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Cam clamp update. Bad News
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=4634		 Page 1 of 1
Author:  Pwoolson [ Fri Jan 20, 2006 6:52 am ]
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Ok, so I assembled the first clamp today. Feeling pretty good to have all the "parts" finished and assemble is the remaining task. I tightened the cam against my bench and "CRACK" the whole thing split in two. I thought, "hmmm, must have been a bad piece of wood, glad I caught it before one of you got it". Then I tried another. "CRACK" This time I thought, "son of a #$%^#$, what the heck is going on". Try #3 yeilded crack #3. After throwing several things around the shop I calmed down and tried to figure out what I had done. As it turns out, I made the "fin" (the part that moves when it is cammed) a little thicker to try to get a little more force out of the clamps. But instead, it isn't flexing enough because it's too thick and it has to crack instead. So I'm off to the lumber yard to get some more beech.
What this means for you: there's going to be a slight delay. I'll crank all weekend and see where I am at that point.
Sorry for the delay but I want them to be right.
Author:  BlueSpirit [ Fri Jan 20, 2006 6:56 am ]
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Paul
This doesn't put you in the red, does it?
Author:  Pwoolson [ Fri Jan 20, 2006 6:57 am ]
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Well, mighty darn close. But that's not your problem, it's my stupidity.
Author:  BlueSpirit [ Fri Jan 20, 2006 7:08 am ]
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I would really hate to see a good deed go south on the person who was trying to do something nice for his fellow OLF'ers.
What can I do to help?
Author:  Pwoolson [ Fri Jan 20, 2006 8:37 am ]
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Thanks guys for the offer. You're a good bunch.
So I went to the lumber yard fully prepared to start this whole thing over again. I was going to go with maple because I knew it had worked in the past. Alas, they were completely out of 5/4 hard maple. Out of soft maple too. Out of Ash too. So I headed home to think it over. I started thinking, " I wonder if there is a way I can reinforce the wood behind the split?" And then I was also wondering,"why don't the manufactured clamps have this problem?" So I stopped by Woodcraft to take a look at the clamps. Sure enough, they have a screw driven into the piece just behind the split. So before I spend another $500 on wood, I thought I'd give this a try. I gave it a try and it worked great. I've been TRYING to break the darn thing and it won't go. I'll test it out on a few more to make sure but I think this is a good fix. If it works, I'll proceed. Rest assured, I'll stand behind every one of these clamps. If you break one, (or more than one) I'll replace it with another, no questions asked.


You can see the screw in question just in front of the metal bar on this one.
Author:  BlueSpirit [ Fri Jan 20, 2006 8:50 am ]
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Nice fix Paul. Keep us posted. We're here for ya buddy.
Author:  crowduck [ Fri Jan 20, 2006 9:46 am ]
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I have some of the clamps from StewMac, and indeed they have that screw just behind the slit. There is also a 1/8" hole drilled through the width at the end of the slit for relief to stop the slit from continuing through.

Crowduck
Author:  Bobc [ Fri Jan 20, 2006 9:48 am ]
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Paul no problem. the screw will work. I also offer any help I can. Just let us know.
Author:  burbank [ Fri Jan 20, 2006 9:53 am ]
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Is the problem as you originally stated that the "bendy" part is too beefy? Could you thin it by increasing the relief, perhaps with a shaper or spindle sander, between the head of the screw and the end where the cork would go?
Author:  Mario [ Fri Jan 20, 2006 10:10 am ]
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Paul, you need to drill a hole at the end of the slit, to relieve the stress riser. In your case, double-bonus, becasue you can make the hole a bit larger than the usual 1/8" or so, in order to help the piece flex, also. The piece will flex where it is weakest, so, make the weakest part the hole you drill. And when you drill it, let the bit "spin" in the hole to burnish the inside of the hole(set your drill press as fast as it gets, too, to help with this). the burnishing will also minimise stress risers....

Old-world engineering....
Author:  Pwoolson [ Fri Jan 20, 2006 10:14 am ]
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Pat, I thought this out but going back to the router table isn't an option because the slit is cut and it is not now a stable solid blank. I think it would chip and explode all over the place.
Mario, I've got an 1/8" hole in there now. I'll give it a try with a larger bit and burnish it a bit too. Thanks for the tip.
Author:  PaulB [ Fri Jan 20, 2006 10:23 am ]
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A couple of these things that I made split in the same place even with the hole. I just glued them and put a screw in them, it's a good fix. These are the one's I use when I want to use a little more clamping pressure 'cause I know they won't break - I'm too busy (lazy) to fix the ones that haven't broken yet.
Author:  KiwiCraig [ Fri Jan 20, 2006 11:17 am ]
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Hi Paul, I'm with pat on this one. I haven't got a spindle sander (curses !) so ,in my case I would use the drill press and drum sander and thin the bendy flap part. This won't make them explode as you say, and should solve all your problems in one go.
The strength of these clamps comes from the material above the bendy flap. Not the flap itself.
I drilled a 4.5 mm hole at the end of the slit and burnished as coach suggests (no screw required and no sign of splits on all I have made )
Except for JUMBO (the one at the rear ) these are made from Tasmanian Myrtle (part of the Euro. Beech family ) I have made quite a few ( funny how you never have enough !!!!!)

Regards KiwiCraig
Author:  Iplaytheoldies [ Fri Jan 20, 2006 3:23 pm ]
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Are there going to be more of these available for purchase? If so, how much?? Thanks, Jeremy
Author:  KiwiCraig [ Sat Jan 21, 2006 11:01 am ]
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I also " tune " mine. By carefully thinning the flap in it's middle .
    This, (upon clamping pressure) alters the upper jaw angle and has it seat at a more suitable angle to distribute it's pressure.

KiwiCraig
Author:  Miketobey [ Sat Jan 21, 2006 12:34 pm ]
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Paul-I doubt that any of us have a guitar stalled waiting for your fine clamps. Please relax,sit back and re-work when it suits you. If you don't, I'll feel guilty every time I reach for one of the clamps.Kindnesses often cost in sweat and worry(sometimes that is,indeed, what makes them worth doing),but none of us want this to become a penance for you. Thanks and kindest regards,
Author:  Pwoolson [ Sun Jan 22, 2006 5:38 am ]
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Ok, I spent the day yesterday reworking them a bit. I used some poplar as it was lying around. So I got the flex where I wanted it and I'm ready to go again on the beech. Then I started thinking, why not poplar? Yes it's soft, but how much abuse do you offer to your clamps? I'll go ahead and make a batch of the remaining poplar I have and send a few to random people to test out. If it works out, my next batch might be from this wood. I REALLY like the weight factor.
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