topic Re: 3D Pocket Stepover not working as expected in Fusion Support Forum

3D Pocket Stepover not working as expected

Anonymous — Mon, 01 Jul 2019 19:07:16 GMT

Hello,

I'm having an issue where my CNC mill is not stepping over in the way I thought it would, based on how I set it up in Fusion 360.

As you can see from the photo, entire chunks of wood are not getting milled away. I did not set a smoothing operation, as I was planning to hand sand the rough bits off anyway. However, miniature walls are a bit of a hassle to remove.

I have the maximum stepover set to 2mm, and my bit is 3.75mm wide. Should be plenty of overlap to avoid these walls.

Below are screenshots of the settings, and I've attached my project file.

Re: 3D Pocket Stepover not working as expected

HughesTooling — Mon, 01 Jul 2019 22:59:56 GMT

Can only be a couple of things. One are you using the correct diameter cutter or 2 flex. You are conventional milling so the cutter will try to pull in the material so if your setup is not ridgid it could flex enough to not clean up. It would need to pull over about 1.25mm with a 2mm stepover. You could try climb milling to see if it cleans up or shows flex the other way.

One thing I did notice backplotting in NC Corrector is in some corners the cut is getting close to 3mm, try increasing the Smoothing deviation to 0.75.

Mark

Re: 3D Pocket Stepover not working as expected

Anonymous — Tue, 02 Jul 2019 15:28:57 GMT

Mark,

Thanks for the response. I'm 99% certain it's not machine rigidity. This is being cut on a Shapeoko 2 with NEMA 17's, with some modifications to increase Z rigidity. My first suspicion is always the machine (since it's kit built), but in this case I reproduced almost the exact same stepover issue on poplar, a very soft wood compared to the red oak in the photo, with the same speeds and feeds used on the oak.

I'll play with the smoothing deviation to see if that helps, since the walls are popping up on curves.

Thanks,

Rich

Re: 3D Pocket Stepover not working as expected

HughesTooling — Tue, 02 Jul 2019 16:39:17 GMT

Have you downloaded NC Corrector? It will allow you to measure between points and lines in the G Code, the code looks good but pretty close to 3.0mm on some corners so apart from that the problem can't be in the code. Double check everything on the machine is tight because every time this sort of problem comes up it's not Fusion but loose screws, pulleys etc..

Mark

Re: 3D Pocket Stepover not working as expected

Anonymous — Mon, 08 Jul 2019 16:08:25 GMT

I haven't downloaded NC Corrector, but I did do some tests over the weekend. I created 2 sets of tests, isolating an axis and moving it back and forth about 100x. I did one for each axis rapiding back and forth 20mm, and one for each axis doing a regular move each axis. I measured the distance by placing a wooden block lined up on a line for X and Y, and by placing it under the Z (assuming a -Z delta would pinch the block tighter to the board.)

X and Z had no discernible delta between the starting points, but in both Y tests, there was about a paper thin gap. This is not enough to cause the walls, and honestly for what I do with the machine, not enough to warrant adjustment.

Even though I trust your opinions, having it machine create these walls at almost the exact same spots in the cut, I still think it has to be code based (either F360, or my gcode sender). When I get more time, I'll play around with F360 and other gcode senders to see if I can find a solution.