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hwingo
04-11-2009, 02:05 AM
Hi guys,

I'm down to cutting some threads and they look strange while forming and for certain look wrinkled or wavy near the point. Is this normal?

I am turning 18 TPI, ID, using 4130. I am using a new carbide insert. As groves are cut, flats are temporarily left. As groves get deeper the flats take on an appearance of "split threads". On close inspection using loupes, edges along the flats appear raised giving the impression that threads have been split. Additional cuts eventually remove the raised areas but when the thread is "pointed", the very edge of the point is obviously wrinkled or wavy.

Is there a cause for this or is the normal?

Harold

oldtiffie
04-11-2009, 02:26 AM
Harold,

as one older "wrinklie" to a younger one, I would guess that your lead-screw half-nuts are not engaging properly such that the "stop" (that limits travel of either or both the half-nuts or the actuating lever) has not "hit bottom" and so the carriage will lag the correct position as the nuts engage too far up the lead-screw thread (probably the "trailing" or back) flank/s.

Can you post some pics please? Those excellent high-contrast black & white pics will do fine as well if needs be.

You can get an indication of the correct meshing/engagement of the half-nuts if you leave the power off your head-stock spindle, and fully engage the half-nuts at any mark on your thread-chasing dial. Turn the head-stock spindle a couple of turns. Check that the indicator/arrow/mark on the chaser is exactly on a mark/line on the chaser dial. Adjust as required.

You will now be able to see if the half-nuts are fully engaged as if they are the line and the pointer/indicator will be co-incident.If not, the lever needs to be pressed further down until it hits that stop.

I suggest that you engage the half-nuts at least 1" out from the start of the screw-thread as this will give you time to either push the lever right down or to disengage the half-nuts or stop the lathe spindle.

Just take your time. This is a classic "Hare and Tortoise" situation.

I would not be concerned about seeming to ask a lot of basic questions as my guess is that many others will "latch onto" them as something they either want to know or comment on or were not confident to ask for themselves - or just didn't think of them until you ask them.

I've had quite a few "head-scratchers" from some of your questions and comments I can tell you!!

Keep 'em coming.

hwingo
04-11-2009, 03:45 AM
Hi Tiffie,

I will be happy to post a few B+W images. It's nearly 2300 HRS in Alaska so if you will just hang in there like a hair on a biscuit, tomorrow morning I will either supply images of that which I turned tonight or better yet I will turn a new piece and photographically record progressive steps through completion. Does that sound ok?

In passing, the original chasing dial's pointer was quite a bit off when installed witnessed by that shown in the following image.

http://i234.photobucket.com/albums/ee38/hwingo_2007/Lathe9-1.jpg

Not being the "sharpest knife in the drawer", coupled with being chronologically challenged (I'm so old that I get my hunting & fishing license free in Alaska:rolleyes: ), I was easily confused by which side of the line I engaged the half-nut so I have removed the factory installed arrow and scribed a line on the chaser's body so that it will line up with lines and numbers. I have also learned tonight that I can fully engage my half-nut half way between each line as shown by the blue lines in the following image. What is the significance, if any, of being able to engage on the blue lines?

http://i234.photobucket.com/albums/ee38/hwingo_2007/Lathe11.jpg


Harold

barts
04-11-2009, 05:32 AM
Harold,

as one older "wrinklie" to a younger one, I would guess that your lead-screw half-nuts are not engaging properly such that the "stop" (that limits travel of either or both the half-nuts or the actuating lever) has not "hit bottom" and so the carriage will lag the correct position as the nuts engage too far up the lead-screw thread (probably the "trailing" or back) flank/s.


I've had similar problems. One way of figuring this out is to set up to thread about ~20 tpi, and just take that very light first pass - and then keep repeating that w/o advancing the compound. Any error in half-nut engagement will be immediately apparent. You can then figure out a scheme for avoiding it or at least being able to feel when it happens. On my lathe I can run into this when I engage late, so becoming more deliberate helped prevent this from happening.

J Tiers
04-11-2009, 08:21 AM
I am turning 18 TPI, ID, using 4130. I am using a new carbide insert. As groves are cut, flats are temporarily left. As groves get deeper the flats take on an appearance of "split threads". On close inspection using loupes, edges along the flats appear raised giving the impression that threads have been split. Additional cuts eventually remove the raised areas but when the thread is "pointed", the very edge of the point is obviously wrinkled or wavy.

Is there a cause for this or is the normal?

Harold

It seems from the description that you are doing the thread dial perfectly, and what you are seeing is displaced metal, that the threading insert pushes out of the way instead of cutting.

This is pretty normal with all threading, but may be worse with carbide and low speeds because carbide is inherently "dull" compared to a honed HSS cutter. Harder, but dull do to being made of little hard bits in a metallic binder.

Some materials also do that, mild steel like 1018 being a known offender. The 4130 I don't know about, 4140 seemed OK to me when I last threaded it, but I was threading it at IIRC 9 tpi, so the turned-over edges would be less noticeable.

Using a sharp HSS cutter will improve it, but any unsupported edge of material will have some tendency to push away instead of being cut, at the low speeds inherent to threading.

A fine wire brush can get rid of the bit that is left when the thread is done.

kmccubbin
04-11-2009, 08:32 AM
(Edit: I gotta learn to type faster, sorry for the repeat info)
Harold, To me it sounds like you're describing a burr being formed that rises above the original OD of the work. I see this on every thread I cut in steel. Some metal gets pushed up and out of the thread rather than being cut off. I deal with it by threading until I reach my target minor dia, then I run a file lightly over the top of the threads, then test the thread with a nut. Then make another cut, file, repeat as necessay. I'm no expert by anyone's standards, but I've asked some "real" machinists who tell me that this is normal, and that's why they make the full form threading inserts... to remove the burr and give the correct shape to the top of the threads. Perhaps someone can tell both of us how to keep it from happening!

Hope that helps,
Kerry

quadrod
04-11-2009, 09:06 AM
i will second the use of HSS cutters. i have not used an insert style carbide, but with the brazed carbide cutters i have tried the point always seems to crumble and then the tread goes to s@#%. try grinding a 60* point on some HSS steel, give it some top rake if using a flat tool holder, of course some side rake too, then use a fine hone to touch up all the edges and give it a try.

Carld
04-11-2009, 09:23 AM
hwingo, you said new insert. Are you using a threading insert and holder or a standard triangle insert and holder to cut the thread?

hwingo
04-11-2009, 01:22 PM
Good Morning Guys,

Just having my first cup of coffee while replying to your overnight post.

Starting with Carld’s question, “Are you using a threading insert and holder or a standard triangle insert and holder to cut the thread?”, I am using a right-hand internal thread insert in conjunction with a right-hand internal threading bar. I see you are from KY. I was born in Dawson Springs, KY.

J Tiers, I wondered about that as I read your reply (to include Kerry and Quadrod). Various things are coming back to me from years past. I seem to recall a similar explanation by a local machinist (from years ago) as he was threading using carbide. Over 20 years ago I had a “hobby shop”. My son was killed and I lost interest in just about everything thus I sold my equipment. Nineteen years later I find myself becoming re-acquainted with new equipment, principles of machining, and a wealth of forgotten information. On reflection, I always used cobalt or HSS threading tools. My threads were clean and well formed throughout the process (unlike what I am seeing today). I cut at very low speeds (using back gears on my SB lathe), hence, I never remember seeing threads take shape like those I described (which were cut at low speed and using carbide). I used the conventional “V Cutter” that was hand-ground and honed when threading steel and aluminum. That likely explains differences I now realize during thread formation when using carbide as opposed to HHS.

Bart, I really like your “testing idea”. I previously promised Tiffie that I would capture some images during thread formation. As soon as I follow through with my promise (which will be shortly), I will definitely do as you have suggested. I have a feeling this will prove valuable for several reasons:

1. It will prove or disprove inaccuracies in my chasing dial
2. Through familiarity I will learn of any “quirks” or irregularities inherent to my machine’s chasing dial and how to circumvent consistent inherent quirks. All machines seem to have their own “personality” and a relationship must be forged between the operator and machine.
3. This test will instill trust in my equipment or at the very least aid me in determining which regions might be "off kilter" on the chasing dial
4. It will serve to build confidence in my abilities to overcome inherent irregularities or recognize problematic areas that should be avoided

So Bart, I really like this idea!

Now, if you guys will excuse me, I must go into the shop and whisper “sweet nothings” into the ear of my beloved lathe with hopes of wooingly seducing her into performing. I shall return with some images.;)

Harold

Glenn Wegman
04-11-2009, 04:55 PM
hwingo,

I may have missed it but I don't believe you stated what the ID of the bore you are threading is. Is it possible that the insert is "heeling" or rubbing due to lack of relief?

Internal threading is subjected to relative relief issues as the bore size decreases.The same tool bit in a 4" bore has far more relative relief that it would in a 1" bore.

