Electroforming of hollow tapered tubing

I am working on a project which attempts to electroform hollow tapered tubing of various cross sections. The tapering tubes range square sections from approx. 8 mm square to 5 mm diameters. I am hoping to use female mandrels which will allow me to grow from the "outside-in", as I care about the surface quality on the outside, and not the inside...I am planning to use a long thin depleting silver anode running thru the center of the tubes...if I am hoping to grow 120-140 microns of silver walls for the tubes, am I going to have problems with anode/cathode proximity being so close?, Of course, presuming that I monitor the growth somehow so that I don't get a short. Also, are there silver baths other than cyanide? that are as efficient ? thanks for any information/help/pointers that anyone can give.

--RICHARD at the SAINTS

Hi Richard. You may be doing the project the hard way! I think you can get a bright, smooth , finish on the outside with an internal mandrel at these thicknesses, as long as you're not trying for an absolutely perfect outside surface. There is a world of difference between the worst electroforms you've seen and what is achievable.

If you do use an internal anode, it seems that a stainless steel one might be a much easier way to go. I don't think there is any reason to worry about close anode-cathode spacing except for short circuits.

Non-cyanide silver plating solutions aren't used for decorative plating yet because the color is a bit off, but they may be okay for functional plating. I'm not sure about the heavier plating for electroforms, but contact EPI / Electrochemical Products Inc. [a finishing.com supporting advertiser] and Zinex and see what they say. Good luck.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey