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DICKEYBIRD
11-25-2009, 09:57 AM
Anyone have hands-on experience using those change gears on a lathe with an Imperial leadscrew?

I've read several places that this solves the Imperial/Metric conversion issue but have never seen any details or pictures as to where they go and how it works. I have a set coming and am wanting to give it a whirl when they arrive.

I measured and found that I do have the clearance needed to fit a 5" gear onto the leadscrew without hitting the table.:)

Evan
11-25-2009, 10:08 AM
I do metric threading on my South Bend using compound gearing made up using the standard change gears that came with the lathe. By compounding two of the standard gears you can thread nearly all the usual metric sizes with no more than a 2 threads per metre error.

http://ixian.ca/gallery/metric/metric.htm

Paul Alciatore
11-25-2009, 11:14 AM
Yes, adding a compound with 127 teeth and a second gear with some round number should allow you to cut metric threads.

You will have to make a new chart to show the gear positions for them. Since inch threads are measured in TPI and metric are measured in actual lead in mm, the two sequences do not correspond well and you will have to calculate the metrics the hard way. I have an Excel spreadsheet that does this for a SB and if you send me your e-mail in a PM I will send you a copy. It was based on a 100:127 compound so you will need to do some changes, but it would be a starting point. You don't say if you use change gears or a quick change box and the the approach is different in each case, so let me know which.

If you have the quick change box, you will be limited to the number of metric threads you can cut. When I did the calculations for my SB with an 8 TPI lead screw and manual change gears, I found that the 100:127 compound gave me more usable combinations for metric threads than either the 50:127 or the 120:127 would have. I hope you have some basis for choosing the 120 for your lathe.

Also, if you are getting individual gears to be combined into a compound one, some threads may more easily be cut by using the 127 by itself with some of the existing change gears.

Another problem is that some gear arrangements for specific threads that might work in theory are not physically possible on every lathe due to mounting constraints. This can be frustrating if you know the ratios work but the gears just don't fit.

DICKEYBIRD
11-25-2009, 11:37 AM
Thanks Paul, PM sent.

Evan, my gear chart shows close combinations for metric threads as well but I thought heck, I'm already ordering an extra set of change-gear hardware & carrier from Grizzly for this project http://bbs.homeshopmachinist.net/showthread.php?t=37869 so I might as get the "proper" gears in the same shipping deal. The 120T is only $13.50 and the 127T is $15.00

small.planes
11-25-2009, 01:04 PM
My CVA (10ee to the yanks ;) ) uses 127 compounded to do metric threads.
Just the day before yesterday I posted pictures over here (http://www.practicalmachinist.com/vb/showthread.php/cva-metric-changewheels-192963.html) showing the setup.

CVA uses 32 DP gears for the metric train, and 16DP for imperial, the smaller size of the gears means the 127 tooth gear fits inside the endcovers, which is nice, as they are interlocked in the electrics :rolleyes:

One thing is that even tho you have a 127 tooth gear you need to leave the halfnuts engaged and reverse the lathe / leadscrew to get back to the begining of the thread for the next pass.

Dave

DICKEYBIRD
11-25-2009, 02:14 PM
Thanks for the link Dave!

My lathe doesn't have a thread dial anyway so no biggie on the leaving the halfnut engaged routine. Makes more sense to me that way anyhoo.

How small are the planes your login name refers too?

juergenwt
11-25-2009, 03:22 PM
Depends on what you are making. If you want it to be accurate you will need 120/127.

Evan
11-25-2009, 03:33 PM
Unless you are making something like a lead screw the approximations will do fine in nearly all cases. The error using my setup is only 2 parts per thousand which means that for one centimetre of thread the error is only 20 microns.

small.planes
11-25-2009, 05:49 PM
The small planes is something I did back in 2000, about 30 grams, 12 - 15 inch wingspan. IR control, back when you had to build the stuff from scratch to get it light enough to fly. Powered by Nicads, before LiPo was available...
A vid here (http://homepage.ntlworld.com/andy.birkett/davelanding.mpg)
Now Im into small helicopters, from about 200mm rotor diameter up.
A long running project is the worlds smallest fuel powered heli....

Back on topic, Evan is correct that there are approximations which will give you almost the correct pitch, and for most practical purposes (IE a few diameters as per normal bolts) it doesnt matter.
However you have a set coming, presumably with a 127 gear in it. Post some pics when you get it, these sort of things get glossed over in a theoretical manner to often.

Dave

firbikrhd1
11-25-2009, 06:28 PM
I have a Logan 10" lathe which can use either 127/100 transposing gears or 47/37 gears with a 1% error. The advantage of the smaller gears is both cost and they will fit under the gear cover. Here is a link to how the Logan setup wirks. The Logan has an 8 TPI lead screw so the gear formulas should work for your lathe if your lathe has the same.

http://www.lathe.com/metric_threading.htm

DICKEYBIRD
11-25-2009, 06:44 PM
Thanks for the link! My lathe has a 16 tpi leadscrew and a 40t gear on the spindle so I'll have to do some cypherin' to convert that chart, as Jethro Bodine would say.:)

oldtiffie
11-25-2009, 07:22 PM
Here is the OP:

Anyone have hands-on experience using those change gears on a lathe with an Imperial leadscrew?

