drum sanding question

[Bruce Thompson]

Making a small travel folding chess set. Each half will be 4 1/2" x 9" playing surface. I used 4/4 walnut and maple for the 4 x 8 square glue-up, then flat sanded both sides. Then I re-sawed into two 3/32" thick halves that will be glued onto a 1/4" Baltic birch ply substrate.

The two "slices" have bowed a little bit, so I think I will have to stick them with double stick tape to a 7" x 24" piece of 5/8 BB ply scrap in order to run through the sander to flatten the halves to a uniform thickness.

I plan to run 120 grit abrasive and take .008" in each of two passes to get down to a final 0.200" thickness. After gluing to the 1/4" BB ply, I would take a final .004" with 180 grit on the drum.

My substrate BB piece has a slight bow in its 24" length, such that when placed on a flat surface it is maybe 3/32" high in the middle, easily pressed flat with one finger; nice and flat across the short dimension. I assume that the leading and trailing rollers of the sander - each 2 1/4" offset from the drum - would flatten the substrate board to the conveyor and give me nice flat work pieces. I would stick a sacrificial piece of stock alongside the workpieces overlapping front and back to prevent any possibility of snipe.

What do you all think? Have I missed anything?

Thanks

[John TenEyck]

My opinion is that you should find a piece of plywood, Melamine, etc. that is flat. Using a curved substrate is asking for trouble. And then run it through your drum sander alone to make sure it's dead flat before you stick your workpiece to it.

John

[johnny means]

I flatten material on a widebelt sander pretty much daily. If everything needed to me machined perfectly planar, my job would be impossible. This is especially true of thinner material that cups or bows one way or another if your hot breath hits it. Sometimes just the heat from sanding will cause it to emerge bowed. You paid for those pressure rollers, let them do their work. Sand your material as it is, it will be fine.