Cliff Rohrabacher
04-20-2007, 8:39 AM
I made a couple of tongue drums from maple over the winter season. They were rectangular. The sides were finger jointed the tops and bases were glued to the edges of the bodies.
Logically the end pieces of the bodies are at cross grain to the tops and bottoms. Because the bottoms are solid laminated maple they are tougher than the tops as the tops have several Saw Cuts in 'em to make for the Tongues.
Then after the recipients came to enjoy the drums the tops peeled away when the glue joint at the cross grain ends failed as the wood changed dimension from humidity changes.
Apparently the glue failure issue is identical to that which causes people to not over do the gluing when bread boarding the ends of table tops.
However, with this sort of construction one does not have the luxury of simply not gluing the cross grain joints at the ends. Failure to make this joint intimate and fixed would result in vibration.
I have to tear the tops off and remount ‘em. I have had a couple of ideas:
1.) To assemble them in-situ where they will live hoping to have a stable humidity – it’s an HVAC home with an older HVAC system.
2.) machining and leaving a small gap (oh say .010”) at the end grain portions of the top where it’d normally contact the sides and simply leafing off the glue.
3.) Doing #2 above but making the gap smaller maybe .002” - .005” and filling that gap with epoxy.
4.) glue the tops on the bodies with epoxy and pray.
5.) don’t glue the cross grain at the top / end intersection but pin it with a screw in the center and plug the hole.
And if doing any of the above (except #5) mount little glue blocks about ¾” across along the inside of the end pieces (like kerfing strips one does in a guitar to increase glue area) but make them at a cross grain with the sides so that they will be inline with the tops and still
Any ideas or thoughts ??
Logically the end pieces of the bodies are at cross grain to the tops and bottoms. Because the bottoms are solid laminated maple they are tougher than the tops as the tops have several Saw Cuts in 'em to make for the Tongues.
Then after the recipients came to enjoy the drums the tops peeled away when the glue joint at the cross grain ends failed as the wood changed dimension from humidity changes.
Apparently the glue failure issue is identical to that which causes people to not over do the gluing when bread boarding the ends of table tops.
However, with this sort of construction one does not have the luxury of simply not gluing the cross grain joints at the ends. Failure to make this joint intimate and fixed would result in vibration.
I have to tear the tops off and remount ‘em. I have had a couple of ideas:
1.) To assemble them in-situ where they will live hoping to have a stable humidity – it’s an HVAC home with an older HVAC system.
2.) machining and leaving a small gap (oh say .010”) at the end grain portions of the top where it’d normally contact the sides and simply leafing off the glue.
3.) Doing #2 above but making the gap smaller maybe .002” - .005” and filling that gap with epoxy.
4.) glue the tops on the bodies with epoxy and pray.
5.) don’t glue the cross grain at the top / end intersection but pin it with a screw in the center and plug the hole.
And if doing any of the above (except #5) mount little glue blocks about ¾” across along the inside of the end pieces (like kerfing strips one does in a guitar to increase glue area) but make them at a cross grain with the sides so that they will be inline with the tops and still
Any ideas or thoughts ??