then the thickness of the metal V's will be correct, but the troughs will be deeper. The procedure I mention is if you use the suggested depth for "national form tool", but have a V form cutter.

oldtiffie
01-22-2010, 10:24 PM
I don't know if the OP wants to start from scratch or not.

If he is - use the table - or to be certain, use "3 wires".

http://i200.photobucket.com/albums/aa294/oldtiffie/measuring/3-wire2.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/measuring/3-wire3.jpg

Two other methods if duplicating an existing thread:

1.
If the outside diameters (OD) are (to be?) the same. put one wire (any size that fits in the thread "vee" - can be a drill bit - anything) and measure over that wire and the original - note the size.

Now start screw-threading and use the same wire and keep screwing until you get to the same dimension over the wire and the work.

Job done.

2.
To get the same thread size without using method 1, use two wires - need not be the same size but both must fit in and touch the sides of the thread. Put them on opposite sides of the thread when measuring.

Measure the original thread (over the wires) and note the size.

Now start screw-threading and use the same wires (2) and keep screwing until you get to the same dimension over the wires and the work.

Job done.

I prefer method 1.

Do use some common sense and take it easy.

Black_Moons
01-23-2010, 12:02 AM
yadayada, while you guys argue id like to post my results:

Turned a 1.6mm thread with 0.04" compound infeed (A little beween the recommended national and V thread form as my tool as a little radius, but not enough to be quite the proper form)

It binded after 1/2" threading into the headstock too.. I thought 'Huu... same depth as the 16TPI'

Turns out, the thread in the headstock was made with a tap(?), the threads after 1/2" are not complete and taper to nothingness, even though the thread is over an inch deep.

Now im not sure if its 1.6mm or 16tpi, and somewhat sure it doesnt matter :P

Pertty cool that I managed to fit it.. if anyones wondering the specs I used where 1.610" OD (10mils under 1 5/8") and more or less standard threading depth.

J Tiers
01-23-2010, 12:19 AM
beanbag is perfectly correct, (with one possible small modification depending on what he meant).

If you cut to the depth of the flat, and THEN move sideways, you end up with the correct width of everything (if you do it right).

This is because you started too shallow, by the difference between the flatted depth and the sharp V depth. So if you did NOT do the sideways move, you'd be too fat in the thread, which would also have a non-spec flat on top, and the wrong pitch diameter..

BUT he said thread to the proper depth....... Depends what he means. If, as I think, he means what I said, he's right. If he means by "proper" , to cut the full sharp point depth and THEN move, that isn't right.

Paul Alciatore
01-23-2010, 12:20 AM
When using a "too sharp" tool, and advancing the compound in the prescribed amount according to a chart, the thread is NOT FINISHED. This is because a too sharp tool cuts a narrower width than a tool with a radius. The remaining metal part of the thread is still too thick. To FINISH the thread, you'd then have to increment the too sharp tool sideways, so that it's cutting cross section matched that of the tool with the flat on it.

Edit: according to the chart posted by glenn, you can take your too sharp tool (V form) and continue advancing the compound in. Then the thickness of the metal V's will be correct, but the troughs will be deeper. The procedure I mention is if you use the suggested depth for "national form tool", but have a V form cutter.


Or, instead of cutting sideways, you can just cut deeper until the pitch diameter is correct. This will make a thread with a sharp Vee at the root. And it will be weaker due to both the reduction of the minor diameter and the stress increase at the sharp Vee. Not a very good idea, but I would bet a lot of threads have been cut this way or close to it with very small flats or radii at the root.

Actualy cutting sideways will not make a flat. It will make a serise of sharp Vees across the bottom: one for each pass. So then you need to get in there with a micro abrasive wheel and smooth them out, being careful not to nick the sides.

Oh, for gosh sakes, a few manual strokes on a HSS tool's tip will round the tip nicely. And one such tool will be OK for three or four thread sizes. Two or three of them should cover 99% of all the threads you will ever cut. Use the "Depth Tables" to get almost there and then measure, by whatever way you want, until you get to full depth.

Video Man
01-23-2010, 12:37 AM
So here's UN

http://img.photobucket.com/albums/v647/Fighter1/MHChart-1.jpg

Something interesting...the corresponding page in my 21st. ed Machinery Handbook (page 1264) gives depth of external thread as pitch * 0.61343, somewhat different from the illustration shown; what gives?

oldtiffie
01-23-2010, 01:21 AM
http://img.photobucket.com/albums/v647/Fighter1/MHChart-1.jpg


Something interesting...the corresponding page in my 21st. ed Machinery Handbook (page 1264) gives depth of external thread as pitch * 0.61343, somewhat different from the illustration shown; what gives?

I think I can sort that out for you VM - good question by the way.

Have a look at the pic I posted previously:

http://i200.photobucket.com/albums/aa294/oldtiffie/Screw_threads/Screw-thread_form7.jpg

Now let's do the math for the threads:

Bolt = 0.6134P (as you say)

Nut = (0.6134 - 0.07224 + 0.1082)P = 0.64936P

Carld
01-23-2010, 02:00 AM
Let me refresh your memory as to what beanbag said in post #21.

beanbag said,

The way I deal with a "too sharp" cutting tool is as follows

1) Thread to the proper depth
2) After the compound is fully advanced... For the next step, advance the coupound MORE, like 5 thou, and move the cross slide BACK by 4.3 or whatever mill it was which results in the threading tool being offset sideways, but not any more forwards. (use geometry for a 30 deg triangle)
3) keep doing this until you have the correct flat at the bottom of the threads

--------------------------------------------------------------------------------------------------------------------

Can you read 1) and now tell me he is threading shallow, I don't think so, he says, "Thread to the proper depth. The proper depth is a finished thread at the correct pitch diameter, unless proper depth has some obscure meaning to beanbag and others. To me proper depth is a full depth thread at correct pitch diameter.

If you want a flat at the bottom of the V then do it right and grind a flat on the threading tool.

Now, I repeat, if he cuts a finished thread and then does what he said the thread will be as I drew in the sketch and worthless. He for sure will never cut a class fit thread that way.

oldtiffie
01-23-2010, 03:20 AM
Many TC thread-cutting inserts have a pre-formed radius/rounded nose for a range of TPI's - so the radius will be not larger than that required for the finest pitch thread in its range.

"Depth" setting from tables may be a "bit iffy" in these circumstances as "depth" also pre-supposes that the tool nose is correct for the thread pitch.

These - because of the back rake - are made for "straight in" - with the top-slide clamped firmly (no "29.5 degrees off" settings needed).

https://www.machineryhouse.com.au/Products?stockCode=L056

Because the "fine nose" and that the 60 degree angle is so accurate it will be a case for a thread micrometer (preferred) or "3 wires" (least preferred).

https://www.machineryhouse.com.au/Products?stockCode=Q129

https://www.machineryhouse.com.au/Products?stockCode=Q1385

http://i200.photobucket.com/albums/aa294/oldtiffie/measuring/Gear-measure6.jpg

beanbag
01-23-2010, 03:43 AM
I don't think so, he says, "Thread to the proper depth. The proper depth is a finished thread at the correct pitch diameter, unless proper depth has some obscure meaning to beanbag and others. To me proper depth is a full depth thread at correct pitch diameter.

When I said proper, I meant "unc form tool depth" according the glenn's chart. At that time, I did not know there was also a specified depth for "v form tool". I DO NOT mean to say to thread to the "v form" depth, and then go sideways.

Black_Moons
01-23-2010, 05:49 AM
oh, I have a thread pitch diamiter micrometer, I just don't know how to use one when Im dealing with an unnatural female thread.

Is it as simple as OD-Pitch = pitch diamiter?

Of course, now if I only knew the proper OD starting from a female thread..

