Surfacing my Spoil board

Hey Everyone, In preparation for surfacing my first layer of spoil board, I put a offcut 3’ x 4’ on the front part of the bed, held with two bolts (subsurface) and some double sided woodworkers tape. The first pass was around 0.030" thick, (Wasn’t using the double sided tape then) and found that the edges of the MDF was lifting. I got some tap and tried it again, second pass was around .015" found one edge still lifting… Ran another pass at .005" Reinforced with more tape and a clamp (till it go to it)… That MDF lifted like a tacoed on all 4 corners! Is this normal? Anyway, What is the acceptable amount on smoothness on the spoil board? I’m noticing that the closer it gets to the front of the machine, the more “ripples” it leaves. I’m thinking this has to do with the fact that the dust collection hose is apply more torque to the gantry. This is a 5x10 machine with 12" Z axis, and the dust collection hose attaches pretty high up on the Z axis. Close to the center, I don’t think it’s pulling as much… hence it’s a bit more smooth. Please note: I’m a Machinist, not a wood worker, and a bit OCD, so, this may be acceptable. But it wouldn’t be for a machinist in metal. I can attach photos later on if needed.

Thanks, Connor

Hey Conner,
Pictures always help. Machinsts are in another universe of precision to woodworkers, so you may well be ok.
Your hypothesis that the hose could be applying torque on the gantry causing the variable tramming is logical I can’t think of an alternative explanation… On my 5x8, my hose was a tad short causing tension at the extremes. I added some length to compensate. Even so, I didn’t notice any difference to the cuts at those areas. You could try some test cuts with the hose off. To test your theory.

Mike

Have you tried flipping the offcut over, refastening, and surfacing what was the bottom? If the bottom was cupped, it might be trying to pull the edges up off the table.

Here are some photos of the setup as it is right now.


I have not. But. It kept getting worse on each pass. I know in metal, if yo take a skim cut of the top of something, it can bow and warp due to stresses being relieved. I wonder if that’s what’s going on here also.