Carld
04-11-2009, 07:28 PM
That's what I am thinking too. That's why I asked what he is cutting with. When I get wrinkled threads internal or external it always seems to be side clearance of the cutter. If the nuts are picking the thread up wrong it will be cross threaded. I always try to use the same number I started on to do the whole thread.

J. Randall
04-11-2009, 07:40 PM
I have to disagree with Quadrod, if you decide to grind a hss tool do not put any rake on it, the top needs to be flat. You will need some clearance or relief on the sides and front of the tool, especially the side that is advancing into the cut.
James

quadrod
04-11-2009, 10:34 PM
J.Randall, that is fine i am a noob too. the SB9A i cut my teeth on ( heck still cuttin them teeth ) has a rocker tool post so top rake was built into the tool holder. now i have a SB13 and a QCTP and the tool bits are flat. flat works and i also tried some top rake too, it worked also but that does not mean it is the correct thing to do.

J. Randall
04-11-2009, 10:42 PM
Quadrod, you might cut a usable thread that way, but the geometry won't be correct. If you have to use a rocker with built in rake grind the top of the tool back flat to eliminate the rake and get a correct thread form.
James

hwingo
04-11-2009, 11:20 PM
Well, well, WELL! This took much longer than I thought but I most definitely learned something while doing this exercise.

Let me first address Glenn before I get started. The ID is 1.01 inches. Glenn, you made a good point which I did not take into consideration when cutting the previous threads, that being, sufficient heel clearance. Before reading your post I decided to wear my surgical loupes so I could really see what I was doing. When it came time to thread, I removed one QCTP and installed my QC threading holder (with tool in place from previous threading). With magnification I could easily see that interference was about to occur so I rotated the bar just enough that the heel would not drag. You can bet your bottom dollar that I was dragging the heel with my previous attempt. So you have made a good point.

On to images. After setting the threading tool where the heel wouldn't drag I applied layout fluid so I could see lines form on the work.

http://i234.photobucket.com/albums/ee38/hwingo_2007/BoltBody3copy.jpg

After making a couple of very light passes I stopped to capture the following image which clearly demonstrates broad flats (still covered with layout fluid) and beginning groves (raw metal).

http://i234.photobucket.com/albums/ee38/hwingo_2007/BoltBody5copy.jpg

I made several more deeper cuts and begin to see, for the lack of a better word, extrusion of metal on each side of the grove. When seeing this three dimensionally, one can easily see metal rising above each "flat".

Closer magnification demonstrates more clearly raised edges.

http://i234.photobucket.com/albums/ee38/hwingo_2007/BoltBody6copy.jpg

When inspecting finished threads, I could clearly see a thin black line on each crest. This can be seen in the following image. It appears that extruded edges have folded (collapsed) on themselves thus forming a pseudo-crest and this concerns me. If this is in fact a false crest then threading is incomplete and flawed. What are your thoughts on this? See following image.

http://i234.photobucket.com/albums/ee38/hwingo_2007/BoltBody7copy.jpg

Harold

dfw5914
04-11-2009, 11:59 PM
Sorry, can't offer any advice on the threading. Just wanted to compliment Hwingo on the exceptionally nice photography and post composition.:rolleyes:

oldtiffie
04-12-2009, 12:21 AM
Harold (and perhaps some others too),

those TC inserts are fine if they are sharp-edged and the set-up is rigid.

But I don't know if you know/realise that there are internal and external indexable TC threading inserts.
https://www.machineryhouse.com.au/Threading-Inserts

At/from the front of the lathe, the "eternal" thread on a right-hand thread slopes to the left (it advances from bottom-right to top-left) as it progresses toward the head-stock, where-as the "front" of the internal thread slopes to the right (viewed from the inside toward the front of the lathe, it advances from bottom-left to top-right).

So if you are using an external insert to cut right-hand internal threads you will certainly get a "rub" due to insufficient side clearance angle/s.

If the inserts you are using are very sharp, and having that "groove" along each cutting edge, they will far out-perform a HSS tool with a "flat top". The "flat top" effectively has a positive side rake equal to the thread helix angle on the leading/front/"cutting" edge and similarly a negative side rake on the "trailing" edge of the thread flank in the "vee". The threading tools are traveling in a helix equal to that of the thread being cut.

The "groove" on the trailing edge of your TC inserts decreases the negative rake on the trailing edge - and is quite often positive. That is why TC inserts cut so well on both sides together and do not need the "off-set 29.5 degree on the top-slide" effort.

I have no problems with back-rake and side rake together (ie "non-flat") on the top of a/the HSS tool at all - in fact it works much better, cuts cleaner and rarely "chatters". The cutting edges can easily be ground to compensate for any errors caused by not having the top "flat". Taps and dies are adequate proof of that.

Here are my "tilt-able" screwing tools that not only have rake but have a template/guide to go with them. They work extremely well. I just tilt to cut either or both sides of the thread to get the finish I need. (Also shown are my similar parting-off tools).
http://i200.photobucket.com/albums/aa294/oldtiffie/I-Fanger1.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/I-Fanger2.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/I-Fanger3.jpg

There is nothing wrong with having just "flats" and no "curves" on the crest and roots of threads as the main bulk of load and location is taken by the "straight sides" (leading and trailing thread flanks/sides). A close look at the thread-form tables/diagrams as well as the tapping tables will pretty well demonstrate that.

If I am doing a large thread or say an acme thread I will use a "parting tool with a point" to get rid of the bulk of the material to be removed. I will use separate tools with adequate side and front clearance and side and back rakes on each flank - which works very well.

Threading is just another type of "form-tool work" with exactly the same problems and solutions. Few would expect a "vee" (or "acme-shaped") tool to just plunge in and cut without adequate rakes and clearances - or without "chattering" either.

"Parting-off" is a "form-tool" job as well and people take more care with that than they do with screwing tools - and yet they are so similar in cause and effect.

J Tiers
04-12-2009, 12:59 AM
Well, well, WELL! It appears that extruded edges have folded (collapsed) on themselves thus forming a pseudo-crest and this concerns me. If this is in fact a false crest then threading is incomplete and flawed. What are your thoughts on this? See following image.

Harold

two things:

1) Threads are completely formed when they are of the correct pitch diameter. If there is a flat on the crest, so be it.

2) measuring the pitch diameter on an internal thread is just not practical in any way you can achieve, so the best thing is, for a critical internal threading job, to make an accurate plug gage to fit, preferably a limit gage with 'go" and "no go" sections. This will be a male thread, which can be very accurately measured.

Getting back to reality, it's right when it fits the part you need it to fit....... even if it has flats.

The only issue is that if you find it is tight, remove the burrs of "extruded material" before you decide to cut the thread deeper. If they are the problem, when you cut it deeper and de-burr it, you will find it is really loose. Removing the burr may make it fit correctly with no more work.

oldtiffie
04-12-2009, 01:25 AM
Hi Tiffie,

I will be happy to post a few B+W images. It's nearly 2300 HRS in Alaska so if you will just hang in there like a hair on a biscuit, tomorrow morning I will either supply images of that which I turned tonight or better yet I will turn a new piece and photographically record progressive steps through completion. Does that sound ok?

In passing, the original chasing dial's pointer was quite a bit off when installed witnessed by that shown in the following image.

http://i234.photobucket.com/albums/ee38/hwingo_2007/Lathe9-1.jpg

Not being the "sharpest knife in the drawer", coupled with being chronologically challenged (I'm so old that I get my hunting & fishing license free in Alaska:rolleyes: ), I was easily confused by which side of the line I engaged the half-nut so I have removed the factory installed arrow and scribed a line on the chaser's body so that it will line up with lines and numbers. I have also learned tonight that I can fully engage my half-nut half way between each line as shown by the blue lines in the following image. What is the significance, if any, of being able to engage on the blue lines?

http://i234.photobucket.com/albums/ee38/hwingo_2007/Lathe11.jpg

Harold

Harold.

I think/hope? I can sort that out for you.

As for your first pic:

Having the static index mark on the body of your thread-chasing dial align with the mark/s on the "moving" dial shows where the half-nuts are fully closed and meshed/mating with the lead-screw threads.

There is a lot of "good feel" and reflexes required in thread-chasing dial work.

I lightly lean on my half-nut lever so that the nuts are just rubbing slightly (VERY lightly - to minimise wear) on the outside diameter of the lead-screw. I can "feel" when the nuts are moving from the outside diameter of the lead-screw and just moving into the thread "grooves". I "close" the half-nuts then and let the lead-screw (and the carriage) "catch-up" to me. This makes full engagement very easy. You can do the same thing by pressing down on the closing lever just before the mark on the dial that you intend to use gets to the "fixed" index mark on the dial body. (I use both together).


As for your second pic:

I'd be truly amazed if you couldn't close your half-nuts at the blue lines.

The 1, 3, 5, 7 are "quarter turns" and the original "in between" black lines are "half of that ie "eighth turns". It follows that your blue lines are "one-sixteenth" turns.

