View Full Version : embarresting question

big job
09-06-2011, 06:47 AM
Should know better at my age, but my question is if there is a standard or
rule on change gearing. 90% of my treading is done on a SB 9A. Once in
awhile will be a very large thread just too big for the SB. So this will be a
job for my heavy Greaves Iv'e had for 30 yrs. I got it free But the change
gear plate is unreadable. Also the complete gear set from about 12" down
to 3"s. The gears are 1918 new never out of the crate. As of now it is set
for acme 8TPI, so I conclued this is what it probably it ever did other than
regular turning. The question is at this time mfg.s had their own standards
being specific to their machines, or, is or were standards of gear changing.
I have been to every website on the planet, this machine is listed but thats
about it. Also I will add I am not running a museum Its just all I can afford,
just wishing somebody cleaning an attic with a manual or something, got
better hope of finding Dino bones out back. thanks sam

09-06-2011, 07:00 AM
I suspect that what you will need to do is figure out the gearing yourself. I think SouthBend's "How to Run a Lathe" book explains how to do it, or L.H. Sparey's "The Amateur's Lathe."

09-06-2011, 07:50 AM
"Screwcutting In The Lathe, Martin Cleeve, Workshop Practice Series, #3", particularly Ch 2, "Principles of Lathe Screwcutting" includes how-to for calculating simple & compound gear trains for the required threads/inch

Another is "The Calculation Of Change Wheels For Screw-Cutting On Lathes, by DeVries, c.1908." I don't have a source tho' the book is annotated that it was "digitizrd by Microsoft"; I am guessing Google Books.

09-06-2011, 10:36 AM
I find that Microsoft Excel (or Open Office.org) works quite well for figuring out gear ratios. Here is a screen shot of one of the set ups I use for a Grizzly lathe, notice the math formula in the box. The formula for your lathe will be different, but when you figure out the formula you can just substitute gear sizes to get the TPI you want.


John Stevenson
09-06-2011, 01:44 PM
Download this piece of software here and follow instructions.


Works ace.

09-06-2011, 04:02 PM
Now that you have some answers, I can say that that is hardly an embarrassing question. For example, asking how to un-superglue your fingers is an embarrassing question.


09-06-2011, 04:10 PM
Haha! Absolutely agreed. Gearing can get complicated, especially if you have quick-change gearboxes and compound geartrains involved.

09-06-2011, 04:29 PM
I found the GearsVB program, from Varmint Al's site, to calculate all the combos for my change gears. Not limited on TPI of your leadscrew.


09-06-2011, 07:09 PM
I second trying to get a copy of the Martin Cleeve book.

When you get it, you then have to recreate his tables for your own leadscrew pitch.

Then, for every pitch you need, you write out all the sensible geartrain options there are.

Then, you strike out the ones that you don't have change wheels for.

Then, you strike out the ones that won't fit on your banjo, and that have gear combinations that interfere with each other.

Then, you group geartrains together to try to minimise the number of gears you need to change when you change pitch.

And that's about it. Oh, you test your geartrain with a very shallow scratch cut before you start to cut your thread, just in case you loused up. Heaven forbid !

Finally, you make a new brass plaque with all this stuff on it.

By the time you've finished, you have a reasonable understanding of what's a driver gear and what's a driven gear.

09-07-2011, 03:32 AM
Now that you have some answers, I can say that that is hardly an embarrassing question. For example, asking how to un-superglue your fingers is an embarrassing question.


Particularly if the fingers are stuck to your fly zip:o ,

or worse - someone else's fly zip :eek: :o :D

big job
09-07-2011, 05:05 AM
Thanks good info here its a gear stack of 20 gears very heavy, but still in the
back of my mind is the time frame of the machine those days they invented
their own bolts & nuts specific to their company, I mean my gear stamped 20
may not be the same 20 gear from machines mfg. 25 yrs later? My next
idea is I know its set up for 8 TPI Acme cause I done that and I will clean
and find the numbers of gears and see if these compare to numbers that
you all provided me thanks again. sam

John Stevenson
09-07-2011, 07:15 AM
Normally it it's stamped 20 it means 20 teeth.
No matter the time frame 20 teeth is 20 teeth regardless of size.

All that matters is the stack is the same pitch, ie they all run together which sounds promising.

If you tell us how many tpi your leadscrew is and what number teeth gears you have I'm sure some kind soul on the forum will work you a thread chart out.