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With CNC router , I've carved the inner circle so I want to make hundreds of trays like this: Simple Circle Tray

what is the best way to paint the "brown part" without affecting the top edges. ( I don't want to paint the yellow part , only the brown side )

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I would try applying blue painter's tape to the plywood before I routed out the inner circle. Then route the inner circle, which will also cut away the tape. Then when you paint the interior, the painter's tape will be perfectly masking the top, so you don't have to worry about slop. When the paint is dry, remove the painter's tape.

The downside to this is, tape residue will get on the CNC bit. I'm not sure how hard this would be to clean. If the path can be set up so it routes the outer part of the circle first and moves towards the inner part, that might make it clean off most of the residue as it routes the rest of the circle. But maybe not. Still, it would be a handy process if it worked, so I'd probably at least give this a try.

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  • wonderful solution. – Mironline Dec 4 '17 at 15:31
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Make another ring (Piece A) that is somewhat larger in outside diameter than your final item, but with the same inner diameter and open at the bottom. Make this from fairly thin material. This will be the stencil/mask to keep paint off the unpainted sections.

Next, make a solid circle that is a close fit for the interiors (Piece B). This should be thicker than the depth of the hole and the thickness of the piece above combined. This will be the locator to position the above disc on your work piece.

To use, place B inside a tray, and slide A down over it. Clamp A in place and remove B. Paint the inside with whatever you want, brush or spray.

Part A can be made from anything that is somewhat rigid - cardboard, wood or whatever. You can make several of these so you can do sort of an assembly line.

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  • Like it! Indeed, if the OP can rout (for example) five or ten cavities, and then make the mask A be suitable for all of them (thus reducing the work to clamp by a factor of five or ten). Once the cavities are painted, then he can use the router to cut the trays out of the plywood sheet. – Martin Bonner supports Monica Dec 4 '17 at 16:41
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It looks like you have a solid disc of plywood, with a ring stuck on the top. If so, proceed as follows.

  • Mark out the inner and outer circles of the discs.
  • Paint the inner circle (but not the outer circle). There is quite a bit of room for error here, so you can use a fairly large brush, or spray with a mask.
  • Cut out the upper rings.
  • Paint the inner edge of the upper rings.
  • Glue each disc and ring together (choose the surface with the fewest paint flecks as the upper surface of the ring).
  • Once the paint is completely hard, use a large sander to remove any flecks from the upper surface.

Edit

It turns out the piece is a solid piece of plywood with the hollow cut out with a CNC router. In which case, I revert to my original (unposted) idea:

  • Make tray.
  • Paint inside as neatly as possible with a brush.
  • Once the paint is completely hard, use a large sander to remove any flecks from the upper surface.
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  • this is a solid plywood , I used cnc router to make an inner circle , thank you for your quick answer , – Mironline Dec 4 '17 at 12:38

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