Metal inlay technique using solder

Here is a technique that I developed to make a metal inlay with solder. I used soft lead solder for this project because it's easy to melt, and I am currently out of silver solder. I imagine the results will be slightly better with silver, since it is harder and will have a better shine.

I attached a piece of .030" thick brass sheet to a thick acrylic spoilboard with double-stick tape (Permacel). Using a 3/64" stub end mill, I CNC cut lettering. I started this cut with WD-40; however, the chip buildup was so large, I switched to water-based flood coolant to get the chips out of there. Cutting specs are: 4000 RPM, about 2.5 inches per minute, .020 depth of cut, 2-flute.


Some edges turned out very clean. For unknown reasons, other edges had a big lousy burr where the cutter pushed metal out of its path (instead of cutting it).
I used a MAPP gas torch to heat small sections of the brass and applied solder after fluxing the piece with acid paste.
I sanded the piece starting with 60 grit (just until I hit the brass), then worked up through each grit until I was using 600 with water. Yes, I use water with the orbital sander, it actually works pretty well! I reattached the piece to the spoilboard with more tape. This makes sanding much easier.
I made a custom polishing tip from aluminum, and a foam-padded piece of felt that was intended to be placed on the ends of table legs. First I used rubbing compound with the custom tip, then white rouge with a loose cotton wheel. I learned that using brown rouge on a spiral-sewn wheel was too aggressive on the soft solder. It preferentially chewed away the solder, leaving the piece uneven and not attractive. I developed the custom tip to distribute the polishing force as much as possible.



The biggest problem is the voids in the solder. I think these are bubbles caused by boiling flux or impurities while the solder is molten. They might also just be low spots where I did not apply enough solder. Oh well, I think it turned out pretty nice. I have also done this technique with acrylic and epoxy instead of brass and solder.