This was a sign project. I created a contour path to cut out the sign. The Contour cutout was done with three tool paths. The first one used a 1/4" end mill to start at the top and cut down to .30 of an inch. The second Path switched to a 90 degree V-bit to add a chamfer to edge. For the final path I copied/pasted the first contour path and changed it to start at .3 and cut to the bottom with tabs. The first two paths went as planned. When the 3rd path started, it did not start in original path, it started about an 1/8" of inch (or slightly more) into the project and removed the chamfer along the bottom of the sign, but it only did this the first time around. As it continued to carve to the bottom, it used the correct path. You can see this in the pictures I took of the left and right bottom corners. I donāt understand why this happened and if it will happen again. It messed up a 3 hour project and I am worried about it doing the same thing again. This did not happen in the simulation.
What sounds odd to me is that after the first pass of the third toolpath it went back to where it was intended to cut, but the first pass was off the ~1/8".
Was this just the Y-axis?
Did it cut above the intended edge at the top, or was it only along the bottom edge?
My first thought was you may have lost steps during the tool change, only for the machine to lose the same amount the other way after the first pass. Maybe the original path at the top forced some missed steps to ācorrectā it?
Have you checked the side belts tension to make sure they are correct/even?
1 Like
The machine did not cut in the wrong place. A CNC cuts exactly where it was instructed to cut. That said there are things that get the CNC off its original path. The material may have moved. One or more axis may have lost steps. A dust host may have caused you to get lost steps by getting hung up on something. Drag chains can get caught or fall off their perch.
So yes the project was not cut like you intended but the software cut exactly where it āthoughtā it should. So if an SO4 Pro or SO5 lubricate your linear rail bearings. On an SO3/4 check your stepper motor pullies and the v-wheel for proper tension. Make sure your rails are clean. Check your dust collection to see if it could have been obstructed.
The software does not randomly move but the software assumes everything mechanically and electrically worked. When something mechanically or electrically went wrong the software has no feed back mechanism to correct itself.
1 Like
Thanks for your reply! It was only the bottom edge. It followed the intended contour path on the other three sides and then all four sides after the first pass around. It must have had a glitch with the code, during the tool change.
I did not check the belts, but I just assembled it a few weeks ago. It has done other detailed work without any issues.
I guess I will chalk it up to a random event an hope it doesnāt happen again.
I donāt think Iād consider it random, so if it does occur again hopefully you will start to see common events or conditions that could contribute to the outcome.
The simulation view in CC is consistent with what is sent to the cutter, so to paraphrase advice @WillAdams has shared on several occasions, āif what you see in CC is different from what you cut, you have a mechanical issueā. Thereās always a reason.
Side note: You could cut the full depth in a single toolpath and just set the tab height where you want it - It wonāt cut the tabs until it gets down to that height. Iāve cut chamfers before and after doing the full cutout and they turn out pretty much the same. Although if Iām cutting something that tends to tear out or splinter easily, I cut the chamfer (GrooVee Jenny from Cadence) first and the edge is usually cleaner. Unrequested 2-cents there. 
1 Like
Thanks again! I appreciate the advice as I am just starting out with CNC. I did the three step cutout based on a Carbide 3D training video. It is great to hear other ways of doing the same thing.
1 Like
Awesome, keep going!
I havenāt seen that video, but if thatās how they recommend, do that.
More than one way to skin aā¦ 
ā¦erā¦ to do things.
This topic was automatically closed after 30 days. New replies are no longer allowed.