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Black Forest
10-08-2010, 02:51 PM
Where can I go to find/learn about change gears? Is there any general rules of thumb or info available? I had someone give me an old lathe with a box of change gears. His father used the lathe and he has no clue. It is an old Ariston lathe. Metric only. The only thing I know is that I don't know anything about making threads!

Robin R
10-08-2010, 03:13 PM
There is a book in the "Workshop Practice" series, by Matin Cleave called "Threading in the Lathe". It is probably as good a source of information on the use of change gears, as you will find.

john hobdeclipe
10-08-2010, 03:33 PM
The old standby is the South Bend book, "How to Run a Lathe." But I think the Atlas (Craftsman) book "Manual of Lathe Operation and Machinists Tables" gives a clearer explanation of change gears and threading operations.

Check eBay and/or Amazon.

djc
10-08-2010, 03:57 PM
Where can I go to find/learn about change gears? Is there any general rules of thumb or info available? ... It is an old Ariston lathe. Metric only.

The 'Screw-cutting in the lathe' book by Martin Cleeve (as already suggested but this time with slightly better spelling) is excellent.

Starting from the basics, you need to determine the pitch of your leadscrew. Easiest way to work this out is to engage the half-nuts and measure how far the carriage moves for one (or ten) turns of the leadscrew. This will be a 'sensible' number of millimetres if, as you say, the lathe is metric.

If you then gear the spindle to the leadscrew with a 1:1 ratio, this is the pitch of thread you will cut.

If you want a coarser thread (unlikely as leadscrews are generally pretty coarse already but we'll do the exercise anyway), you have to change the ratio of the gearing so the carriage moves further/faster for one spindle revolution. In other words, for one rev. of the spindle, the leadscrew must make greater than one rev. Hence you have to gear it up (bigger gear on the spindle, smaller gear on the leadscrew).

If you want a fine thread, you have to slow down the carriage so it moves less/slower. For one rev. of the spindle, the leadscrew must turn less than one rev., hence you have to gear it down (small gear on spindle, large gear on leadscrew).

Working out the gear ratios requires nothing more than a high school level of familiarity with fractions.

Black Forest
10-08-2010, 04:08 PM
Thank you for the answers. I will buy the books suggested. Anymore info offered would be appreciated.

oldtiffie
10-08-2010, 05:23 PM
Where can I go to find/learn about change gears? Is there any general rules of thumb or info available? I had someone give me an old lathe with a box of change gears. His father used the lathe and he has no clue. It is an old Ariston lathe. Metric only. The only thing I know is that I don't know anything about making threads!

BF.

This should help. It is from a Technical and Further Education (TAFE) Department in one of our Universities of Technology in Australia (OZ) and as OZ is a metric country it is predominantly metric.

It may seem like "heavy going" but its not really as all the basics and fundamentals are there.

Just take it slowly and steadily and you will be OK.

If I can be of any further help, please don't hesitate to ask and I will do what I can to assist.

Part 1 (Chapter 14):

Part 2 (Chapter 29):

whitis
10-08-2010, 06:25 PM
Where can I go to find/learn about change gears? Is there any general rules of thumb or info available? I had someone give me an old lathe with a box of change gears. His father used the lathe and he has no clue. It is an old Ariston lathe. Metric only. The only thing I know is that I don't know anything about making threads!

Change gears can be pretty simple for an imperial only or a metric only lathe with a clean design but can get a bit more complicated for machines that try to cut both or that try to get by with too few gears and need more complicated setups, or use weird leadscrew pitches, etc.

When you mesh two gears, the driven gear turns at the speed of the driven gear multiplied by the number of teeth on the driving gear and divided by the number of teeth on the driven gear, but in the opposite direction. If you insert an idler gear between them, the ratio doesn't change but the direction of rotation is reversed. If you insert a pair of gears coupled together on the same axle, with one meshing with the driving gear and the other meshing with the driven gear, then the ratio of the number of teeth on the two new gears affects the results.

You should have at least three axles on which to mount gears. One on the spindle or the output of the tumbler reverse or coupled directly to the spindle with a fixed gear (that isn't changed because the spacing isn't adjustable). One on the lead screw. And one on a "banjo" which is a part that pivots around some point and has a long slot; between these two degrees of freedom, you can move the axle so the gear(s) on it mesh properly with the others. Each axle (with possibly one exception), should have the ability to mount 2 gears or 1 gear and a spacer the width of the gears. You may have additional axles, as well, to permit more complicated gear ratios.