Is it just 0.6134-0.0722P to go from the ID of a female thread to the male of the thread to mate with it?

Carld
01-23-2010, 10:06 AM
I am not trying to make you mad beanbag but here's my point. If there is some way to know EXACTLY how many thousandths to feed the compound in with a sharp V tool and then start going sideways I would like to know it.

I have been cutting threads since 1962 when I got my first lathe, in fact that is one of the first things I tried and it wasn't long after that someone gave me the chart. I think it was the same machinist that gave me a Federal .0001" dial indicator. It didn't take me long to find out the chart was a guide and not written in stone. Even the MH charts are somewhat of a guide because I don't know of common measuring tools to measure some of the numbers given in the charts.

I have used The chart posted on the first page for years and the finished thread NEVER is what is in the chart when you measure the pitch diameter with wires or thread triangles. That is to say, it would be a shot in the dark to run the compound in a given distance and then go a given distance sideways and end up with the correct pitch diameter and a perfect V. Even the charts in the Machinery Handbook are a guide and the pitch diameter is the number to shoot for.

It's even a shot in the dark to go exactly the compound feed the chart shows because at first I did that and the thread always was a sloppy fit as I mentioned above.

I have not seen a tool on the market to measure the very bottom of a sharp V or a V with a flat to measure the minor diameter. You can use calipers but they have a flat on them also. You could grind it to a sharp edge and use it for measuring the minor diameter of the thread but why. Just grind the cutter, put the correct flat on it and cut the thread and measure it with wires for the thread pitch.

Short cuts are sometimes acceptable but not this one. If you need or want a flat in the bottom of the V put the required flat on the tool, that is the only acceptable way to cut a thread with the correct flat.

Using your method is wrong and can lead others to think they are cutting a correct thread and then wonder why it is sloppy and don't look right.

If your just turning a sloppy fast thread go for it but if your cutting a thread for a customer at work you best not use your method. What you do at home for your own stuff is your business but it won't be a correctly cut thread. Nor will the funny looking flat at the bottom with all the grooves be acceptable unless you file them out.

Now consider all the time you spent to guess the depth, guess the side step, clean up the bottom of the V compared to doing it right the first time.

Now as to a sharp V tool, I don't put the correct flat on the end of the threading tool. I sharpen the tool and then stone a small flat on the tip. Then I cut the thread and either use a test nut I made or a store bought nut or thread wires or thread triangles to measure it.

It's true that a sharp V does have a stress issue but in all these years I have seldom seen a thread fracture for that reason under normal loads. Under excessive loads I suspect even a flat bottom has stress issues and the only stronger thread form would be a radius at the bottom of the V. We don't normally use a radius on V form threads both Imperial and Metric. However, there is a thread form that does use a radius. Just stoning a small radius on the tip would go a long way to eliminate any stress issues. We had to do that on boat prop shafts that were spec'ed for a radius in the keyway.

Early in 2009 I bought a Dorian vertical insert threading tool and have used it for every thread since then. The insert has a small flat on it. I was told in another thread that there are inserts available for each thread tpi which surprised me somewhat. However, I am not going to buy 40+/- inserts to cut the correct flat will you?

J Tiers
01-23-2010, 10:38 AM
You can't do a truly accurate "thread to depth" anyhow, unless you know a lot of things which you probably do NOT know.

I doubt a person could "PRACTICALLY" cut a thread that way, but a person COULD "theoretically" do that and make a proper thread. One can come up with many OTHER "possible" ways to make the thread.

Just because a procedure is impractical does not mean it "won't work" it just means one would never USE it.

Threading to a specific depth is one of those. If you KNOW the OD of the part, and you have a very accurate crosslide, and you know the precise shape of the tool, and you can determine to a couple microns where the tool hits the work, you could THEORETICALLY advance to a correct depth manually.

or if you KNOW the crosslide reading when the tool is exactly on center to the rotational axis of the work, to a few microns, you THEORETICALLY could advance to put the pitch diameter at any value you wanted.

I refer to the correct depth as being to a high class fit with PD accurate to tenths according to the thread tables.

But in the real world, with manual machines, threading to depth will generally make only a "commercial" thread....... about as good as the sloppy screws on cheap shelving. This is because you do NOT know most of those details.

naturally, if you set stops, and set them to produce the correct dimensions, you can thread to the stops, after turning the OD to stops, etc, and make a good thread. Screw machines do that. But it isn't the same thing at all, and probably still won't produce the ultimate in accurate PD, form , etc.

Carld
01-23-2010, 10:57 AM
I totally agree with everything you said JT.

BobWarfield
01-23-2010, 02:29 PM
The charts are handy. I have similar information on my G-Wizard calculator:

http://www.cnccookbook.com/img/GWizard/GWizThreadsUNISO.jpg

That left hand with the cut depths and tapping drills is where all the action is when I'm cutting threads.

Cheers,

BW

Video Man
01-23-2010, 02:36 PM
@Oldtiffe: thanks...but my question is the MH page illustration that shows external thread as 0.54127*P...where does that come from, or am I misinterpreting that entry?

Carld
01-23-2010, 03:28 PM
I looked through this whole thread and no where has Black_Moons or Video Man stated the tpi of the thread they are asking about.

So, BM and VM, what it the tpi of the thread.

spope14
01-23-2010, 04:07 PM
OK, quick formula for cutting threads. If you are using the compound rest set at 29 degrees off center perpendicular (or 61 degrees to centerline, depends on the lathe), use the following formula to determine the compound rest infeed to make a class 2 fit (common) thread

.708 / number of threads per inch or .708 x pitch of thread.

Source, Machine Tool Practices - Kibbee et al, has worked for me for fifteen years now since I got a review text of this book.

0.54127*P is an internal thread cutting infeed on the compound formula, same source.

Black_Moons
01-23-2010, 04:13 PM
carld: 16tpi.. or 1.6mm, I really can't decide as both only threaded in 1/2" before binding (Due to what I now suspect is a 'tapered thread' produced by the tapered part of the origional tap)
But it doesnt really matter, its the math/charts I needed, Not a spoon fed awnser. And you guys allready awnsered it.. the thread is done.. it fit first time without measurement.
you can stop argueing now.. really.. any page now.......

Glenn Wegman
01-23-2010, 04:14 PM
Something interesting...the corresponding page in my 21st. ed Machinery Handbook (page 1264) gives depth of external thread as pitch * 0.61343, somewhat different from the illustration shown; what gives?

Are you sure you are not looking at American National?

beanbag
01-23-2010, 05:28 PM
Hi Carl,

Since you've cut way more threads than than me, let me just put it this way - the procedure I mention is for when you've decided you'd rather start making the troughs wider instead of deeper IF YOU'RE GOING TO SLICE OFF ANOTHER SLIVER FROM THE THREADS ANYWAY. You don't HAVE to stop at a certain infeed depth if you don't want to :)

In my case, I was cutting threads on the OD of a thin tube, so the deeper I cut, the weaker the part got.

To do this procedure, all you have to do is remember the three numbers of a 30 degree triangle, namely 1, square root 3 and 2. IOW, if you feed in the compound by 2, and move back the cross slide by 1.7, then the tool will have moved over by 1. The number I initially gave were 5 on the compound and 4.something on the cross slide, which means the tool moves over by 2.5 thou. In my case, the "too sharp" tool was a carbide insert with a nose radius of 4 thou (or was it 8?), so it's hardly going to make sharp stress riser grooves at the bottom of the trough.