If I recall previous posts on that subject, your lead-screw has a pitch of 1/8" and your "chaser gear" (which engages the lead-screw) has 16 "teeth". The "gear" will advance one tooth for each turn of the lead-screw, which as said is 1/16 of a turn of the gear and the chaser dial which it drives. So, 16 turns of the lead-screw drives the dial one turn exactly. Further, if the lead-screw is stationary and the half-nuts are not engaged, if the carriage is moved 1/8" the gear will rotate 1/16 of a turn as before. Now, moving the carriage 2" (which is 16 x 1/8" lead-screw pitch) will also rotate the threading dial 2" (1 full turn).

The blue lines are equivalent to 1/8" movement of the carriage or 1 turn of the lead-screw. They come in very handy if you are threading anything that is a multiple of 8 tpi - 16, 24, 32, 40, 48, 56, 64 etc. which just so happen to be able to be engaged anywhere. The blue lines show you where that 1/16 = 1/8" position is.

Or put another way, if the thread is indeed 8tpi or a multiple of 8 tpi then as you can drop in anywhere, and providing your "feel" on/for the half-nut engaging lever is OK, you can forget about the threading dial altogether or just leave it disengaged. You will/may need the threading dial for any other threads.

As previously, despite the confusion and some justified adverse comment about the marking/numbering of your lathe threading dial and the screw-threading diagram plate on your lathe, both used together will work just as well as any other lathe.

I hope I have clarified this somewhere between "somewhat" and "completely".

If not - please do get back to me as I want to get it right as much for my own satisfaction as for yours.

As I said in a previous post, you have a knack of asking the questions that a lot of others - for their own reasons - will not, and once you "kick off" and get the ball rolling it almost develops a momentum of its own, which hopefully benefits some others as well.

There are a few others here with the same knack - Teenage Machinist aka "TM" is a very good case in point.

Keep 'em coming Harold.

hwingo
04-12-2009, 03:22 AM
Hi Tiffie,

To answer a question you posed in a previous post about differences between internal and external indexable inserts, yes I was aware of the differences but it was only recently that I became aware of this fact. A local friend helped me pick the inserts and bar I needed to accomplish the task of internal threading while explaining differences between the two.

To address if the half-nut will "fully close" on the blue lines, the answer is yes. I had already been "feeling" the half-nut into closed position as you had described when I discovered the additional closure points, i.e., the blue lines.

I was in hopes that you might say, "These blue lines can be used for fabricating dual-lead threads." Years ago I was attempting to make a screw-in shotgun choke. I had purchased a tap from Brownells specifically designed to thread the inside of a shotgun barrel for a specific brand choke. I'm going to make up my numbers by saying the thread pitch was 20 TPI. I made a very nice choke @ 20 TPI and the darn thing would not screw into the barrel. So I measured again, started over, and when finished the new choke would not thread into the barrel. I took the tap, a factory make choke, and my homemade choke to an old machinist who was serving as my mentor. Having been around the Horn and having seen the White Buffalo, it didn't take Mr. Wells long to recognize that I was dealing with dual-lead threads. He explained that on one line (possibly and even number) I would begin threading at 10 TPI and on what I think was an odd number, I would also begin threading at 10 TPI. Both leads began 180 degrees out from the other and essentially I was splitting the 10 TPI and when finished the threads had full form *appearing* to be 20 TPI except both threads had two different starting points. He said it was also possible to cut tri-lead threads but he didn't tell me how to do that so I never tried. I was using a SB lathe at that time. I thought that was sooooo cool to be able to cut dual-lead threads and I am hoping that I can do the same thing with this lathe with no less difficulty.

Would you mind addressing dual-lead threads and if my lathe has this capability, would you please tell me exactly what I need to do in order to cut various dual-lead threads on my lathe? Also do you think I would be able to cut tri-lead threads as I would surely like to give that a try?

Harold

hwingo
04-12-2009, 05:02 AM
Sorry, can't offer any advice on the threading. Just wanted to compliment Hwingo on the exceptionally nice photography and post composition.

Thanks dfw. I appreciate your compliment.

Harold

oldtiffie
04-12-2009, 05:48 AM
Thanks Harold,

you are making excellent progress as some of this is difficult to visualise as a concept - and you are managing it OK.

Well done.

Yes, it is quite possible - but always, perhaps with(in) limitations - to cut multi-start threads on your lathe.

But a new term or concept that is essential with regard to multi(ple)-start threads - thread lead.

Thread lead and thread pitch are often used inter-changeably - which they are in single-start threads - but not in multi-start threads.

Thread pitch is the distance along the work axis between identical points on successive threads - ie "point-to-point" if you like.

Thread lead is the distance the thread/spiral of a single groove moves along the work axis in a single revolution.

For example, a 1/8" pitch 2-start thread has a lead of 1/4" and similarly a 1/4" pitch 3-start thread has a lead of 3/4".

I will address this matter either later this evening or tomorrow (Monday) in-so-far as it relates to the lead-screw, gear-train, quick-change/threading gear-box and thread-chasing dial on your lathe.

I have no doubt that having got this far that you will comprehend this and master it as well.

Glenn Wegman
04-12-2009, 09:35 AM
Harold,

Exactly what size thread are you trying to cut? 1 1/16 18?

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


Glenn

Glenn Wegman
04-12-2009, 10:29 AM
Harold,

Another observation:

By rotating the tool slightly downward to eliminate the "heeling" I believe that you have now introduced a slightly negative interface between the tool and the part. This, at the surface speed you are threading at, my have an effect on the finish as the tool may be plowing rather than cutting. I can't quite visualize it without being at my lathe which is 35 miles away, but it may have an effect on the tool geometry when feeding in at 29° and possibly causing the ridges.

Just looking at the insert, I would guess that it is most likely oriented toward CNC threading which would be accomplished at much higher surface speeds. For manual threading I prefer the style which is just ground flat on top with no chip breaker or land. If you run your thumb nail perpendicular to the cutting edge it should easily scretch it, indicating it has a sharp edge.

Glenn

38_Cal
04-12-2009, 10:38 AM
Just to inform the non-gun folks online, the double lead choke tube Harold was referring to, if in 12 gauge, would be .795"-44dl or .775"-44dl, depending on which choke system he's using, standard TruChoke or Thinwall. So, opposite start points of 22 tpi.

David
Montezuma, IA

Glenn Wegman
04-12-2009, 11:31 AM
Just thought of another possibiliy!

Which way do you have the compound swiveled?

Hopefully with the handwheel 29° to 29.5° to the left of center for internal threading. (Assuming that the handwheel is toward you)

I usually finish threading by cutting the last .002" or so using the cross slide rather than the compound and taking it in a couple of passes to smooth out the thread form. Works very well if you have a good sharp tool. Peels off a nice thin ribbon and leaves an excellent finish if executed correctly.
Glenn

Carld
04-12-2009, 02:03 PM
hwingo, it looks to me that the insert may still be wrong. If I grind a tool to thread internally the front of the tool is ground away just below the cutting tip so it rolls away from the radius of the bore.

What you need to do is grind the front of the V from just under the top toward the bottom in an arc that will allow the cutter to clear the threads as it advances. This is more critical for internal threads than external.

The insert in your photo looks to be an external insert.

oldtiffie
04-12-2009, 07:36 PM
Harold,

please post new pic/s of the gear-train on the head-stock of your lathe (from the head-stock spindle to the input to your threading and feeding quick-change gear box) as well as any other tables/diagrams regarding threading and feeding on your lathe.

Too many is better than not enough as I will sort them out.

I need them to give you a reply specific to your lathe as regards multiple-start threads.

I don't need this one at this stage:
http://i234.photobucket.com/albums/ee38/hwingo_2007/Lathe1.jpg

I will stay out of the discussion regarding tool setting, use and shape etc. for a while and just concentrate on the multiple-start threads

Thanks.

hwingo
04-13-2009, 12:52 AM
Hi Tiffie,

Attached are the remainder of charts/graphs with exception of metric. Since I have little need for metric (someday perhaps) I did not include these charts.

Are you requesting that I include actual images of the gears and pulley system in the head stock or images of graphs/charts?

Harold

http://i234.photobucket.com/albums/ee38/hwingo_2007/Lathe10.jpg

http://i234.photobucket.com/albums/ee38/hwingo_2007/Lathe3.jpg

hwingo
04-13-2009, 12:59 AM
hwingo, it looks to me that the insert may still be wrong. If I grind a tool to thread internally the front of the tool is ground away just below the cutting tip so it rolls away from the radius of the bore.

What you need to do is grind the front of the V from just under the top toward the bottom in an arc that will allow the cutter to clear the threads as it advances. This is more critical for internal threads than external.

The insert in your photo looks to be an external insert.

Hi Carld,

The insert looked strange to me but it is the correct insert.

On a different note, I was back in Dawson Springs KY last summer to visit mom and picked up a lot of tooling from previous years some of which were hand ground threading tools for my SB lathe. I may clean these up and give them a go. My SB had a rocker TP (which I liked) and my new lathe has QCTP which I also like but sometimes the QCTP is not as expedient as the rocker system.

