Cutting Metric thread on an Imperial lathe

[Donald MitchellParticipant @donaldmitchell68891]

[Donald MitchellParticipant @donaldmitchell68891]

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

[Russell EberhardtParticipant @russelleberhardt48058]

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

Russell.

[Donald MitchellParticipant @donaldmitchell68891]

Thank you Russell, I already have that data.

Donald Mitchell

Bonnie Scotland

[John Stevenson 1Participant @johnstevenson1]

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.

[Donald MitchellParticipant @donaldmitchell68891]

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

[Roderick JenkinsParticipant @roderickjenkins93242]

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

[Brian OldfordParticipant @brianoldford70365]

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..

[John Stevenson 1Participant @johnstevenson1]

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

[KWILParticipant @kwil]

RDG have 32 tooth, not cheap though.

[Roderick JenkinsParticipant @roderickjenkins93242]

Posted by Brian Oldford on 09/10/2015 21:26:00:

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..

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

[JasonBModerator @jasonb]

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.

[Roderick JenkinsParticipant @roderickjenkins93242]

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

Cheers,

Rod

[JasonBModerator @jasonb]

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

Do Myfords cut 19pti pipe thread pitch easily?

[Brian OldfordParticipant @brianoldford70365]

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

[Roderick JenkinsParticipant @roderickjenkins93242]

Posted by JasonB on 10/10/2015 07:45:31:

Do Myfords cut 19pti pipe thread pitch easily?

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

Rod

[AjohnwParticipant @ajohnw51620]

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

–

[Ady1Participant @ady1]

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

[Roderick JenkinsParticipant @roderickjenkins93242]

Posted by John W1 on 10/10/2015 09:04:42:

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

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

[Neil WyattModerator @neilwyatt]

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,

Example	Table	Here
15	99	Rat
20	42	Cat

Neil

[BazyleParticipant @bazyle]

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.

[AjohnwParticipant @ajohnw51620]

This is about as far as I have gone, tending to overdrive the gearbox as the fine feed is so low with the normal gearing.

Still some compounds to get rid of and I suspect I am gear short to do that but can hit 0.35mm to 3/4um. I haven't checked if the compounds will mesh. As far as I know all are with standard boxford gears. They came with the lathe when I bought it.

The basic gearbox drive is 20 – 56 and setting as per this

i hadn't thought about using the feed ratio as that uses the rack to move the saddle so wouldn't be so accurate. It works out at about 2.9 : 1 compared with the lead screw feed.

I recently downloaded the find the gears application from lathes co but haven't set it up yet. I did these iteratively on paper Tedious.

John

–

Edited By John W1 on 10/10/2015 11:12:56

[BazyleParticipant @bazyle]

On the CVA I believe it is arranged such that the gear train, including 127 has a 50 and gives 1.00 mm. Then the 50 is changed to give the metric intermediates eg 60 for 1.2mm, 70 for 1.4 etc which is fairly straightforward and uses standard gear numbers, and of course the gearbox can halve or double anything easily.

 

Edited By Bazyle on 10/10/2015 11:54:04

[Roderick JenkinsParticipant @roderickjenkins93242]

Posted by Neil Wyatt on 10/10/2015 11:04:42:

Rod,

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.

What I tried to do yesterday was to copy my table from Excel into Word and then paste that into into the forum reply window. It told me my post was about 20 billion characters too long and that I should split the post! I ended up pasting unformatted text.

I'll give it another try sometime.

Cheers,

Rod

[Ady1Participant @ady1]

An "allowable error " throws up a huge range of additional gearchange options when looking for strange tpi cuts

For 59tpi a huge range of options suddenly becomes available with 0.0001 error either side, I have placed my results in another thread to avoid polluting anywhere else

Edited By Ady1 on 10/10/2015 11:42:46

[Author]

Posts