Finally, I have never threaded with a HSS tool, so I haven't experienced the pleasure of putting a flat on the tip, and then having to re-grind off an entire side the next time I wanted to cut a finer pitch. The laydown carbide insert I have claims 8-48 tpi, so if I am doing finer threads, the nose radius will be about right, and I won't have to use this sideways procedure, but on coarser threads, the tool will become "too sharp".

oldtiffie
01-23-2010, 06:03 PM
@Oldtiffe: thanks...but my question is the MH page illustration that shows external thread as 0.54127*P...where does that come from, or am I misinterpreting that entry?

Thanks VM.

Here's the pic. My reasoning follows that:

http://i200.photobucket.com/albums/aa294/oldtiffie/Screw_threads/Screw-thread_form7.jpg

I haven't checked my Machinery' Handbook (MH 27) but I will try and sort it out on the pic above.

The depth on the chart above is 0.6143P

Your query is 0.5417P

The difference is: 0.6143P - 0.5417P = 0.0726P

That is very close to the 0.0722P which is the full thread depth - the depth of the flat sides/flanks of the external thread.

It is the theoretical optimal contact face depth entirely on the straight flanks/side with no contact on the curved surfaces at the bottom of the thread.

I hope that I am correct and if that is so, that it helps.

Black_Moons
01-23-2010, 06:12 PM
Finally, I have never threaded with a HSS tool, so I haven't experienced the pleasure of putting a flat on the tip, and then having to re-grind off an entire side the next time I wanted to cut a finer pitch.

PRECISELY why I put a radius thats 'too small' on the tip of my threading tool. Im never regrinding the whole dang tool for each job and im not making 14+ threading tools considering how long it takes me to grind one to the level of perfection I want, if I grind another threading tool it will probley be because I need a left handed tool for clearance. Maybe i'll make a slightly more rounded tool, but not for awhile.

I don't even think id want to put forth the money to buy a 'full profile' threading insert set either. Just not worth it to me for how few threads I turn.

Hence why I wanted to know the *sharp* V thread depth.
I know my tool has a radius, but its somewhere beween proper thread form and Vee thread for whatever TPI, so I know i'll have to cut somewhere beween the specs of national and Vee thread. ie I know I have to cut at LEAST X and less then Y, thats a really helpful starting point.

Black_Moons
01-23-2010, 06:36 PM
Wait, if threads are based on a modifyed 'V' form
Should'nt you be able to make a thread by simpley doing the following:

Turn stock to exact OD of declared thread (ie 0.500 for 1/2")
Thread stock untill the crest of the thread is a perfict V with no top (Opticaly), Alternatively, thread untill the OD is altered (By measurement, but will produce an undersized thread unless the origional peices OD was oversized)
Basicly, produceing the V thread form since its easyer to compair/measure, but with a rounded root (Rounded to whatever the radius of your tool is, non critical as long as the radius is smaller then required for the TPI)

Then, top the threads by turning the recommended amount by the charts

Assumeing your tip radius (for the threading tool) is smaller or equal to required radius, should'nt this produce a 'textbook' perfict external thread? (aside from the root being a little deep if your radius was smaller)

beanbag
01-23-2010, 06:52 PM
Wait, if threads are based on a modifyed 'V' form
Should'nt you be able to make a thread by simpley doing the following:

Turn stock to exact OD of declared thread (ie 0.500 for 1/2")
Thread stock untill the crest of the thread is a perfict V with no top (Opticaly), Alternatively, thread untill the OD is altered (By measurement, but will produce an undersized thread unless the origional peices OD was oversized)
Basicly, produceing the V thread form since its easyer to compair/measure, but with a rounded root (Rounded to whatever the radius of your tool is, non critical as long as the radius is smaller then required for the TPI)

Then, top the threads by turning the recommended amount by the charts

Assumeing your tip radius (for the threading tool) is smaller or equal to required radius, should'nt this produce a 'textbook' perfict external thread? (aside from the root being a little deep if your radius was smaller)

This procedure is wrong because if you keep threading until the tops of the threads are sharp, you've already cut too much. You can't get the required flats on the top of the threads unless you reduce the diameter. I suggest the following (should have mentioned this initially)

1) Using the bluntest tool that is still "too sharp", keep cutting until you reach the "UNC thread form depth". You should notice that the tops of the threads are still too wide, because your tool is still too narrow compared to the tool with the even blunter radius.

2) Go in a little bit more on the compound. Just because

At this point you have two options:
a) the "usual" way, which is to keep incrementing the compound until the thread crest flats are the right amount. This will probably make troughs that are too narrow and too deep, but might be ok for your application

b) start moving sideways until the thread crest flats are the right amount. This, in theory, is the closest you are going to get to the UNC thread form, unless you start doing even fancier moves.

Basically, the big unknown in the threading operation is the true effective tip radius or flat of the cutting tool. IOW words, you know based on the compound how much you've advanced in, but you don't really know how wide of a cut you are making. (Since everything is measured relative to when the tip of the tool first touches the workpiece).

Thus the only things you can be sure of when cutting the threads is how deep of a trough you cut, and the thickness of the threads as according to the flats at the crests.

http://i139.photobucket.com/albums/q286/beanbag137/cuttingthread.png

Carld
01-23-2010, 07:36 PM
beanbag, I have said all I can to point out any problems. If your way works for you do it. Having to keep the minor diameter of the root of the thread shallow I may have tried what you did too. What I was trying to point out that way is not something you want to do on every thread you cut. The problem is the V would be shallow on that tube but if you open the bore on the part that screws on it may and probably did work.

Black_Moons, the chart below shows why you can't use the major dia. and cut the thread as you described. There is a max. and min. diameter for the major diameter of the thread. There is also a max. and min. for the pitch diameter of a thread. The thing about threading is there are so many variables you can't do some things people try and get a good thread. On the other hand there is some lee way. When you cut a class fit thread each tighter class has tighter tolerances so you almost have to use the charts in manuals to do it right.

Personally I go for the middle rather than the high or low side. It gives me some play room.

http://i82.photobucket.com/albums/j276/yeathatshim/threadchart-1.jpg

beanbag
01-23-2010, 07:48 PM
One correction, in one of my earlier posts I said to watch the width of the trench, but it might be better or easier to watch the flat at the crest.

Carl, I am not knocking anything you suggest, just that at the time, I had to make both internal threads and external threads, so not knowing any better I just tried to follow the thread form as closely as possible, minus a bit for looseness of fit.

Carld
01-23-2010, 07:51 PM
After you explained why you did it I understand how and why it worked for that application.

The thing is we covered a lot of ground with this thread and I think that is good.:D

Black_Moons
01-23-2010, 08:07 PM
beanbag: reread my post, I allready said TO reduce the diamiter afterwards to produce the flats at the top of the thread. Carld's chart says that the actual major diamiter of an external thread is slightly smaller then the 'stated' diamiter. (stated diamiter being just 1/4" or whatever)

So im saying, If you thread untill perfict pointed crests at the *stated* diamiter of a thread, and THEN reduce the diamiter to produce the proper crests and major diamiter, Is the threadform proper?

My theory is the reason threads major diamiter is smaller then the stated diamiter (ie a 1/4" thread is speced as 0.2491~0.2436) Is that its based on a V thread of the stated diamiter with flats added for clearance and roots rounded out for strength?

Carld
01-23-2010, 08:12 PM
BM, the only way to know is to measure the Pitch Diameter. The flat on the OD or the flat on the root of the V has nothing to do with the Pitch Diameter and the pitch diameter determines the fit of the thread. In the first column of the chart is the class fit. As the class goes from 1A to 3A the pitch diameter min-max gets less hence less slop in the thread fit.