Harold

oldtiffie
04-13-2009, 01:15 AM
Hi Tiffie,

Attached are the remainder of charts/graphs with exception of metric. Since I have little need for metric (someday perhaps) I did not include these charts.

Are you requesting that I include actual images of the gears and pulley system in the head stock or images of graphs/charts?

Harold

http://i234.photobucket.com/albums/ee38/hwingo_2007/Lathe10.jpg

http://i234.photobucket.com/albums/ee38/hwingo_2007/Lathe3.jpg

Thanks Harold.

That helps but I do need pics of the gear-train and the spindle gear as well as a confirmation that the first gear is either 24 or 48 teeth.

If the first driver gear in the gear-train is not attached to the end of the spindle, I may need your head-stock gear-box schematic diagram. Most/many lathes have the first gear in the gear train attached to the spindle - but not all. My lathe has a fixed 4:1 reduction in the head-stock gear-box between the spindle and the primary/first gear in the train.

If the 24 and 48 toothed gears in your diagrams/pics are in fact attached to the spindle end then we are in luck as I need/prefer a gear with a multiple of 2, 3 (ie a multiple of 6 ie 18, 24, 30, 36, 42, 48 etc) for 2 and 3 start threads and for 2, 3 and 4 start threads I need a gear with a multiple of 2, 3 and 4 - ie 12, 24, 36, 48, 60, 72 etc. so those 24 and 48 teeth gears are just what is needed.

I will reply when I have your pics.

hwingo
04-13-2009, 02:17 AM
Just thought of another possibiliy!

Which way do you have the compound swiveled?

Hopefully with the handwheel 29° to 29.5° to the left of center for internal threading. (Assuming that the handwheel is toward you)

I usually finish threading by cutting the last .002" or so using the cross slide rather than the compound and taking it in a couple of passes to smooth out the thread form. Works very well if you have a good sharp tool. Peels off a nice thin ribbon and leaves an excellent finish if executed correctly.
Glenn

Good Evening Glenn,

It has been 20 years since running my SB lathe but the compound on that lathe was set to read zero when the compound wheel was facing my belly. This lathe's compound is set up differently. The compound reads zero when the hand wheel is facing the tail stock. To cut internal threads I must push the hand wheel away from me to get 29.5 degrees as shown in the following images.


http://i234.photobucket.com/albums/ee38/hwingo_2007/Compound1.jpg

When taking the picture I was over the top of the bed for orientation purposes.



http://i234.photobucket.com/albums/ee38/hwingo_2007/Compound2.jpg

Closer view from same vantage point.


If cutting an external thread I must swing the wheel toward me to get 29.5 inches (not illustrated).

Harold

hwingo
04-13-2009, 02:24 AM
Just to inform the non-gun folks online, the double lead choke tube Harold was referring to, if in 12 gauge, would be .795"-44dl or .775"-44dl, depending on which choke system he's using, standard TruChoke or Thinwall. So, opposite start points of 22 tpi.

David
Montezuma, IA

David:

You've hit it right on the button. It was the TrueChoke. It's been 20 years since that time and I had forgotten the name of the Choke System. Thanks for pointing that out and helping me to remember.

Harold:)

hwingo
04-13-2009, 03:12 AM
Good evening Tiffie,

This is about the best I can do regarding images. I have labeled the image so I hope that helps.

Harold


http://i234.photobucket.com/albums/ee38/hwingo_2007/Gears1.jpg



http://i234.photobucket.com/albums/ee38/hwingo_2007/Gears2.jpg

oldtiffie
04-13-2009, 04:43 AM
Good Evening Glenn,

It has been 20 years since running my SB lathe but the compound on that lathe was set to read zero when the compound wheel was facing my belly. This lathe's compound is set up differently. The compound reads zero when the hand wheel is facing the tail stock. To cut internal threads I must push the hand wheel away from me to get 29.5 degrees as shown in the following images.


http://i234.photobucket.com/albums/ee38/hwingo_2007/Compound1.jpg

When taking the picture I was over the top of the bed for orientation purposes.

http://i234.photobucket.com/albums/ee38/hwingo_2007/Compound2.jpg

Closer view from same vantage point.

If cutting an external thread I must swing the wheel toward me to get 29.5 inches (not illustrated).

Harold

Harold.

The 29.5 degrees must be from the centre-line of the cross-slide, not 29.5 degrees from the axis of the lathe spindle.

As a guide, the angle set on the compound should be 0.5 degree less than the slope of the trailing side/flank of the thread you are cutting so that the path of the tool is about the same as the thread side/flank.

Put a large thread (tap, bolt, screw - doesn't matter) and you will see what I mean.

Glenn Wegman
04-13-2009, 05:50 AM
Harold,

Ahh, that's what I suspected! You need to be 29° from being PERPENDICULAR to the spindle axis! Not parallel to it.

Creates a little confusion some times!

If you prefer to swivel the compound in that direction, on your machine, you'll need to continue swiveling to 61° to get to where you need to be.

The other option is to re-mark the compound. Just swivel it back to where it is perpendicular to the spindle axis and check it by by sweeping it with a dial indicator stuck to the carriage while running the cross slide in and out to insure it is square and then lock it down. Then go 90° to the left side of the compound and place a index mark there corresponding to zero. This way you will have a zero reference for perpendicular and a zero reference for parallel to make it easier to set the compound depending on what you are doing. That way you can just use the new index mark and count 29° from the compound being perpendicular to the spindle axis and have the handwheel toward you if that would be preferable to being away from you.

You're getting closer to threads by the minute!

Glenn

oldtiffie
04-13-2009, 06:52 AM
Good evening Tiffie,

This is about the best I can do regarding images. I have labeled the image so I hope that helps.

Harold

http://i234.photobucket.com/albums/ee38/hwingo_2007/Gears1.jpg

http://i234.photobucket.com/albums/ee38/hwingo_2007/Gears2.jpg

Thanks Harold.

I see that the primary/first gear in the gear train (24 teeth) is not directly attached to the spindle.

What I need now is either the ration between the spindle and the 24 tooth gear or a pic of a scan of the gear-box schematic diagram from the lathe manual/hand-book - or even better - both.

I need them to sort out one of the several methods of screw-threading multiple start threads.

I will concentrate on two methods.

I will advise further when I have the info I require.

As Glenn Wegman said, we are getting there - thanks Glen.

J Tiers
04-13-2009, 09:05 AM
Interesting. No mention was made of odd thread form, that was not in the question.

That is the usual question whe the 29 degrees is at fault.

Incidentally.....

Is it then impossible to have the handwheel on the operator side of the spindle axis and get the angle required?

Most lathes allow the compound to point the handwheel at the operator. From your statements, it seems that you are saying the handle won;t rotate towards you. That seems wrong...

Glenn Wegman
04-13-2009, 09:54 AM
J,

From the images I believe that the degree markings on the compound are such that they would not correspond to an index mark if it were to be rotated toward the operator.

Adding an index mark as I suggested in my above post pretty much takes care of that little glitch.

Perhaps it's something to do with the Chinese reading from right to left, or bottom to top, or whatever it is they do :)

Glenn

madman
04-13-2009, 10:40 AM
NICE PHOTOS how did you do those? I am planning on making a eeffort to finally learn to post pictures on this HSM Site. I was amazed at how well youre photos came out. ALSO why is youre Lathe so clean? Is it Brand New LOL ?? Mike

Carld
04-13-2009, 12:39 PM
Yes, hwingo's compound is set at the wrong angle.

hwingo
04-13-2009, 12:40 PM
NICE PHOTOS how did you do those? I am planning on making a eeffort to finally learn to post pictures on this HSM Site. I was amazed at how well youre photos came out. ALSO why is youre Lathe so clean? Is it Brand New LOL ?? Mike

Madman:

My other passion is Landscape Photography. More specifically, my “other” past time enjoyment is Large Format Photography. Ordinarily I use either a Sinar F2 or Shen Hao 4” x 5” camera. For those not knowing, 4X5 indicates the size of film that’s used. I have larger formats but they are too heavy to pack into the field. My Medium Format is a Hasselblad (2.250 X 2.250) and my Small Formats are 35mm. I have a comprehensive “wet lab” in which I process B+W and color film and print B+W or color prints.

These images were captured using a NIKON D2X using a NIKKOR Medical MACRO lens. I have often used an intra-oral ring strobe as this give good, flat lighting on reflective surfaces. Diffusion material on the ring strobe also aids in preventing “hot spots”. The human brain hates hot spots and doesn’t deal with glare well so I endeavor to reduce hot spots with every twist and turn. I have portable studio lights which I often use for these images. Primarily, for images such as these, I use MultiBlitz strobes with soft boxes. My Digital Lab is also comprehensive. I have resisted digital work at every turn of the road as I pride myself in being a conventional photographer; I am slowly embracing digital work.

