Myford change wheels

This topic has 44 replies, 19 voices, and was last updated 2 January 2017 at 00:17 by Hopper.

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28 December 2016 at 17:25 #274081
Andrew Tinsley
Participant
@andrewtinsley63637
I seem to have only half a dozen change wheel on my Myford ML7. From memory I seem to remember that there were 14 changewheels for an Imperial set. I have tried to work out what these should be. It is good practice at setting up the various threads per inch. However I cannot work out all the threads per inch. I have worked out 7 pitches, but I may have made an error or two and cannot work out all the pitches anyway!

So can you please tell me what comprise the Myford set of 14 changewheels?

Thanks in advance,

Andrew.
Advert

28 December 2016 at 17:25 #8460
Andrew Tinsley
Participant
@andrewtinsley63637
28 December 2016 at 17:34 #274082
Robbo
Participant
@robbo
Andrew,

2 x 20 Teeth, 1 each of 25, 30, 35, 38, 40, 45, 50, 55, 60, 65, 70, 75 Teeth
28 December 2016 at 17:36 #274083
Michael Gilligan
Participant
@michaelgilligan61133
Andrew

This, from a previous thread, should tell you all you need: **LINK**

https://goo.gl/images/IOq08M

It's from the official handbook.

MichaelG.
28 December 2016 at 17:38 #274084
pierre ehly 2
Participant
@pierreehly2
Andrew,

and for metric thread

20, 21, 21, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75

p-mick
29 December 2016 at 11:36 #274172
Brian Oldford
Participant
@brianoldford70365
I'm pretty certain others are available too e.g. 28, 63 etc.
29 December 2016 at 13:42 #274200
Andrew Tinsley
Participant
@andrewtinsley63637
Thanks Everyone!

A great help and even metric change wheels too!

Andrew.
30 December 2016 at 00:21 #274343
Hopper
Participant
@hopper
YOu should be able to find a copy of the Myford change wheel chart on the net if your lathe does not have one attached. Much easier than calculating each one.

If you get Martin Cleeves' little book "Screwcutting in the Lathe" (7quid or so) it also has charts of how to cut metric threads with the standard set of imperial change gears, using compound gearing. Very handy indeed.
30 December 2016 at 01:04 #274346
Georgineer
Participant
@georgineer
Posted by Brian Oldford on 29/12/2016 11:36:42:

I'm pretty certain others are available too e.g. 28, 63 etc.

Yes, but I don't know why, since the standard set covers all usual requirements. Can anybody suggest a reason?

George
30 December 2016 at 06:49 #274357
Jens Eirik Skogstad 1
Participant
@jenseirikskogstad1
You can use the program to calculate size of threads and set up change gear wheels –> **LINK**
30 December 2016 at 09:07 #274374
Sandgrounder
Participant
@sandgrounder
Posted by Georgineer on 30/12/2016 01:04:54:

Posted by Brian Oldford on 29/12/2016 11:36:42:

I'm pretty certain others are available too e.g. 28, 63 etc.

Yes, but I don't know why, since the standard set covers all usual requirements. Can anybody suggest a reason?

George

Isn't the 63T gear used for metric screw cutting as as it's almost half of a 127T or a quarter of 254? It's less than a 1% error.

John

Edited By Sandgrounder on 30/12/2016 09:07:36
30 December 2016 at 09:13 #274378
Michael Gilligan
Participant
@michaelgilligan61133
^^^

I suspect that Neil might be along soon, to explain.

MichaelG.
30 December 2016 at 10:04 #274393
SillyOldDuffer
Moderator
@sillyoldduffer
Another potentially useful metric/imperial ratio is 2160:85, which is close to 127/5.

An 85 toothed wheel drives the leadscrew, and the 2160 is achieved by compounding.

So, if you happen to have a 6mm metric leadscrew, Imperial threads of 'n' threads per inch can be cut using the formula:

2160 ÷ 6 × n

For example, 12 tpi. 2160 ÷ 6 × 12 = 30

and 30 can be got with the gears 40 × 45 ÷ 60

Dave
30 December 2016 at 10:46 #274399
Hopper
Participant
@hopper
Posted by Georgineer on 30/12/2016 01:04:54:

Posted by Brian Oldford on 29/12/2016 11:36:42:

I'm pretty certain others are available too e.g. 28, 63 etc.

Yes, but I don't know why, since the standard set covers all usual requirements. Can anybody suggest a reason?

George

28 comes in handy for compound gearing sometimes, such as when holding work in the lathe chuck while using a slotting tool to cut splines etc. The change gears, often compounded, are used for indexing, with a plunger to engage on the last gear. I know I have used the 28 and the 24 in my set for this purpose, can't remember the specifics though. I have to dust off numerous grey cells every time I do that stuff and somehow muddle through it. I always wondered why those two gears were in the pile, along with the standard set, until I started indexing via change gears. The 28 can be compounded with say a 40T to give a 7:10 ratio, or with a 35T to give a 4:5 ratio, and so on. The 24T, being divisible by 2, 3,4,6, 8 and 12 can be compounded with a number of other gears too, 24/60 giving a 2:5 ratio or 24/40 giving 3:5. No doubt it could be used in compound gearing for oddball pitch screwcutting too.

As mentioned above, the 63t can be used for metric threads on an imperial leadscrew. The Drummond uses it in conjunction with a 46T for this purpose.

