I am putting together a basic machine for “pad printing” extremely small and precise parts. The design is very much the same as most homemade drill presses and consists of linear rods, flanged bearings and compression springs, but in place of a drill bit is a 30mm conical silicone rubber pad/stamp. The object being stamped will be positioned underneath on a precision XYR stage. A basic hand lever will be used to press the the rails/block downwards, applying minimal pressure. Scale will be approximately 10-15” tall. The blocks will be made of aluminium at this point and will be mounted to a very large solid base. Screws will he used to fix each component together. My goal, once set up, is for the pad to land in the exact same spot every time and with absolutely no movement or variation. It needs to be very rigid and with no slop.
I would like to know what diameter linear rods I should use, and if it makes much difference. I was originally looking at 40mm but this seems large?
Should I use standard steel rods? I have also considered introducing a ball spline shaft to prevent rotation.
I am not sure what size or type screws would be best suited for holding this thing together.
Are there any other factors I am overlooking that will help out?
I have come up with a few different layouts and I may be overthinking it. Do any of them make a difference to the overall result and accuracy of the press? Is there any particular direction I should be taking?