Cutting metric threads on an imperial lathe with changewheels that rise by fours

[John CoatesParticipant @johncoates48577]

For one of my motorcycle projects I need to make some new collars having an M30 x 1.5 internal thread

 

My lathe is imperial (1947 Barker 5″ x 24″). I have bought Martin Cleeve’s book “WPS 3 Screwcutting in the lathe” and read Section 3. My questions are in relation to Table 4 on p.45

 

My changewheels are “rising by fours” but in this section Martin uses examples for a changewheel set “rising by fives”. This seems important to me when considering the relationship between the 50t and 127t wheels to establish the conversion from imperial to metric

 

Does this mean that I cannot cut metric threads using his methods with my change wheel set? Or do I have to make changewheels of the same DP for the missing “fives” and 127t from Table T4? (I have 20, 40 and 60t wheels in my set so would need to make or get made 25, 30, 35, 45, 50, 70).

 

Thanks

 

John

[John CoatesParticipant @johncoates48577]

[John Stevenson 1Participant @johnstevenson1]

John,

List the total gears you have at the moment please, I’m presuming you have more than the mentioned 20, 40, 60 ?

Also is it 8 tpi screw ?

 

John s.

[John CoatesParticipant @johncoates48577]

Hi John

Yes it is an 8 tpi leadscrew

The set is 20, 24, 32, 36, 38, 40, 44, 48, 52, 54, 56, 60 and 80

Cheers

John

[John Stevenson 1Participant @johnstevenson1]

John,

 

The 38 driving the 80 on the leadscrew with any idler fitted will give you 1.508mm pitch.

Would image that’s good enough for your project ?

 

John S.

[John CoatesParticipant @johncoates48577]

John S

 

Thanks ever so much. Didn’t realise it would be that simple. Will other combinations achieve other metric approximations and is there a formula for working them out?

 

John

[Keith LongParticipant @keithlong89920]

John C

Have a look at the lathes.co.uk website and find the section on screw-cutting. In there you’ll find a link that allows you to down load a program called “NthreadsP” – it’s free. This allows you to put in the details of your lathe, lead-screw tpi, and change wheels (you can save the details). You then enter the number of tpi you want OR the pitch for metric, put in the error percentage that you feel is acceptable and let it run. The program will run through and give you as many combinations of your change wheels that it finds will satisfy your criteria. Then it’s simply a matter of picking a suitable combination from those given that will fit the lathe.

A VERY handy utility.

Keith

[John CoatesParticipant @johncoates48577]

Posted by Keith Long on 27/06/2011 17:09:35:

In there you’ll find a link that allows you to down load a program called “NthreadsP”

 

And an .EXE file which Firefox on my Linux system can’t run

Ah well I got my calculator out and did some number crunching and have an idea as to how the maths work so I’ll have a go at generating some change wheel combinations for the common metric threads

 

Thanks for all the help

 

[Harold Hall 1Participant @haroldhall1]

If you go to my website

 

http://www.homews.co.uk/page28.html

 

you will find listed the results for every combination of gears using
20 to 75 by fives plus 21 and 38 giving in excess of 66000 results.
The list leaves out the very course and very fine results displaying
those between 6 and 50 TPI. This is using an 8 TPI leadscrew.

For easy reading the list is broken
into smaller ranges typically 6 to 7TPI

Also listed are the results using a
metric leadscrew of two mm

If your gears are in increments of
fours then just select the value that suit you but then use typically
20 teeth in place of 25, 24 in place of 30, 28 in place of 35 and
the results will be the same

This is explained on the website as is
using the list for other leadscrew pitches.

The lists find values for metric
threads on a lathe having an imperial leadscrew which are more than
adequate making a 127 tooth gear unnecessary for all but turning a
machine leadscrew where any error is to be avoided.

 

Unfortunately, the program I developed is DOS based and I am now far to old to consider produce a windows version

 

Harold

[Harold Hall 1Participant @haroldhall1]

I should have added that the program finds many combinations that produce the same value so if you are missing a gear or two then it is still likely that there will be a combination that you can set up with the gears available.

 

Harold

[John Stevenson 1Participant @johnstevenson1]

John.

 

1mm pitch = 0.992 mm true 20 driving a 48 over 24 driving 32 on leadscrew

 

1.25mm pitch = 1.253mm true 24 driving a 32 on leadscrew

 

1.5mm pitch = 1.508 mm true 38 driving a 80 on leadscrew.

 

1.75mm pitch = 1.746mm true 24 driving a 60 over 44 driving 32 on leadscrew

 

2.0mm pitch = 2.005 mm true 24 driving 38 on leadscrew

 

2.5mm pitch = 2.501 mm true 52 driving a 44 over 24 driving 36 on leadscrew.

 

3.0mm pitch = 3.0007mm true 36 driving a 38 on leadscrew.

 

These should give you all the popular threads.

 

John S.

