UNF reducing bush

[michael howarth 1Participant @michaelhowarth1]

Can anyone assist in locating a 7/8 (male) x 3/4 " (female) UNF reducing bush. I am blowed if I can find one on Google.

Mick

[michael howarth 1Participant @michaelhowarth1]

[Roderick JenkinsParticipant @roderickjenkins93242]

Have you tried searching for adapter rather than reducing bush?

Rod

[HOWARDTParticipant @howardt]

I doubt you will find one, the difference between the core diameter of 7/8 and the old of 3/4 only leaves around 0.032” in diameter. Unless you can accomodate an adaptor.

[OldironParticipant @oldiron]

HowardT beat me to it. Had a look through all my books but cannot find one

regards

[Howard LewisParticipant @howardlewis46836]

For concentric threads, IF you are prepared to live dangerously, assuming that the 3/4 is the male item, you could try making one.

Drill and tap or internally screwcut the 3/4 thread and then screw it onto the 3/4 bolt /shaft.

Turn the OD and screwcut the 7/8 thread, but VERY gently.

You may get lucky and succeed, but with only 0.023" a side, you have little metal to provide strength..

If there is space for an adaptor with the threads end to end, you could make the 3/4 internal thread, and a little way, (at least 0.0625" ) beyond it start to cut the 7/8 external thread.

HTH

Howard

[Ed DuffnerParticipant @edduffner79357]

A few results from Google <here> …will need some further lookup from the results, based on the required application (air, water, gas etc).

Search term "7/8 male to 3/4 female UNF reducer". You could also try 'coupler'.

Ed.

[Speedy Builder5Participant @speedybuilder5]

Helicoil ??

[Martin ConnellyParticipant @martinconnelly55370]

The standard UNF threads have 3/4" x 16 tpi and 7/8" x 14 tpi. Hard to helicoil with two different pitches.

Martin C

[not done it yetParticipant @notdoneityet]

Posted by Ed Duffner on 20/06/2020 14:56:38:

A few results from Google <here> …will need some further lookup from the results, based on the required application (air, water, gas etc).

Search term "7/8 male to 3/4 female UNF reducer". You could also try 'coupler'.

Ed.

They are adaptors, not bushes. I expect that is likely what the OP needs, mind.(see Rod’s post earlier).

[Martin ConnellyParticipant @martinconnelly55370]

I bet "reducing nipple" pulls up some unexpected Google results

Martin C

[Speedy Builder5Participant @speedybuilder5]

I wouldn't discount a helicoil, agreed 14/16 tip mismatch is not the best, but a compromise may work it all depends upon how much load you need to put on the insert, do you need to undo the joint often etc etc. Perhaps more info on what you are trying to achieve would help.

[Chris GunnParticipant @chrisgunn36534]

Could you open up the 7/8" thread to say 1", and then you will have more wall thickness to make a 1" to 3/4 adaptor? or find what adaptors you can get, and open up the 7/8" to suit. Without knowing what you are trying to fit together it is hard to advise a good solution.

Chris Gunn

[MacolmParticipant @macolm]

In most cases this “thread adaptor” problem is easily solved, provided you have a little proficiency in screw cutting. (I previously posted how I converted M12 threaded Morse parts for a 3/8 Whitworth drawbar). Clearly a wire thread insert works fine, so the problem is to make a similar item if the available wall thickness will be insufficient to support the cutting forces

However, we can trade wall thickness against the depth (or percentage engagement) of the external thread by truncating the inner portion of the thread form. Decide the minimum diameter necessary, and bore out the thread which needs converted to this size. Now turn up the adaptor per the sketch. Cutting the external thread is very easy to do using an ordinary V lathe tool, though preferable with a flat on the nose of the V. A pilot length that is a nice fit in the bored out mating part makes sizing easy.

Do not set over the topslide, but cut the thread increasing the depth to reach the pilot diameter. Now take cuts at this diameter advancing the topslide until the full thread is reached. You can check this using something with the same (full) thread.

Clearly it is best to cut the smaller internal thread first to allow a relatively thin wall.

[Paul LousickParticipant @paullousick59116]

Because of the thin wall section between the 2 threads, can you do someting like this ? Probably cannot buy a commercialy made adaptor and would have to make it yourself.

Paul.

[MacolmParticipant @macolm]

That`s the obvious way where there is enough room for the extra length, and including any considerations about cross section if there is axial loading. In the case of something like a drawbar thread, it needs to keep within the original profile and also take the tension force.

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