Regarding newness of my lathe, it’s nearly two years old. I make a conscious effort to keep my equipment clean. Each time I finish, even one part of a multifaceted project, I clean between each step. When finished, I coat my machines with a special spray to prevent oxidation. Even my previous (second-hand) Bridge Port and South Bend lathes were care for in the same manner. When it’s time to start a new project, I remove the protective coating and “go at it again”.

Harold

hwingo
04-13-2009, 12:54 PM
Yes, hwingo's compound is set at the wrong angle.

OH MY HEAVENS!!!! Don't tell me that. Does this mean that all my work on this project has been ruined?

Harold

hwingo
04-13-2009, 01:59 PM
Most lathes allow the compound to point the handwheel at the operator. From your statements, it seems that you are saying the handle won;t rotate towards you. That seems wrong...

Then I have certainly given the wrong impression. According to the degree markings on the compound, I can swing the compound either left or right by 40 degrees. I am currently at work and unable to provide conscise images but when I get home I will attemtp to illustrate what the compound looks like and *exactly* what I did to setup and cut internal threads.

I hope I haven't screwed things up but it seems I may have. Perhaps I am not beyond recovery ...... yet.

Harold

oldtiffie
04-13-2009, 06:03 PM
Harold,

there is nothing wrong with your compound index marking - at all.

http://i234.photobucket.com/albums/ee38/hwingo_2007/Compound2.jpg

The "standard" and "home" positions of the compound slide - ie its "zero"/default position - is with it parallel to the lathe axis. It follows that 90 degrees is at 90 degrees to the axis of the lathe and the head-stock spindle.

It further follows that the "29.5 degrees off-set" setting is (90 - 29.5) = 61.5 degrees on the "dial".

As regards your - and many others too - scales only extend to 45 degrees and so the 29.5 degree off-set cannot be set using your scale.

Its a simple mistake to make.

Further yet, as we are into "0.5 degree territory", I am reluctant to use the scale anyway and so I use a protractor or bevel guage either on the face of the lathe chuck or on the job itself to set the off-set angle.

Don't worry - you are doing OK - at least you are "up front" and doing the "leg work" (and for others too I suspect).

Glenn Wegman
04-13-2009, 06:58 PM
Harold,

As regards your - and many others too - scales only extend to 45 degrees and so the 29.5 degree off-set cannot be set using your scale.



This is why I suggested in my above post to place a second index mark on the compound to indicate zero with the compound perpendicular to the spindle axis. (Sweep it in with a DTI) Simple to do and makes the graduated "dial" meaningful again. :) It may possibly have one already. It also makes the compound more useful for operations other than threading.

Just as a suggestion, I would also be less concerned with hitting 29.5° to the tenth of a degree, and be more concerned with sweeping the actual cutting tool with a DTI to where it is square with the part for a proper thread form. This is why I grind OD threading tools on a surface grinder using a magnetic compound sine plate. The shank of the tool can be used as a reference to sweep. An internal type like Harold is using "most likely" has the insert in correct index with the shank so the shank or possibly the edge of the tool holder could be used.

Not meant to step on your toes Tiffie, just trying to make some heplful suggestions. :)

Glenn

Carld
04-13-2009, 08:16 PM
My compound is marked the way hwingo's is and I have to set the compound on the 60 deg marks to be 30 deg from perpendicular to the work. The first time I cut a thread with it I set it on 30 deg and it didn't look right and I used a protractor on the side of the crossfeed and against the compound to set it at 30 deg and saw it was at 60 deg on the scale.

From then on I was very carefull to start thinking before I did anything requiring moving the compound to a certain angle.

Put mind in gear then release the clutch on the hand motion mechanism.:rolleyes:

oldtiffie
04-13-2009, 09:15 PM
Originally Posted by oldtiffie
Harold,

As regards your - and many others too - scales only extend to 45 degrees and so the 29.5 degree off-set cannot be set using your scale.



This is why I suggested in my above post to place a second index mark on the compound to indicate zero with the compound perpendicular to the spindle axis. (Sweep it in with a DTI) Simple to do and makes the graduated "dial" meaningful again. :) It may possibly have one already. It also makes the compound more useful for operations other than threading.

Just as a suggestion, I would also be less concerned with hitting 29.5° to the tenth of a degree, and be more concerned with sweeping the actual cutting tool with a DTI to where it is square with the part for a proper thread form. This is why I grind OD threading tools on a surface grinder using a magnetic compound sine plate. The shank of the tool can be used as a reference to sweep. An internal type like Harold is using "most likely" has the insert in correct index with the shank so the shank or possibly the edge of the tool holder could be used.

Not meant to step on your toes Tiffie, just trying to make some heplful suggestions. :)

Glenn

Many thanks Glenn,

good practical and sensible suggestions.

You are certainly not "stepping on my toes" as this thread is certainly not my property. I certainly don't regard it as any sort of a contest either.

My sole aim is to assist Harold as best I can in company with any other sensible, constructive and practical suggestions - as you are doing - so that we can assist Harold collectively and learn from each other.

I am quite willing to acknowledge and concede to other advise as I, as much as any other, am here to learn as well. If I can assist, then that's another benefit and incentive to/for me.

Glenn Wegman
04-13-2009, 09:51 PM
I could not agree more!

Thank you!!

Glenn

J Tiers
04-13-2009, 10:20 PM
Well, there are two questions.....

1) does the compound physically rotate that far? Not so stupid a question, I see that it is apparently held by two t-nuts...... so it is possible (but not so likely) for it to have limited travel.

2) Do the marks mean anything when it is rotated? And the answer seems to be that they won't have an index in that case, unless another one is provided by the user.

I would have to assume that the compound actually rotates that far..... I don't quite agree with the idea that the "natural" position is at 90 to the crossfeed. Mine is usually within 45 deg of parallel, and only once in a while, when using the milling attachment, or cutting a taper, does it go to 90 deg or nearly so.

The 90 deg "normal" setting is really somewhat of a holdover from watchmakers and model-makers lathes, where there is no longitudinal feed at all, and the compound IS the longitudinal feed. Those feeds may have nearly as much travel as the lathe has swing....


And, the usual question regarding the wrong angle is "why am I cutting buttress threads when I want normal 60 deg threads?" The shallow angle shows up in one flank of the cut thread.

hwingo
04-13-2009, 10:33 PM
J Tiers, et al,

Please don't give up on me. I am currently "thinking". I am also capturing some images of the lathe so I an ask question and so I can answer question. J Tiers, you asked the question, "will the compound swing that far because of T bolts. And that is a good question because left and right rotation is quite limited; to the best of my memory, my SB lathe was not so limited. I will find out more about the compound shortly.

I am not running from this thread! I acknowledge there has been recent post activity since this morning and I have every intention to "hang in there" with questions and answers.

Give me a couple of hours to "get my act together" and I will be back with pictures, answers to question about the lathe compound, and what I think will be questions that will serve as "food for thought".

Harold

Glenn Wegman
04-13-2009, 10:41 PM
One of my lathes is graduated similar to the one here. The other is graduated over 180° of compound swing or 0°, 90°, 0°, where the 90° mark is alighned with the index mark when the handwheel is toward you and the compound is perpendicular to the spndle axis. When the compound is parallel to the spindle axis the index mark corresponds to "0". I would consider this correctly marked as it reads in degrees from the spindle axis which would be 0°.

For what that's worth!

Glenn

hwingo
04-14-2009, 02:20 AM
Forever more and a day! I am so confounded. Work with me on this fellows. Follow me if your can because I’m not sure that I follow what I am about to say. But before I make a total fool of myself, let’s go to the images I have captured.

The first image is what I will call, be my definition right or wrong, “home position”. The compound is parallel to the axis of the spindle (or work piece). The scale reads “0” in this position. The boring bar is also parallel to the work and the pointed end of the thread-cutting insert is setting perpendicular to the work. **Note, because of the angle from which these images were captured, you cannot see the index mark so I have added one in red.


http://i234.photobucket.com/albums/ee38/hwingo_2007/Compound1a.jpg

With regard to the second image, as the compound is turned to 29 degrees on the scale from home position, and the compound’s hand wheel is pushed away from me, the tool bar follows the compound’s direction thus it’s necessary to loosen the QCTP and swivel the tool post back (not the compound) until the cutter is once again perpendicular to the work which is shown in image three. Image three was the setup when I created internal threads in several parts.


http://i234.photobucket.com/albums/ee38/hwingo_2007/Compound2a.jpg



http://i234.photobucket.com/albums/ee38/hwingo_2007/Compound3a.jpg

If I am hearing you right, to cut conventional 60 degree threads, compound’s angle setting of 29 degrees is derived from perpendicular ….. not from parallel. So I’ve really screwed the pooch. If that’s the case, I’m off by 15 degrees. I would have been more accurate (though wrong) to have forgotten about turning the compound 29 degrees and left the setup as shown in the first image. If I screwed the cross feed out during threading (and not touched the compound), I would have likely gotten a more accurate thread.

