WM250 thread cutting

If the 30 tooth is only a spacer then it has no effect on the ratio so just use a larger gear to make up the space between the headstock gear and the 50 tooth gear.

Les.

Edited By Les Jones 1 on 21/09/2017 14:07:04

Hi Mark,

A picture would help. I think Les means that the 30 tooth gear is used only to transfer rotation from the headstock to the other gears. As a gear used that way doesn't alter the ratio, you can use any gear. Just pick one big enough to physically mate with the headstock without worrying about how many teeth it has.

My metric WM280, which I believe to be similarly geared to the WM250, suggests 60t where you have the 30t.

Dave

Looking at the screwcutting chart for my WM250V, the 20 TPI config is:-

H 30

.....|     (had to put dots in to get the connector in the right place )

75 80

|

60 H

...with feed setting A.

I've found the charts to be correct for screwcutting on those that I've done.

Is the WM250 without the 'V' a different animal?

Edited By Mick B1 on 21/09/2017 16:10:15

Have you swung the banjo on its pivot so that the 30T engages with the gear on the spindle?

Edited By JasonB on 21/09/2017 16:21:40

What is the leadscrew pitch on yours?

That gear train with a 40T on the spindle would give 1.275mm pitch which is about right for 20tpi at 1.27mm if it were 3mm pitch.

You could put a 60T in place of the 30T and use lever position C which would give same ratio but the 60T may reach the spindle

Mark, I have the older (2007) wm 250 with 3mm pitch leadscrew. I have cut threads with the 30 tooth gear at the top and it definitely meshes with the spindle 40 tooth gear. I know it works with

H 30
60 80
85 H

You have pivoted the banjo over to the left? As Jason says in this case the top gear is just an idler and you couls fit a larger gear without problem.

John

It's not an idler as changing it to some other tooth count will alter the ratio. I suggested making it a 60 and also selecting position C which will counter the effect of using a 60 instead of a 30, one doubles the ratio and the other halves it so cancelling each other out.

Mark, Can you post a photo of the gear chart off the front of the machine

Beg to differ my maths is pretty shoddy but I came up with this:-

It took me ages to get to grips with this, doesn't work if you have a five gear setup so safer to use all the ratios!

John

Not the plate but the manual page:-

Note the entry for 1.75 pitch should read:

H  30
70 80
60 H

or similar the plate on my lathe annd the manual is wrong for the M12 thread. Will have to think about the 26TPI one.

John

Edited By Journeyman on 21/09/2017 18:42:13

yes sorry, 3 in a vertical line makes the middle an idler

Mark, I notice that your lathe plate has the same error as mine for M12 thread. I had a go at working out the 26TPI gear train. My maths is always suspect so check carefully.

26TPI = 1.023622mm pitch
this requires an overall gear ratio of 0.341207 (spindle to leadscrew) if you use the following:-

H 30
45 80
65 H

you get a ratio of 0.34615 giving a pitch of 1.03846mm which is only about 1% too big. As threads go this is pretty close and unless the thread is particularly long should be OK. (I haven't actually checked to see if this gear combo fits)

John

I told you my maths was ropey I got the first line wrong I think 26TPI should in fact be 0.97692mm pitch. The gear set up should be:-

H 30
45 80
70 H

this gives an overall ratio of 0.32143 as opposed to the required ratio of 0.32564 and gives a pitch of 0.96429 which again is about 1% too small.

Sorry for the confusion perhaps someone with better maths skills than me can double check....

John

Edited By Journeyman on 22/09/2017 10:51:33