Friday, July 11, 2008

Hydraulic Press Tips

Habeas Corpus Brooch, 2008
Photography by Larry Sanders

First night of a new class, the first offered in the summer and it is filled beyond capacity! I'm juggling three levels and several students working independently. 

We have a Bonnie Doon  hydraulic press, which I have coveted ever since my student days. The College of Marin in Kentfield, CA where I first studied jewelry with Glen Campbell (no not that one), had a drop hammer. I don't know how much that thing weighed, solid steel over 5 feet tall with an enormous wheel. It looked like a medieval torture devise. Turning the wheel cranked the platen up, giving it a push would unwind and lower it with I don't know how many psi of force and a very distinctive sound, "whomp", after which it was named "The Whomper". Let me just say, I formed  .25 " 24 gage metal soldered to 1.5" 22 gage through a plexi matrix die, one time, getting a nice deep form. The 20 ton hydraulic press is kid stuff in comparison, however it has been developed into a truly useful tool, by Lee Marshall who founded Bonnie Doon. 

The 22 k bimetal in my Habeas Corpus Brooch (see above) was formed in the B.D. press with a matrix die. I used clear .25 " plexi, this made it easy to see the fine silver design and line it up properly, also it's what I had on hand. I prefer black plexi because it cuts much better with a jeweler's saw blade. It doesn't gum up and get stuck. If you leave the paper covering on you can draw registration marks on it and the metal to aid alignment.

 From bottom to top we used: plexi spacer, .25 plexi die, 24 gage copper, urethane pads and more  plexi spacers. You want to keep the metal in the middle of the presses' range for optimum power. After annealing your metal, start with 2500 psi, re-anneal and increase psi to 3500, 4500, adding force bit by bit. If you have an extra 80-durometer urethane pad you can cut several pieces that fit into your die, adding one at a time in between annealing. Pauline Warg, explains this well in her book, "Making Metal Beads"
What I like about her approach is you can easily judge when to stop adding pressure. Stop when the top plexi spacer comes in contact with the metal.
If you want a deeper effect you can either cut your die out of .50" plexi, or cut it twice in .25 and use carpet tape to stick them together. For additional safety, use duck tape around the edges as a precaution against the plexi cracking (not something I've had happen).

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