180 degree minus 29 = 151 divided by 2 = 75.5 degrees
90 degrees minus 29 = 61 divided by 2 = 30.5 degrees
This is a feed difference of 45 degrees.

Now that parts have been fabricated with internal threads fed at 75 degrees, the question is what must I do to cut matching external threads in order that I “save the day”?

Now comes my bright, shining stupidity as I make an argument for maybe not having screwed up too badly. Knowing, by all that’s Holy, a proper form thread is achieved using a 60 degree cutter when fed at 29.5 degrees, I must say that I’ve known individuals (and you have too) who have never fed using a compound, rather, the cutter was set perpendicular to the work and fed by cross feed. Similarly, I have seen Mr. Wells “set his jaw”, engage the half nut, and cut an 8 TPI thread, in one single pass on this giant machine while dodging blue-hot chips that resembled projectiles.

It would seem that if a cutter was “pointed up” at 60 degrees (inclusive of both angles), and the cutter was perpendicular to the work, regardless of feed angle, it would eventually produce a 60 degree thread. If people cut threads in a single pass or cut threads using their cross feed without any apparent problem, one would think that a 75.5 degree feed angle (45 degrees off from acceptable) would still produce a 60 degree thread because the cutter is 60 degrees.

In the end, when I place a thread pitch gauge on the incorrectly cut 18 TPI threads, the thread pitch gauge fits like a glove. Why?

Now, on to my illustration regarding position of the compound when the 29 degree angle is set correctly. If the compound and cutter “begin life” from the perpendicular position and internal threads are desired, it would seem that whether the hand wheel is turned away or turned toward the operator a proper thread would be cut. If the compound is turned away from the operator, the hand wheel would need to be turned clockwise; if turned the opposite direction the hand wheel would be turned counter-clockwise. In any event, since the cutter is 30 degrees on one side and 30 degrees on the other, either way you feed the angle will still be the same ….. 30 degrees.



http://i234.photobucket.com/albums/ee38/hwingo_2007/Illustrationcopy.jpg


Now that I’ve shown my ignorance, how will I obtain 29.5 degrees from perpendicular or 61 degrees from parallel since my degree scale represents neither?

Is it possible to cut external, incorrect threads to accurately mate with the internal incorrect threads that have been cut.

This has been a bad day but it’s better to find out now than never at all. I most certainly didn’t have this problem with my SB Lathe.

Harold

dp
04-14-2009, 02:31 AM
#2 in the final picture is correct. The cutter is properly aligned to the work, the compound is properly aligned to provide the correct cut. The next step is to use the handles correctly.

1. Zero the cross feed dial
2. Address the work with the cutter using the compound
3. Zero the compound dial
4. Back out the cutter with the carriage handle
5. Start the lathe
6. Advance the compound 0.010 or so
7. Mind the threading dial, engage half-nuts at the mark
8. Disengage the half-nuts at the end of thread *and*
9. Move the cross-feed handle to disengage the cutter from the work
10. Back out the cutter with the carriage handle
11. Zero the cross-feed
12. goto 6

Glenn Wegman
04-14-2009, 05:56 AM
If the compound and cutter “begin life” from the perpendicular position and internal threads are desired, it would seem that whether the hand wheel is turned away or turned toward the operator a proper thread would be cut. If the compound is turned away from the operator, the hand wheel would need to be turned clockwise; if turned the opposite direction the hand wheel would be turned counter-clockwise. In any event, since the cutter is 30 degrees on one side and 30 degrees on the other, either way you feed the angle will still be the same ….. 30 degrees.Harold

Correct!



If I am hearing you right, to cut conventional 60 degree threads, compound’s angle setting of 29 degrees is derived from perpendicular ….. not from parallel. So I’ve really screwed the pooch. If that’s the case, I’m off by 15 degrees.
Harold

Correct!



#2 in the final picture is correct. The cutter is properly aligned to the work, the compound is properly aligned to provide the correct cut.

DP,

#2 is NOT correct as the compound is set to an incorrect angle of approx 60° from perpendicular.

Glenn

oldtiffie
04-14-2009, 06:52 AM
Harold and Dennis,

first of all, I generally agree with Glenn.

Secondly, it needs to be reiterated that we are referring to a bored/internal thread in this instance.

ALL of the diagrams in Harold's pic are wrong if using the "29.5 deg off-set":

http://i234.photobucket.com/albums/ee38/hwingo_2007/Illustrationcopy.jpg

Diagram 1 has no off-set at all and is quite correct if only using the direct plunge-in method (zero off-set with the tool cutting on both flanks).

Diagram 2 is incorrect in two ways:
a.
the off-set is 60 degrees from the axis of the cross-slide instead of 29.5 degrees - which can be achieved by off-setting 29.5 degrees from the cross-slide axis (ie with the hand-wheel/dial set at the back and rotated 29.5 degrees clockwise); and

b.
the "slope" of the right-hand flank/side of the cut/groove should be parallel to the line of approach of the tool (parallel to the top-slide axis) and NOT the side of the tool if the groove/cut is made using the top-slide only.

Diagram 3 is incorrect in three ways:
a.
the off-set is 60 degrees right from the axis of the cross-slide instead of 29.5 degrees left - which can be achieved by off-setting 29.5 degrees from the cross-slide axis (ie with the hand-wheel/dial set at the front and rotated 29.5 degrees clockwise; and

b.
with the tool cutting as shown, the thread is being cut on the trailing/back face/flank instead of the front/leading edge face/flank

c.
the "slope" of the right-hand flank/side of the cut/groove should be parallel to the line of approach of the tool (parallel to the top-slide axis) and NOT the side of the tool if the groove/cut is made using the top-slide only.

In short, the top-slide (at the hand-wheel/dial end) needs the be off-set 29.5 degrees RIGHT of CLOCK-WISE from the axis of the CROSS-SLIDE (which is at right angles to the lathe spindle and work axis).

There are two positions which meet this criteria which (using a 360 compass with its zero/north vertically up the "page" as drawn). These are at:
a.
0 + 29.5 = "North" + 29.5 degrees = 29.5 degrees - in which case the cutting tool will be "pushed" into the cut/groove/thread as the hand-wheel will be to the back of the lathe; and/or

b.
180 + 29.5 = "South" + 29.5 degrees = 209.5 degrees - in which case the cutting tool will be "pulled" into the cut/groove/thread as the hand-wheel will be to the front of the lathe (toward the front of the chuck). This is the preferred option.

I hope this helps - if not, get back to me and I will keep keeping on.

Glenn Wegman
04-14-2009, 07:53 AM
For the particular thread being discussed: 29° to 29.5° infeed of the compound slide.
http://img.photobucket.com/albums/v647/Fighter1/Thread-1.jpg

Harold,

Have you looked to see if there is not another index mark for the compound at 90° to the one you used?

Glenn

J Tiers
04-14-2009, 09:08 AM
IMO this is about what you should see for threading, if the compound will swing there. Sorry for lousy contrast, I'm off to work now, no time for better lighting than the flash. You can see the tools as appropriate. Please ignore the person behind the belly in photo 1.

EXTERNAL
http://img.photobucket.com/albums/0803/jstanley/thrd_ext.jpg

INTERNAL
http://img.photobucket.com/albums/0803/jstanley/thrd_int.jpg

The alternative of having the handwheel *behind* the centerline will "work" but is very inconvenient, to say the least.

oldtiffie
04-14-2009, 09:15 AM
That's clarified it more than some-what JT.

Good pics of both internal and external "29.5 degree off-set" threading set-up.

Many thanks.

The Fixer
04-14-2009, 09:26 AM
I think most of us have played that game... when is 29.5 degrees not 29.5 degrees? But I think that's been explained enuf here.
I have found that threading and parting with a cutting oil ALWAYS gives a better surgace finish.
just my .02
al

hwingo
04-14-2009, 01:45 PM
Gentlemen,

Abundantly, I recognize where errors have occurred. It’s not a matter of conceding error, rather, a matter of “taking ownership” of fault, understanding how fault has come about, and making a conscious effort to reconcile incorrect machining methods. Simply being reminded that 29.5 degrees is from perpendicular and not parallel, has made all the difference in understanding wherein my folly lies.

Clearly, the degree marking on my lathe is different from that which was on my SB; therein lies the source of my confusion. I assumed too much by thinking that all lathes would be marked the same never stopping to think things through. It is perplexing, at this time, why the maker of this lathe elected to mark the lathe this way. Oh well, I will need to learn how to circumvent this issue. Remarking the compound is one possibility and using an instrument (protractor???) may be another option. Will ask for discussion on this later.

Indulge me just one more time because I am still trying to convince myself that, regardless of incorrect feed angle, my threads are likely correct …. or close to correct. Allow me to prosecute my position. Glenn’s latest post illustrates a properly formed thread and an improperly formed thread. I acknowledge and agree with his contention that an “angled thread” would be cut *provided that* the cutting tool was not set perpendicular to the work/axis after the compound was turned. However, in spite of my compound being turned to a horribly incorrect angle, my cutter *was* adjusted, after the compound had been turned, so that the tool bar and cutting tool *were* perpendicular to the work.

