Trad Gang
Main Boards => The Bowyer's Bench => Topic started by: Krasus on January 31, 2015, 01:46:00 AM
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Just had my second bow explode due to a glue void in my limb. Only built 3 bows so far. I just got some aluminum strips for my clamp ups. My trilam looks good that I just glued up using them with my claps. Nice smooth curves. No kinking.
It is just my inexperienced with my glue ups? Pointers and tips would be great.
Thanks gang
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what glue are you using, white glues need smooth, perfect mating surfaces- unibond and epoxies are gap fillers and like the surfaces to be roughed up.
neither glue likes over clamping- which leads to glue starvation.
any pics etc, and of your clamping system will help folks give an opinion- sorry to hear that your bow failed
keep on keeping on!
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Will you post pics of the break. It might be other than the glue.
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I'm using smooth on ea40. I rough up all surfaces and then I cook it in my heat box at 170 f for 8 hours. Then allow to cool over night.
No pics yet. Still trying to figure out how to post them.
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well sounds like you are doing everything right. the only concern now is possibly glue starved joints. but like pat says pics will help heaps.
i am not saying clamps dont work- a lot of folk get them to work extremely well, in fact. i just dont think i am smart enough to get them to work- too many variables for me- :D thats why i rather use the airhose- or rubber bands- but just whatever you can make work is good!!
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How old is your glue?
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The thing I don't like about clamps is as the glue squeezes out, the clamp pressure decreases.
When doing a riser, I tighten slowly and take my time, checking several times before it goes in the hot box. Still the clamps aren't as tight when you are done....
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Never liked using clamps.
If your not using the fire hose method. I would recommend using tire tubes. I have always had problems when using clamps... even pressure is always my problem. That being said. I do use them around the riser only.
Make sure you butter both mating surfaces, and have no voids. Once you have brought two mating surfaces together, don't pull them apart. Try your best to get them where they need to be the first time.
These are just a few things that I do. Hope it helps a little.
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How old is your glue?
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Glue is maybe 3 months old. I'm super careful when mixing my part a with part b. I use separate spoons and a separate mixing spoon.
The clamps I use are just 2 inch spring clamps (nice even pressure). I do 2 clamps every 3 inches. I also use 2 strips of 1/8"aluminium (on top and one below) my lams to distribute the clamping pressure evenly.
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sounds good!!???!!
do you have a photobucket account- set one up- its pretty easy- also can try imagelinkey
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I have been quite lucky even using TT3 with some slight not so good mating surfaces. I rough all pieces with 50grit and use a vacuum cleaner to clean the mating surfaces. I believe this is best becasue it gets all the microscopic particles deep down in the wood fiber.
Take it for what its worth but I have not had a glue failure since...! Bad design Yes......Bad tiller Yes...! Overstressed Yes..!
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Oh. . I never even thought of that. Good one thanks
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How are you preparing the lams?
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I rough all of them using a pull scrapper I modified with a section of hacksaw blade. Works great to rough up the wood.
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Dumb idea but you guys who mentioned not liking clamps and in-consistent torque issues. Couldn't you rig a special socket (couple slots to accept the clamp handle) on a torque wrench to get even pressures at the clamps at least?
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I don't have a lot of faith in spring clamps.
I've also read where a hack saw blade is not the proper tool to rough up the surface. I use a toothing plane on all surfaces that will be glued together. Then blow the surfaces off with an air hose, then wipe them down with denatured alcohol. I apply a nice coat of glue on both surfaces with a paint brush. I use unibond800, so a paint brush would be tough with smooth on. I pad the back and belly of the bow so my clamps don't indent the surfaces. I place a clamp every two inches, alternating their position from side to side. I snug down the clamp and then go about another 1/2 turn.
(http://i47.photobucket.com/albums/f165/ROY-CHRIS/2014bow6.png) (http://s47.photobucket.com/user/ROY-CHRIS/media/2014bow6.png.html)
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Roy you are right about the hacksaw blade.Rip up your wood to a bunch of broken splinters and thats what you have holding your glue just broken splinters not solid wood.Why attach to wood that is already broken up?
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I'll give the toothing plane a try. I don't use c clamps cause once you heat them they loosen.
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cut your oven time down. I only go 4 hours
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Very possible that you are getting hot spots. If the thermometer is reading 170, it may be hotter in other parts of the box. 212 will damage wood and glue.
the 8 hours isn't the problem and not likely the grit either as I know of guys finishing veneers with 120 and glass is only 80.
Glue starved gets blamed for a lot of things that we can't explain. More often it is another problem all together. If you peel a perfectly good lamination apart (pretty easy to do) It will appear as there is no glue present..or very little.
BigJim
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Out of all the bows I have built and blanks I used to sell the only delamination fron SmoothOn I had was from over heat.
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My heatbox is pretty getto. Lol I'll try heating for less time.
My first trilam glued up perfectly. I've already tillered it and no issues. Didn't do anything different from what I had been doing on my glass bows. Starting to think I'm not going to work with the glass anymore.