Cutting Metric thread on an Imperial lathe

Hi Engineers,

Hopefully someone out there could tell me what driver gear and gearbox setting to use to enable me to cut a reasonably true 2.5 metric thread on my Imperial Myford S7B with gearbox.

I have successfully cut Metric gears on this lathe before but the chart I have does not include a 2.5 pitch.

Thank you.

Donald Mitchell

Bonnie Scotland

Don't have a Myford but you could have a look at this

Russell.

Thank you Russell, I already have that data.

Donald Mitchell

Bonnie Scotland

Use a 33 gear instead of the 24 on the input gear then select 14 tpi on the box.

You can get virtually all metric threads on a gearbox equipped Myford without resorting to changing all the banjo over by using a 33 or 34 as input gear.

Thank you very much John, I suspected you would have the information at your finger tips, that is exactly the answer I needed.

The chart I have gives the input gear and the gearbox setting for a ton of Metric threads including 2 and 3 pitches but sadly not 2.5.

Regards.

Donald Mitchell

Bonnie Scotland

John's method is simply brilliant. A little work with a spreadsheet shows that you can get good approximations for all metric and BA pitches with very few extra gears.

I've got the metric banjo and gears for my Myford but I'll never use them again. Buy your 33 and 34 gears from John, he deserves the business for bringing this method to our notice (if not for his sense of humour)

Rod

Not so much a thread but I've been asked to make some single layer coil formers for an amateur radio application using my clunky old S7. To prevent the wire moving I'm proposing to machine a shallow semi-circular groove at a similar pitch to the wire diameter. In this case the insulated wire is 1.3mm O/D. I've got a pretty comprehensive collection of change wheels including a 127 tooth. Accepting I mustn't open the half nuts, can anyone suggest a change wheel set-up to cut that pitch or very slightly coarser..

Brian,

You don't say if you have the gearbox model or not but if so a 32 T driver and 26 on the box gives 1.3

32 is a special and probably not stocked but 35 on the driver and 28 on the box gives 1.32

RDG have 32 tooth, not cheap though.

If you are without gearbox then here are some options:

Driver Driver Driver Driven Driven Driven Metric pitch

60 25 40 30 75 65 1.30256

60 35 21 30 55 65 1.30552

30 35 70 55 65 50 1.30552

60 25 40 30 65 75 1.30256

25 50 65 45 63 70 1.29992

45 21 65 40 50 75 1.30016

There are endless variations, depending on which changegears you have.

HTH,

Rod

Edit: sorry about the formatting, trying to post a table is a nightmare!

Edited By Roderick Jenkins on 09/10/2015 23:14:04

As you say you don't mind slightly coarser why not go with 20tpi, not far off 19.53tpi which is what 1.3mm works out at. I'm sure 0.002" between wires won't be too much of a problem.

I know it's early but I think 20 tpi is 1.27mm pitch...

Cheers,

Rod

Your right Rod, 20tpi is FINER that 19.5, back to bed for me.

Do Myfords cut 19pti pipe thread pitch easily?

Many thanks for all the suggestions. I'm sure the solution is there.

19tpi (1.34mm pitch) is in the gearbox on a Myford

Rod

Has anyone come up with some magic gears for a Boxford with gearbox ? I can post as far as I have got if anyone is interested.

John

-

A critical gear in nearly all the funny tpi's I have looked at is 59teeth

If anyone has a 59 then they have a very useful beast

I'd be interested even though, in my case, it's only academic . What does the gear train from the spindle to the gear box look like? On the Myford the ratio is 1:1 (or 9:1 if the fine feed cluster gear is reversed)

Rod

Rod,

If we enabled the 'table editing' icon it would also make lots of other formatting options available - fine in principle but in practice it would make editing more confusing. However, if you paste a table in, you can edit it.

If you make a table in Word then paste it in, if you right-click it you can edit the column widths etc. Select rows and use the 'table properties' selection for advanced tweaks.

This can take a couple of tries before you get it to fit properly,

Neil

Someone on the forum was working on the Boxford equivalent. Don't want to put him on the spot by naming so give him 24 hours to see the thread.