Assuming the first gear connects directly to the spindle or on an axle that rotates once per spindle revolution, then basically compute the ratio of the thread pitch/lead you want to the one on the lead screw and choose a combination of gears with the same ratio.

Simple gearing:

(spindle gear) (idler gear) (leadscrew gear)
spindle gear drives idler gear which, in turn, drives the lead screw gear.

Example:
Desired pitch: 2mm pitch
ratio 2:1 (two leadscrew revolutions per spindle revolution)
Spindle gear: 40 tooth (for example)
Leadscrew gear: 20 tooth (half as many teeth as spindle gear)
Idler gear: any gear which will fit and allow you to mesh with the two important gears.
You could also use 32/16, 60/30, 72/36, 36/18
Swap the two gears, and you will get 0.5mm pitch.

If you can't find a simple gearing combination which works, you have to resort to compound gearing:

| | |
[GEAR A] [GEAR B] |
| | |
[GEAR C] [GEAR D]
|

Ratio: A/B*C/D
Here, gears B and C are on the same axle and keyed to rotate together. Spindle turns gear A, Gear A drives Gear B, C shares an axle with B so it turns at the same rate, and gear C drives gear D. The middle axle turns at a rate of A/B times the rate of the spindle and the leadscrew turns at a rate of C/D times the middle axle, or A/B*C/D times the spindle. If need be, you can insert any gear as an idler between gears A and B or gears C and D and it doesn't have any effect on the ratio other than reversing the direction of rotation.

For really complicated ratios, you bring a 4th axle into play.

It is easy to get confused and make your ratios upside down making a finer pitch when you wanted a coarser one, or vice versa, but easily fixed by swapping gears.

If you have a 127 tooth gear, you should be able to cut exact imperial sizes; if you don't you may be able to get a close enough approximation good for short threads using some pretty weird gear ratios.

If your lead screw is a sensible pitch related to other standard metric pitches by a simple ratio, your gear setups should be fairly simple. If they used one of the weirder sizes, it gets more complicated. In some cases you can setup one combination of gears that converts that pitch to a more reasonable starting point and leave that setup for most uses and just add other gears.

There will often by multiple gear combinations that will work, though some might not physically fit due to something getting in the way.

Here is an example of simple gear combinations with a 1mm lead screw and a few random gear sizes (12, 16, 18, 28, 30, 32, 36, and 48 teeth)

1mm*12/12 = 1 mm
1mm*12/16 = 0.75 mm
1mm*12/18 = 0.66666667 mm
1mm*12/28 = 0.42857143 mm
1mm*12/30 = 0.4 mm
1mm*12/32 = 0.375 mm
1mm*12/36 = 0.33333333 mm
1mm*12/48 = 0.25 mm
1mm*16/12 = 1.3333333 mm
1mm*16/16 = 1 mm
1mm*16/18 = 0.88888889 mm
1mm*16/28 = 0.57142857 mm
1mm*16/30 = 0.53333333 mm
1mm*16/32 = 0.5 mm
1mm*16/36 = 0.44444444 mm
1mm*16/48 = 0.33333333 mm
1mm*18/12 = 1.5 mm
1mm*18/16 = 1.125 mm
1mm*18/18 = 1 mm
1mm*18/28 = 0.64285714 mm
1mm*18/30 = 0.6 mm
1mm*18/32 = 0.5625 mm
1mm*18/36 = 0.5 mm
1mm*18/48 = 0.375 mm
1mm*28/12 = 2.3333333 mm
1mm*28/16 = 1.75 mm
1mm*28/18 = 1.5555556 mm
1mm*28/28 = 1 mm
1mm*28/30 = 0.93333333 mm
1mm*28/32 = 0.875 mm
1mm*28/36 = 0.77777778 mm
1mm*28/48 = 0.58333333 mm
1mm*30/12 = 2.5 mm
1mm*30/16 = 1.875 mm
1mm*30/18 = 1.6666667 mm
1mm*30/28 = 1.0714286 mm
1mm*30/30 = 1 mm
1mm*30/32 = 0.9375 mm
1mm*30/36 = 0.83333333 mm
1mm*30/48 = 0.625 mm
1mm*32/12 = 2.6666667 mm
1mm*32/16 = 2 mm
1mm*32/18 = 1.7777778 mm
1mm*32/28 = 1.1428571 mm
1mm*32/30 = 1.0666667 mm
1mm*32/32 = 1 mm
1mm*32/36 = 0.88888889 mm
1mm*32/48 = 0.66666667 mm
1mm*36/12 = 3 mm
1mm*36/16 = 2.25 mm
1mm*36/18 = 2 mm
1mm*36/28 = 1.2857143 mm
1mm*36/30 = 1.2 mm
1mm*36/32 = 1.125 mm
1mm*36/36 = 1 mm
1mm*36/48 = 0.75 mm
1mm*48/12 = 4 mm
1mm*48/16 = 3 mm
1mm*48/18 = 2.6666667 mm
1mm*48/28 = 1.7142857 mm
1mm*48/30 = 1.6 mm
1mm*48/32 = 1.5 mm
1mm*48/36 = 1.3333333 mm
1mm*48/48 = 1 mm