Black_Moons
01-23-2010, 08:24 PM
carld: the diamiter you start at to produce a perfict V crest will directly influance the pitch diamiter, reguardless of threading bit tip radius. (Assumeing you bothered to grind it to a perfict 60 degrees at least, I do)

Thats my point, there should be a direct starting diamiter to end with a pitch diamiter when you can visualy see a perfict crest (or measure it because 1 mil deeper then perfict crest will reduce the OD, and thats easyest to measure), Produceing the flat crests afterwards for clearing the external threads rounded root is just a single turning operation using normal feed and a normal tool (or your threading tool if you wanted to maintain tool offsets)

IE: don't start with flat crests and try and measureing some oddball thing that requires an oddball screw pitch micrometer to measure (Even though I have those and love them and will likey still use them, Im just thinking outside the box), start with V crests that you can easily measure/verify as being properly shaped so your pitch diamiter is correct, and THEN turn them into flat crests for the proper major diamiter.

Even if my idea of stated starting diamiter is wrong, that still holds true.

Video Man
01-23-2010, 08:24 PM
Are you sure you are not looking at American National?
Nope, my reference is "American Standard Unified Thread Form Data". ,page 1264, 21st ed MH.
The formula for depth of external thread there is 061343* P. The formula in the MH handboook image that was kindly uploaded is from a different version of MH and shows a formula of 0.54127*P for "depth of internal and external UN thread". So there's a descrepancy somewhere or I'm missing a step in the calculation... maybe I'll just buy some big dies and say the heck with it...:)

Carld
01-23-2010, 08:30 PM
That's not true BM, the thread fit is determined by the pitch diameter not the OD of the shaft. You can cut the OD down and as long as the pitch diameter is correct the thread will fit good but will not have any strength.

The reason the chart posted on the first page works is because you start off with a shaft of the correct size and "0" from there and use the compound travel shown to get close to the fit but you have to test the fit and that is where the pitch diameter starts coming into play.

You can't be very short of the right root diameter but the OD can be a lot undersize and still have a good thread.

It's always the pitch diameter you shoot for. There is no guaranteed starting diameter to end up with the right pitch diameter. It don't work that way. You have to measure the pitch diameter, nothing else.

Black_Moons
01-23-2010, 08:42 PM
mmm I think your misunderstanding what im trying to say here.
I realise the pitch diamiter is the actual diamiter of the wedges themselfs, nothing to do with roots or flats.

Im saying, If you turn a perfict Vee threadform, your pitch diamiter is directly related to crest diamiter-pitch (ie major diamiter-pitch), because your crests are well, perfict crests, no flat to worry about, So it actualy IS related but only for V crests.

*THEN* you reduce the OD to produce flat crests, turning it into something that will fit national threadform, since interiour threads have a rounded root and can not accept flat crests.

All without caring just how much tip radius there was (because that screws up the 'infeed' calculations as previously mentioned unless your using the right radius for the TPI)

Please stop just saying 'it won't work' without trying to visualise what im saying and reading it carefuly, unless you actualy have a reason why the pitch diamiter is unrelated to major diamiter of a VEE (crested) threadform.

Glenn Wegman
01-23-2010, 09:02 PM
It's simple.....

Turn a thread using your method of relying on the OD and infeed and when you are done, measure the thread with wires and see how close you are to the correct PD for that thread.

Use dimensions for a standard Class 2 thread and don't try fitting a nut on it or any other form of reference while you are cutting it.

I realize this is all home shop stuff and you really just need two parts to screw together, which is fine. But doing such an exercise may help you understand threading better.

beanbag
01-23-2010, 10:13 PM
OK, I just read this thread over again, and carl and others are right that the pitch diameter is the thing that you are really supposed to watch out for. In my particular case, I was able to make both internal and external threads, so I could sort of calculate what the dimensions will turn out to be by measuring things like diameter, crest flat, trough, etc. But if you are given a nut with a specified thread and told to make a class whatever fit, then yeah, one should always keep an eye on the pitch diameter.

But from a more practical standpoint, it's better to cut while measuring the pitch diameter, and then chop off the crests, than to calculate the outer diameter, cut until there is no more flat, hoping that the pitch diameter is correct, and then chopping off the crests. But I guess if you don't have the 3 wire measuring things (I don't either) then your way kind of makes sense.

BM, to answer your question in post 58, wouldn't one also need to know the class of fit? If you can give a specific example of what exact thread you are aiming for (including class of fit, I guess), I can practice my geometry and tell you if your method works or not.

Black_Moons
01-23-2010, 11:03 PM
beanbag: Well, How about just trying the math on a standard UNC 1/4" or 1/2" OD for a Vee form thread and seeing what pitch diamiter that comes out to and what class fit that is closest to.

oldtiffie
01-23-2010, 11:18 PM
BM.

The answers are in Machinery's Handbook and many other shop and thread related books and tables.

Do you have a copy of MHB or one of those books or tables?

oldtiffie
01-23-2010, 11:42 PM
Following on from my post at:
http://bbs.homeshopmachinist.net/showpost.php?p=512742&postcount=43


Many TC thread-cutting inserts have a pre-formed radius/rounded nose for a range of TPI's - so the radius will be not larger than that required for the finest pitch thread in its range.

"Depth" setting from tables may be a "bit iffy" in these circumstances as "depth" also pre-supposes that the tool nose is correct for the thread pitch.

These - because of the back rake - are made for "straight in" - with the top-slide clamped firmly (no "29.5 degrees off" settings needed).

https://www.machineryhouse.com.au/Products?stockCode=L056

Because the "fine nose" and that the 60 degree angle is so accurate it will be a case for a thread micrometer (preferred) or "3 wires" (least preferred).

https://www.machineryhouse.com.au/Products?stockCode=Q129

https://www.machineryhouse.com.au/Products?stockCode=Q1385

http://i200.photobucket.com/albums/aa294/oldtiffie/measuring/Gear-measure6.jpg

For Glenn Wegman and Carld.

Re my post above and some comments about the pitch cylinder and the measuring of it.

While I will concede that the "gold standard" was and is the "3-wires" method, it is fraught with practical difficulties, not the least of which are the keeping those three wire in place and measuring over them accurately and consistently to a "thou" let alone to a couple of "tenths".

And that is after you wend your way through the tables and calculations.

Too many chances of a mistake - or losing a "wire" - as well as your temper and dignity.

A "thread" micrometer does it very well. Just set the required pair of anvil insert and spindle sleeve, slacken the anvil clamp, set the micrometer to zero, re-clamp the anvil, re-test for zero, if not OK - re-set again, if OK you are set to go.

Read the pitch diameter directly as with normal use of any other micrometer.

It is easy to read to tenths if required.

It is as accurate as "3-wires" as both rely on the thread form angle being precisely 60 degrees and symmetrical about an axis normal to the axis of the job on which the thread is being cut.

They are expensive but are soon amortised if you do a fair bit of work that requires 3-wires.

After that its gravy.

beanbag
01-23-2010, 11:43 PM
My understanding is the pitch diameter is the halfway point of the full "triangle".
Thus the formula if you cut the thread your way (sharp crests) is
pitch diam = Dmax-sqrt(3)/2*pitch

For 1/4-20, that comes out to .2067

according to this web page
http://alphathreadgage.com/refsheets/REFthrdWRKplg.htm

They show
NOMINAL SIZE Go 3A NoGo 3A Go 2A NoGo 2A
1/4-20 UNC .2175 .2147 .2164 .2127

For 1/2-13, you'd end up with a pitch diameter of .433, which is smaller than even the class 1a numbers Carl posted in that other thread.

Your pitch diameter is too small, i.e. you cut too much thread off

Black_Moons
01-24-2010, 04:18 AM
Ok so we make the initial diamiter .2175 + sqrt(3)/2*pitch, And then cut it.

So 0.2175+(0.866*pitch) = 0.2608 starting diamiter.
pitch diamiter+(0.866*pitch) = starting diamiter.