Edited By Hopper on 30/12/2016 10:52:40
30 December 2016 at 11:04 #274401
Ian Roberts
Participant
@ianroberts40159
its 73 and 46 that Drummond used. In general, selection of changewheels is not some mystical process, but was done by someone who had learned basic maths.
30 December 2016 at 11:47 #274408
Nick Hulme
Participant
@nickhulme30114
I use the nThreadp calculator which can be downloaded via Tony's site –

http://www.lathes.co.uk/latheparts/page14.html

I use a 127T for metric as simple gear trains are more often available, I know pitches with small errors are popular with many but just I don't see the point (no pun intended) when you can use the correct pitch.

Nick
30 December 2016 at 12:17 #274415
Roderick Jenkins
Participant
@roderickjenkins93242
Posted by Nick Hulme on 30/12/2016 11:47:32:

I use a 127T for metric as simple gear trains are more often available, I know pitches with small errors are popular with many but just I don't see the point (no pun intended) when you can use the correct pitch.

But, sadly, 127 teeth change wheels are too big to fit on most home workshop lathes.

Rod
30 December 2016 at 12:28 #274419
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Roderick Jenkins on 30/12/2016 12:17:05:

Posted by Nick Hulme on 30/12/2016 11:47:32:

I use a 127T for metric as simple gear trains are more often available, I know pitches with small errors are popular with many but just I don't see the point (no pun intended) when you can use the correct pitch.

But, sadly, 127 teeth change wheels are too big to fit on most home workshop lathes.

Rod

.

Ah But … as we have previously discussed: Martin Cleeve had a good work-around: **LINK**

http://www.model-engineer.co.uk/forums/postings.asp?th=113302&p=3

MichaelG.
30 December 2016 at 13:20 #274436
Andrew Tinsley
Participant
@andrewtinsley63637
My goodness! I seem to have started something here! I calculated as many thread pitch set ups as I could, on the basis of "if you can do it from first principles then at least you understand what is going on" much better than looking them up in a table!

I now have access to a Myford chart, so I am more than satisfied.

Thnks everyone,

Andrew.
30 December 2016 at 13:26 #274437
Roderick Jenkins
Participant
@roderickjenkins93242
Posted by Michael Gilligan on 30/12/2016 12:28:33

Ah But … as we have previously discussed: Martin Cleeve had a good work-around: **LINK**

http://www.model-engineer.co.uk/forums/postings.asp?th=113302&p=3

MichaelG.

Indeed he did, but why go to all that trouble when a simple combination of existing change wheels will give you a result indistinguishable* from the theoretically perfect solution?

* as measured in the home workshop

Rod
30 December 2016 at 13:36 #274442
Michael Gilligan
Participant
@michaelgilligan61133
No reason, Rod; I just thought it needed referencing, for the record.

These questions come-up quite frequently; so it's obvious that the indexing of previous threads leaves something to be desired … I remembered posting it, so it was perhaps a little easier for me to find.

MichaelG.

Edited By Michael Gilligan on 30/12/2016 13:40:11
30 December 2016 at 19:20 #274529
Nick Hulme
Participant
@nickhulme30114
Posted by Roderick Jenkins on 30/12/2016 12:17:05:

Posted by Nick Hulme on 30/12/2016 11:47:32:

I use a 127T for metric as simple gear trains are more often available, I know pitches with small errors are popular with many but just I don't see the point (no pun intended) when you can use the correct pitch.

But, sadly, 127 teeth change wheels are too big to fit on most home workshop lathes.

Rod

Sorry Rod,

I read the thread title and responded for the OP 😀
30 December 2016 at 20:05 #274536
Roderick Jenkins
Participant
@roderickjenkins93242
Posted by Nick Hulme on 30/12/2016 19:20:29:

Sorry Rod,

I read the thread title and responded for the OP 😀

I accept your apology in the spirit in which it is offered.

Being the unfortunate owner of a gearbox equipped Myford S7 lathe I am unable to offer any practical experience of fitting a 127T gear in the 20DP change-wheel train but note that Martin Cleeve (as alluded to by MichaelG) had to use 30DP 127T and 40T gears to get his system to work on his Myford ML7.

Rod
31 December 2016 at 03:25 #274566
Hopper
Participant
@hopper
Posted by Ian Roberts on 30/12/2016 11:04:24:

its 73 and 46 that Drummond used. In general, selection of changewheels is not some mystical process, but was done by someone who had learned basic maths.

You are correct. It is in fact a 73/46 combo used on the mighty Drummond. Well, I did say I have to dust off numerous grey cells and muddle along whenever I do this stuff!! I have never sourced either gear for my M type, instead using Martin Cleeve's tables of compound gearing using the standard set of gears to cut metric threads. Errors within one thou per several inches are more than good enough for me, and probably more accurate than the lathe's 78-year-old leadscrew, even when it was new! I have never had a problem using his method.

I'd post a copy of his table from his book "Screwcutting in the Lathe" as it is very handy but it's copyright and the book costs only about seven quid so everyone with a lathe should really buy one, IMHO. The table applies to Myfords and other lathes too.

Edited By Hopper on 31/12/2016 03:27:01
31 December 2016 at 08:55 #274587
John Stevenson 1
Participant
@johnstevenson1
Myfords when they brought the ML series lathe out worked out a set of gear suitable for imperial and metric screw cutting and from 1947 onward's – pre internet forums and over stuffed armchairs -tens of thousands of uses from all walks of life managed to cut near perfect threads with this combination.

It's only since the advent of internet forums where anyone can be an engineer, that we have the armchair warriors with nothing better to do and having less skills that they care to show, who now come up with alternatives that are no better than the original set of tables.

True a 127 will give the perfect metric thread on an imperial machine give that the machine is capable but has anyone ever seen a thread map for a Myford leadscrew ? I certainly haven't and I'll bet that no one else has either.

So without this it's impossible to know total accuracy or rather inaccuracy.

However this won't stop the warriors pounding forth on something they can't prove or even possibly do ?
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