Ping pong paddle, un-warping laminated wood

[Pedro Reyes]

I (for fun) tried making a ping pong paddle, some of the folks at the office play, and figured I could make one custom. There are some desirable properties based on your style of play (softer back hand, etc.). I made one with a balsa core and 3 plies of spanish cedar (soft side) and 3 plies of bubinga, these were the veneers I had. From a woodworking standpoint this was cake. The middle bubinga ply is laid at 90 degrees for extra rigidity on the hard side.

Everything was fine, but today I brought it into the office, it had been very flat for a while sitting between two granite plates. I applied a piece of paper with spray adhesive on the bubinga side so I could cut the paddle shape, and now it has bowed. The cedar side is concave and the bubinga side (with the paper) is convex. The only changes were:


Sprayed with adhesive and glued paper pattern
rought cut from rectangle to paddle shape
moved paddle from garage to office



I know some people heat a side to un-warp wood, could this work on this laminated monstrosity? Which side, what else is recommended (wet, heat gun?)

Any help appreciated, I can't plane this back to flat ;-)

/p

[Pat Barry]

My suspicion is that the move from your garage to the office created a moisture uptake issue. I doubt that the spray adhesive (was it water based??) caused the problem. I also assume you removed the paper but that is likely inconsequential. If its moisture driven you may be stuck this time. Next time, you might be able to minimize the problem by alternating the stacks of bubinga and cedar on each side of the paddle. Of course, I don't know how important the overall thickness of the bubinga and cedar are to the performance of the paddle. Just for the sake of information, what adhesive did you use for the lamination itself?

FYI - I just checked and bubinga has a lot more shrinkage than does spanish cedar. If this is the case, then the moisture uptake would cause growth on the bubinga side compared to the cedar side and this would lead to the curvature you have discovered. Bubinga was noted as 4 to 7% radial shrinkage and spanish cedar was noted as 2%. These were noted by different sources so take that with a grain of salt.