Thats a pertty simple formual and method isent it?
I mean at least its a way to generate a thread pitch without knowing your tip radius, as many HSM won't for thier home ground bit
(Ok, I confess to buying a set of radius gages.. my HSS bit is uhh.. somewhere beween 1/64 and 1/32" radius.. most likey. Yea..... Helps me a ton...)

lets try 3/8" * 16UNC.
0.375 + 1/16 = 0.4375 starting diamiter.
Now to verify. 0.3266 to 0.3331 pitch diamiter is called for 1A fit
0.3331 + 0.05412 = 0.3872

Weird how little that is over 0.375 the nominal size.. I guess the ratio depends on diamiter and TPI.

I conceed my theory that National thread forms are based on modifyed Vee threadforms of nominal sizes was wrong. (unless sqrt(3)/2*pitch is wrong for triangles)
However I still think my idea of a starting diamiter and visualy monitor untill the crest is a peak (Or simpley messure the OD untill it feeding in the compound causes the OD to shrink) And then turn the crests into flats by simpley turning it down to the required major diamiter satasifys all the design requirement for a pratical thread, reguardless of tip radius (as long as its got a sharp enough radius)

beanbag
01-24-2010, 06:03 AM
yes, it seems like your idea will work, if you are somehow unable to measure pitch diameter and don't have the mating piece to test. But there are other dirty tricks that accomplish the same thing, without having to start with an oversize rod. For one, you can use whitis' idea of a calibrated fishtail gauge, to tell you where the virtual tip of your threading tool is. You can go to the part of the thread where you would normally cut the exit groove, and plunge two grooves spaced P apart until they touch, and used the cross-slide infeed to calculate where the virtual tip of your tool is. (There might be a more clever variant of this). It also requires one calculation and table lookup. Etc etc, but I think most normal people just try to measure the pitch diameter

Black_Moons
01-24-2010, 08:05 AM
Often I start oversized anyway. Todays thread will be 1 5/8" 16tpi outta 3 1/4" stock, weee.
Well, thats because of other features needed on the same part.. :P Yea I considered welding two peices togethor but then I got a good deal on the last 14" of 3 1/4" stock, and the end of the bar was badly mangled, so turning it down removes the mangled part :P

Carld
01-24-2010, 03:03 PM
Here is how I approach cutting a thread. If the thread is just for normal stuff then I have nuts for testing the thread, some I made and some off the shelf and I run a tap through them to be sure they were tight and I cut some metal out of. I keep them in a drawer.

When I want to thread I get one of those nuts the size I want then I set up the lathe. I look on my chart to see what I want to use for the compound travel and start cutting. Before I get to the travel recommended I start trying the nut and take .001 or .002" off each pass until the nut starts on the shaft. Then I only take .001" each pass until it fits as I want it to. Then I clean the threads and I am done.

I have thread wires and triangles and the only time I use them is when I want a tight class fit more than the 1A.

There are many ways to approach cutting a thread and a go/no go gage or a test nut is the best way for general threading. To depend on starting at a given diameter and cutting a certain depth with the compound or cross slide has a lot of issues. If you don't test the thread with a nut or go/no go gage or wires or triangles you are simply HOPING the thread will turn out right. Basically that is a shot in the dark.

What I don't understand is, what is so hard about using a nut to test the thread rather than depending on guess work.

J Tiers
01-24-2010, 03:38 PM
What I don't understand is, what is so hard about using a nut to test the thread rather than depending on guess work.

I suspect it is the perceived greater "accuracy" of working to a mathematical formula vs the cut and try method. Cut and try seems so crude...............

Carld
01-24-2010, 03:50 PM
Yes, to some cut and try seems that way but if they ever worked for a living as a machinist they would soon get over all the analytical bull and start working.

Like I said or implied at least, there are times to be exact and use wires to measure and times to just cut the damn thread with a test nut and go to the next job.

At home you can spend hours with a calculator and paper or magic formulas you have devised to do something. In the end it's do you want it right and to work or do you want to think it will work.

I guess that is my problem for having been a machinist for a living compared to someone doing it for fun. I find when I am in my shop working I automatically go into a work for pay mode and do things in an organized time saving method when I should be screwing around and drinking a beer. :D :rolleyes:

That's one reason I liked the PM site but I just could not stand Don and his antagonistic ways but I promised him I would never return to his site and I won't.

Black_Moons
01-24-2010, 04:19 PM
Heh, I wanna know how to do it without 'test fiting' because more then once iv had to mate with threads on my lathe that either A: I could'nt buy a test nut (pesky larger metric threads) or B: where non standard anyway (headstock thread) and just trying it, taking apart the lathe to test fit and puting it all back togethor and pickup the thread for another 0.001" pass is very tedious.

J Tiers
01-24-2010, 04:33 PM
So get thread mics, or make a gage when you need to do that. You are supposed to make an exact gage if you have a threaded nose lathe (not that I have) for just that reason.

Glenn Wegman
01-24-2010, 05:25 PM
Black Moons,

That's exactly what we've been trying to tell you since this thread began.

It's the PITCH DIAMETER that counts. You can easily and inexpensively measure it with THREAD WIRES, or as JT and others suggested, thread mics.

There is no need for test nuts. If the tool is 60 or whatever is called for, and ground and aligned properly, and the pitch diameter is within the specs, tho parts WILL screw together!

J Tiers
01-24-2010, 05:28 PM
You can easily and inexpensively measure it with THREAD WIRES, or as JT and others suggested, thread mics.


You need both. The wires calibrate the mics......

Black_Moons
01-24-2010, 05:31 PM
Glenn Wegman: how do I measure the pitch diamiter of an inside thread? Solution under $100 please.

oldtiffie
01-24-2010, 05:47 PM
Bingo B_M.

I've been waiting for this as it implies and requires "Class of Thread Fit".

There are other items of "unfinished business" as well.

Carld
01-24-2010, 06:14 PM
Well, you have a problem. If you have a female thread I don't know of a tool to measure it. What I do is make a male thread that fits the female thread with no slop, just does go in all the way and is snug. There can be no slop and a slight drag is good.

Now you have a gage to use and measure and if the fit is good and you measure the pitch diameter of the male thread you will know fairly close what the PD of the female thread is.

If your making another female thread you can now use the male thread as a go/no go gage.

You can't be sloppy in your work here, it has to be as exact as possible because when transferring the PD of the internal thread to the external thread it almost has to be an interference fit but that is impossible to do for testing.

There is no way I know of to get the exact PD of an internal thread with a measuring tool. I have made a male thread to fit as close as possible to measure but it is not perfect, on the other hand, nothing is perfect except God if you believe in God.

Glenn Wegman
01-24-2010, 07:03 PM
As Carl stated, Go-No go Gauges are the standard for fitting internal threads.

Or make your own plug using wires to match the internal thread you are trying to fit. Everything has a standard. This is how you would thread a backing plate for your threaded lathe spindle as an example.

I use a simple program that gives me the proper Go-No Go dimensions for a given size and class thread.

http://img.photobucket.com/albums/v647/Fighter1/thread-2.jpg

There are plenty of published specs for thread dimensions available for cutting proper size threads.

I sense a sketch about to appear.......:)

Sparky_NY
01-24-2010, 07:31 PM
Just went through this yesterday. I needed to make a part for a lever collet closer. The piece that threads onto the outboard end of the spindle. The outboard spindle thread was 1.5 mm (using a thread gauge) and measured 1.9538 od. A quick check found that 50mm was 1.9685 inches, so I assumed the thread to be a "nomimal 50mm". Further research on the subject led me to the machinist handbook. Table 10 in there listed .014 inches as a grade 8 fit for a male thread this pitch, the exact amount the shaft measured vs a true 50mm. This was the sloppiest class of thread listed.

