This is my first time finger jointing 1/2″ 9-ply birch (or any kind of plywood) and the joints are consistently too tight to assemble by hand. I’ve checked my setup, it works fine with regular pine, I assume because pine is softer and ‘moves’ a little creating a nice tight joint. Once I do get two pieces to start to fit together the joint locks -it appears the end grains are binding. I expect the force needed such as a rubber mallet will damage the joint as it closes and worse damage would occur when separated.
If there is something wrong in my setup I expect this will become clear in time -but on the off chance that I just should not be trying to finger joint birch ply in the first place -I am hoping someone can enlighten me about this~!
Gary
“Whatever you can do or dream you can, begin it. Boldness has genius, power and magic in it. Begin it now!” -Goethe
Replies
Gary,
What technique are you using to cut the joints? In any case it sounds as though you should "tweak" your set-up to gain a little more clearance.
-Paul
Paul,
I'm using a jig on a table saw sliding table much like shown here http://www.plansnow.com/dn3076c.html where there is a pin offset from the dado blade by the width of the finger.
I've made tight joints with pine where the smooth long-grain to long-grain contact allowed the movement necessary for assembly. I was convinced my set up was wrong, but on further thought wouldn't the amount of pressure present in the long-grain joint be a problem with end-grain to end-grain contact?
Perhaps I need to make a looser joint, which I think means a second jig for the second half of the joint. I've never heard of anyone using two jigs this way.
I'm wondering if generally people don't use box joints on plywood?
Gary
"Whatever you can do or dream you can, begin it. Boldness has genius, power and magic in it. Begin it now!" -Goethe
Edited 1/15/2007 7:27 am by GaryPC
Gary,
Sorry, I may have mis-understood your initial post. Test cut a set and glue them-up using a set of cauls cut to fit against the joints' profile. If I gather correctly, you are having trouble with a dry fit. This may not be the case when gluing. Like you said , it is probably the different plys grabbing onto one another. Usually the plywood is stout enough to take a little pressure on this type of glue-up. Once the set-up is dialed in and you are confident about the glue-ups you shouldn't need a dry fit test.
-Paul
P.S. The dado blades are nice and sharp, right?
Paul,
Thanks yes the dry fit is not working. They looked spot-on but in double checking the tongues are 12 thou larger than the sockets! It seems I could get away with this with the softer smoother pine.
I just read Jeff's suggestion - I see this is exactly what I need to do.
Thanks,
Gary
"Whatever you can do or dream you can, begin it. Boldness has genius, power and magic in it. Begin it now!" -Goethe
Edited 1/15/2007 8:22 am by GaryPC
Gary
If the joint is tooooo tight, either move your guide closer to the blade by a hair, or add a paper shim. That will loosen the fit by the thickness of the shim.
Jeff
Jeff,
it seems I didn't want to see what (now) appears to be obvious
thank you-
Gary"Whatever you can do or dream you can, begin it. Boldness has genius, power and magic in it. Begin it now!" -Goethe
I made these 1/2" BB ply boxes this last summer for tool storage using pretty much the same setup as your jig - except mine was a much cruder one-time only jig. It did take several test setups both with the spacer offset and the spacer thickness before I got joints that lined up right and went together well but in the end, no problem using the box joints on BB ply.
If you build it he will come.
Very nice, that's the look I am going for only these are drawers for a workshop cabinet
Gary"Whatever you can do or dream you can, begin it. Boldness has genius, power and magic in it. Begin it now!" -Goethe
Beautiful boxes. Almost too nice to use for just tool storage.
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