Budget Substitute for Sign Foam

Today we cut the first parts of the Make a Difference Engine No.3. The Meranti Epicor plywood is like working with luan sandwiched over butcher blocks of balsa wood. It is lightweight and dimensionally stable. But, it trades in some strength for lightness.

The surface is darker in color than the interior layers. When peck drilling the spots to mark our holddown polymer nails, the locations are very visible. Working with maple plywood, we have missed hold downs since the holes blend without strong light.

The first lesson is adjusting the tab density on the toolpaths. We normally run tabs every 8 inches, 1/8 inch thick and 1/2 inch long. With this plywood we needed to cut the tab spacing in half and not go all the way through the surface layer.

The issue isn’t holding the parts in the sheet during machining. More tabs are needed to hold the sheet together when lifting it off the ShopBot table. When we lifted the first sheet some of the large gear pieces broke out of the sheet. For safety, snapping plywood while hovering in the air is asking for trouble. For the parts, the edges splinter and the finished layer peels off making re-work.

Pieces Broke Free

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Test Assembly of an Odd Sector

These are just the parts stacked together to check fit.

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Overall, the Meranti Epicor plywood (or Meranti LC BB/CC 18mmx48x96 Block Board Core at $37/sheet) looks like a good substitute for Sign Foam on interior projects on a budget.