Now, after reading this thread, and everything else I could get my hands on, I ran into the issue of threads with a standard thread form vs threads cut with a sharp V. The plot thickened, I assume the spindle thread was a standard form but the mating female piece I have to cut will be with a V tool.

I ended up boring the part to 1.890 and cutting the thread .03197 deep(5/8H (H being .05115)) This appeared to meet all the specs and agree with the standard thread form. I got the bore size from 1.9538 (the shaft OD) minus 2x the thread depth (1.9538-2x.3197=1.890) The lathe has a tenth reading DRO.

The part fit, but was loose as a goose. I think it will be OK for its purpose and I am not going to recut it unless absolutely necessary. BESIDES, I wouldn't know what dimension to recut it too!!!!!!

So much for theory! Fortunately, most of the time I have the mating part in my hand to test fit.

oldtiffie
01-24-2010, 07:45 PM
..........................................
Fortunately, most of the time I have the mating part in my hand to test fit.

+1

Me too!!!!!!

Not having much luck tho'

lakeside53
01-24-2010, 07:51 PM
:D :D :D :eek:

Glenn Wegman
01-24-2010, 07:51 PM
Sparky,

That's a perfect example of why using thread wires to measure the spindle end threads, and making a threaded plug to match it is the way to do it for a nice fit when making the mating threaded part. No math or charts required. Just make the dimension on the plug threads match the spindle thread measured dimension.

oldtiffie
01-24-2010, 08:51 PM
As Carl stated, Go-No go Gauges are the standard for fitting internal threads.

Or make your own plug using wires to match the internal thread you are trying to fit. Everything has a standard. This is how you would thread a backing plate for your threaded lathe spindle as an example.

I use a simple program that gives me the proper Go-No Go dimensions for a given size and class thread.

http://img.photobucket.com/albums/v647/Fighter1/thread-2.jpg

There are plenty of publishhttp://en.wikipedia.org/wiki/Lassitudeed specs for thread dimensions available for cutting proper size threads.

I sense a sketch about to appear.......:)

And that's the truth - but not all of it!!!

Later.

Some are going to have fainting fits when they see how much "Hillbilly" there is in Machinery's Handbook.

Severe lassitude and total loss of anal sphincter control are quite possible.

I suggest that some undertake an intensive course of "Pelvic Floor Exercises" - "just in case ................. ?"


Benefits for men
Though most commonly used by women, men can also use Kegel exercises. Kegel exercises are employed to strengthen the pubococcygeal muscle and other muscles of the pelvic diaphragm. Kegels can help men achieve stronger erections and gain greater control over ejaculation.[6] The objective of this may be similar to that of the exercise in women with weakened pelvic floor: to increase bladder and bowel control and sexual function.

from:
http://en.wikipedia.org/wiki/Pelvic_floor_exercise

and:

http://en.wikipedia.org/wiki/Pelvic_Floor_Muscle_Disorder

I suppose I could say that I will be enjoying that.

PixMan
01-24-2010, 09:50 PM
I just read through ten pages of posts about this, and all I can say is that I'm glad I'm out of it. ;)

I got my ticket out by spending the money on O.D. tools and internal threading bars that use lay-down ER/IR-style inserts, the anvil sets for both I.D. and O.D. work, and I've never looked back. Or, ground a tool. :D

I have a growing collection of pitch-specific inserts. They cost me about $20 each, and I get three edges. More importantly, I get a perfect thread form every time, and no burrs or chatter. I turn O.D.'s to the nominal diameter, and let the threading insert cut the O.D. to within specification for the given thread class I'm doing. For I.D.'s I do consult the software I have for threading data (TT Gen) and leave a few thousandths for the insert to clean off.

This is great software for tool selection and cutting parameters:

http://www.vargus.com/vardex/template/default.aspx?pCatId=9

I know few people here would invest in doing it the way I have, but I have no regrets for making the nicest threads I've ever been able to do. I just made a 1/2"-10 Acme for a friend this way, and the screw for his Atlas shaper looks and works perfect. And the edge I used on the insert looks as though it could make hundreds more. :)

Carld
01-24-2010, 10:12 PM
Sparky_NY, why didn't you make a male thread as a plug gage from the exact dimensions of your spindle threads? Had you done that you could have eliminated any guess work when doing the internal thread for the cap and it would have fit the spindle just as it did the gage you made.

My problem is just the opposite of yours.

I have a project that has set for over a year because I have to make a male thread on a part for a female thread that is metric and not a standard size. Several times I have tried to figure the math and was wary of making the cuts. The major diameter of the male thread is the problem I have to determine.

I have machined the part that will be the actual tool and I don't want to spoil it.

What I am doing is making a part to screw into the rear of the spindle with three screws to center a shaft in the head stock while the chuck holds the other end. Rather than destroy the part I have made I will try to cut a thread on scrap until it fits as I wish. Indexing the part as I remove it to test the fit has been on my mind but I have solved that issue. Now to just find the time to do it. I can use the same indexing method on the scrap piece to test the fit as I thread it. Removing it from the chuck during the threading and re indexing is serious work and not to be taken lightly.

Perhaps Glenn or Tiffie has the answer for my dilemma and I will be waiting with bated breath. With hope and anticipation I await an answer and hope it is not so much that my simpleton mind can't encircle it and comprehend with exceeding pleasure and delight.

Did I wax eloquent enough Tiffie?

Glenn Wegman
01-24-2010, 10:33 PM
Carl,

Use a moulding compound to make an impression of the internal thread and measure that for the proper PD.

They make specific compounds that do not shrink just for that purpose. One of the compounds actually shrinks initially for easy removal and then grows back to it's original size within a short time.

Carld
01-24-2010, 11:53 PM
Gosh, I didn't think of that. Is it the same stuff the gunsmiths use to measure the chamber size. What is the name of the stuff your talking about. It would take a good amount of it because the spindle bore is about 1 1/2" and the threads are bigger. I guess I could wrap some around a shaft smaller than the bore and that would work.

I didn't even think about the stuff they use for chambers.

I spent about two weeks measuring and thinking and doing math and I can't find the paper I wrote the notes on. All I have is the part I made to cut the threads on. I should have rolled the paper and stuck it in the part.

lakeside53
01-25-2010, 12:19 AM
Maybe something like Bismuth alloy -melts as low as 158F... or Indium alloys at 117F....

8921K22 looks cost effective and still melts in hot water.

http://www.mcmaster.com/#bismuth-alloys/=5iu2kq

oldtiffie
01-25-2010, 05:11 AM
Carl.

If you turn the job between centres and drive it with a lathe dog, re-setting and re-indexing will not be a problem at all.

My guess is that thread was cut for a pretty standard 80% contact of/between the thread flanks.

If you know the TPI or pitch (mm or inch - doesn't matter) as well as you're pretty well almost there.

If the thread is say 16 tpi, find a 16 tpi thread in any tapping drill chart (diameters don't matter here) and work back-wards for the difference between the nominal OD and the tapping drill size.

Measure the spindle thread id. A couple of thou is near enough.

The Pitch diameter can be presumed and forgotten about as it will be a function of the thread profile, pitch and depth.

I would work on the standard tables to get the thread OD.

This is into the darkest hinterland of wildest Hillbilly Land, but as the part is easily and accurately relocatable between centres (and dog-driven) you can save yourself a lot of unnecessary angst if you just "wing" it in large part and just keep threading and reducing the OD (turning tool or filing in the lathe) and take it slowly and you will get there.

Its only a lathe spindle "spider" after all.

As long as as its not too tight at one extreme and at the other is not as loose as a dick in a shirt-sleeve - and it works - its OK.

Near enough is not good enough but if its near enough its good enough.

