First soft-jaws for CNC machining

While working to build the reduced weight moteus servo mk2, I got tired of hand machining the first operation on a manual mill and lathe for the front and back housings.  It was necessary, primarily to enable workholding on the PocketNC v2-50, but also because it allowed me to remove much of the excess material more quickly than could be done on the PNC.  So, I got trained up on the AA CNC Bridgeport and went to town.

The manual work I did on the mill used V blocks to hold the round stock, but for this I wanted something that was more repeatable and would offer more gripping power.  Thus I decided to try my hand at soft jaws for the first time.  I got some blanks from MonsterJaws which would fit the vise there and got started.

For the CAD/CAM, I grabbed a random 6″ Kurt vise model from the interwebs and stuck my part in it.  Then I added the vise blanks and used a “combine” operation to subtract out the stock from the blanks.


Then, when doing the CAM, I just ran a 3d adaptive followed by a finishing contour pass:


When I ran the actual toolpath, I messed up and had the spindle running about 1/3 of the speed I wanted, which made for some nice chomping noises, but it did cut.

Blanks ready to cut
Stock mounted!

2 thoughts on “First soft-jaws for CNC machining

  1. Why torque in video can be up to 30Nm with a ratio of 6:1. This motor has a maximum torque of only 2.8Nm. So the actuator is only 2.8 x 6 = 15Nm at max


    1. It is a valid point that I don’t have an independent measure of the torque for short duration events like this.

      I’ve measured a torque constant of 0.0679 Nm/A for this motor, and have measured applying phase currents of up to 60A for very brief periods (milliseconds). That actually only works out to a 25Nm torque at the output of the gearbox. For the throwing in that previous video, I commanded a torque of 30Nm, which would have been a phase current of 73A. I didn’t have instrumentation at the time to know if it was able to achieve that current for any period of time although subjectively the throws were slightly higher than when I commanded 25Nm.


Comments are closed.