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Threading/change gear chart

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chris bale 113/11/2021 19:46:39
10 forum posts
9 photos

Anybody know of a chart for change gears on a 10Tpi drummond:B leadscrew?

Bazyle13/11/2021 23:41:25
6295 forum posts
222 photos

The Drummond B-type isn't usually 10tpi, it is usually 8tpi
The Drummond Roundbed is 10 tpi.

The tables for the 10tpi are on the Drummond group files section. Somewhere. However it does depend on what set of changewheels you have. The early ones had even numbered wheels while the later ones have steps of 5.

I also published some combinations for metric threads for both 8 and 10 tpi on the groups site in a thread not the files some 6-9 months ago.

chris bale 114/11/2021 11:38:19
10 forum posts
9 photos

im missing a few of the gears, what i have are 60,2x20,65,63,30 and the back gear arrangement, you are correct with it being 8tpi just had a double check. Armed with a 3d printer ive managed to run off a few of the gears i dont have as a temp measure

Howard Lewis14/11/2021 15:24:41
6005 forum posts
14 photos

Changewheels for many lathes often increment by 5T, so at a wild guess, you could be looking for 35, 40, 45, 50, 55T.

An extra 20T or two may be useful, as possibly another 60T.

Arranged to give large enough ratio between chuck and Leeedscrew, you can get quite a low feed rate for turning. (You would be looking for something of the order of about 27 to 30:1 with a 8 tpi Leadscrew ).

The 63T should be useful if you want to cut Metric threads. It won't be absolutely accurate, but as Brian Wood's book shows, the errors can be small enough to be acceptable.

The Back Gear will allow the spindle to driven at a lower speed, (Possibly 6:1 slower? ) which can be very useful when screw cutting.

But don't forget to unlock the bull gear when using back gear, or everything will lock solid, at best; or do damage at worst.


Howard Lewis14/11/2021 15:28:00
6005 forum posts
14 photos


If you can't find a chart already printed, (Possibly from another lathe with a 8 tpi Leadscrew ) you can always set up an EXCEL spreadsheet and calculate your own, for almost every conceivable combination of gears.


Keith Long14/11/2021 15:31:57
876 forum posts
11 photos

Chris the "official" list of gears for your lathe would be 2x20, 2x30, plus 1 off of each of the following 35, 38, 40, 45, 50, 55, 60, 65 and 1 off 63 to allow for "near enough" metric threads.


chris bale 114/11/2021 19:41:51
10 forum posts
9 photos

Thanks for the reply's

Jon Lawes17/11/2021 06:52:50
872 forum posts

Good use of 3D printing there, I like it.

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