And here are a few examples of 4 gear compound combinations which would give inch threads (A/B*C/D):

1/(1mm*12/12*127/30) = 6 * 1/inch
1/(1mm*12/16*127/30) = 8 * 1/inch
1/(1mm*12/18*127/30) = 9 * 1/inch
1/(1mm*12/28*127/30) = 14 * 1/inch
1/(1mm*12/30*127/30) = 15 * 1/inch
1/(1mm*12/30*127/32) = 16 * 1/inch
1/(1mm*12/30*127/36) = 18 * 1/inch
1/(1mm*12/30*127/48) = 24 * 1/inch
1/(1mm*16/30*127/32) = 12 * 1/inch
1/(1mm*18/12*127/30) = 4 * 1/inch
1/(1mm*18/30*127/30) = 10 * 1/inch
1/(1mm*32/16*127/30) = 3 * 1/inch
1/(1mm*32/30*127/48) = 9 * 1/inch
1/(1mm*36/12*127/30) = 2 * 1/inch
1/(1mm*36/18*127/30) = 3 * 1/inch
1/(1mm*36/30*127/30) = 5 * 1/inch

[NOT APPLICABLE] If you have one special gear which mounts on the spindle which isn't interchangable with the other gears (different hole size), your gear settups get a little more complex. If you have a change gear with the same number of teeth as the special gear, try mounting that one on the lead screw and then you may be able to do most thread setups by just stacking two gears on the same axle with the ratio you desire.

[NOT APPLICABLE] If you do not have a tumbler reverse, you change between left and right hand threads by either adding or subtracting an idler gear.

Found a picture of your lathe here:
http://i853.photobucket.com/albums/ab91/burnandreturn/lathe2.jpg
Looks good. You have a 127 tooth gear so you can do inch/metric. You have a tumbler reverse. You appear to have a 4th axle, pivoted out of the way. You have 7 gears on the lathe, plus the aforementioned box of gears.

Start by checking your tumbler reverse and make sure that the axle nearest the spindle (the one coming from the tumbler reverse) rotates exactly once per spindle revolution. It can cause confusion if it does not.

In the configuration shown in that picture, the middle gears are just acting as an idler and it is doing inch/metric conversion because the 127 tooth gear is in play (actually, it may be a useless setup because the 127 tooth is in the wrong place if your leadscrew is really metric). The second gear on the middle axle is just acting as a spacer. The stack of gears in the back are doing nothing. You appear to have a spacer on the outside end of the leadscrew shaft.

There is a good chance that when not doing imperial/metric conversion your gear setups may be fairly simple for standard threads.

If you need help with the gear combinations, post your lead screw pitch and the number of teeth on each change gears you have available.

Mike Burdick
10-08-2010, 06:36 PM
The old standby is the South Bend book, "How to Run a Lathe." But I think the Atlas (Craftsman) book "Manual of Lathe Operation and Machinists Tables" gives a clearer explanation of change gears and threading operations.

Check eBay and/or Amazon.
Or....here is a free equivalent of "How to Run a Lathe" ....

