Additional Screw Cutting Gearbox

**LMMasterMariner** · Jul 3, 2018, 01:01 PM

Hello to everyone.

Decided to make additional screw cutting gearbox as my next project.
(once I modify and complete external headstock gearbox)
Already made calculations and drawings for that.

My Chinese lathe CQ6128x660 (also G0602, Birmingham YCL-1126BD, RDX 11x26 and many others)
already have screw cutting gearbox with 9 different combinations with every pair
of change gears, so one additional external gearbox is required in order to have
'full norton' lathe. Read: No more messing with change gears.

Calculation is based on 45 and 40 teeth change gears.

As almost all threads which I did were metric (except 20TPI once) my idea was to have full
scope of metric pitches from 0.20 to 4.0 mm. Excellent for this size of the lathe.
So, I bought the following 17 gears; metric module 1, just because these are change gears
size in banjo gear train: 2 x 22T, 1 x 33T, 2 x 40T,1 X 42T, 4 X 44T,2 X 45T, 1 X 48T,
1 X 50T, 1 X 55T and 2 x 66T. Also bought 3 x 42T in module 1.5 which will be used
For geared rack/shifters.

Without changing gears will have the following metric threads: 0.20, 0.25, 0.30, 0.35, 0.40,
0.45, 0.50, 0.60, 0.70, 0.75, 0.80, 0.90, 1.00, 1.25, 1.50, 1.75, 2.00, 2.50, 3.00,
3.50 and 4.00. And then I got idea to install additional banjo at the gearbox and enable
cutting of imperial threads. When placing 40T gear at 127T gear will get the following
imperial threads (TPI): 6, 7, 8, 10, 12, 14, 16, 18, 20, 21, 24, 28, 30, 32, 35, 36, 40,
42, 48, 50, 54, 56, 60, 63, 64, 70, 72, 80, 84, 90, 96, 100, 108, 120....and plenty more
down to 432 TPI. OK, I am missing some important threads in range 6 - 120 TPI threads like
9, 11, 11.5, 13, 27 and 44, but I am not going to cry about it.
Those who are TPI orientated can use different gears and get full scope of imperial threads
and loose some metric threads.

Also will have pitches for fine feed in range from 0.056 to 0.222 mm, which is better
than smallest one (0.063 mm) which I presently have.

I will start with this job once I am back home but I don't mind if someone of you make it
in the meantime.

Unfortunately I am unable to attach excel file, so I attached 3 printouts in pdf format and by zooming out
it is possible to get clear picture how I planned to do it.

Best regards
LMMasterMariner

**PJs** · Jul 5, 2018, 10:11 AM

Most impressive LM!! Quite the spreadsheet and most impressed with the idea of a second banjo.

Way back when I first got my mini I delved into the the gear train to see what was actually possible and found a VB program on Varmint Al's site (one of our mentors here) by Paul Bussieres in Quebec that wrote a program called (latest) "gearsvb61" which can be downloaded from Al's site. It will run in Windows 7, has both metric and imperial and can pretty much come up with anything thread wise. The thing that impressed me was it had a +/-% accuracy column so one could choose the best accuracy for the pitch you were trying to produce for the application.

Your spreadsheet seems to go well beyond into the wee thread pitches and more importantly you fingered all of the gear train and that rack drive is the bomb in my opinion. Can't wait to see how it all turns out. First Cabin LM!!

Thanks for sharing all of this with us...fascinating!

PJ

**NortonDommi** · Jul 6, 2018, 02:49 PM

PJ,
I use another program called LatheGears that does the same and that percentage utility is great for working with really oddball threads.
https://www.dropbox.com/s/10upeqzdyv...GV1.2.zip?dl=0

**LMMasterMariner** · Jul 6, 2018, 10:16 PM

Thank for the comments and nice words PJ.
In the meantime managed to add one more pair of gears insie gearbox keeping the same length of gearbox. 4 gears will be discarded (will be used in another project) and will buy 6 gears; 64/32, 24/72, 48/48 and will get the following pitches: metric 5, 6, 7 and 8 mm. Imperial 3, 3.5, 4, 9 and 15. Still working on another combinations to get more imperial pitches (at least 27 and 44) and will post result once final calculations and drawings are completed.

Best regards
LMMasterMariner

**LMMasterMariner** · Jul 6, 2018, 10:38 PM

Hello NortonDommi,
Thanks for the advice. Have that program and also have G0602 Threading Guide program which is specifically written for G0602 and my lathe as well. They are both good for finding which change gears are required for certain pitch, but I don't want to mess with change gears anymore.

Best regards
LMMasterMariner

**PJs** · Jul 7, 2018, 10:28 AM

Originally Posted by NortonDommi

PJ,
I use another program called LatheGears that does the same and that percentage utility is great for working with really oddball threads.
https://www.dropbox.com/s/10upeqzdyv...GV1.2.zip?dl=0

Thanks NortonDommi, I got it from you link and will have a look.
PJ

**LMMasterMariner** · Jul 7, 2018, 03:13 PM

FINAL UPDATE
=========

This is final calculation. No more changes will be done.

Will have all metric pitches from 0.2 to 8 mm and will have almost all imperial pitches except 4 1/2, 11 1/2, 13 and 17.
3 pictures and 3 excel spreadshets in pdf format posted.

Best regards
LMMasterMariner

**wizard69** · Jul 14, 2018, 06:16 PM

This will be a most interesitng build

**DIYer** · Oct 8, 2019, 05:14 PM

Thanks LMMasterMariner! We've added your Screw Cutting Gearbox Plans to our Machining category,
as well as to your builder page: LMMasterMariner's Homemade Tools. Your receipt:

Screw Cutting Gearbox Plans by LMMasterMariner

tags: cutting, threading