Spoil board flattning

Not sure when this occoured, but my spoil board on the “Y” axis is not level. I have a pro 60x120 machine. I put a 5’ straight edge on the table, and about 3’ from the home end it starts to lose levelness. At 5’ out I can get a .02" feeler gauge under the straight edge. I have run a flattening bit across the spoil board twice. I have zeroed the spindle at the home end and adjusted the contact .001". I then ran the gantry down the “Y” axis 5’ and I still had the same .001" contact. This doesn’t make since to me. If I have the same clearance from the bit to the surface of the spoil board then why isn’t the surface true. Can someone give me some things to try so I can figure this out?


My first guess would be to check if your linear rails are flat. sounds like they probably have a dip in the middle? When i first set mine up i just used the little block they give you, moving it down the extrusion, and mine ended up a little off. I used a 12 foot straight edge to figure out where mine was off. If your longest straight edge is that 5 footer you should borrow a longer one from someone if you can.

Not saying this is your problem but do check;

Once you take that waxy layer off MDF it will begin to absorb moisture and mushroom out. It will do so at uneven rates and distances. Kind of like in patches.

This is because of uneven adhesives in the wood pulp when the sheet is pressed.

You will need to resurface often. More often the higher you shop’s relative humidity.

I find that the shop being kept around 26% to 35% RH greatly reduces the speed at which the MDF expands after the top layer is removed.

Anything above that and your MDF will need regular resurfacing.


It is easy to write a script to check this. It’s the same script you would use to map the table.

After a grid probe just load the output file into Fusion 360 and you can use it as a guide for resurfacing. Save some cash by only taking off what is needed to return the surface to flat.

Do you find that it makes any difference it your try to seal it with shellac or something else after the initial surfacing?

To be honest, if you are going to go to that much effort you should use HDPE instead.

Email these folks and tell them where you are located and what size you need and they will direct you to a local distributor.

And yes, they make 3/4" x 61" x 121" sheets for the PRO60120, just don’t drop it on your toes :rofl:;


That is a thought. I just hadn’t considered it due to the fact, that when I was running a surfacing pass along the “Y” axis I didn’t notice any variations in the amount being cut. It was only when I was trying to surface a 5-1/2’ board and couldn’t seem to get it flat. That is when I put my 5’ precision straight edge on the spoil board and discovered it wasn’t truly flat. That is when I tried to re-surface the spoild board and still couldn’t get it flat.