Myford change wheels

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.

Andrew,

2 x 20 Teeth, 1 each of 25, 30, 35, 38, 40, 45, 50, 55, 60, 65, 70, 75 Teeth

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.

Andrew,

and for metric thread

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

p-mick

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

Thanks Everyone!

A great help and even metric change wheels too!

Andrew.

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.

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

George

You can use the program to calculate size of threads and set up change gear wheels --> **LINK**

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

^^^

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

MichaelG.

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

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

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.

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

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.

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.

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

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