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43 TPI

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Chris Trice23/12/2021 15:39:22
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I've got to cut a 5BA thread on something which is a horrendously inconvenient 43 TPI. Can anyone suggest a set of change wheels running off an 8 TPI lead screw (Myford Super 7). A tiny error might not matter but I need to be close. While my maths is good and the principles understood, this is taxing me. Comparing notes will help.

JasonB23/12/2021 15:49:29
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Couple of charts in this thread and plenty more on the net

Les Jones 123/12/2021 16:05:55
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Hi Chris,
Here is a link to a program that will do the calculation for you. You give it a list of the change wheels you have, the leadscrew pitch and the pitch you want to cut. It tries all combinations and tells you the percentage error for each suggested combination.

Edit. I've just tried the link on that page to "Nthreadp.exe" but it does not seem to work. I have a copy of the program which I could email to you or if you post a list of the change wheels that you have I will run it and give you the results.

Les.

Edited By Les Jones 1 on 23/12/2021 16:18:11

Brian Wood23/12/2021 16:10:28
2549 forum posts
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Hello Chris,

Two results for you:-

Gearbox lathe Mandrel 20 Gearbox set for 36 TPI Result Pitch = 0.588 mm [42.2 tpi]

Plain lathe Mandrel 20 1st stud Driven 60, onwards driver 35 2nd stud Idler leadscrew 63 Same result as above

Regards Brian

JasonB23/12/2021 16:22:23
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The one I linked to (now below) looks closer or 0.6mm pitch is very close

Edited By JasonB on 23/12/2021 16:23:28

bernard towers23/12/2021 21:25:57
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Why do you find it necessary to screwcut a 5 ba thread??

Oldiron23/12/2021 22:05:32
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Posted by bernard towers on 23/12/2021 21:25:57:

Why do you find it necessary to screwcut a 5 ba thread??

For lack of a die ?? devil Hiding behind the sofa .

regards

Chris Trice24/12/2021 03:35:58
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Thanks everyone for the replies. I managed to get the thread calculator working and managed to get it within 1/10th of a tooth over 1" which is more than enough as I'm only machining about 3/8th" of thread. In answer to the question what's it for, I'm machining the body threads on an old Devilbiss airbrush and although the bore is about 11mm, the thread is the same as a 5BA machine screw. I suspect they may have used 5BA Coventry die head chasers as a cutting tool. It's not 44tpi and it's not 42tpi. The only thread I can find inbetween is 5BA which is 43tpi. I may braze up a tool from a die head as a cutting tool. The important thing is it's close enough to do the job.

JasonB24/12/2021 07:29:11
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Strange they would have gone with a BA pitch being an American maker and the other threads like the one for the hose are UNEF

bernard towers24/12/2021 11:53:31
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Have you tried 0.6mm pitch?

Neil Wyatt24/12/2021 15:23:08
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Posted by Chris Trice on 24/12/2021 03:35:58:

Thanks everyone for the replies. I managed to get the thread calculator working and managed to get it within 1/10th of a tooth over 1" which is more than enough as I'm only machining about 3/8th" of thread. In answer to the question what's it for, I'm machining the body threads on an old Devilbiss airbrush and although the bore is about 11mm, the thread is the same as a 5BA machine screw. I suspect they may have used 5BA Coventry die head chasers as a cutting tool. It's not 44tpi and it's not 42tpi. The only thread I can find inbetween is 5BA which is 43tpi. I may braze up a tool from a die head as a cutting tool. The important thing is it's close enough to do the job.

It's not just M0.6 is it?

Howard Lewis25/12/2021 11:31:34
6004 forum posts
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Possibles.

5 BA is 47.5 degree thread, 0.59 mm pitch, 0.126" diameter.

5 - 44 ANF is 60 degree thread, 0.125" diameter.

As it being an American product, I would suspect 5-44 ANF being what you want.

Howard

peak425/12/2021 12:10:26
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Posted by Howard Lewis on 25/12/2021 11:31:34:

Possibles.

5 BA is 47.5 degree thread, 0.59 mm pitch, 0.126" diameter.

5 - 44 ANF is 60 degree thread, 0.125" diameter.

As it being an American product, I would suspect 5-44 ANF being what you want.

Howard

Howard, apparently the bore is about 11mm, it's just the pitch that's odd.
Maybe like Herbert used one-off threads for their die heads, so one had to go direct to them for spares.

Bill

Ady125/12/2021 13:14:38
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Whenever possible I always redo an imperial with a metric tap

Almost all my Drummond cross slide/saddle stuff has been converted to metric hex bolts for example

Just an option to consider

Michael Gilligan25/12/2021 23:13:58
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I don’t know if this will be of any interest, Chris … but it seems worth a mention:

**LINK**

https://www.everythingairbrush.com/product/aerograph-replacement-handle-fits-sprite-sprite-major/

[ Reading between the lines, I’m guessing this has the thread in question. ]

MichaelG.

Chris Trice26/12/2021 03:25:15
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I know Everything Airbrush as they are the official inheritors of the Devilbiss brand and spares. One of the guys there worked for Devilbiss assembling the airbrushes on the production line. It's not 0.6mm. I took a silicone mould of the internal thread and then compared it to various thread gauges viewed through a jewellers loupe with an engraved scale. As mentioned, 44 gauge is too fine and the 42 gauge is too coarse. Incidentally the originator of the DeVilbiss Aerograph airbrush was American but they have been manufactured exclusively in England for more than a hundred years, essentially unchanged apart from modern materials being introduced. The external air valve thread as mentioned is 3/8 UNEF and the thread in the handle (still available) is 5/16 x 32. The thread I'm chasing (see what I did there?) is the thread in the forward part of the body. All the dimension of the airbrush appear to be imperial (needles are 3/64" diameter rather than the more common 1.2mm. Unless anyone can suggest another thread with a virtually identical pitch, 5BA (43 tpi) is all I've got.

Chris Trice26/12/2021 03:38:46
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devilbiss.jpg

Michael Gilligan26/12/2021 08:24:43
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Posted by Chris Trice on 26/12/2021 03:25:15:
.

I know Everything Airbrush as they are the official inheritors of the Devilbiss brand and spares. One of the guys there worked for Devilbiss assembling the airbrushes on the production line. It's not 0.6mm. I took a silicone mould of the internal thread […]

.

So … have you checked that the thread form is BA ?

If [as you have reasonably assumed] the parts were originally made using BA tooling then the form should match.

MichaelG.

JasonB26/12/2021 10:05:56
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Thury and Lowenherz would be close pitches to 5BA particularly Thury at 43.1tpi

Chris Trice26/12/2021 11:48:35
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That's a thought. The thread is so fine though I'm not sure the actual thread form is going to play a big part. I have to say looking at the thread, it's more akin to a regular 55 or 60 degree thread form than the rather more rounded BA thread.

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