View Full Version : Expanding Copper Pipe?

19-08-2015, 02:35 PM
I need to make some bass ports for a small speaker - 400 of them!

I was going to use PVC pipe which is easy to form when heated in an oil bath. However It takes a lot of time.

Each speaker has 2x 20mm OD ports and if I could get 28mm OD pipe (1mm wall thickness) I would only need one per speaker. PVC pipe seems to go up from 25mm to 32mm, so no help. However copper pipe is 28mm with 1mm wall.

Do you think I would be able to form it in the shape shown? How? I've seen a metal ram used for more basic expansion. I am thinking the end flare might be too extreme and crack the pipe. The edge of the lip needs to end up at 90 degrees to the pipe length. Any tips?


19-08-2015, 03:43 PM
Hi Tenson
You could have a go @ spinning them you would need a to have a lathe big enough to take the pipe in the chuck, preferably gripped in soft jaws with a mandrel down the pipe, pipe would need annealing first. possibly a polished former/ template so they all come out the same. have a look on youtube for metal forming in the lathe. the special machines are pretty heavy duty but copper is soft when annealed.

21-08-2015, 10:04 AM
Annealed copper pipe may be pliable enough to get you such a severe change in section but I think it is unlikely to be easy to do.

The best way would be to make a mandrel that you can spin a sheet of copper over, taking care not to kill yourself in the process. Look up sheet metal spinning it is how they used to make lampshades.

Failing that, make from billet.

21-08-2015, 10:20 AM
I think you would be able to press form annealed copper sheet, with custom tooling, in several stages, with annealing between stages,

21-08-2015, 10:43 AM
Thing is guys he needs to make 400 !
Do you have a lathe with a 32mm or greater mandrel bore ?
Do you have a hydraulic press ?
Whats the overall length of trumpets ?

Boyan Silyavski
21-08-2015, 02:06 PM
I don't see how copper would be easier than plastic. Copper should be done in steps with annealing in between, that shape i mean.

Plastic could be heated/ gas torch/ , pressed over shape and rapidly cooled in cold water. Then next...

21-08-2015, 11:33 PM
I had a go with some copper pipe. It does work and will form to the shape without splitting, no need for heating. Copper pipe for plumbing comes in 'half hard' or 'full hard' spec and the 'half hard' stuff is suitable for bending and flaring. - https://www.youtube.com/watch?v=3e103_ULgpI

However... it took a LOT more pressure than I expected. I pressed a mandrel into the 28mm pipe using a bearing puller and even that found it tough. I had hoped to rig up a big lever to press it, but no way would it be strong enough. Okay I could build a machine to do it, but I'd probably spend longer making the machine than simply getting on with the plastic ones. So I'll go with plastic.

22-08-2015, 05:31 AM
I think that copper will only be as quick as pvc if it can be shaped in one stage.
And then it will still need some fancy tooling.

Doing it in pvc would only need simple tooling, a few for shaping and some holding device to place the ends in to be heated at only the area that needs to be formed.