I reverse laser engrave legend plates, device labels, operator panels and sometimes prototype membrane switches. I've also done front surface engraving. I assume that's what you're doing on these switches. The big problem with that is that fingers activating the switches will erode the paint from a front engraving.
If you're stuck with front surface engraving, then I'd engrave deeply and use a lot of paint, or several layers of paint and several layers of clear coat on top. Another trick that can work well is to use a liquid paint instead of a rattle can of spray paint, fill the deeply engraved letters with it rather than using several coats of spray paint, and use a solvent to remove the excess paint from the top surface of the key cap. Make sure the solvent is compatible with the key cap plastic. Or, let the paint dry thoroughly and mechanically remove it from the top of the key cap so it only remains in the engraved letters. Fine sandpaper or ScotchBrite works well for this. If you want a glossy surface instead of the brushed finish you'd get with unidirectional sanding or the matte finish you'd get from random sanding, you can finish with 600 grit paper and then Micromesh or Abralon (1200-1500 grit foam backed ultra-fine sandpaper). I have an EFD-1500 electronic fluid dispenser that I've used with a very fine gauge needle on the syringe to dispense paint into engraving. It helps to use a lighted magnifier, have a steady rest for your hand, and go easy on the caffeine for this delicate operation, but the paint wicks well and fills the engraved letters with no mess on the unengraved top. Model paint from a hobby shop might work well for this. Fingernail polish might work too. For engraving jobs with large and simple fonts, there are paint sticks that look somewhat like felt tip markers. They dispense paint instead of ink, so they fill the engraving well and the paint is fairly opaque. You might have some luck putting tape over the top surface, engraving it, spray painting it, allow the paint to dry and then remove the tape which served as a spray shield. This would probably work a lot better for laser engraving rather than rotary engraving with a small cutting bit. There is typically better coverage with a good brand of paint like the Krylon that you're using because there is apparently more pigment in the paint, and the solvent in the better brands of paint seems less likely to orange peel when applied to plastic than the 99 cent el-cheapo paint. I used some black spray paint recently from a major manufacturer, probably purchased at Lowe's, that advertised twice the coverage. It was marketed as something like "ultra coverage" or "ultra coat". That might help your translucency problem. I hope you bought extra buttons for a little trial and error. This one-off prototype stuff usually involves some waste. I recently got in a hurry and accidentally had the laser cut about half an inch off the edge of the $32 ultra scratch resistant polycarbonate sheet that I was reverse engraving for the top of the tool rack for my soon-to-be-CNC milling machine. Then I decided to try to front surface engrave the HDPE substrate even though I knew that was unlikely. Sure enough, the material didn't engrave well and required five passes to get the engraving depth I wanted. Then the paint wouldn't stick to the waxy surface, chipped and flaked out, and looked awful. I bought another $32 sheet of polycarbonate and laser engraved it the night before last, painted it yesterday, and I'm going to epoxy it to the HDPE substrate. Hopefully the two square feet of surface area will provide a strong enough epoxy bond, even on the HDPE. If not, I'll use countersunk flat head screws... or I'll use PVC for the 3/4" thick substrate. I'll test the bond strength with the botched piece of polycarbonate and a scrap of HDPE first. I don't want to buy a third sheet of $32 plastic! Oh, the joys of prototypes and one-off custom work. Good luck! On 12/07/2012 08:25 PM, Erik Friesen wrote: > I painted some of these > http://www.digikey.com/product-detail/en/1WD16/679-2144-ND/2034700 buttons > today, and engraved them, but find that the paint is not curing like I > would like (not very durable), and the paint is soft enough that they did > not engrave very nice. Not only that, these are backlit buttons, and the > paint I used(flat black krylon from wal-mart) is a little translucent. Any > suggestions about a better type of paint? > ------------------------------------------------------------------------------ > LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free Trial > Remotely access PCs and mobile devices and provide instant support > Improve your efficiency, and focus on delivering more value-add services > Discover what IT Professionals Know. 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