Ok, Spent the day at work, earning triple time and wasting the company's money designing a jig to engrave watch cases, lol. Tell me what you think, this is the first thing I ever designed in CAD for a 3D printer, and like the 3rd actual thing I'll be printing, lol. It's gonna use a LOT of filament.
The two end pieces will have bolts with wing nuts through the holes for tightening. It's plastic, so I doubt I'll be able to get enough pressure to actually damage anything, lol. The two "Blocks" are for 19mm and 20mm lugs (the 19mm has a relief cut but I marked them with text because I'm prone to mistakes, lol).
There's about 20mm of parallel on each side, plus a notch and groove to keep things aligned. I'm pretty confident it will break before it lets a case get misaligned. I'm not sure what the tolerances are for a 3D print, but I assume there will be sandpaper involved for final fitting of the 3 components. Maybe some butter or spit to make things slide easier...lol.
Will share the STL file as well for anyone who wants it, or thinks they can improve on it...if you do, please share the upgrades so we can all benefit!
Future upgrades will probably include a means to attach it directly to the engraving machine, so an add on vice won't be necessary. Just have to figure out how to center it and where the bolt holes would go. Maybe if I get fancy, I'll add a relief cutout for the actual watch case to sit in, but I doubt that's practical, since there's so many variations. Maybe one for 34mm cases, one for 36mm cases, and one for Subs/GMTs, but I'm geting WAY ahead of myself.
EDIT: FWIW, it's occurred to me that this would probably work without the part marked "20mm." If you print only the 19mm part, it would work as a 20mm by turning it on its side...it would just have a small depression where the case would sit. I guess I could make the entire block 22mm, and have the same block work for 4 different sizes...2 on one end, and 2 on the other. Maybe I'll tweak it to be usable with 19, 20, 21, and 22mm lug width. Could probably do more if I tweak it a bit more...maybe add 18mm and 24mm, although I don't know of any watches of that size that have engraving between the lugs.
3D design Watch Jig for engraving created by David Patterson with Tinkercad
www.tinkercad.com