127 tooth translation gear

[stupoty]

I have a LeBlond reagal lathe that has a massive gear in the change gear leading to the quick change gear box. It is imperial threading.

if i want to cut a metric thread does the 127 tooth gear replace the big one in the chain or does it go on the same stud as the big gear and drive the gear box? Or is it the other way round?

I havn't got the gear yet so i cant just fit it and check the feed rate, i'm planning to make it out of a spare disc brake rotor.

Any advise on the translation gear set ups for lathes much appreciated.

Stuart

 

[stupoty]

I might have found a detailed answer to my own question yay , i have googled this before i promis.

hears a copy and paste of the pertanant bits, if theirs anyone with experience doing this, does it seem correct? I thought their were other issues with making aome of the pitches?

Stuart

"LeBlond recommended a 127-120 set of transposing gears to cut metric threads. The two idler gears are joined together. To use these gears the 32 tooth drives the 127 tooth gear on the transposing set and the 120 tooth gear on the transposing set drives the 32 tooth gear that drives the QCGB. This setup will allow you to cut 10 different metric pitches by selecting the following TPI settings on the QCGB.


TPI -> Metric
4 -> 6mm
6 -> 4mm
8 -> 3mm
12 -> 2mm
16 -> 1.5mm
24 -> 1mm
32 -> .75mm
40 - .6mm
48 - .5mm
96 -> .25mm"

 

[Izzy]

Sorry to bring up an old thread but this was a huge help for me!

 

[bfd]

since there are 25.4 mm in an inch the first whole number you can have to equally divide an imperial lead screw to make metric ratio is 5 times 25.4 which is 127 tooth gear. for what its worth whole number is required because you cant Have a 25.4 tooth gear. bill

Typo fixed

 

[British Steel]

25.4mm... Just saying

Dave H. (the other one)

 

[stupoty]

Glad it's of help , i have also writen out a spreadsheet that gives the metric equivelent pitch of the imperial threads, it includes the error per thread and a percentage error for all the common metric threads, interestingly a lot of common sizes can be cut using the imperial threading with little problem (so long as its not requiring the acuracy of a micromitor thread).

Stuart

 

[Izzy]

I've just recently purchased an imperial lathe and have to do some metric threading it has be to very accurate as it's threading into a part that has about 3" of internal thread I tried 13tpi once to match m55x2.0 and it only threaded half way into the part then jammed I'm.gonna give this a shot!

 

[stupoty]

I've just recently purchased an imperial lathe and have to do some metric threading it has be to very accurate as it's threading into a part that has about 3" of internal thread I tried 13tpi once to match m55x2.0 and it only threaded half way into the part then jammed I'm.gonna give this a shot!

Yeah that might be an issue, 13tpi might even be an issue for use with nuts and regular depth of thread engagement with 0.277" error over 6 threads but 3"(76mm) of thread works out to 1.75" error owch.

Sometimes you can get away with cutting them undersize to help with the error.

Depending on what lathe you have theirs a smaller option to the 127 gear option 47/37 , it's slightly less accurate but it might help if theirs no room for the bigger gears on the gear quadrant.

Stuart

 

[Izzy]

Its an old machine, the 127 tooth gear would fit fine it doesn't even have a gear box cover!(planning on making one at some point) Lol do you have a link to that thread with the chart you made?

 

[stupoty]

Its an old machine, the 127 tooth gear would fit fine it doesn't even have a gear box cover!(planning on making one at some point) Lol do you have a link to that thread with the chart you made?

Hello, I havn't uploaded the spreadsheet , I just tried but I cant figure out how to upload a file to the document library

Stuart