machining 2 BA thread

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machining 2 BA thread

This topic has 25 replies, 14 voices, and was last updated 6 March 2016 at 16:31 by JasonB.

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4 March 2016 at 13:11 #228241
phil burley
Participant
@philburley12227
I have 2 lathes one imperial one metric , I would like to screw cut a 2 BA thread . But the pitch doesn't seem to be either . What am I missing here ?
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4 March 2016 at 13:11 #32662
phil burley
Participant
@philburley12227
4 March 2016 at 13:16 #228243
Nobby
Participant
@nobby
HI Phil
Could yo use a die ?
Nobby
4 March 2016 at 13:17 #228244
Emgee
Participant
@emgee
2BA TPI is 31.35 and metric 0,81mm pitch.

Emgee

Edited By Emgee on 04/03/2016 13:19:26
4 March 2016 at 13:22 #228246
Lambton
Participant
@lambton
Phil,

Do as Nobby suggests.

If you use a good quality tail stock die holder you will be OK. There is no point in trying to screw cut any BA threads by "normal" methods. the posh way to cut them is to used a Coventry die head.

Eric
4 March 2016 at 13:50 #228256
Michael Gilligan
Participant
@michaelgilligan61133
Posted by phil burley on 04/03/2016 13:11:41:

What am I missing here ?

.

Some fairly specialised change wheels

On your lathe of choice … screwcut part-depth, at either 32tpi or 0.8mm pitch

This will give a track for the die to follow … finish with the die.

MichaelG.

.

Obviously, the acceptable 'part-depth' will vary according to the pitch error and the length of thread.
4 March 2016 at 13:52 #228257
Roderick Jenkins
Participant
@roderickjenkins93242
If either of your lathes has changewheels as opposed to a Norton type gear box then you can very likely find a combination of changewheels to give a good enough thread using the program at **LINK** If you have a Myford with a gearbox then replacing the 24 tooth tumbler stud gear with a 20T gear and selecting 26tpi on the gearbox will give you a metric pitch of .814.

HTH,

Rod
4 March 2016 at 13:56 #228259
Neil Wyatt
Moderator
@neilwyatt
On an imperial lathe 63:57 is a starting point that should allow you to add a further gear pair and get 2BA.

For Metric, fit them the other way round 57 driving 63.

Neil
4 March 2016 at 16:14 #228294
AndyP
Participant
@andyp13730
Just to be perverse I put 0.81mm pitch into the little programs I use to work out gear trains for screwcutting on my C1 lathe and a different program for my metric Boxford AUD. In both cases I came up with a gear combination to cut that pitch either exactly for the C1 or with an error of 0.006% for the Boxford so it is possible at least.

I would use a die though.

Andy
4 March 2016 at 16:22 #228295
Michael Gilligan
Participant
@michaelgilligan61133
Andy,

Just out of interest … what is the train for the C1

Thanks

MichaelG.
4 March 2016 at 16:53 #228300
Ajohnw
Participant
@ajohnw51620
My understanding is that BA is a metric specification. Try converting the diameters. 2BA for instance is 4.7mm dia.

A quote from the wiki

The pitch of 0BA is 1 mm and the pitch of each higher numbered thread is obtained by multiplying the pitch of the lower number by 0.9 so K-BA has a pitch of $scriptstyle p=0.9^K$ .^[1]^:12 The major diameter is given by $scriptstyle 6p^{1.2}$ ^[1]^:12 and the hex head size (across the flats) is 1.75 times the major diameter.

All derived no doubt when there wasn't precisely 25.4mm to the inch. It's essentially an instrumentation type thread. It's closer to metric coarse than fine

Lotus used 0BA to fix the radius arms to the rear hubs on the Europa. That cause me a lot of grief as other threads will fit and then work loose.

John

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4 March 2016 at 17:36 #228306
Bazyle
Participant
@bazyle
Goodness you people are slow today. You have a metric lathe and M5 pitch is 0.8mm. Don't try to tell me you are bothered by the .01 pitch error.
4 March 2016 at 17:51 #228308
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Bazyle on 04/03/2016 17:36:16:

Don't try to tell me you are bothered by the .01 pitch error.

