Don Stephan
Posts: 825
Joined: 2003-07-18
Location: Cincinnati, Ohio
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A year ago a customer asked me to veneer flat-topped pyramidal plywood sculpture stands. Olive ash burl was bookmatched on the four sides, and walnut veneer bookmatched on the top. They can be seen at www.stephanwoodworking.com.
With no "3D" vacuum veneering experience I chickened out and ironed on the veneer using yellow glue. Had to flatten the olive ash first, and alternated fresh newsprint for 4 days, but the veneer apparently never completely dried. (Next time I'll "clamp" veneer in the vacuum press after applying the flattening solution, and monitor drying with a moisture meeter.) Result was a nightmare, with every seam opening up. Spent a good 40 hours hiding filler with touchup fresco powders.
Yesterday the customer said he would like some additional sculpture stands, this time simple cubes. Determined this time to press the veneer in a vacuum bag.
I used dado joints to assemble the tapered stand with no problem, but will probably use splined miter joints this time as it seems a better choice (dado and butt joints have the potential to telegraph through the veneer using using two ply). When veneering the cube, my inclination is to place the cube on its side and veneer and the top and bottom sides; then similarly veneer the other pair of sides. Finally, I would position the cube upside down and veneer the top. Like the tapered stands, won't be any effort to veneer the inside surfaces.
I can think of two possible methods that would allow assembling the cube before starting with the veneer.
1. Filling the cube's core with plywood struts doesn't seem workable. Stuff the cube with vertical pieces of styrofoam to resist vacuum clamping pressure. Leave a 2" gap between pieces of styrofoam to be able to grasp and remove them after veneering finished. (Could rabbet the bottom edges of the sides and glue a bottom on the cube after veneering finished if the customer so desires.) Would have to cut the styrofoam to exact size, re-install it after veneering the first pair of sides, and the styrofoam would be an additional cost and disposal need. The sides of the cube likely will deform slightly during vacuum pressing, even if the styrofoam fits very tightly. With a layer of glue and veneer, the sides likely will stay somewhat deformed, and the styrofoam may have to be removed in pieces.
2. Use airform bladders to fill the cube during vacuum veneering. Since the cube would already be assembled, I'm concerned that I wouldn't be able to tell if the bladder completely fills the corners where the sides of the cube meet the top, allowing the cube to deform during vacuum clamping. It would seem there would also be a problem when vacuum veneering the top of the cube. The excess air bladder would protrude out the top of the upside down cube, and be pinched between the vacuum bag and plywood edges of the cube during vacuum pressing. Would likely have to have a top "caul" over the plywood edges and fiddle with the air bladder to get just the right amount of air, taking time and adding stress to yours truly.
The "Working in a Vacuum" video available on this web site is excellent, but doesn't address closed shapes such as these sculpture stands. Has anyone worked with closed shapes like these stands? Thanks.
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