Flattening on CNC

[srhardwoods]

I figured I would start a new thread instead of continuing on the other thread which was kind of hijacked.

Daniel, this is how I flatten on my table. The ply under the slab is sacrificial. couple blocks and wedges to hold it in place. It doesn't take a lot of pressure to hold it and alternate the direction of the wedges. This was a 42" x 102" Sapele slab for a odd shaped table top I'm building for a customer. Once the top was flat, I flipped it and used the vacuum to hold it, but you can just wedge it again if you are not using a vacuum

If the board is really rough and twisted to begin with, I usually use a 3/4" downcut endmill as it can take a lot of material per pass. If it's fairly flat I use a 4" diameter surfacing bit from Amana however in figured woods, that bit can have tear out. It took 9 minutes each side using the 3/4" bit

 

[srhardwoods]

this was the finished project tonight. A Outside grill/bar area that the top flips over on top of itself to save space. Customers specs.

 

[tri4sale]

cool, thanks for the pics.

So your sacrificial plywood, that sits ontop of your regular sacrificial board and is just held down by your vacuum?

 

[srhardwoods]

Correct. 90% of what I cut on this machine is plywood for cabinet shops so keeping my spoilboard clean for maximum vacuum is important. I pull 24" of vacuum and additional holes would give me leakage. So, a scrap piece of ply I can screw into works well. On my 4x4 machine I use plugs that are inserted into the spoilboard where I can use T bolts and clamps. Works really well

 

[SubGuy]

I've given long thought to a manual version of this with a big router and a spoilboard bit. I have used a rudimentary version when I flattened a slab for a brewery. Basically wood rails and a plywood jig, but it took hours and produced some minor tearout.

 

[tri4sale]

Thanks, I run a vacuum on my ShopBot (2 FEIN vacs to 4 zones) so don't want to eat up sacrificial board any more than I have to. I've got some cypress to flatten, so I may give it a try this way instead of my planer since they are just a bit wider than my planer can handle.