I've read several places that this solves the Imperial/Metric conversion issue but have never seen any details or pictures as to where they go and how it works. I have a set coming and am wanting to give it a whirl when they arrive.

I measured and found that I do have the clearance needed to fit a 5" gear onto the leadscrew without hitting the table.:)

DICKEYBIRD.

The reason that a 127 tooth gear is used in conversions between and metric is that:

1" = 25.4mm

So, the ratio is 1:25.4 - but we need "full" teeth on our gears - not partial teeth.

So:
25.4 x 5 = 127 ("full") teeth.

It works whether cutting inch threads with a metric lead-screw or if you are cutting an inch thread on a metric lead-screw.

The "where they go" bit is usually given on a diagram on your lathe change-gear cover.


If your 127 gear is say 20DP its Pitch Circle Diameter (PCD) will be 127/20 = 6.35"

If it is 25DP the PCD will be 127/25 = 5.08"

If it is 30DP the PCD will be 127/30 = 4.2333"

Outside diameter (OD) = (PCD + (2 x 1/DP)) = (PCD + 2/DP)

If space is "tight" in the gear-train, there are other combinations -including "ganged" or "cluster" gears (2 or more gears acting as a single unit).

aboard_epsilon
11-25-2009, 07:45 PM
I do metric threading on my South Bend using compound gearing made up using the standard change gears that came with the lathe. By compounding two of the standard gears you can thread nearly all the usual metric sizes with no more than a 2 threads per metre error.

http://ixian.ca/gallery/metric/metric.htm

Looks like useful information for the yahoo south bend group .

Ive turned it into a pdf ..
is it OK if i upload it to the group .

i will credit you as the source

all the best.markj

DICKEYBIRD
11-25-2009, 08:02 PM
Thanks 'Tiff. Unfortunately, my lathe's "Where they go" chart doesn't show a 127T gear or any metric combinations at all. Calculating the dia/teeth ratio on my other gears, I had guessed the 127T gear would be about 5.08" dia when it arrives which matches your 25DP figure perfectly. Now I know what my lathe's gear DP is.:)

It'll probably take a bit of experimenting when the gears arrive for me to get my head around some sort of system to calculate the gearing and where the gears need to go.

My goal is to procure an R8/ER32 collet chuck for the mill and an extra nut to use with a home made flange mount ER32 chuck for the lathe. Maritool shows the ER32 nut threads to be 40mm x 1.5.

oldtiffie
11-25-2009, 08:16 PM
DickeyB.

These should help. They are from a "Metric" book published by one of our Universities in OZ - but it works in "inch" as well.

Just ask if you need any further info:

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting1.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting2.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting3.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting4.jpg

Don Young
11-25-2009, 09:49 PM
Thanks 'Tiff. Unfortunately, my lathe's "Where they go" chart doesn't show a 127T gear or any metric combinations at all. Calculating the dia/teeth ratio on my other gears, I had guessed the 127T gear would be about 5.08" dia when it arrives which matches your 25DP figure perfectly. Now I know what my lathe's gear DP is.:)

It'll probably take a bit of experimenting when the gears arrive for me to get my head around some sort of system to calculate the gearing and where the gears need to go.

My goal is to procure an R8/ER32 collet chuck for the mill and an extra nut to use with a home made flange mount ER32 chuck for the lathe. Maritool shows the ER32 nut threads to be 40mm x 1.5.

Although possible, it is unlikely that your gears are 25DP. They are more likely to be 24DP or metric Module 1. Grizzly should have a chart showing the recommended gear trains for metric threading. You can certainly figure it out once you understand it and know the parameters of your lathe. Do not be surprised if the first metric pitch you need to cut is not on the chart or possible with the gears you have as there are an awful lot of metric threads used and many setups are fairly limited. Check on "ISO262" to find the modern recommended metric threads.

oldtiffie
11-25-2009, 10:47 PM
Although possible, it is unlikely that your gears are 25DP. They are more likely to be 24DP or metric Module 1. Grizzly should have a chart showing the recommended gear trains for metric threading. You can certainly figure it out once you understand it and know the parameters of your lathe. Do not be surprised if the first metric pitch you need to cut is not on the chart or possible with the gears you have as there are an awful lot of metric threads used and many setups are fairly limited. Check on "ISO262" th find the modern recommended metric threads.


You are right Don.

I just pulled numbers at random from out of the air.

I agree that for a non-Chinese lathe the DP is more likely to be 24.

In that case the PCD is:
127/24 = 5.292"

The addendum at 1/DP = 1/24 = 0.042"

The OD = (5.292 + (2/24)) = 5.292 + 0.083 = 5.375"

If it is an Asian lathe it is likely to be Module 1.