"Text Book of Turning" by P.T. Hercus

http://bbssystem.com/viewtopic.php?t=89

Robin R
10-08-2010, 08:58 PM
[QUOTE=djc]The 'Screw-cutting in the lathe' book by Martin Cleeve (as already suggested but this time with slightly better spelling) is excellent.

That will teach me to recommend a book I haven't looked at in a couple of years, without checking first.

john hobdeclipe
10-08-2010, 09:01 PM
Or....here is a free equivalent of "How to Run a Lathe" ....

"Text Book of Turning" by P.T. Hercus

http://bbssystem.com/viewtopic.php?t=89

Excellent! Thanks for this link.

GUMPER
10-09-2010, 01:02 AM
In Machinery's Handbook 23rd Edition there is a section in the contents titled 'Threads and Threading' with a subsection titled 'Tapping and Thread Cutting' which contains information on 'Change Gears for Thread Cutting'.

If you have a copy of Machinery's Handbook you already have the info that you need to figure what gear combinations you will need to cut any thread pitch that you need.

gumper

Black Forest
10-09-2010, 06:57 AM
Thank you for the links and pictures. I am studying now!

Black Forest
10-09-2010, 10:44 AM
Ok. If any of you need any advice on change gears I am the go to guy!

I know everything there ever was or ever will be known about change gears. I am the Google of change gears. I know every size of every make of every system on any lathe ever built or will be built.

I am your Change Gear Guru.....

Thank you for all the great info. I have been reading most of the afternoon and I think I will try tomorrow to cut some threads on this 100 year old relic.

It is not often I get a chance to relax like I did this afternoon.

John Stevenson
10-09-2010, 11:27 AM
Black Forrest.

PM box full.

Black Forest
10-09-2010, 01:04 PM
Well damn John, if you would stop sending me messages my box wouldn't be full.

John Stevenson
10-09-2010, 01:44 PM
It's only because the begging letters look so naff on the forum......

Arthur.Marks
10-09-2010, 03:00 PM
Okay, you asked :D I started this a couple weeks ago but never found the time to finish. It is a calculation sheet for working out a change-gear chart for metric pitches with a 12tpi leadscrew lathe. I did the calculations as far as the "driver/driven" ratios, but never broke those down into usable gear correlations. I still mean to, but if you beat me to it, I'll have to send you a beer :p The spindle has a 28T on the rear which then proceeds through a tumbler reverse with a 22T gear... then on to the change-wheels. See HERE (http://i771.photobucket.com/albums/xx357/Arrak_Thumrs/Dalton/DSCN3496.jpg).

Chart is HERE (http://i771.photobucket.com/albums/xx357/Arrak_Thumrs/Dalton/CGccalcs.jpg)

Black Forest
10-09-2010, 03:58 PM
First Arthur, I live in Germany.

Second, I don't have a clue what you need to do!

Maybe you didn't get my facetiousness about knowing all about change gears!

Sorry!

No wait, hmm let me say it this way.

The information that you seek is so obvious that it would be too easy for me to answer so I will let some of the lessor machinists on this board answer. They need some encouragement.

rohart
10-09-2010, 07:17 PM
Whitis is perfectly correct about using a 127 tooth gear to convert from metric to imperial or vica versa.

However, once you get Cleeve's book, look at some of the tables he provides. He lists the errors involved if you use alternatives to the 127 gear. For example, using a 61 toother, you can get a 1 in 1520 error IIRC. This error means that if you cut a 20 tpi thread you'll be 1 pitch out in 6 feet. As long as the thread engagement is less than an inch or so, the error is less than 1 thou. Your leadscrew will likely have more error than that.

So don't worry about not having a 127, which can be a big gear.

Find the pitch of your leadscrew, and look up Cleeve's tables.

Then construct a list of your favorite set-ups. You'll find metric pitches on a metric machine quite straightforward. Suppose you've got a 3mm pitch leadscrew. To cut a 1mm pitch you need to slow down the leadscrew from the spindle by a factor of three. Doesn't matter how you do it - 20 drives 60, 20 drives 40 and 30 on the 40 axis drives 45, and so on. Remember an idler can be any size - teeth in = teeth out, so no effect.

