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Powerfist Rotary Tool Holder for MPCNC

mpcnc powerfist rotary tool holder

This week I built a holder to attach my Powerfist rotary tool to the MPCNC universal mount.

Princess Auto in Canada sells a variety lower-priced tools under the Powerfist brand. I intend to use my Powerfist rotary tool as my first spindle with my Mostly Printed CNC. Whether this tool will be strong and accurate enough for the long run, I don’t know. But, I have one and will give it a try.

Previously, I decided to use the MPCNC Universal Mount system available on Thingiverse. The package of models includes a “maxi mount with a 10 mm offset” which is provided in STEP format. STEP is a widely used data exchange format for CAD drawings. I was able to easily import this file into my CAD program and use it as the basis for modifications specific to the Powerfist rotary tool dimensions.

After carefully measuring the tool’s dimensions, I decided to make the attachment with two mounts, both centered on the tool’s central axis.

  • The bottom mount is part of the tool holder. It provides a smaller hole which fits over the tool’s output shaft and is secured in place with the umbrella nut.
  • The top mount is separate and clamps over the Powerfist rotary tool body which is circular. It is attached to the main tool holder using a closely fitted slot with a central screw to hold it tightly in place.

Printing the Powerfist rotary tool holder

The models for this part were developed in CAD and then printed using ABS plastic. While the universal mount is made from PLA, ABS should be stronger and more resistant to the heat that will flow out of the power tool when used. The most challenging part was printing the top mount so that it fit into the main body. And, especially, making provisions for both the head of the screw and the holding nut to be properly recessed so they do not interfere with either the tool or the universal mount. Everything has to slide together.

I was actually amazed that, after printing, everything did fit together very nicely. The only problem was that the holes for the four screws that connect the holder to the mount were slightly off, perhaps 0.2 mm. I needed to file the bottom of the holder by a similar amount, so I could create the proper alignment.

As far as I can tell, the Powerfist rotary tool sits parallel with the Z axis and there is no wobble when I run it fast. Of course, at this stage my measurements are by eyeball and ear. I have some 1/8 end mills on the way so that I will be able to test run this tool with the MPCNC when it is assembled. That day is getting closer.

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