If I had that problem and needed "quick (and effective) fix" I'd forget about the thread altogether and make the spider with a flange for the screws (3 or 4 - your call) and spigot that was a fair to loose sliding fit in the spindle bore plain section (forward of the internal thread) and a bit better fit in the id of the thread.

If the spider is bearing on the flange at the back of the spindle and if it and the lathe chuck are holding the job the spider will be held in position when its locating screws contact the job (also held by the chuck).

If you want to ease your mind, just wind a bit of Plumbers teflon tape on the spider where it will be in the thread. It will hold well enough. You can always put more teflon tape on.

Ma and Pa Kettle and Jeb Lambert would give it 100% - "It ain't purty but it works".

What an accolade!!!

Not a Machinery's Handbook or a PD or "wires" etc. in sight.

This is an "experience" and "gut-feeling" job.

Oh well - back to the old rocking chair under the shade tree with a corn stalk in my teeth and jug full of the "doin's" ("moon-shine"?) - and let the worriers and the world go by.

I suspect that some of the hard-line theoreticians are having heart attacks and apoplexy by now.

If they are frothing at the mouth and if they look as if thay may have rabies - do us all a favour - and shoot 'em.

You can't be too careful.

And don't give 'em a go at that jug!!!

Carld
01-25-2010, 09:07 AM
I'll take your and Glenn's ideas in mind. When I finish it I will post the way I did it and a photo.

Sparky_NY
01-25-2010, 09:19 AM
Sparky,

That's a perfect example of why using thread wires to measure the spindle end threads, and making a threaded plug to match it is the way to do it for a nice fit when making the mating threaded part. No math or charts required. Just make the dimension on the plug threads match the spindle thread measured dimension.

Sadly, this is probably true. I considered it but realized the plug would have to be a exact duplicate of the spindle in every respect otherwise it would do more harm than good.

I was looking for a KISS method of doing it. It does not exist. Even using thread wires and making a perfect duplicate plug shaft, it still comes down to hand fitting when threading the internal matching thread.

The good part is that I learned more about thread forms than I ever knew. This will no doubt make future threading projects go smoother.

I found this hard to believe, I now believe.

Carld
01-25-2010, 10:56 AM
Every machining operation is a learning experience for something in the future.

I could not stand to ignore the centering tool for my lathe anymore. I just measured the threads again and wrote them down and will put them with the part to thread.

What I found is the bore is 1.725 and the thread pitch is 1.5mm. I measured the single depth of the thread with a short 60deg tip dowel and it is .029"x2=.058" double depth. That makes the OD of the male thread area 1.783" but of course it can't be that big or it would be an interference fit.

Next I measured the area on the part to thread and thank goodness it is bigger than the 1.783" so I did leave "room to move" as John Mayall sang in one of his blues tunes.

What I am thinking is to use an Imperial thread that closely matches the 1.5mm pitch so I can release the half nuts on each pass. The reason is I have to thread as close as possible to a shoulder because the thread is only about 1/2" long.

I will start a new thread on how it goes. BTW, I can't turn it between centers because the part is to short but I think my indexing idea will work and I can test it for a good fit. I'll show that as well.

I really like cutting threads but I don't get to thread as much since I retired. At work I got to thread a lot.

Black_Moons
01-25-2010, 04:39 PM
Carld: we'r in the same boat now! start bailing!

Ok well, honestly, from my experiance, mine is 16tpi or 1.6mm, Can't decide what. doesnt seem to really matter.. I think I might go with 16tpi since it seems to be 1 5/8" (Only standard thing on the entire lathe?)

For the whole 'shoulder' thing, turn yourself a *left hand* (my mistake first time around.. now to go grind another) threading bit, and use it upside down
You can still crash doing the halfnut method.

Then you can thread with your lathe in reverse
to reset the position, use forward till within a couple turns, then manualy spin the chuck to get it RIGHT on the spot. Yea I know that chuck is heavy and the gearingyadayada, if it helps any you CAN disengage the motor drive gearbox while hand spining the chuck, the feed box should be connected directly to the spindle.

Im allready setting up my lathe to turn a 3" long 'test plug' outta aluminum beween centers... Now I just gotta make a 2" lathe dog.

Protip: Center drill your workpeice *before* removing your 4 jaw chuck, droping it on your finger only to realise you have to replace the 4 jaw chuck to center drill the work.

Carld
01-25-2010, 08:04 PM
:mad: row, row, row the boat, gently to the shore, before the damn thing sinks and makes you swim for the shore.

I had thought about threading from the shoulder but I haven't ruled anything out yet. My lathe has a foot brake and I can stop it so fast it's scary. To cut metric I have to leave the half nuts engaged. I have room at the shoulder to undercut and have room to stop.

Got some thinking and planning to do. These reasons is why it has set on the tool box for a year but it's time to s**t or get off the pot as mom used to say.

Black_Moons
01-25-2010, 09:19 PM
Carld: My idea is im gonna make the length to shoulder about 3/4" and use a 1/4" washer to cover up my 'landing' groove.. but really its because I needed a washer, honest.

Course, Now I realise I don't have a dog for the test plug peice I wanna do.. I could drill/tap a hole in it.. but I kinda wanna make a dog, especialy after realising the smaller one I bought won't even fit into my faceplate.... of course that means putting the chuck back on.... -_-;

oldtiffie
01-25-2010, 10:02 PM
:mad: row, row, row the boat, gently to the shore, before the damn thing sinks and makes you swim for the shore.

I had thought about threading from the shoulder but I haven't ruled anything out yet. My lathe has a foot brake and I can stop it so fast it's scary. To cut metric I have to leave the half nuts engaged. I have room at the shoulder to undercut and have room to stop.

Got some thinking and planning to do. These reasons is why it has set on the tool box for a year but it's time to s**t or get off the pot as mom used to say.

Carl.

I think that I have the answer for you.

It will be obvious when you see the work sheet.

All that I need now from you is the id (bore) at the threaded part of the back end of your spindle.

I need that to finalise the nominal OD of the thread.

As it is an Asian lathe (presumably), I have assumed that it is a metric thread with a 1.6mm pitch (which is ~ 15.875 ~ 15 7/8 tpi).

I have checked the difference if using an inch thread with 16 tpi = 1/16 = 0.015625" pitch and the difference is near enough to 0.008" (8 thou) per inch length of thread.

I have assumed that the manufacturer has allowed for the 80% pretty well bog-standard thread flank contact length.

I suggest that you use a HSS tool with very keen edges and as small a nose radius as you can get.

If you have a set of soft-jaws, I suggest using them.

I also suggest that you drill and tap (3 or 4?) adjusting screw holes on the spider flange and insert one (say hex headed socket) screw and a spring washer and a lock-nut to use as an indexer against one of the soft jaws. The soft jaws will locate the job for axial (length) position as well as concentricity.

This will allow you to remove the job from the lathe chuck soft jaws for testing for "fit" and/or "way to go" in the spindle thread and then to re-position it accurately in the lathe for any further cutting.

I'd leave parting-off until the job it finished

I have to "tidy up" my work-sheet (math) and I will post it here for all to see.

And here's the "Hillbilly" bit:

I did not need "wires", pitch (cylinder) diameter or Machinery's Handbook - just a table that I've posted here previously.

I can almost hear the chorus now: "bull-$hit", "no way", "utter crap", "rhubarb" (UK), "boo", "hiss", "get him off", "toss him out", "wanker", "tosser", "smart-ar$e", "bluddy OZ ba$tard", etc. etc.

Probably all true.

(And that's my "friends" - both of 'em - ie me MUM (twice!!!).

If this works - a I hope it will - you may be giving your Dear Old Mum's "pot" a good working-out - at last!!!

This might help Black_Moons as well as he has a similar pitch thread in rear of his lathe spindle.