Concentrate on one imperial pitch at a time, and draw out your whole set up once you've used it successfully. Soon you'll be working them out for yourself.

My Lorch has a 2mm leadscrew, and I can cut a 4mm pitch if I turn the spindle by hand.

Cutting to the right depth, cutting to a shoulder, feeding in at 29 degrees, cutting acme/trapezoidals, internal threads with the tool on the far side of the ID - there's lots of fun in store for you !

oldtiffie
10-09-2010, 07:35 PM
Black Forest (BF).

My guess is that as you live in Germany (all metric) that your lathe will be "metric" as will most, if not all, threads you need to cut.

If that is the case, then inch>metric>inch etc. will not be an issue.

In that case the "127 gear" will not be an issue either.

I would not be concerned about the technicalities of using a metric thread chasing/screwing dial either - just leave the half-nuts engaged and stop and reverse the lathe. The time saved by using the threading dial is not worth the worry and learning-curve required to use the metric threading dial.

Black Forest
10-18-2010, 05:15 AM
I have read about the change gears. I don't quite have it yet.

I want to cut a 1.5mm thread. My lead screw is 6mm

I have 13 change gears.
127
120
65
64
60
55
45
40
38
35
30
24
20

So how do I figure this and what gears can/should I use?

I have read, read, read, but I still don't get this thing figured out.

oldtiffie
10-18-2010, 05:46 AM
BF.

In other words if your lead-screw half nuts are engaged it will require the head-stock to rotate 4 turns to each turn of the 6mm lead-screw.

That being the case a screw thread would have 4 complete pitches cut for each turn of the 6mm lead-screw - ie 4 X 1.5mm threads if you wish.

From your gear selection the best (only?) 4:1 ratio ratio is the 30 and 120 tooth gears.

Put the 30 tooth gear as near as you can to - or on - the head-stock spindle and the 120 tooth gear on the end of your lead-screw. Fill in the gap between those gears with other gears - no compound gear (2 gears connected together on the same spindle) and add or subtract one gear if the the lead-screw is rotating the wrong direction (ie driving the saddle toward the tail-stock instead of the head stock when the lathe head-stock spindle is going forward).

Leave the half-nuts engaged for the whole job - to get the saddle to go toward the tail-stock, stop and reverse the head-stock motor.

I have assumed that you not have a "quick-change" gear-box for the lead-screw.

I am working blind here so a few pics of your head-stock gear-train and the front of your head-stock will be a big help.

I hope it helps.

MuellerNick
10-18-2010, 05:50 AM
Oh, you posted the question at the forum too.
Bad boy, don't PN and post. A link to the question in the forum would have been better!

Here is my answer I PN-ed:

The principe is very simple:
If the lead screw would be directly coupled to the spindle, one revolution of the spindle would make one revolution of the lead screw and thus you'd get a 6mm pitch.

Now, the lead screw rotates too fast by a factor of: 6 / 1.5 = 4.

We need to find a pair of gears that does that. Smallest gear is 20, so this would require a gear with 80 tooth. No find. But we do have 120 teeth, so a 30 teeth one would match. But I doubt your lathe has just one stage, normally they do have two stages.
OK, factor 4 in two stages would be for example 2 * 2 = 4.
New try:
Gear set 1: 20 & 40 makes factor 2
Gear set 2: 30 & 60 makes factor 2
Now you might discover, that the gears still won't mesh, because the distance between spindle and lead screw is bigger. Just pick other gear sets for a factor of two: 120 & 60; 60 & 30; 40 & 20; that's what you got.

With the example of 20 & 40 and 30 & 60, the gears would be arranged that way:

20 : SP
40 : 30
SP : 60
---- spindle

SP is a spacer, short piece of tube, often found. I don't know your lathe and what you've got.
The gears 40 : 30 are on one axis and are coupled with a key!

HTH,
Nick

Black Forest
10-18-2010, 06:18 AM
I sent you a PM because I wasn't sure you would read the post. But now I know!

Thank you for the answers. Now it is clear to me.

I try it after lunch.

Black Forest
10-18-2010, 06:23 AM
THis is a link to the lathe.

MuellerNick
10-18-2010, 06:26 AM
I sent you a PM because I wasn't sure you would read the post.

