TIPS

Photo-etching Made Easy (sort of)

by Sid Siegel

I recently acquired a photo-etching set up (Auto-Etch Bench Top Photo-Etch System, P.O. Box 12921, Philadelphia, PA 19108, (215) 751-0025) for the purpose of making gun port hinges for my Dutch model. We've all seen the fine photo-etched brass parts produced commercially, and thought how great it would be if we could make our own custom parts. Now we can, but it takes a bit of doing.

The system includes a table-top machine and 6"x B" brass plates that are photo-sensitized on one side (.005"thick) or both sides (.010"). Instructions are very clear, and if one follows them carefully, the results will be quite good.

The first step is to draft the parts to be produced on Mylar, with black areas where the brass is to be removed. The drawing is made at 300% (18" x 24") to be reduced to fit the 6" x 8" plates. Careful consideration should be given to the design of the drawings. They would best be done by computer, especially for many small parts. The drawings should also be made modular, say three or four 4" x 5" size, which could then be arranged to make an 18" x 24" sheet. The spaces between the modules would allow for unetched strips across the plates to maintain their rigidity during the etching process. Parts should be drawn with sprues rather than etching all round, as I chose to do.

Hand drafting is becoming a thing of the past, but I managed to get the drawing done with Rapidograph pens and special ink on acetate, since I couldn't find Mylar. The next step involved getting the drawing reduced to one-third size mirror image copies on acetate. This proved difficult. A photo lab couldn't do it, and the blueprint shop used a xerographic process which did not result in accurate and clean reproductions. I should have tried a local print shop, but instead I went to Continental Graphics, who got the job done for $20.

Using the reduced acetates, I exposed the plates. it works fine when instructions are followed to the letter. Unfortunately I gave one of the plates an extra minute of sunlight for good measure, and it burned the plate out. Once the plates are properly exposed, the etching process begins. Etchant is Ferric chloride obtained from Radio Shack. Since my drawing had the parts etched all round, I had to use Plasti-Dip as recommended to hold the parts, and it complicated the process as well as warping the etched plate to some extent.

The etching process is somewhat uneven, and I think the best method would be etching from both sides with trees to support the parts rather than Plasti-Dip. Paul Greenlee gave me an article on photo-etching by hand, and it had some useful tips. Since my .005" plates warped, they could not be raised and lowered into the machine repeatedly, so I finished the etching process by hand with an eye-dropper, which worked OK. The final results are mixed, but I think with experience I will do a lot better. I made more hinges than I could ever use, though some were nicer than others. (I could have made the hinges by hand easier and cheaper.) I also made some nice lantern brackets that I could never have made by hand, and some miscellaneous decorative parts, as well as brass diamond paned windows that would also be impossible to do by hand.

This process has definite uses, and would make a nice cooperative group project if we had enough people who wanted special brass parts. (Nickel-silver plates are also available) If we could generate the acetate drawings by computer, there would be no end of parts we could make. Of course, this process is much more useful for making miniatures of modern metal parts than for reproducing old-style metalwork, but its uses are only limited by the imagination.