Thread cutting, which gear goes where?

This topic has 11 replies, 8 voices, and was last updated 10 August 2017 at 23:13 by Robbo.

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10 August 2017 at 15:28 #311351
Nige
Participant
@nige81730
Help please! I am trying to set the ML4 up to cut 26 TPI (1/4 BSF) I have the screw cutting table, photo below, but I am confused in identifying the various wheels under the column headings. I'm not sure which is the Mandrel gear, I'm guessing it is the one with a 25 tooth gear shown in the second photo below.

The first stud I believe is the one that currently has a 50 and 20 tooth gear on it and the 2nd stud has the 55 tooth with a 20 tooth behind? The only thing I am sure of is the 65 tooth lead screw gear which is the correct one anyway.

I believe the 'idle wheel' needed on the 1st stud (from the table) is a 20 tooth gear but 1st stud has two gears on it at the moment one of which is a 20 tooth, what do I replace the 50 tooth on that stud with? For the 2nd stud the table is blank, does that mean the 2nd stud has nothing on it? I am completely at a loss as to what is going to go where !!!
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10 August 2017 at 15:28 #8830
Nige
Participant
@nige81730
10 August 2017 at 15:43 #311354
Jon Gibbs
Participant
@jongibbs59756
Hi Nige,

The ML7 handbook in pdf can be downloaded from here **LINK**

Pages 25, 26 and 27 show the same nomenclature to help with your setups.

HTH

Jon
10 August 2017 at 15:53 #311356
Russell Eberhardt
Participant
@russelleberhardt48058
I don't think the table you have is the right one for your lathe. Yours has a tumbler reverse which changes things a bit. The mandrel gear is the one mounted on the rear of the spindle which in your photo seems to be another 25 tooth gear. You can't change that unless you remove the tumbler. The tumblers just act as idlers so don't change the ratio.

The gaps in the table are where idlers should be fitted. They just transfer the drive from one gear to the next without changing the ratio. They do, however, change the direction.

You will need to calculate the gears required yourself or use a simple program such as NthreadP which can be found on the lathes.co.uk website.

Russell
10 August 2017 at 16:41 #311359
Nige
Participant
@nige81730
Thanks Jon: It looks as if the gear they term 'Mandrel' is the interchangeable gear on the end of shaft that also carries the Tumbler reverse gear. Those diagrams in the ML7 handbook make things a bit clearer its a shame they didn't do that level of information in the ML4 booklet which is where the Screw cutting table comes from. Ill go and have a look see.

Russell: Thank you. As mentioned above the table comes from Myford sales booklet for the ML4 which is very short on other useful info! Fortunately it looks like the ML7 Handbook is similar enough to get me where I need to be
10 August 2017 at 16:43 #311360
JasonB
Moderator
@jasonb
25T on the spindle drives a 20T on the tumbler/mandrel = 1.25

That 20T drives a 25T on stud 2 via anything on stud 1 = 0.8

Another 20T driver on stud 2 drives a 65T on the leadscrew = 0.307

1.25 x 0.3 x 0.307 = 0.307

8tpi leadscrew gives 0.125" per rev

So 0.125 x 0.307 = 0.0384"

26tpi = 0.384"

Simples

Edited By JasonB on 10/08/2017 16:44:02
10 August 2017 at 16:48 #311361
JasonB
Moderator
@jasonb
So change the 25T on the tumbler for a 20T

remove the 50T and 20T from stud No1 and fit a fit something that fills the space

remove the 20T and 55T from stud No2 and fit 20T & 25T

leave 65T on the leadscrew
10 August 2017 at 17:59 #311363
Nige
Participant
@nige81730
A bit of confusion introduced by referring to the ML7 Handbook as it says I would need an 'Idle 70 wheel' which suggests the need for a 70 tooth gear which I don't have. The table from the ML4 booklet only refers to an 'Idle Wheel'. I finally phoned Tony Griffiths of lathes.co.uk asking what the equivalent gear is on the ML4 and he explained that in this instance the 'idle gear' can be any spare gear I have that I can adjust to fit in the space between the driver and the driven gears. back to the lathe after tea

JasonB: Thank you, only just seen your post which will do the job as well

Edited By Nige on 10/08/2017 18:02:40
10 August 2017 at 18:29 #311366
Brian Wood
Participant
@brianwood45127
Nige,

Jason has shown the way, but I also suggest you update your table to show a second idler on the second stud.

The maths is straightforward 20 mandrel drives 65 on the leadscrew with idlers filling the spaces to make up a gear train. As you have already found out, idlers work as a belt linking two pullets, they play no part in the calculations.

Regards Brian
10 August 2017 at 18:31 #311367
Howard Lewis
Participant
@howardlewis46836
As long as the "idler" wheel can be meshed with both the gear on the Leadscrew and the compound "driving" pinion, within reason, it does not matter how many teeth it has. It is just there for fill the space and transmit the drive, without affecting the overall gear ratio, but one Idler will reverse the direction of rotation, so you may need to use the tumbler to ensure that you cut a R H thread rather than a L H!

later, you will probably be able to buy, or even (with help) make any gears that you need. Myford gears are 20DP, but can't remember whether the Pressure Angle is 14.5 or 20 degrees. Someone will confirm.

Dealers such as Home and Workshop Machinery in Sidcup usually have a selection of gears for the Myford.

A plea on the "Wanted" section of this Forum may find what you want. If not prowl around Shows, looking for what you want.

Final thought, would it be easier to buy a length of 1/4 BSF studding from somewhere like Cromwell Tools?

Howard

Edited By Howard Lewis on 10/08/2017 18:32:22
10 August 2017 at 19:10 #311372
Neil Wyatt
Moderator
@neilwyatt
The three gears on the reversing stud are all idlers and have no effect on the gear ratio at all, except changing the direction of rotation.

Neil
10 August 2017 at 23:13 #311419
Robbo
Participant
@robbo
Quote "later, you will probably be able to buy, or even (with help) make any gears that you need. Myford gears are 20DP, but can't remember whether the Pressure Angle is 14.5 or 20 degrees. Someone will confirm."

14.5 degrees.
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