Can you lend him that pot after you've finished with it as the sooner he gets on it and "does his thing" the better.

oldtiffie
01-26-2010, 12:37 AM
And a nuthery for the "Hillbillies"and us "Shade Tree Muck-a-nicks".

"Whiskey in the Jar"

(I used to get through a bottle of "Glenfiddich" a day over three days or so -plus - not all that long go - nearly killed myself - straight off it - "cold turkey". Love that "glenfiddich").

http://www.youtube.com/watch?v=46EXY4oP1Do

http://www.google.com.au/search?hl=en&source=hp&q=glenfiddich&meta=&aq=0s&oq=glen+fi

oldtiffie
01-26-2010, 02:47 AM
Thanks Carl.

I went back through the thread and found this:


Every machining operation is a learning experience for something in the future.

I could not stand to ignore the centering tool for my lathe anymore. I just measured the threads again and wrote them down and will put them with the part to thread.

What I found is the bore is 1.725 and the thread pitch is 1.5mm. I measured the single depth of the thread with a short 60deg tip dowel and it is .029"x2=.058" double depth. That makes the OD of the male thread area 1.783" but of course it can't be that big or it would be an interference fit.

Next I measured the area on the part to thread and thank goodness it is bigger than the 1.783" so I did leave "room to move" as John Mayall sang in one of his blues tunes.

What I am thinking is to use an Imperial thread that closely matches the 1.5mm pitch so I can release the half nuts on each pass. The reason is I have to thread as close as possible to a shoulder because the thread is only about 1/2" long.

I will start a new thread on how it goes. BTW, I can't turn it between centers because the part is to short but I think my indexing idea will work and I can test it for a good fit. I'll show that as well.

I really like cutting threads but I don't get to thread as much since I retired. At work I got to thread a lot.

From:
http://bbs.homeshopmachinist.net/showpost.php?p=513438&postcount=102

What I found is the bore is 1.725 and the thread pitch is 1.5mm.

It is exactly what I was after.

I measured the single depth of the thread with a short 60deg tip dowel and it is .029"x2=.058" double depth.

You got that pretty right too!!.

I have all the info now.

The thread is a metric 45mm x 1.6mm pitch - right on!!

I will finish off and tidy up the work-sheet and will post it shortly - hopefully today.

Later.

oldtiffie
01-26-2010, 05:43 AM
For: CarlD.

Carl.

First of all - here are:

a.
the screw thread form/profile details for metric and UNC and UNF - they have identical 60 degree profiles. I have used this as a reference.
http://i200.photobucket.com/albums/aa294/oldtiffie/Black_book/Black_book2_P23_1.jpg


b.
my work-sheet.
http://i200.photobucket.com/albums/aa294/oldtiffie/Sketches/M45x16mmthread1.jpg

I suggest that you print both of these out together as it will be easier to read/follow on the desk than it is on the screen.

In short/summary, your "bolt/screw" (male) adaptor will be M45x 1.6 ie. 45.00mm (1.772") nominal diameter with a 1.6mm (0.063" ~ 15.875 tpi) pitch thread with the standard/universal 60 degree profile/form.

Keep as small a radius on your screwing tool as you can.

The aim is to have the 0.125P "flat" reduced to 0.008" (a half of a 1/64" graduation on a Machinist's "inch" steel rule. You eye should do this easily to within 0.002" - or better.

At that stage, I'd suggest that you start trying the fit in the female thread inside th rear of your lathe head-stock spindle - just "nibble away" at it until it "feels OK" to you.

If it were me, I'd aim for "medium" to allow for grit pick-up and to minimise "galling".

If you'd like to discuss it further - just post and ask away!!

I am very interested to see how this works in practice.

I hope it works well.

I hope it is of use the Black_Moons as well.

Best of luck.

I'm off back the chair and the jar under my shade tree.

Carld
01-26-2010, 09:46 AM
:D Tiffie, you won't believe this but, The method I devised last year to remove and test the thread is as follows:

I machined the part to size with the thread area oversize and marked the part where #1 jaw was. I drilled and taped the three centering bolt holes. I then put one bolt in one hole that lined up real close to the mark, I didn't get it drilled exactly where I wanted but it's very close. Now I can install and remove the part from my 3 jaw and stay within +/- .001" for testing the thread fit.

The problem was the math to get the thread size. Since I am not good at math I had to be creative as always. I have worked backwards on threads like this before but never on metric. Having to keep the halfnuts closed was a big concern, hence the delay to cut the thread.

I read your work sheet and will print it out and study it. I wish I could work math like that but alas, I can't. When I checked the thread I used my metric thread gages I have a 1.5 but don't have a 1.6 and my lathe only has a 1.5 thread on the chart. The 1.5 gage fit the thread very well and I don't think it will hurt it the thread is really a 1.6 if I cut it 1.5 since it's only about 3/8" long.

1.5x.03937=.059055=.059"

1.6x.03937=.062992=.063"

Will the .004" difference between the thread pitches make a difference on this short of a thread? I really don't think so.

My metric thread gage has maybe 15-20 gages and sometimes I wish it had 50.

EDIT: I just used a feature to copy to my documents that Google Chrome has that is extremely handy, will be using that a lot from now on. Since I am snowed in I will cut the thread today.

Black_Moons
01-26-2010, 03:05 PM
Carld: use a smaller 1.5 or 1.6 pitch bolt to get the thread pitch.

Or buy some of these awsome gages:
http://www.landroverclub.net/wilberforce/jpgs/thread%20gage.gif

oldtiffie
01-26-2010, 03:44 PM
Thanks Carl.

I am not the least bit surprised that you intended to use the same principles for indexing and location. I'd have been disappointed if you hadn't. You did not let me down.

Many thanks.

The usual "metric way" would be a thread with a ".5" in the pitch for it in it as opposed to a ".6" so I'd opt for the "1.5" and go for the 45 x 1.5 instead of the 45 x 1.6.

The effect will be minimal as regards this project.

I'd set for M45 x 1.5 and get going.

The difference in the with of the"flat" will be so small that I doubt that you'd see it or that it will matter at all either.

There is a lesson to be learned here - by me included I guess.

We all seem to have been "sucked in" by how "close" the 16tpi (0.0625" = 1.5875") is to 1.6mm (0.0630") are to each other when using a 16tpi thread guage and not a 1.5mm or 1.6mm pitch guage.

A short length (say 1/2") of a bit of bolt or "all-thread" M10 x 1.5 or M14 x 1.5 (for metric) 3/8"-16 or 3/4"-16 (for inch) laid in the spindle thread would have soon and very clearly have shown the difference much better than a 16 tpi thread guage would have or could have.

Perhaps I'd better leave the thread pitch guage in the bin where it resides with the "3 wires" and "pitch diameter" for some of these sorts of jobs.

My approach on this was based on the profiles (read: ratios) of the threads being constant but the actual sizes depended on or were conditional on one of the diameters and the pitch.

Once I had your bore and pitch and guessed at the "80% of thread" the rest pretty well fell into place.

As its so bloody hard to measure any internal thread ordinarily I went for the "width of flat" for approximate size and relied on your "feel" and common sense and experience.

It IS quite possible to measure internal threads for "diameter" and "class of fit" without a thread guage - but that too relies on the good sense of the operator.

I will keep that for a future thread (sorry) in this forum.

Best of luck.

So - more lessons learned

Carld
01-26-2010, 04:05 PM
Tiffie, I looked in the MH book and it listed a M45x1.5 thread so I used that with the figures you posted and they matched very close so that is what I used.

The outcome is in another thread and has good and bad outcomes.

I've had to use some pretty creative ways to index a part to remove it and test it and this worked in the past so it should work and did. I do prefer turning something between centers if I have to remove it for testing.

You really have to watch for left hand threads though.