Trunnion thread tools/cutters

[RobThomas]

I was wondering if anyone had come across the tools for rethreading suspension legs. I have the details o the thread pattern to make new tooling but hoped that perhaps someone had a lead on finding some used tools before I spend out on new stuff. I'm looking at having some original Series MM ones rebuilt, along with Morris Oxford stuff.

Thanks

Rob

[les]

If I'm reading your post correctly, that would mean finding undersize knuckles to suit wouldn't it? ------and I can't see them being readily available.

[RobThomas]

Ah, I was looking at having the original threads restored and built up by a friend in the aviation industry, hence the need for any help in recutting threads. Getting the tooling made will be quite pricey but there MIGHT just be something lying around on a shelf somewhere. Worth a try!
3/4 by 11tpi truncated Whitform truncated to 0.72 in.

[philthehill]

Rob
Cutting the threads should be reasonably easy if you have access to a long bed lathe which has a 11 TPI thread feed.
The cutter can be ground to suit the thread by using the threads on a unworn swivel as a pattern/master.
The Minor stub axle can be pressed out so as not to foul the lathe bed when the Minor swivel is mounted between centres.
Phil

[philthehill]

Rob
As I cannot edit the above post for some reason I will just add that the lathe will need to be able to cut both right and left handed threads.
Phil

[IslipMinor]

Rob,

Yes, yes and yes!

I have:

A lathe (Harrison M300) that will take the upright between centres up to ~25", and will swing the whole thing (up to 6.5" radius), including the steering arm.

It can do 11 tpi AND I have a carbide tip that is preformed for 11 tpi Whitworth.

It can do both RH and LH threads.

We are near Oxford, a bit south of the junction of the A34 and J9 on the M40. Could offer you a 'do it while you wait' service, might take a hour or so for a pair. Re-reading you original post, how many uprights need to be re-threaded?

The attached pictures show a spare RH upright in the lathe to make sure that I can actually do what is required. N.B. I will NOT hold one end directly in hard chuck jaws - it was put in just to check clearances.

BUT, a quick powered rotation showed that my spare RH uprights is scrap, because the bottom trunnion thread is badly bent out line to the rest of the upright. The lower trunnion screws on fully, so the bend is not noticeable, until it is rotated in the lathe, so Rob, thank you very much for prompting me to try it before fitting to the car and having a potential upright failure!

Please let me know if I can help.

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[RobThomas]

Wow! Thanks for the offer Richard.

I'm not sure yet how well the plan to build up the threads will go so I have given them one old leg to look at. Since the original Bronze trunnions seem to have lasted well I did wonder if Harlings could cast some new trunnion blanks to be threaded slightly undersize, thus negating the problem of having to build threads back up. There are quite a few Oxford legs floating around that need a solution. I'll ask around to get some numbers.

I have a slight suspicion that new Minor legs might have unified thread form instead of Whit.


PS. I should add that lots of good info has come direct from Jonathon at JLH, without whom I would never have discovered the secret thread pattern!

[philthehill]

Richard
If not putting the threads in a hard jaw chuck do you have a soft jaw chuck or will you put the swivel between centres and use a drive plate and drive dog to turn the swivel.

Rob
The question as regards the swivel thread profile has been asked on here without success for many years - so where did you glean the information that the thread is 3/4" x 11 TPI truncated Whitworth truncated to 0.72".
Not trying to undercut your information just interested to know the source.

Phil

[RobThomas]

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Morris Motors original factory blueprint for the Minor!!!!!!!!!

[philthehill]

Rob
Many thanks for that.
That will put the thread question to bed.
Phil

[pgp001]

Just need somebody to knock up a tap to the same dimensions now
It would be handy for cleaning up stiff trunnion threads, I had a brand new one that was too tight to use recently.

Phil

[RobThomas]

Not too hard a job to machine but it is beyond my limited lathe skills.

I'd also be keen to see if new trunnions are cut with the correct thread pattern. The manufacturers can't be blamed too much since I guess we are still getting a lot for our money.

[Declan_Burns]

Tracy tools sell standard 3/4 x 11tpi Whitworth taps and dies.
Regards
Declan

[RobThomas]

Thanks, Declan.

They have dies but taps are out of stock. I'll give them a call.

Cheers!

Rob

https://www.tracytools.com/taps-and-die ... ct_id=1126

[IslipMinor]

Phil,

I have soft jaws for the chuck, but would more likely either use a 6-jaw collect chuck, or run it between centres and use a driving dog. If the collet chuck did not mark it, that would be simpler to do.

Just noticed on the BMC drawing that the original upright threads are 'rolled', so much better grain structure than thread cutting.

[philthehill]

Richard
Many thanks for the reply.
Phil