.

That, Bazyle, would rather depend on the length of the thread.

… As yet unspecified

MichaelG.
4 March 2016 at 18:01 #228310
Bazyle
Participant
@bazyle
But it's patently not a leadscrew, just a fixing, so the engaged length is not going to be very long. Also it is possibly part of a Stuart Beam engine?

Edited By Bazyle on 04/03/2016 18:04:07
4 March 2016 at 18:04 #228312
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Bazyle on 04/03/2016 18:01:18:

But it's patently not a leadscrew, just a fixing, so the engaged length is not going to be very long.

.

Are you clairvoyant, Bazyle?
4 March 2016 at 18:06 #228313
AndyP
Participant
@andyp13730
Michael

I always have difficulty understanding other peoples change wheel descriptions so this may be wordy but hopefully clear.

36 (fixed) on the spindle driving a 54 idler driving a 40 which shares it's stud with a 24 which drives a 40 on the 1.5mm pitch leadscrew.

Andy
4 March 2016 at 18:11 #228318
Michael Gilligan
Participant
@michaelgilligan61133
Thanks, Andy

Not much help on my little Jason lathe [which has 32 (fixed) and a 16tpi leadscrew] but appreciated anyway.

MichaelG.
4 March 2016 at 18:29 #228322
Ajohnw
Participant
@ajohnw51620
Personally if i didn't have a 2BA die I would replace it with M4.5 coarse. Really these days when people are buying things like taps and dies it's probably best to go for near metric sizes and forget BA. Arc for instance sell a set of the smaller sizes that starts at M1 that will cover the small BA sizes. A few more will cover BA's range.

The only problem with older designs is that some 40 tpi and 32 tpi may be a good idea but metric fine may substitute for these in some cases.

To me BA sizes don't need to be screw cut unless some one just wants to do it for fun. I wouldn't bother. Save it for bigger diameters.

John

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4 March 2016 at 18:48 #228326
JasonB
Moderator
@jasonb
I'd hazard a guess that its for th piston rod on the Stuart beam which you do want a true as possible and being stainless a bit harder to cut with a die and not have it slip in the chuck putting marks all down your piston rod. Though skimming the piston to finished dia once its on teh rod is the best bet to get things concentric

As suggested screw cut it 80% at 0.8mm pitch and finish with a die if you are not happy that your die will do it straight off

John where are you buying M4.5 taps and dies, I've never seen them
4 March 2016 at 18:52 #228328
Ajohnw
Participant
@ajohnw51620
Just as an example Jason

**LINK**

It's part of the extended series. Not sure when the size steps exceed 0.5mm.

LOL Forgot to mention I haven't bought any of these as I have a decent range of BA. However I did know that this size is about.

John

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Edited By Ajohnw on 04/03/2016 18:53:25
4 March 2016 at 19:19 #228334
phil burley
Participant
@philburley12227
thanks everyone, its in stainless steel and my die is well worn , I wasn't allowing for a bit of an error , just comparing the exact pitches that I could produce , please excuse my beginners ignorance .Yes it is part of a ST beam engine

regards Phil
4 March 2016 at 19:30 #228338
Anonymous
If you can't easily cut a 2BA thread change to 3/16" by 32 or 40 tpi. Taps are readily available and so are threading inserts that will give the proper Whitworth thread form.

Andrew
4 March 2016 at 20:12 #228347
Ajohnw
Participant
@ajohnw51620
Michael came up with the best suggestion really if there is a die about. You could probably screw cut to 90% plus depth and the die will still correct it.

John

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6 March 2016 at 14:02 #228591
Tim Stevens
Participant
@timstevens64731
Have you neglected the option of using 2BA studding?

Or changing the thread to 3/16 BSF which is so near you would never notice?

Tim
6 March 2016 at 14:21 #228594
Mike
Participant
@mike89748
Tim, you beat me to it. I'd have substituted 3/16BSF – in fact, I'd been thinking about it since this thread started.
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