Brook Cub motor off Myford… funny thread?

[Philip Edwards 2Participant @philipedwards2]

Stripping down Brook "Cub" motor off Myford Super 7 lathe. It has 4 long studs threaded each end holding the front and rear casings together.

The studs are 5/32" diameter with a thread which is 24 tpi.

What thread form would that be? It doesn't correspond to anything I'm familiar with. Some of the threads are damaged so I need to tidy them up and was hoping to run a die down – nothing is ever as simple as you'd hope!

Thanks,

Phil.

[Philip Edwards 2Participant @philipedwards2]

Long studs holding front & rear end plates

[HopperParticipant @hopper]

Possibly BA? Commonly used on old British electrical gear. Plenty of BA thread charts online to check.

Edited By Hopper on 28/03/2020 10:12:23

Edited By Hopper on 28/03/2020 10:16:37

[Clive FosterParticipant @clivefoster55965]

Technically its probably specified as Admiralty Fine as all sizes below 1/2" are 24 tpi Whitworth form. Admiralty being notorious for appearing on all sorts of odd-ball sizes.

Good luck with finding a die! Maybe a thread reforming file will be close enough.

In practice I guess its just "the thread wot they used". Seems to be common on smaller UK made motors of a certain era.

BA, as suggested by Hopper, is too fine. 4 BA and 3 BA are close in diameter at 0.1425" and 0.1610" respectively  (5/32 is 0.1563" ) but the threads are 38.7 and 34.8 tpi respectively.  I've seen several motors with 3 BA studs.

Clive

Edited By Clive Foster on 28/03/2020 10:26:07

Edited By Clive Foster on 28/03/2020 10:26:37

[HopperParticipant @hopper]

Might be easier to make new studs.

[duncan webster 1Participant @duncanwebster1]

If its just 5/32 diameter with a nut on each end can you use M4 studding, with new nuts obviously

[Howard LewisParticipant @howardlewis46836]

Although electrical, it doesn't sound like BA. Nearest to 5/32 dia is 3 BA at 0.161 dia but that is 34.8 tp[i

5/32 BSW is 32 tpi, no 5/32 BSF that I can find (which would be even more tpi )

M4 is 0.7 pitch so again, too fine a thread.

Won't be ANC as these are 32 tpi about that size

On the basis of 24 tpi, 3/16 BSW is the nearest

Howard

[SillyOldDufferModerator @sillyoldduffer]

Posted by Philip Edwards 2 on 28/03/2020 09:53:55:

…

The studs are 5/32" diameter with a thread which is 24 tpi.

…

Sounds non-standard, but could the measurements be off? I usually manage to miscount TPI.

Any chance of a close-up photo of the screw-thread laid next to a rule?

Dave

[Philip Edwards 2Participant @philipedwards2]

Yes, def. 24 tpi. See photo.

Admiralty thread is not one I've come across before.

I'll try tidying with a file or as Duncan suggest, substituting M4 studding .

Thanks for all the help/suggestions.

Phil.

[Clive FosterParticipant @clivefoster55965]

Very few of the books include Admiralty Fine as it was primarily intended for special jobs where normal threads wouldn't be appropriate. Usually odd ball diameters or where you don't want a standard fastener thread used to protect against the wrong thing being screwed in. ( 0 BA in 1/4 BSF being the classic example of where the wrong thing can be screwed in with potentially disastrous results as the joint is very weak and has insufficient wedging action to reliably stay tight. )

Admiralty fine is whitworth form:-

24 tpi up to 1/2" diameter

20 tpi from 1/2" to 3/4" diameter

14 tpi from 3/4" to 1" diameter

12 tpi from 1" to 2" diameter

8 tpi from 2" to 4" diameter

6 tpi above 4" diameter

Clive

[Ian ParkinParticipant @ianparkin39383]

That stud has rolled threads….spoke thread?

[SillyOldDufferModerator @sillyoldduffer]

I like Clive's Admiralty Fine suggestion because nothing else comes close in any of my books! I was going to bet the farm on ASME #8-24, which would be a brilliant answer if it existed.

I wonder why they put an unusual thread on Phillip's motor? BA would seem more sensible.

Dave

[duncan webster 1Participant @duncanwebster1]

The tail end of the thread looks very truncated. I'd try a 3/16 bsw nut if you've got one

[Author]

Posts