is that it?

Can you read the gears for 7, 28 or 56tpi on your worn chart, if so you probably just need to move the 3 speed lever to another position when set to that gear train

Edited By JasonB on 09/09/2021 20:21:37

mid one is probably an idler so makes no difference.

So ignore the mid gear in the 40-100-70 gear train and you get 40/70 = 0.571

Assuming an 8 tpi lead screw so one turn = 0.125" then 0.125" x 0.571 = 0.071" which is 14 tpi

Jason –

The leadscrew on an L5 is of 1/4 " pitch, not 1/8" . At least on mine it is.

Verify the tooth-count on the spindle pinion: on my lathe it differs from that given in the manual.

Otherwise, depending if a 40T or 20T pinion and my arithmetic not being all up the creek:

4/14 = 40/140 = 20-idler-70

or perhaps 40 – [70+30] – 60 (compound).

The leadscrew gearbox should be on the 1:1 position (I think that is "A" ).

Thank you Jason –

Just dug out my copy of the manual.

What confused me was that the top shaft wheel on my L5 is of 20T and appears not removeable as the book suggests it should be, whereas the table in the book is for a 40T top shaft wheel for 14tpi.

It gives 40 – 100(idler) – 70 then gearbox position A… 2:1 reduction; but for my lathe I need 20 – idler – 70 and C (1:1).

Fizzy –

The plates on top of my lathe are all worn away too!

Though not cheap I suggest you buy one of Tony Griffith's (lathes.co.) facsimiles of the L5 manual. It is a very comprehensive operating and servicing book, and includes the change-wheel tables for both imperial (any thread-form) and metric threads. If you are going to do a lot of screw-cutting it would be worth hanging copies of the tables up by the lathe – you could laminate the copy or protect it simply with a polythene bag.

Pong

No the 20 drives a 40T, then the 100T or whatever you have to fill the gap driving a 70T on the gearbox input.