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Cracks in crotch mahogany veneer5/27
I am working with crotch mahogany veneer for some door and drawer fronts I’m building. The veneer was first flattened using veneer softener, then glued to a backing veneer to make it more manageable, and finally glued to a curved door that was made up of bending plywood. I used Unibond 800 for all the glue-ups. Somewhere between construction and finishing (the doors sat for about 8 months before I started on the finishing), the veneer started to develop small lateral cracks across the grain – see photo. Is this to be expected with crotch veneer, or did I screw up somewhere?
How long did the veneer sit after having the veneer softener applied? What was the MC of the veneer when glued to the backer? What was the backer material? Was the backer at a 90 degree angle to the grain direction of the face? What was the MC of the two plied face as it was pressed? How long did the two ply face sit before it was pressed?
Sorry for so many questions, but crotches can be a bear to work with. I had a face maker here in NC tell me some horror stories about working with mahogany crotches, and he works with them all the time. He was very secretive about his processes.... press temp for pressing the crotch after using the veneer softener, press pressure while pressing the two plies together with the tego glue film, spraying them down after they came out as a two ply, and then laying flat under pressure after the faces came out of the press.
He told me that during one two day stretch in his plant, that he had followed all of the details as he usually had for years..... but two days worth of work, and about $30k worth of material and labor went into the trash dumpster.
It looks like some movement between the face and backer layers. The checking is occurring across the grain, not with the grain. Hope this helps,
After treating the MC of the CR Mhg needs to be about 8-10% (assuming you are hot pressing.
The backing veneer grain needs to be 90 degrees to the face. It should be at least 1/24" -1/20" thickness and something like poplar, basswood or mhg.
Bending ply is not all that stable.
You need to hot press everything using Urea Formaldehyde resin glue.
You in no way can offend the Woodworking Gods or all bets are off.
Thanks for the help. Although I did some things right and others not so much, I'm starting to suspect the bending plywood is the main problem. I've looked through a bunch of off-cuts of the crotch/backing veneer assembly, and there is absolutely no indication of cracking. The only cracking is taking place on the assembled doors.