The MPCNC universal mount system looks like it will do the job.
Previously I described printing the MPCNC universal mount and attaching it to the vertical axis. This system was designed by a user and is available on Thingiverse. It is comprised of a central mounting device, as well as a variety of tool holders that will fit into it. Various users have contributed a variety of tool holders that will work with this system.
Shown on the left is a “pen holder” tool attachment. Like most novices, I will start out using a pen to have the Mostly Printed CNC draw on paper while I learn how to control it.
The holders fit into the MPCNC universal mount using shaped flanges that fit into a central slot. Then a couple of screws are used to hold the tool tightly in place. I was very pleased with the accuracy of these printed parts. The width of the slot in the mount was a perfect match for the width of the flange on the tool holder. The two pieces fit together perfectly without any need to file or sand the plastic on either part. And the fit is snug. For the pen holder, it almost does not need the screws.
MPCNC Universal Mount – 3 mm nut holder is a challenge
The MPCNC universal mount is designed to hold four M3 nuts in place on the back side. There are hexagon shaped holes for the nuts. However, printing a shape this small with accuracy is not easy. As shown above on the right, the nuts do not want to fit exactly into the holes.
Trimming a shape this small is hard work for three reasons. First, you cannot really sand the shape; you need to use a very small file or a utility blade. Second, trimming PLA plastic not easy. Third, you do not want to trim too much because then the nut will be loose in the hole. This would not be good, as you want the plastic to hold the nuts in place when you remove the screw.
I am using 12 mm M3 screws to hold the tool holder in place. I may end up trying to use duct tape on the back side to make sure the nuts stay in place.