Padded Flat Platen

If the parts are box shaped with flat parallel sides you could use a vacuum fixture so clamping and releasing would be quick. Use a cheap one-stage rotary pump and assume about 5-7 lbs of clamping force per square inch, with a foam rubber oring as gasket. We used 3/16" or 1/4" foam rubber cord stock from McMaster Carr, in square grooves depth about

1/2 to 2/3 the cord diameter. Just butt the ends or superglue them together if you must. Don't use regular solid firm orings, they don't seal unless you are clamping a large surface area. For reliability we needed at least 16 square inches of clamp surface in the CNC mills but for sanding you could probably cut that in half.

For a pad on your belt sander platen I'd suggest polyethylene foam, maybe 1/8" thick or less. Would have the best lubricity so the belt doesn't drag and chew it up immediately.

Interesting problem. Ok, back to lurking :-).

There is a graphite (I think) fabric backed material designed just for platen use . The main factor we were looking at (Corian fabrication) was the low friction thus low heat . It's just "soft" enough to conform as you want . I'll have to look , I might have a small piece that followed me home from work here somewhere .

Here's one ... probably a lifetime supply for what you're doing .

That might be just the ticket, and I could use it on the 2x72 I keep telling myself I am going to build someday.

The one thing it won't do is give a light sand to a flat surface. The slack belt will just sand the edges, and the hard platen leaves streaks of shinny spots. I was wondering if something in between might be the trick.

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I haven't noticed that problem on mine. Can you check the platen for flatness and the belt for thicker areas?

I'm trying to pretty up "as extruded" surfaces without having to setup up and take a skim cut with a fly cutter.... and I am sure my falling apart 1x30 belt grinder is not as flat is it could be.

I'm trying to pretty up "as extruded" surfaces without having to setup up and take a skim cut with a fly cutter.... and I am sure my falling apart 1x30 belt grinder is not as flat is it could be.

Bob La Londe

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Rubbing the platen on fine sandpaper face-up on a milling machine table will quickly show you high spots and reduce the worst of them. Mill tables are somewhat better protected from abrasive grit and easier to clean than lathe ways, especially at the ends.

I found a very flat cast iron lapping plate and the multipurpose vee block I mentioned earlier in a second-hand furniture store, of all places. He had bought an estate lot that included a machinist's tool chest. Both make good and easily cleaned flatness test surfaces and sanding blocks. 1-2-3 blocks work well too.