Imperial brass bushes

[SUNRAY]

Any chance anyone on here has a stash of male bushes to fit ¾OD conduit?

Some bright spark removed the surface mounted back boxes for upgrading but didn't think to keep the bushes.
There isn't space for adapters to metric as the tubes come in from all directions. I think it's about 20 required.


EDIT: Or a source for the female/female adapters, I can only find male/female versions now.

 

[333rocky333]

What about them knock on fittings, not sure how tight they would fit, think Edmunsons stock a range

 

[sparkwright]

What about them knock on fittings, not sure how tight they would fit, think Edmunsons stock a range

You mean, remove the old coupler end, and fit one of those modern fittings that you secure with a grub screw?

Good shout, don't know how well it would tighten against the threaded end of the old conduit though. And I suppose being an imperial system, there may not be a separate cpc wire.

Assuming we are talking about the same thing though - apologies if not.

***
I take it that it definitely is imperial, and that you have tried a modern metric 20mm bush JUST in case?

 

[333rocky333]

You mean, remove the old coupler end, and fit one of those modern fittings that you secure with a grub screw?

Good shout, don't know how well it would tighten against the threaded end of the old conduit though. And I suppose being an imperial system, there may not be a separate cpc wire.

Assuming we are talking about the same thing though - apologies if not.

***
I take it that it definitely is imperial, and that you have tried a modern metric 20mm bush JUST in case?

I was thinking pull the wires back and cut the thread right off, some have grub screws but i think some have a metal pressure tag inside riveted on.

 

[333rocky333]

Cef do these and you can use 2 lockrings

https://www.cef.co.uk/catalogue/pro...8DY_vIEixhuIJlAuVlRoCnbkQAvD_BwE&gclsrc=aw.ds

https://www.cef.co.uk/catalogue/products/135816-20mm-x-inch-adaptor-galvanised-sold-in-1-s

 

[SUNRAY]

What about them knock on fittings, not sure how tight they would fit, think Edmunsons stock a range

You mean, remove the old coupler end, and fit one of those modern fittings that you secure with a grub screw?

Good shout, don't know how well it would tighten against the threaded end of the old conduit though. And I suppose being an imperial system, there may not be a separate cpc wire.

Assuming we are talking about the same thing though - apologies if not.

***
I take it that it definitely is imperial, and that you have tried a modern metric 20mm bush JUST in case?

Oh yes it's really imperial, it feels like it's screwing on but very sloppy and a 20mm bush feels like it's engaging but is far too big to start screwing in.

The existing boxes were removed after the rubber/cotton singles and I assume there were no earth wires.

I hadn't even thought about the threadless stuff, infact not encountered it anywhere yet. Thanks for the idea I'll check it out.

 

[SUNRAY]

Sent a message to a colleague, I'm picking up a couple of 20mm threaded Conloks tomorrow to play with but he reckons they don't really work on imperial tube and the threaded tube makes it sit pi**ed crooked.

 

[SUNRAY]

Cef do these and you can use 2 lockrings

https://www.cef.co.uk/catalogue/pro...8DY_vIEixhuIJlAuVlRoCnbkQAvD_BwE&gclsrc=aw.ds

https://www.cef.co.uk/catalogue/products/135816-20mm-x-inch-adaptor-galvanised-sold-in-1-s

They were my first thought, and I have some, but most boxes have tubes entering from both sides, some even from all 4 sides.

 

[sparkwright]

Just thinking out aloud here, and have no solution, but maybe something will lead to another idea.

If the old imperial coupler was removed, and cut in half, and one half was screwed back onto the conduit, would a 25mm threaded conlok coupler slide over the imperial coupler, and then secured by the grub screw?

And then fit a 25-20mm reducer nipple in the threaded section of the 25mm conlok coupler, with some of the 20mm section shortened, with 20mm lock ring inside the socket box.



Bad idea, but maybe this could lead to a proper solution...

 

[333rocky333]

I have a Vice, bender and dies if you want to borrow them

They were my first thought, and I have some, but most boxes have tubes entering from both sides, some even from all 4 sides.

Do a search of these, maybe better
Lewden PD1452A or PD1452B
Possibly grind head off to make a 3/4 steel bush

 

[plugwash]

Apparently a 20mm conduit thread is 1.5mm pitch, while a 3/4 inch conduit thread is 16 TPI which works out to a 1.5875 mm pitch. In terms of diameter 20mm is just over 3/4 inch.

A short bush is about 13mm long, or about 9 threads, so the difference over that distance would be about 0.8mm or around half a pitch. So if you tried to re-thread a 20mm bush as 3/4 inch the threads would start out lining up, but by the time you bottomed out you would be basically destroying the existing thread. I suspect though that while the re-threaded bush would be ugly as **** it would probablly work adequately. You really only need a few good threads to make a satisfactory joint.

Apparently the 3/4 inch conduit thread is pretty close to 3/4 inch UNF, so it may be possible to buy a 3/4 inch UNF bolt and drill out the middle to make a bush.

I'm quite sure that a competent machinist could make bushes out of hexagonal bar without too much difficulty, no idea how much it would cost through.

 

[SUNRAY]

I have a Vice, bender and dies if you want to borrow them

Do a search of these, maybe better
Lewden PD1452A or PD1452B
Possibly grind head off to make a 3/4 steel bush

Oh FFS talk about stating the bleeding obvious, you're a star. I'm now wondering if I can do something with these

too as I have a number.

For a bit of info this is a grade 1 listed building, with buried tube work, they recently had a minor electrical fire and being totally rewired (1947 although it's reckoned the tube predates that) the switches and sockets are being changed including backboxes. I'm sure tube replacement or alteration would have happened by now if it wasn't buried. It has been in the cellar where it's surface mounted and much was very rusty.

What about them knock on fittings, not sure how tight they would fit, think Edmunsons stock a range

I tried a couple today, as warned it struggles to work on threaded tube, and much more so with undersized tube. Basically it tightens up crooked, Until your latest idea we were intending to fit one box with them but tighten the grub screw after the box and bushes. The other thought has been to squash one end of a 20mm coupling.

 

[SUNRAY]

Apparently a 20mm conduit thread is 1.5mm pitch, while a 3/4 inch conduit thread is 16 TPI which works out to a 1.5875 mm pitch. In terms of diameter 20mm is just over 3/4 inch.

A short bush is about 13mm long, or about 9 threads, so the difference over that distance would be about 0.8mm or around half a pitch. So if you tried to re-thread a 20mm bush as 3/4 inch the threads would start out lining up, but by the time you bottomed out you would be basically destroying the existing thread. I suspect though that while the re-threaded bush would be ugly as **** it would probablly work adequately. You really only need a few good threads to make a satisfactory joint.

Apparently the 3/4 inch conduit thread is pretty close to 3/4 inch UNF, so it may be possible to buy a 3/4 inch UNF bolt and drill out the middle to make a bush.

I'm quite sure that a competent machinist could make bushes out of hexagonal bar without too much difficulty, no idea how much it would cost through.

Many years back I used to use adaptors just as you describe, we did try to rethread a coupler but it was so tight we made a real mess of holding or releasing the coupling; holding it in a vice required so mush pressure to stop it turning it distorted it using a length of 20mm tube with 4 locknuts for the coupler to stop against tightened the coupler to the point it was very dificult to release it. The next idea was going to be enlarge the hole in a lathe and have another try with the tap.

 

[sparkwright]

Out of interest, who lost the bushes, and has he been forgiven yet?

 

[SUNRAY]

Out of interest, who lost the bushes, and has he been forgiven yet?

Actually he's been sacked for selling scrap metal... but that's another story.