CNC Job To Level a Sacrificial Board

I am attempting to mill a PC board on my Snapmaker 2.0. I figured out quickly that securing the board directly to the CNC platform did not work well. Some places on the board the V bit took out some material and in some places it didn’t touch the board at all.

I’ve seen some videos where people use a sacrificial board secured to the platform and mill it flat. In most cases a comment is made along the lines of “create a job to mill the board flat”. I’m new to CNC and it’s not obvious to me the steps required to do that. I’ve watched several videos including ones from Snapmaker, but I’m still clueless about exactly how to go about milling the board flat so that I can then attach the PC board to this flat surface and then mill the traces.

I would very much appreciate any suggestions on how to accomplish this task. If there’s a video that shows this step by step, I would welcome that. Or if someone can spare some time to map out the steps, that would be great too.

Thanks In Advance,


Simply create a square of the bed size in Luban and give it a stepdown of what you need, maybe 0,5mm.
Use the biggest flatend mill you have.

Won’t help. The supports have too much flex at the extremes. Almost impossible to do level CNC Awork across the entire area.

Unless you install the rails…

It is possible to flatten a wasteboard even with the SM flex. You just have to keep your step-down small and speed low. I’ve used a 1" spoilboard surfacing bit successfully running at a .2mm step-down and 300mm/m.

How large of a pc board are we talking?

I make my paths in Fusion 360. Luban is pretty worthless for cnc. But as @xchrisd said, you just have to create a rectangle a little larger than your pc board.

You should also probably do a search for “tramming” on here to make sure your z-axis is parallel to your wasteboard.


The board I’m making is 3.3 inches by 3.3 inches. So while it’s probably true that a much larger board would not work due to flex, a board this size probably will. My raw single sided board stock is 5" x 7".

I did as @xchrisd suggested, I made a simple rectangle the size of the sacrificial board. I did have to configure the path as “fill” which I didn’t do the first time.

I reran my cnc file for the traces and could see that I did get traces where the first try did not. So some success here. Several of the traces going to components got eliminated by the isolation routes, so it looks like I’ll need to change some of the design parameters to make wider traces. This was just a first try so I wasn’t expecting success on the first go around.

I did run the hole and the board edge cnc files and they worked fine. I did destroy a drill bit when I clicked on the “move to work origin” button while setting up the drill cnc process. I should not have set the work origin with the Z axis properly touching the surface of the PCB. The drill bit was clearly longer than the V bit so when the cnc head moved in the Z axis the bit busted. Lessons learned.

So progress, but not perfection. I’ll keep at it.