Hi delter,
I have a great deal of experience with sandblasting. This includes equipment, technique, and even keycaps. So here are some of my thoughts from around 15 years of experience.
The photos you provided potentially illustrate a couple/few issues. The first being that you were likely far too close to the object as the patern on the stroke looks narrow and the "burn in" is a very tiny circle. The second is that with that distance you were likely going far to slow as well. The amount of dig is not that clear but it looks significant and perhaps that line pressure is bit high as well for this particular application. In the even that your nozzle is really tiny and it's a small booth then I would still suggest moving a bit further back, completing a full pass (as you already likely know from your shooting experience) and perhaps turning down the pressure. If you were at the high end of 80psi I would suggest moving towards 60psi and see what that gets you (while observing distance and patern/stroke). If this happened because you are at something like 100psi+ turn that sukkka waaaay down. Below 50psi you might have issues with getting the lettering to come off nicely without it taking a year.
You might also try moving transverse to what you were doing. As you are already aware you need so follow the contour of the piece. This is very important when working small around the size of a keycap. ;) I notice that you are going left to right and "against" the ridges. Try turing the key or spraying in the other direction since following such a tiny contour would be difficult and you want to avoid extra errosion on the edge.
When holding the piece make sure that your device (even if fingers) does not rest above the surface of the object as this could deflect particles or concentrate them to the edges of the piece leaving that more heavily erroded.
Regarding media, I would not go with something fine (baking soda) as the finer the grit and the constant rate at which the blaster works will just make the surface way to fine and will take forever to remove the legends, especially if there is any contour to the legend at all (e.i. raised, recessed). The heavier the grit and the lower the pressure can net you some nice texture similar to some finely textured keys. You could also do two different grits, one for scrubbing and one for finish.
If you're really brave and hate the sandblasting and silicosis (lol), you can try making a heated texture stamp and pressing the key into it and triming off the excess (if needed, but not always necessary). However it does not work well with legends in place and would need to be removed with some other method.
And for a couple quick last notes...
For those that complain about how long it takes to manually sand keys. Get aquainted with a rotary device and practice, maybe try a very soft abrasive wheel or compound. You could also just find a rounded form and place the sand paper around it so that it follows the contour of the keycap and... away you go!
Careful when blasting white or light colored plastics as they can turn grey-ish, usually it's directly due to the media, but not always. Light colors may get darker and dark colors may lighten. A good cleaning (maybe even ultrasonic), or a good coating of your favorite plastic friendly toxic spray.
Oops, one last thing, you can mask of any areas you don't want blasted with some rubbery tape of your choice. Duck tape can work, but it's sometimes a bit messy and holds a poor edge.
Good luck and have fun.
-cc =)
You can pretty clearly see they got too hot, this is a common problem with sand blasting.
Even metal workers have to watch out for heat distortion due to sand blasting. Classic car restorers have pretty much abandoned it for soda and bead blasting, or acid dipping as the sand just causes a lot of problems.
Lowering the air pressure, gluing the keys to a plate (water soluble glue or try clay), keeping the gun farther away, and most importantly, constantly moving is your only option. Even then it could still end in failure.
Sorry for the bad experience.
Yup, mostly a practice thing. Many think that it's heat that warps the metal but in the vast majority of cases I'm postivie it's the force in which it's being blasted. A heavy mesh size + high pressure will make that metal dance.
Second on using a less aggressive medium. Possibly try baking soda.
That's a bit too fine, but it would give you a very, very, fine texture. It's also terrible to shoot.
For the TLDR crowd:Why are you even reading this, go play with another ephemeral "app".