Let’s assume that the compound is turned to an angle of 45 degrees off parallel but the point of the 60 degree cutter is set to be perpendicular to the work. Let’s also assume that the depth of your properly formed thread is .040” from crest to valley. Now, adjust the cross-feed to full depth of thread (.040”) and plunge-cut the thread. Regardless of compound setting, the thread should be close to accurate form because the cutter was perpendicular to the work when the cutter made the single pass to depth. Right?

Now, let’s continue with this setup but instead of adjusting the initial depth of cut with the cross feed, let’s use the compound, that is set at 45 degrees and “dial up” .040”. Though the compound moved .040”, the depth of cut is only .020” because of the compound’s angle. Right? Material is removed in a single pass and you have a half formed thread with the valley being .020” deep. Right?

Now, run the carriage back to starting position, advance the compound another .040”. This means that you’ve advanced the cutter a total inward distance of .040”. Take another cut. Since the cutter has been advance a total inward distance of .040” (.020" with the first pass and .020" with the second pass), are you not essentially in the same position as if making a one-pass-plunge-cut? Granted, the physical position of the thread will have changed from the first cut, but thread form and depth should be “correct” because the cutter is perpendicular to the work. Right? Or am I failing to take into account that some of the original thread height is lost because with each pass, forward material is being removed from the original grove as the cutter is advanced. Regardless, would it not stand the test of logic that eventually, with succeeding passes, the thread would ultimately point-up to correct form and depth?

Let me reiterate that my cutter was set to perpendicular *after* the compound was set to the incorrect angle. Where is my logic flawed?

Harold

Glenn Wegman
04-14-2009, 07:39 PM
Hello Harold,

I hate to change directions here but this is the only illustration that I could readily come up with. The reason I say "change directions" is that it represents the progression of an EXTERNAL right hand thread being cut. It is being cut in six pases with the compound rest set to infeed at 29°. The "1°" indicates 1° less than the 30° flank angle of the thread form.

http://img.photobucket.com/albums/v647/Fighter1/Thread1bmp.jpg

The significance of this is that depicts why the infeed is set to 29° from perpendicular to the spindle axis for cutting a 60° V form thread. The direction of cut would be from right to left. The arrow shows the direction and path of the infeed for each of the six passes. What is happening here is that the majority of the cutting is being done by the LEFT cutting edge of the tool bit while the right cutting edge of the tool bit is basically just "scraping" the right flank of the thread to keep it from having a "wrinkled" appearance and give it a nice finish. If the compound was fed in at 60° perpendicular to the spindle, as yours was set, I believe you may now see why, if making the same six passes, you would end up with a thread form like the one in the image I previously posted.

Another way to look at it would be to compare it to cutting a chamfer on the end of a piece of round bar. If you set the compound to cut a 29° chamfer and use the compound to feed the tool in, it will cut a 29° chamfer on that round bar regardless of the shape of the tool bit! If the compound is set to cut a 60° chamfer, it'll cut a 60° chamfer regardless of the tool bit shape!

Another reason for infeeding with the compound as above is that feeding straight in or "plunge cutting" a thread using only the cross slide puts considerably more load on the tip of the tool bit and can chip it or break the tip off. Cutting with primarily the leading side of the cutter lets the chip form and roll right off rather than bunching up in the center as it does when plunging.

I hope this helps a little as I'm better at identifying problems than I am at explaining how to correct them!

I'm quite sure you have a good understanding of this stuff, but it's just been a while since you had to do it so it is probably just a little fuzzy.

Glenn

oldtiffie
04-14-2009, 08:18 PM
Excellent explanation Glenn.

Harold, don't worry - just stick in there and see this out.

This is a classic case of finding out the "why?" behind the "what".

In other words, doing it by rote because that is what someone is told or taught or "found out that it works" is not a solution at all.

That is the "what".

Finding out why it is or was so is that big step further.

That is the "why?".

Once the process is understood it is not only better remembered ("learning by doing"?) but can either be extended or re-developed from first principles.

I am pretty sure that you won't be the only one that learns a lesson or two here and will have good cause to remember it - but you are soldiering-on and doing a lot of leg/spade work for others. I hope they appreciate your dedication to getting a satisfactory answer and solution.

I will extend this later by discussing other ways of mounting the tool and where to start the cut. Internal threading is difficult in that it is hard to see the tool and when it has got to where the half-nuts have to be opened/disengaged. It will be very obvious - but only when the basic or first principles are mastered using set-ups as per J Tiers pics and Glenn's explanation and diagrams.

Once you have this under your belt, we will take up the matter of multi-start threads again.

hwingo
04-14-2009, 09:47 PM
Once you have this under your belt, we will take up the matter of multi-start threads again.

I am in total agreement. Early this morning I was thinking about this matter while "sitting on the throne". I have absolutely no business discussing multi-lead threads when I can't even properly cut a regular thread.:eek: So let's table that discussion until I get the current issue under control.

Now, I have threads to cut as I have a pressing project. I have a metal protractor and if you, or someone else, could post a picture showing how the protractor is to be placed on/next to the compound so as to ensure a proper angle setting, I would be most appreciative. A picture is worth a thousand words.

In the meantime, I will study the illustration presented by Glenn. I must get this straight in my challenged brain.:o

Harold

oldtiffie
04-14-2009, 10:34 PM
Originally Posted by oldtiffie
Once you have this under your belt, we will take up the matter of multi-start threads again.


I am in total agreement. Early this morning I was thinking about this matter while "sitting on the throne". I have absolutely no business discussing multi-lead threads when I can't even properly cut a regular thread.:eek: So let's table that discussion until I get the current issue under control.



In the meantime, I will study the illustration presented by Glenn. I must get this straight in my challenged brain.:o Now, I have threads to cut as I have a pressing project. I have a metal protractor and if you, or someone else, could post a picture showing how the protractor is to be placed on/next to the compound so as to ensure a proper angle setting, I would be most appreciative. A picture is worth a thousand words.

Harold


I have absolutely no business discussing multi-lead threads when I can't even properly cut a regular thread

Harold,

you have every business and every right to do as you choose, but I agree that the "one logical step at a time" is the best approach. Multi-start threads are only identical equi-spaced threads on a shaft or in a hole - nothing more.

But, as you say, that is best left for later.


Now, I have threads to cut as I have a pressing project. I have a metal protractor and if you, or someone else, could post a picture showing how the protractor is to be placed on/next to the compound so as to ensure a proper angle setting, I would be most appreciative. A picture is worth a thousand words.

No problem at all - I will do it later in the day and post the pics. If I am lucky, Glenn and J Tiers will assist as well as they are very good indeed at the "explain and show" bit.

As a precursor to the pics, there are two settings with the protractor - the top-slide/compound slide and the cutting tool. (I often prefer to transfer the protractor setting to a bevel guage as it is easier to get into awkward spaces).

You really are tenacious and determined aren't you? A lot of lesser souls would not have started this thread in the first place nor having started it, would they have persevered as you have done and are doing.

Later.

Glenn Wegman
04-14-2009, 11:01 PM
It says 30°, but use 29° to 29.5°.

http://img.photobucket.com/albums/v647/Fighter1/Thread2.jpg

hwingo
04-15-2009, 10:24 AM
Good Morining Guys,

First off, a big AIRBORNE OOH-RA and a "tip of the beret" to Tiffie, J Tier, Glenn, et al for providing soooo much assistance AND for hanging in there with me. Truly, you guys have leaned forward in the fox-hole. This has been priceless ..... a real positive learning experience. You guys need to hear this because it *needs saying*.

OK, here's how "the cow ate the cabbage". I have resigned myself to having made a major blunder. Both pieces of my project are unrepairable ..... a vessel that can't be salvaged. Resigning to having failed at an attempt? Yes. Surrender? Never! Retreat? Not by anything that's Holy! This just makes me more determined to "fuzz up", fall back and regroup. A lesson earned is a lesson learned. New metal is on the way.

What have I done to correct my wicked ways? I've placed an indicator on the face of my chuck, turned my compound perpendicular to the spindle axis, and indicated the compound (front to back while moving the cross feed) until my indicator read Zero. This should make my compound "square" with the axis. With the compound in that position I placed a permanent mark on the carriage that's adjacent to the zero on the compound. Now I have a witness mark making it possible to "return to zero" when cutting either internal or external threads. I've learned that the witness mark is just a "starting point" and a general reference. I suppose if one wants precision, it would be necessary to use a precision instrument and indicate in 29.5 degrees but I think this would be over-kill on my part. But the point is, I have learned that just because one turns their compound to an index mark is by no means an indicator that they achieved precision. One could easily be off .080" (from front to back) and not detect this using the eye-ball method.

It's time to go to work so when I return, I will provide images of what I have done and how I've done it to improve on correctness and abilities.

