Metric Screwcutting on Super 7B with 127 Tooth gear

Well, I've acquired a Myford 127T gear. Apart from using it as an occasional table, the intention was to pair it with a 100T gear to convert the Imperial gearbox to Metric (when needed). Using this will give exact metric threads within the original accuracy of the leadscrew. Obviously, the clasp nuts will have to remain closed - it's crying out for Graham Meek's wizzo widget!

It's apparent that the Gearbox Cover won't close on it when fitted.

Has anybody actually used one on a Super 7B? Is the metric conversion banjo large enough to accommodate it, or is it a case of making a special one?

No you have to run case open or removed depending on if it's a S7 or ML7 due to size

Hi there,

When my ML7 was new (to me) and I was all super keen, one of the goodies I bought was a 127 tooth change wheel. I have to confess that I've never used it.

I haven't checked the tables but I seem to remember that there was an alternative method that used 2-off 21 tooth wheels.

Best regards,

Swarf, Mostly!

This thread was started 8 years ago and got no real answers ! Like Nigel and Swarf Mostly, I got hold of a 127 change wheel ! Can any body give us instructions as to using it ? Does one have to make a new banjo, what calculations does one need to do to work out the gear train, are they listed somewhere ? Noel.

Well, I can't really help much, since I have had my ML7 with a 127 tooth gear and have never used it either. My father also had it for a few years before that, and to the best of my knowledge he never used it either. The gear itself was salvaged along with a set of change wheels from a lathe that had gone for scrap. I don't know what the lathe was but the change wheels are the right DP for Myford, albeit with smaller holes and greater width, which was easy enough to fix.

The main reason I have never tried to use it is that it would need a slot cutting in the stand the lathe sits on, and acceptable accuracy is available just using the 63 tooth approximation, which is close enough for anything I will ever be likely to need. But the 127 tooth dinner plate looks impressive hanging on its nail on the wall.

John

Gearing of Lathes for Screwcutting by Brian Wood. ISBN 978-1-78500-250-2. Covers this topic extremely well, Chapters 1 & 2 .

Doug.

Confused as i bought the 34 & 36 tooth gears to cut most metric sizes , without touching the gearbox. Never used them but i have all the data somewhere explaining how it is done.

Steve.

Hey Steve, The 127 tooth gives a precise conversion to/from metric since it is the smallest prime factor of the ratio between inches and millimetres. (The end result will still only be as good as the leadscrew.) There are other approximations using more reasonable size gears that work perfectly well for all normal purposes. So yours will be fine for anything you are likely to want to do.

regards

John

One great proponent of the 127 tooth gear was Martin Cleeve … but he, very wisely, used a reduced pitch on his ML7.

MichaelG.

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

Edited By Michael Gilligan on 01/11/2021 06:27:54

You need to be very specific concerning your machine details to receive any meaningful answer.

Particularly, if it is a changewheel-only (non-gearbox) machine, the solution will be different to whether it has a gearbox.

Myford S7 Late 60s X2 ! One change wheel and the other with a gearbox!. Many thanks, Noel.

The problem when using a 127 gear on a Myford 7 changewheel machine
is simply the size of the gear if you have it as 20 DP,the lead screw centre
distance to tumbler stud = 3.785" and is equal to the size od a 149
tooth gear .As a pair of gears in line maximum that can be fitted in is a
20 tooth and 127 tooth .

As Michael G pointed out ,One great proponent of the 127 tooth gear was
Martin Cleeve … but he, very wisely, used a reduced pitch on his ML7.

I have gone down this same route using a 0.8 module 127 and 60 tooth
gear with the exceptions of 2 pitches the rest can be done using only
the remaining standard changwheel set supplied with the machine
using the standard banjo and being able to shut the cover.

Here is the screw cutting chart a horizontal version is in the album
"gears" as this is easier to print out in nearly A4.

John

127 works fine, just be careful where you put your fingers when you have the cover off. Niko.

When I had a ML7, a 127T gear soon became part of my Changewheel collection. (Just in case ) But, as far as can be recalled, never found the need to use it.

However, the first Metric thread that I cut was 1 mm pitch, fortunately on my lathe which includes a 120/127T compound in it the feed to gearbox.

Howard

I have a 127t gear for my old Super Seven.

Not used it for a good while but it worked well for the metric thread I required from what I recall. You do need to keep the door open but I didn't find that a problem in practice. BTW - I don't have a 100t gear but used a 50t one instead as part of the gear mix.

Regards,

IanT

Edited By IanT on 01/11/2021 10:21:25

I don't have a 127 tooth gear, but looking at my gearing spreadsheet and using the metric conversion set, with:

Tumbler stud - 30t

Gearbox input gear (gear X) - 127t

First stud driven - 60t

First stud driver - 80t

Gives exactly:

A1 - 1mm pitch

B1 - 0.5mm pitch

C1 - 0.25mm pitch

A4 - 0.8mm pitch

B4 - 0.4mm pitch

C4 - 0.2mm pitch.

The arrangement looks like it will fit the standard metric conversion banjo.

The standard metric conversion set using the 63t gear gives an error of .00125mm per 10mm of thread length in all the metric pitches.

Steviegtr, surely you mean 33 and34 teeth.

My lathe uses 16DP gears except for the metric set which utilises 127 tooth. They are 32DP. I expect that a Myford 7 would get away with 40DP conversion gears but 32DP would do just as well being ever so slightly finer than 0.8MOD.

Edited By Pete Rimmer on 02/11/2021 16:36:55

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To the extent that, in some circles, they are considered interchangeable and meshable !

… purists, of course, cry: “perish the thought”

MichaelG.

I'm not sure if anyone in this thread has yet pointed out that for most practical purposes you don't need a 127 tooth gear to get acceptable accuracy metric threads for fasteners. There are a number ot tables around giving gear combinations for this. I also bought a 127 tooth gear for my S7 once, it languishes in a draw with all the rest of the change gears since I just use the CNC....