After first considering soldering them up from parts, I decided to electroform.
Here is a picture of my wax mandrel. It is made from injection moulding wax. It turns ok if you don't try to take too much off in one go.
I parted off and heated a bit of copper wire and stuck it in to the end. Then I was ready for conductive coating.
There are a few options here. Sputter, chemical silver, electroless copper, conductive paint, graphite.
I decided to go with graphite because it was the simplest and I had it at hand.
Then I bunged it in graphite powder. I made sure it was all covered before the white spirit flashed off.
After a minute I brushed the excess powder off with a makeup brush.
A very important note here is that burnished graphite powder is significantly more conductive than non burnished.
Just rubbing with the bristles of an artist paint brush is enough to burnish it.
I need to reach into the interior ring to burnish the graphite there before it would plate properly.
I electroformed for 8 hours giving me 8*24microns so 0.2mm in theory!
I then very carefully annealed the tube, in the process evaporating the remaining carbon. I pickled
and ultrasoniced the remaining crud off.
And then disaster!! The inner rings were so thin that they cracked in the ultrasonic. They came out with some small holes and
I had always planned on re electroforming inside the tube as I thought they would be a little thinner. But they are significantly thinner and quite brittle.
So I placed a copper pipe electrode into my copper plating solution and began plating from the inside.
In retrospect I would do this differently. I had a huge problem with the shape of the mandrel causing different plating thickness
I bet anyone with plating experience could have seen that coming. So for the next electroformed copper bellows I will follow these guides:
- Interior corrugations must be wider than they are deep.
- Returns must be angled to face the electrode for copper plating reasons.