Tag Archives: fusion360

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!

Fusion 360 3D adaptive and thin walls

I have been trying to improve the tool paths for the BE8108 gearbox sun gear holder.  The first time, I ended up slowing things down a lot and actually took some of the initial adaptive passes in several iterations as I fixed problems, so it wasn’t clear that any one iteration would be functional from start to finish.

So,  I tried it on a fresh piece of stock, with settings that I thought would resolve the pullout issues I had seen earlier.  Lo and behold, what did I find but more pullout!  It appeared to happen in exactly the same situations as before.  The adaptive clearance would leave a thin sliver of material, then “round it off” very rapidly, resulting in a large chunk of sliver hitting the mill at once.  Increasing the minimum cutting radius and tolerance helped reduce the problems some, but didn’t get rid of them entirely.

Eventually, I managed to find this thread on the Fusion 360 forum where others were having exactly the same issue.  From there, I discovered there is an undocumented parameter, only available in the “Compare and Edit” screen called “Curve in Radius”.  By default, it is calculated based on the tool diameter, but I found that I could add a random fudge factor of approximately 1mm to whatever the calculated version was and boom, the thin slivers were handled in a much more appropriate way and the tool never rolled over them until the sharp point was gone.

I still have more bugs to work out of this toolpath, but at least that’s one down.