Harold:)

Carld
04-15-2009, 02:34 PM
hwingo, anything between 29 and 30 deg will work. I have been using 30 deg on the compound for over 20 years now and I can cut precision class threads any time I want to. You don't have to set it on 29.5 deg. The more you go towards 29 deg the more the cutter will chase on the trailing edge of the cutter.

The thread is a 60 deg V and setting the compound at 30 deg will work, it just don't chase the trailing edge much but I have never had a problem doing that. Just don't get hung up on getting exactly 29.5 deg.

hwingo
04-15-2009, 03:32 PM
hwingo, the thread is a 60 deg V and setting the compound at 30 deg will work, it just don't chase the trailing edge much but I have never had a problem doing that. Just don't get hung up on getting exactly 29.5 deg.

Hi Carld,

I'm not too "hung up" on the 29.5 degrees. I know that various people use anything from 29 to 30 degrees with success. I suppose that the reason I keep talking about 29.5 degrees is because Mr. Wells (a previous mentor) taught me to do it that way. With that said, I now realize that the compound's scale is not "dead nuts on". Even if it was "smack on", without additional instrumentation we would be unable to consistantly repeat a *precise* degree setting using the "eye ball method" so I see this as only "Kentucky Windage" ..... which seems to work quite nicely for most individuals.

Thanks,

Harold

hwingo
04-16-2009, 12:38 AM
I thought I would post a couple of images demonstrating how I squared my compound in preparation for placing a witness mark in a different location. I am also presenting an image of the witness mark.

I placed my magnetic indicator base on the face of my chuck and extended the indicator so that it would engage the side of my compound. In doing this I have obviously made several large assumptions:

1. The face of the chuck is flat and square to the spindle axis
2. The side of the compound is flat

Assuming the best, the compound was loosened and the cross feed was moved near and far as I watch the indicator needle move. I gently tapped the compound in the appropriate direction (from side to side) and each time I would move the cross feed in and out until the needle no longer moved. My indicator measures in .0005". I carefully tightened the nuts on the compound and again indicated making sure nothing moved. Once secured I use a cobalt threading tool and placed the "V" adjacent to the zero mark and lightly tapped the threading tool with a small hammer imprinting a small notch on the cross feed.

With this in place, I can now turn my compound 29-30 degrees from perpendicular in either direction for internal and external threading.

If you see fault in what I have done you had better "sound off" in the event that a Wayfaring Stranger stumbles across this thread deciding to emulating my re-indexing attempt.

Harold


http://i234.photobucket.com/albums/ee38/hwingo_2007/SquaringtheCompoundBW.jpg



http://i234.photobucket.com/albums/ee38/hwingo_2007/CompoundWitnessMark.jpg

tattoomike68
04-16-2009, 01:07 AM
many people thread slow and take small cuts. that works but you get all kind of anomalies.

Go faster. I thread 1" 14tpi at 750 RPM and even 6" -12tpi at 225 rpm. The threads look great. you are using carbide, speed that stuff up.

lets say Im threading a 12 TPI on any size. I dont use the compound so I sock it in .100 then .120 and then about .127 and grab a fast gear and the threads look great. You can one pass a 12 tpi if you want to haul ass and have a good lathe.

Also put a bit of drag on the lathes longitudanal axis so it cant coast when you let off the half nut, that helps alot.

Thats my advice, learn to thread fast. I can thread 2" of 1" shaft in about 40 seconds. Smoke boils off the tool and that bitch is done, I dont dick around.

Over the years my bosses have told me not to thread fast in front of customers. Its not cool to charge 15 minutes for one minutes work. :( :D

oldtiffie
04-16-2009, 02:19 AM
I thought I would post a couple of images demonstrating how I squared my compound in preparation for placing a witness mark in a different location. I am also presenting an image of the witness mark.

I placed my magnetic indicator base on the face of my chuck and extended the indicator so that it would engage the side of my compound. In doing this I have obviously made several large assumptions:

1. The face of the chuck is flat and square to the spindle axis
2. The side of the compound is flat

Assuming the best, the compound was loosened and the cross feed was moved near and far as I watch the indicator needle move. I gently tapped the compound in the appropriate direction (from side to side) and each time I would move the cross feed in and out until the needle no longer moved. My indicator measures in .0005". I carefully tightened the nuts on the compound and again indicated making sure nothing moved. Once secured I use a cobalt threading tool and placed the "V" adjacent to the zero mark and lightly tapped the threading tool with a small hammer imprinting a small notch on the cross feed.

With this in place, I can now turn my compound 29-30 degrees from perpendicular in either direction for internal and external threading.

If you see fault in what I have done you had better "sound off" in the event that a Wayfaring Stranger stumbles across this thread deciding to emulating my re-indexing attempt.

Harold


http://i234.photobucket.com/albums/ee38/hwingo_2007/SquaringtheCompoundBW.jpg

http://i234.photobucket.com/albums/ee38/hwingo_2007/CompoundWitnessMark.jpg

OK so far Harold - you are pretty well on top of this (not to be confused with the "agh - *uck it" - and proceed to "do it" approach though!!! (I hope))!!!!

As Glenn showed both in his diagram and his text that the 29.5 degree bit is not cast in stone - it can be anywhere between 29 and 30 - or even down to 28 or so. The dial scale you are using on your top/compound base is more than adequate.

The next thing is to leave the top-slide "as is" and set the screwing tool so that it is "square" to the job - either use a screwing tool "fish" or a simple angle guage or protractor. The angle of the screwing tool is 60 degrees. So you should have a ((180 - 60)/2) = 180 - 120 = 60 degrees between the job and the tools (both sides).

You should now be set to go.

Speaking for myself, I don't worry about the "depth of thread" (either "straight in" or along the "29.5 degree slope") as I generally ignore the "curves" on the thread crest or root as they don't do much (the straight angle sides/flanks do all the work) and most screwing tools are for a range of threads and consequently have a small radius to suit the finest thread in the range of the tool.

But the 60 degree angle of both sides/edges of the cutting/screwing tool to the job (or more precisely, to the axis of the lathe and the head-stock spindle axis) IS important and should be a close as you can get it.

This can often be done for internal threading by setting the square and of the TC-insert boring bar to be parallel to the face of the chuck (jut run it up to the chuck and adjust the TOOL-POST and NOT the pre-set compound/top slide.

For external threading with an indexing TC insert in its tool-holder, it will usually suffice if you get the side of the tool-holder parallel to the chuck (just by eye is good enough - surprisingly accurate really - the old Mark 1 Eye-ball - persons seeing for the use of (old Military stores labeling jargon/BS!!!) is very hard to beat in many ways.

So, I usually skim a bit off the OD for outside threads and skim bit off the bore for internal threads. I then just "thread to fit" a mating part as it is - to put it mildly - difficult to measure (3-wires etc.) an internal thread.

I would make sure that the boring-bar was as rigid as possible (largest boring bar and least "over-hang") as well as making sure that my cross-slide and top-slide gibs were very well adjusted.

Now to lay another old shibboleth to rest in that as Glenn says the 29.5 degrees bit is not important except that it does do a better job on the trailing/back side/flank as regards finish - his diagram makes that pretty obvious.


Today, in the English language, a shibboleth also has a wider meaning, referring to any "in-crowd" word or phrase that can be used to distinguish members of a group from outsiders - even when not used by a hostile other group. The word is also sometimes used in a broader sense to mean jargon, the proper use of which identifies speakers as members of a particular group or subculture.from:
http://en.wikipedia.org/wiki/Shibboleth

If the "straight in" (direct plunge cut) is say 1" (the hypotenuse on a right-angle triangle) then the "slope" along the nominal 30 degree off-set is 1/Cos 30 along the slope. 30 degree slope is 1.1115, the 29 degree slope is 1.1143 and along the 28 degree slope is 1.1132. So the difference in lengths of "slope" per inch of "plunge cut" is 1.1155 - 1.1132 = 0.0022" - yes only 2.2 "thou" per inch of plunge cut equivelant between 30 and 28 degrees. And if your depth of cut is say 0.100" the difference of the slope lengths is now 0.0022/10 = 0.00022" yup just 2.2 "tenths".

Anyway, if in doubt or you have a query, just post it here and I am sure that some of us (me certainly) will be there to help.

I like your "never-say-die/give in" attitude.

In Naval parlance - "don't give up the ship"
http://en.wikipedia.org/wiki/Don%27t_Give_Up_the_Ship

http://en.wikipedia.org/wiki/Don%27t_Give_Up_the_Ship!

Or in the immortal words of John Paul Jones:

John Paul Jones (July 6, 1747(1747-07-06) – July 18, 1792) was America's first well-known naval fighter in the American Revolutionary War. Although he made enemies among the American ruling class, his actions in British waters during the Revolution earned him an international reputation which persists to this day.

During his engagement with Serapis, Jones uttered, according to the later recollection of his First Lieutenant, the legendary reply to a quip about surrender from the British captain: "I have not yet begun to fight!"
http://en.wikipedia.org/wiki/John_Paul_Jones

Have at it Harold!!!

Good luck.