Wednesday, November 14, 2012

Copper bellows again

I decided I wasn't going to let the peskey bellows defeat me, so I went for it again. My copper bellows MkII are a success! Here's what I did...

As before, I made a wax model on the lathe. This time I stuck to the rules I mentioned in my other copper bellows effort above.
So my recesses are tapered and wider than they are deep.
Wired, dipped in white/mineral spirits, covered with graphite powder. After a bit, burnished with a Qtip with more graphite on it.
Copper plated at very low current.
Below is the bellows just out of the plating solution.
It had two sessions in the plating solution. One to get the form strong enought to survive a bit of handeling and the burn-out. And another to build up a decent thickness of metal. 

Another warning note here: I was calculating on the assumption that the solution was putting down 1 micron every 2.5mins, as I read in the literature.

But even after 6/7 hours I only ended up with 150 microns or so. Measured from the waste I cut out of the top of the form. I'm sure the vertical parts of the cylinder are thicker but the important flexing parts are only that thick, if not less. I would like to have gotten .3mm or even more. As there is serious strength,brittleness and porosity issues with simple electroforming like this.

I realised later that the problem was that even though I had calculated my current density ok, I was using voltage control to achieve it. So my overall power/wattage was less than it should be. Hence the thin deposit.