[John CoatesParticipant @johncoates48577]

John S

 

Thanks ever so much. That is exactly the kind of help that makes this site and its community such a pleasure to be part of

 

I’d better start practising my screwcutting now and take a look at the making of one of them thar flip up tool holders

 

t’other John

[graham bramleyParticipant @grahambramley85289]

Hi all

My name is Graham and have just signed up as have a question regarding a similar lathe(Barker) to the one above. ( the lathe is new to me )

I am trying to cut an external thread 32mm dia x 1.5mm pitch on a steel bar,(it is for an exhaust nut and pivot for a mobylette moped )

What I am finding is that when I drop the screw cutting lever in using the same number each time on the thread dial ,it dose no't follow the same path . I am not sure why this is , it seems to drift from the pitch and after several passes it removes the crest of anything I have tried to cut.

I end up with a course turned bit of bar.

Has anyone any idea why this would happen please.

Regards Graham

[John Stevenson 1Participant @johnstevenson1]

Graham,

You need to engage the half nuts and then leave them in.

This means stopping at the end and then reversing either by hand or under power to clear the work, then put the next cut on and start again.

This is common for metric thread on imperial screws and visa versa.

[AjohnwParticipant @ajohnw51620]

Posted by John Coates on 27/06/2011 18:07:13:

Posted by Keith Long on 27/06/2011 17:09:35:

In there you'll find a link that allows you to down load a program called "NthreadsP"

 

And an .EXE file which Firefox on my Linux system can't run

Ah well I got my calculator out and did some number crunching and have an idea as to how the maths work so I'll have a go at generating some change wheel combinations for the common metric threads

 

Thanks for all the help

 

If you install wine I think you will find it will run. It's easier to install q4wine as well as that allows you to specify what directory the app runs in each time it's run. This helps with some applications – another helper called swine doesn't.

You will also need to install winetricks. Use google to find out how.

I'me fairly sure once wine and q4wine is installed it will pop up if you run an exe from a browser. If not just download and save somewhere and then click on it from the desktop.

John

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Edited By John W1 on 27/12/2015 20:23:02

[JasonBModerator @jasonb]

John W1, I think the other John will have got it sorted by now as the thread was 2011

[AjohnwParticipant @ajohnw51620]

Posted by JasonB on 27/12/2015 20:21:36:

John W1, I think the other John will have got it sorted by now as the thread was 2011

wasit doin up ere then ?

John

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[graham bramleyParticipant @grahambramley85289]

Posted by John Stevenson on 27/12/2015 19:34:07:

Graham,

You need to engage the half nuts and then leave them in.

This means stopping at the end and then reversing either by hand or under power to clear the work, then put the next cut on and start again.

This is common for metric thread on imperial screws and visa versa.

Thank you for your reply John. Do you think ,if I changed the pitch to 1/6" tpi it would be close enough to 1.5mm.

I used your gear suggestion to achieve 1.5 pitch (38/80), do you know what the 1/16" pitch would require .

It has an eight TPI lead screw.

Cheers Graham

[JasonBModerator @jasonb]

40/80 should do nicely for 16tpi

[graham bramleyParticipant @grahambramley85289]

Posted by JasonB on 27/12/2015 20:41:44:

40/80 should do nicely for 16tpi

Thanks Jason.

[Ady1Participant @ady1]

Has anyone any idea why this would happen please.

The changewheels get out of phase because there is only one proper pick up point in the gearing, but often 2 or 3 pickups on exactly the same point of the dial indicator

The easiest way to see whats going wrong is to draw a straight line with tippex between the bottom two gears, the leadscrew gear and the next one up, at the starting point for your threading run

when you bring your saddle back to the starting point after a thread cut everything will look fine, the right start point, the right dial indicator point… but have a look at your tippex line on the gears and the chances are that it will be out of alignment.

(Put it back into alignment at the saddle start point and you will be fine)

[Ady1Participant @ady1]

The alternative is to use the permanently engaged leadscrew nut system but this isn't much use for power threading up to a shoulder or a blind cut off

[John HaineParticipant @johnhaine32865]

Unless of course you are using cnc…

[Gordon WParticipant @gordonw]

For a short thread, I'm assuming, I use a spindle handle. Do the lot by hand, does not really take much longer and a lot more relaxing.

[AjohnwParticipant @ajohnw51620]

Posted by Ady1 on 28/12/2015 01:38:29:

The alternative is to use the permanently engaged leadscrew nut system but this isn't much use for power threading up to a shoulder or a blind cut off

An indicator can still be used. Disengage at the shoulder as usual, stop machine, reverse and re engage at the same indicator position. The lead screw shouldn't turn sufficiently to loose sync while the machine is stopping. It's easy to do it all quickly in practice. Very easy.

I'd guess people know that the tool has to be wound out too at some point.

John

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Edited By John W1 on 28/12/2015 11:07:19

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