I recently started playing around with Autodesk’s Fusion 360 3D modeling and CAM software. I managed to fumble my way through making some quick designs and setting up a simple cam job to make a tool holder. Designing the part was quick and so was setting up the CAM operation. However when exporting the G-Code through the grbl post-processor I discovered the G-code was using G28 (return to home) which isn’t supported in a stock ShapeOKO 2. Limit switches would need to be installed for this to work and for it to be turned on in grbl. The default startup G-Code using the grbl post processor looks like this:
(T4 D=6.35 CR=0 - ZMIN=-19.525 - flat end mill)
G28 G91 Z0
I was cutting on my ShapeOKO 2 last weekend and having major issues with missing steps on the Z. During fast retracts the Z would just hum resulting in passes where the tool wouldn’t clear the work resulting in more or less catastrophic failure. Either the work piece was damaged or the bit from trying to be forced through way more material it should be before I hit the e-stop. After some research I came to the conclusion that the stepping was the culprit. The steppers are configured correctly, wired correctly and moving as freely as possible but the controller would step at a rate that was causing issues on the Z.
After a little research I found that there was an update to GRBL version 0.9G that in addition to having a better acceleration planner the maximum feed rates could be configured per-axis. This is a pretty big deal because in 0.8C all the axis are limited by your slowest axis – which is the Z. Because of this cutting speeds are severely limited on the axis that one spends most of the time cutting on.
I made this nice cantilever wine bottle holder out of 3/4″ walnut and engraved it for my friends wedding. I ripped off a 2 1/2″ piece of black walnut from a piece of walnut I had purchased from The Woodery in Fitchburg. This isn’t an advertisement, but I do take notice when someone has excellent customer service and a fantastic selection of hardwoods, softwoods and exotics. I could spend all day in there picking out lumber.