I might have missed it. When I click "new Posts" a lot gets lost. Don't know why.
So it is absolutely OK for me to PN me a link, if you think I'm the one to ask.

Nick

rohart
10-18-2010, 06:46 AM
oldtiffie - you asked how you could help.

You could help by getting the rest of that excellent looking publication into pdf format and onto the forum.

Or into jpgs like that chapter, and someone else can do the rest.

Come on now - something to cheer us miserable northern hemisphere gits up as the winter closes in !

oldtiffie
10-18-2010, 06:55 AM
Thanks for the compliment Richard but I can't see a publication I used in this thread.

I am probably at or pushing past the limits now so I'd rather not push my luck any further.

Which publication is it?

Show me a pic and I will recognise it.

oldtiffie
10-18-2010, 07:17 AM
THis is a link to the lathe.

Thanks BF.

These pics will be fine:
http://i853.photobucket.com/albums/ab91/burnandreturn/lathe_dirty.jpg

http://i853.photobucket.com/albums/ab91/burnandreturn/changegear.jpg

http://i853.photobucket.com/albums/ab91/burnandreturn/clean.jpg

I will use the last pic.

I see that you have a Forward-Neutral-Reverse lever for your gear-train so you can mount the gears required as you choose.

Remove the top gear (to the left of the F-N-R lever) and replace it with the 30 tooth gear.

Remove the large gear on the end of the lead-screw and replace it with the 120 tooth gear.

You are now set to go.

I do wish that you'd have told me that you had previously PM-ed Nick and given him a chance reply as I feel as if I've whacked him the eye. I realise that it was unintentional - so no hard feelings.

Nick - sorry - unintentional.

BF - please keep us posted on your progress.

MuellerNick
10-18-2010, 07:38 AM
Nick - sorry - unintentional.

What? Everybody is free to answer first.
Often enough, explaining things in a different way helps the one who asked to understand better.

I don't think BF wanted to ask only me, because I'm better. But just because I live in the same time-zone and he wanted to cut that thread right now. He even phoned me, but I was not available.

So, no problem at all! For anybody involved.

Nick

Black Forest
10-18-2010, 08:23 AM
Oldtiffe don't worry about whacking Nick in the eye, He probably deserves a whack now and then. I just needed an answer and Nick is lazy sometimes about reading some of the threads unless he thinks he can insult someone or otherwise pitch a hissy fit!

Don't worry about him getting upset at what I write. He won't understand my English.

Black Forest
10-18-2010, 12:29 PM
So with printouts in hand I went to the shop and installed change gears.

I used a 20 to a 40 mounted with a 30 on the same axis. The 30 to a 60.

I needed another gear to take up the space and a 55 fit perfect. Everything went great. I turned a 1.5 thread on a 10mm bolt. Nut went on perfect.
Thank you for the help.

http://i853.photobucket.com/albums/ab91/burnandreturn/18-10-10_1813.jpg
http://i853.photobucket.com/albums/ab91/burnandreturn/18-10-10_1600.jpg

MuellerNick
10-18-2010, 01:08 PM
unless he thinks he can insult someone or otherwise pitch a hissy fit!

That thread came out quite blurry! Did you cut it with that rusty nail you found last week?

No really, looks very good for a farmer.

Nick

oldtiffie
10-18-2010, 06:59 PM
So with printouts in hand I went to the shop and installed change gears.

I used a 20 to a 40 mounted with a 30 on the same axis. The 30 to a 60.

I needed another gear to take up the space and a 55 fit perfect. Everything went great. I turned a 1.5 thread on a 10mm bolt. Nut went on perfect.
Thank you for the help.
http://i853.photobucket.com/albums/ab91/burnandreturn/18-10-10_1813.jpg
http://i853.photobucket.com/albums/ab91/burnandreturn/18-10-10_1600.jpg

unless he thinks he can insult someone or otherwise pitch a hissy fit!

That thread came out quite blurry! Did you cut it with that rusty nail you found last week?

No really, looks very good for a farmer.

Nick

Don't worry about it BF - its a fine thread a a sharp pic too - just fine.

It only looks "blurry" to Nick because his eyes watered when you screwed him (up?).

Just be sure he doesn't come back - if you can - or if you want to.