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#1
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Joints in plywood canoes
advice wanted on joints in plywood. I am making a canoe out of 4mm plywood
and it mentions scarf joints, which I now know about. The question is could I make the Joints biscuit joints and woiuld they be as strong? (joining 2 x 8x4 to make one 16ft long plank) fred --- Outgoing mail is certified Virus Free. Contains no anthrax or other artificial flavours. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.543 / Virus Database: 337 - Release Date: 21/11/2003 |
#2
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Joints in plywood canoes
Biscuit joints would not give enough strength, the idea of the scarf joint
is that the angle increases the surface area of the joint between the two pieces of timber giving a stronger bond, generally if your using an epoxy resin you should be able to get a very strong joint, so long as the scarf's are the same, a thicker filleting mix of epoxy can help fill any voids. if you're really worried you can also lap over fibreglass tape, but you can spoil the look of the boat. If your not bothered about the looks then it's not a problem though. If you get in touch with SP systems and West Systems (both epoxy makers) they will send you loads of free info about practical uses of their products. John "Fred" wrote in message ... advice wanted on joints in plywood. I am making a canoe out of 4mm plywood and it mentions scarf joints, which I now know about. The question is could I make the Joints biscuit joints and woiuld they be as strong? (joining 2 x 8x4 to make one 16ft long plank) fred --- Outgoing mail is certified Virus Free. Contains no anthrax or other artificial flavours. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.543 / Virus Database: 337 - Release Date: 21/11/2003 |
#3
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Joints in plywood canoes
"Fred" wrote in message ...
advice wanted on joints in plywood. I am making a canoe out of 4mm plywood and it mentions scarf joints, which I now know about. The question is could I make the Joints biscuit joints and woiuld they be as strong? Probably no, and no. Strength aside, a biscuit joint won't bend properly. |
#4
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Joints in plywood canoes
I can't see how you could biscuit joint 4mm plywood, there just isn't
enough material to cut a slot in is there? There are 2 ways that I can think of that plywood can be joined end on in boatbuilding, the scarf or scarph joint and butt joint. The scarph involves cutting both ends to be joined at an angle so they overlap (you finished plank would be less than 16' by the length of the overlap) the longer the overlap the more area for the glue as John says, so the stronger the joint. It is fiddly if you don't have a bench saw or sander with suitable jigs to get the angles. An alternative way to make the scarph is to cut down to 1/2 depth and then remove that half of the material (count the veneers?) out to the edge - then you can overlap the boards without getting a step. I'm not sure if this would actually be easier than cutting the angle, I guess you could do it with a chisel, plane and sander but it might be worth sorting your technique out on some scraps first! More commonly plywood is simply butt jointed, but obviously it needs some reinforcement if you do this. In the stitch and glue method of construction, the adjoining edges have holes drilled in through which little bits wire are threaded and then twisted to draw the edges together (this is useful where the "planks" are joined at chines but can be used just as well for seams). Once everything is right fibreglass tape is resined onto one side (a more modern method involves epoxy filleting the inside joint to level that will hide the wires) and when dry the wires can be cut on the other side and sanded flush before being taped over. In the first case the original tape needs to be removed (hot air gun works well) and the wires on that side pulled out or tidied up before taping neatly. As you don't have any shape and are presumably joining before bending you might get away with laying them together and taping one side, and then when it's dry, turning over and taping the other side. Another effective method is to screw and glue a batten or say a 3" - 4" wide strip of plywood over the butt to reinforce it. Obviously this does not look as neat unless the batten/strip is going to form part of your internal arrangement (on my dinghy the sheets are all joined at a frame so not seen from inside), and obviously don't put the strip on the outside which you want to keep smooth for resistance reasons! JIM Fred wrote: advice wanted on joints in plywood. I am making a canoe out of 4mm plywood and it mentions scarf joints, which I now know about. The question is could I make the Joints biscuit joints and woiuld they be as strong? (joining 2 x 8x4 to make one 16ft long plank) fred --- Outgoing mail is certified Virus Free. Contains no anthrax or other artificial flavours. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.543 / Virus Database: 337 - Release Date: 21/11/2003 |
#5
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Joints in plywood canoes
Thank you all for your advice. I think I will stick with the scarf joint.
fred "Fred" wrote in message ... advice wanted on joints in plywood. I am making a canoe out of 4mm plywood and it mentions scarf joints, which I now know about. The question is could I make the Joints biscuit joints and woiuld they be as strong? (joining 2 x 8x4 to make one 16ft long plank) fred --- Outgoing mail is certified Virus Free. Contains no anthrax or other artificial flavours. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.543 / Virus Database: 337 - Release Date: 21/11/2003 --- Outgoing mail is certified Virus Free. Contains no anthrax or other artificial flavours. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.543 / Virus Database: 337 - Release Date: 21/11/2003 |
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