Hello Cliff,

Even the Newall PCD function only goes up to 99 divisions so you are not making any mistakes.

Rather than grapple with making an awkward 127 hole change wheel, you can use a combination of 63/80 instead. The error difference is too small to worry about and Southbend themselves recommended the combination as a good working alternative.

Regards Brian

I think that Anilam is a CNC controller, not a DRO!

How large a plate do you want, and what size holes? I think I have a spare aluminium circle somewhere, it would be a matter of moments to sling it on the CNC mill and drill a plate for you if you only want something that'll be used a few times.

If your unit won't go over 100 then do 64 holes over an angle of 178.68deg and then a second set of 64 over 181.42 using same center location and PCD

On my south bend 9 a , i just make the change gear out of tufnol as and when required to cut metric threads with the least possible error. Last one i cut was for a 2mm thread. I bought a boxford 79 teeth and made i think a 20 or 24teeth one from tufnol.

You can do a lot of metric threads with a 79 teeth gear + one of either 20,24.30 and 40 teeth .Though i have the gear box on my south bend.

You just fit the 100/127t gears back to front. Nobody has a 135t gear, AFAIK.

Murray

Or 63/80t may be more convenient.

Edited By Muzzer on 13/11/2017 21:56:03

In that case you'll need to write to all the major manufacturers and get them to correct their manuals!

The maths is very simple.

If you have a 3mm leadscrew (like the example in hand), and you want to cut imperial, you need to speed up the leadscrew slightly. The simplest example would be to cut an 8tpi thread which has a 25.4 / 8 mm pitch ie 3.175mm. So for that you drive the 120t gear and the 127t gear drives the 3mm leadscrew gear. This gives you the correct ratio, as 127 / 120 x 3 = 3.175.

Going the other way, if you have an 8tpi leadscrew (3.175mm again) and require a 3mm thread, you need to slow down the leadscrew by that ratio. So you drive the 127t and the 120t will drive the leadscrew gear.

It's really not rocket science.

Murray

Hello again Cliff,

A further variation which might be more useful is 80/85, with 80T as the onward driver

The maths are; 127/135 = 0.94074 and 80/85 = 0.94198

You might even have these wheels as standard supply

Regards Brian

Cliff,

A small error in my suggested 80/85 combination. as a substitute for 127/135

The decimal value is better than I stated earlier at 0.94118 which is only 0.00044 larger than the 127/135 combination value of 0.94074. The working error will be small..

Murray

My apologies, I misquoted your combination as 120/135, it should of course have been 120/127, it has been nagging at me this afternoon

Regards Brian

Edited By Brian Wood on 14/11/2017 18:04:01