So the PCD will be: 127 x 1 = 127mm (~ 5.000")

DP =1/mod = 1/1 = 1.00mm

OD = PCD + 2DP = 127 + 2 = 129mm ~ 5.079"

For Dickybird:

If you post a pic of your lathe gear train as well as the details of the pitch of your lead-screw and a listing of your gears I will try and work it out for you and will post the result and my workings.

It will be easy once you see it done.

DICKEYBIRD
11-26-2009, 06:56 AM
Here you go 'Tiffie. The plastic gear meshes with the 40T spindle gear and the gear on the opposite end is keyed to the 16 TPI leadscrew. The setup in the pic is for fine feed.

I hate to admit my ignorance but I can't seem to get my head around changing from TPI to metric pitch.

Thanks very much for your interest in this. As long as you're working with it, try to arrive at a 1.5 mm thread combination.:)

http://i57.photobucket.com/albums/g227/DBAviation/QCBox3.jpg

http://i57.photobucket.com/albums/g227/DBAviation/QCBox2.jpg

DICKEYBIRD
11-26-2009, 07:13 AM
Oops, here's my gear choices: 20, 25, 30, 35, 40, 50, 55, 60, 65, 70, 75, 80, 80, 80, 120 and 127

oldtiffie
11-26-2009, 08:03 AM
Thanks DB.

I will get into it shortly.

Evan
11-26-2009, 08:10 AM
Looks like useful information for the yahoo south bend group .

Ive turned it into a pdf ..
is it OK if i upload it to the group .

i will credit you as the source


As long as you put a link to the source it is ok.

aboard_epsilon
11-26-2009, 08:44 AM
hmmm

well links are posted on a seperate page in the yahoo groups ..
i can put an inactive link to it ..

i was going to put it on my smart and brown group as well. .as smart and brown make a copy of the southbend.

all the best.markj

DICKEYBIRD
11-26-2009, 08:54 AM
'Tiffie I read the document you posted above (duh, I should'a read it to start with) and it looks like 1.5 mm works out to 120/127 with my 16 TPI leadscrew. I'm not sure but my lathe probably isn't big enough to use both big gears at the same time no matter what kind of juggling is done.

We'll see on Monday when the big ones get here. I do better with parts in hand than in the brain.;)

Than again, I may be looking at this totally wrong!

JCHannum
11-26-2009, 10:38 AM
About the best book for the lathe hand is the Atlas Manual of Lathe Operation. I strongly recommend that any beginner or even experienced HSM get a copy and read it. It has a lot of good sound information for using the lathe. It is common on eBay and I believe reprints are available.

It has a large section devoted to threading which covers metric threading using the common Atlas 52 & 44 tooth gears. Gear combinations are given for metric pitches from 0.5 to 7 using these gears. It is nothing new or difficult. This is one area in which a change gear lathe has an advantage over a QCGB.

Jim Hubbell
11-26-2009, 03:28 PM
In the Nov./Dec. issue of HSM I explained and illustrated the method I use to obtain metric threads.

By using the 127 tooth conversion gear it was simple to arrive at most any common metric thread and be " dead on ".

Using 32dp for the 2 or 3 gears allowed plenty of room on the quadrant.

There are many ways to skin a cat.

Edit: 2007 issue of HSM

DICKEYBIRD
11-26-2009, 04:01 PM
Thanks Jim, I'll pull that issue from my stack and check it out.:)

Evan
11-26-2009, 05:19 PM
Marv Klotz has a bunch of utilities that run in a DOS box on XP. Included are everything you need to figure out the ratios for your lathe.

CHANGE.ZIP
(~61 Kbytes)
05/21/05 Finally took a stab at writing a program to select change gears to obtain a desired thread pitch/carriage feed. With the usual data file for tailoring to your equipment. New improved version added 6/2/01.

GEAR.ZIP
(~32 Kbytes)
02/23/05 John Cooper's article on gear making in the 4/99 issue of Machinist's Workshop inspired me to collect his clearly explained calculations into a program that produces a data file to carry to the shop for reference.

GEARFIND.ZIP
(~97 Kbytes)
12/01/04 Given a desired gear ratio and associated tolerance, this program will search for a gear train that produces that ratio. Similar to GEARATIO but doesn't presume a pre-existing set of available gears.

GEARATIO.ZIP
(~29 Kbytes)
08/14/03 If you have a set of gears (e.g., change gears from a lathe), you may want to use them to establish a ratio for some other application. This program automates the process of deciding which gears to use to obtain a desired ratio. See also GEARFIND.

GEARPA.ZIP
(~21 Kbytes)
01/31/06 An experimental program to allow HSMs lacking sophisticated gear measurement tools to distinguish between 14.5 and 20 deg pressure angle gears. Feedback on the (non)utility of this program is requested.

GEARSPUR.ZIP
(~20 Kbytes)
01/31/07 Enter any two of number of teeth, outside diameter, pitch, or pitch diameter and this program will calculate all the other relevant data for a spur gear.


http://www.myvirtualnetwork.com/mklotz/#shop