Wednesday, September 10, 2008

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.


  1. The little burrs you got on parts of the machining is due to the direction the spindle is spinning vs the direction of travel. I don't know exactly how it works but I know that's what does it.

  2. Climb Cut Vs Conventional Cut

  3. this is great! Always something new to learn on the internet...thanks for the inspiration! Have you tried ferric chloride to etch designs on metal? Fun...