Primitive Archer
Main Discussion Area => Bows => Topic started by: DC on January 11, 2017, 12:47:33 pm
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Does anybody have a slick method of telling if they are clamping a glue joint too hard? I want to try another glued on riser and my success has not been stellar. I was just looking at a bow on Simpsons site and I'm sure my bows have been thicker in the handle(before riser glue-up) and the joint has separated where it feathers out. I'm wondering if I'm clamping all the glue out?
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I've have similar problems with other woodworking projects, and a horn bow splice in the past. Less pressure is more in this situation. Gentle pressure is all you need. I know, that's pretty subjective, but don't squeeze living tar out of the joint and make sure you do a good sizing coat before glue up, and let the wood soak up what it can before clamping. This has even worked on a slightly flexing handle for me, although it was intentional nor do I recommend it.
Eric
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It's that magic thing called "feel". I use rubber strapping and just heave it as hard as I can and make sure that I have at least 2 layers, pretty foolproof. It's probably easy to over tighten with G clamps or a vice, I'd go with firm figer pressure. Problem with clamps is getting enough to give even pressure IMO. I've seen some horrendous pics where there is only one clamp every 4" or so :o
Del
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I do it 3 ways, is there enough friction, look up into the light if you see light coming thru its a bad fit, and thirdly use a piece of thin paper or feeler gauge. Use more than enough glue and apply on both pieces.
Clamp tight enough to get glue squeeze out all around. That pretty well covers it.
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different glues like different clamping pressures. have you looked at the location of the glue line in respect to where the limb stresses intersect the handle?
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I've found with tire inner tube wraps you can't wrap too tight. Almost fool proof.
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Baker goes into detail in TBB 1 regarding how much pressure to apply depending on the type of glue used.
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If it is a board bow spring clamps work just fine, on a stave innertubes are the way ro go, if you see theglue moving in front of the pressure it is plenty tight
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An email to the glue manufacturer will get you the datasheet. This will have optimal clamping pressure on it.
What said above is all good advice too.
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I prep handle add ons by mating them as good as I can get them (no daylight visible between them anywhere), then prep all gluing surfaces with an ever-so-slightly convex toothing plane blade, just until the teeth reach full depth, glue with Smooth On epoxy, or Unibond, and clamp good and snug with C-clamps... with a shop light nearby for warmth. Haven't had a problem since. It would be really tough to starve such a joint with any 'normal' amount of clamping pressure.
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DC, are you gluing a handle piece on a board?
That is difficult to do properly.
It may not be a question of staving the glue joint.
The handle needs to sit on top of the board proper and feather into into the board itself.
I wish I had a photo of that.
I don't because I make bend in the handle board bows.
Jawge
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George's statement is a possibility but A friend of mine that makes FG bows and uses smooth-on always says 60 to 70 pounds of pressure if you want a number on that kind of glue.If a wood is not sized properly starving it does'nt take much with too much pressure.All the statements of feel/seeing it ooze out good/using enough/dry fit properly/different type surface for different type glues are all correct.
Usually the only type glues I use for wood joints are hide glue/smooth-on/ superglue/Tite bond 3.C clamps and inner tubes is all I ever use for clamping.
It might be informative to state what type of glue you plan on using.
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It's Ocean Spray staves. I can get the pressure from the manufacturer but they are going to say 100psi or something. How many turns on a C-clamp is that? How many tube wraps? Clamps and tubes don't come calibrated.
Is very dense wood harder to glue?
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gap-filling glues like smooth on or epoxies require little pressure, just enough to ensure gaps are filled. If clamped too hard they will ooz out and the joint won't be as strong. Any glue that shrinks like titebond, wood glue, or hide glue you need an almost perfect fit, and lots of pressure is good. I may be mistaken but I think the gap filling ones don't soak into the material like the non-gap filling because they are usually designed to glue nonporous materials together like metal, plastic, and glass. So if there's too much pressure there isn't any glue to hold the material together unlike the wood or hide glue which soaks into the pores so it doesn't matter if a lot is squeezed out.
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On a board, and i have done a lot of board bows spring clamps and a good fit are all you need. On a stave you need a good fit and either stretch wrap or tubes will work, if you can see the glue moving ahead of the pressure you have enough pressure we ain't building glass bows and you aren't laminating the whole bow. How much are you building it up leather, rawhide and cork can all be used to fill the hand any way you want
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OS has a bad habit of splitting through the handle. I have cut a "V" along the split and inlaid a piece but it's a lot of work to get a good fit. I have also filled the crack with bondo or sawdust and epoxy. The couple of times I have cut the handle off and tried to glue on a solid handle it has tried to pop off. I always use West105/205 epoxy. I'll try again. This time I'll score it lightly and use less pressure.
As an addition, when the handle tried to pop off I flooded the crack with CA and the joint held after that. Does that sound like it may have been starved the first time?
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DC
do you use a filler or thickener with the 105/205? I have used cabosil in the past, but avoid fillers on critical or difficult to glue joints.
I have had good luck with using time and temperatures modifications to the resin without fillers.
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I usually use a little Cabosil and I have a small oven(box with a lightbulb) that goes to about 120 degrees. I can't say for sure if I used both of these on the joints that popped. I've been doing a little reading about clamping pressure and it appears that I am using way too much, especially with epoxy, so I will modify my methods. I will have to prep a stave and pop it in my hot box for a few weeks and see what happens.
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DC....If done properly smooth-on does go into the pores.The wood needs to be warm along with the glue and a 36 grit surface is your best type of surface to use.C clamp pressure is a by feel thing and inner tubes as tight as I can get them.I personally have not had a failure from doing it this way on quite a few different bows.If done properly with smooth-on the wood will pull apart before the glue line will.
A person can calibrate a C clamps pressure if you think hard enough.Inner tubes too.By just using a poundage tester,but I really don't think it's necessary.I think you are over thinking this problem.I never turn a C clamp down as hard as I can.After contact just a couple more turns is all without much effort.
Wood glue like elmers and tite bond do not shrink.Neither does epoxy.Only hide glue shrinks.Hide glue can pull pane glass apart or etch it so to speak.That's as smooth a surface as your gonna get.
I'm speaking from using all glues I've mentioned extensively.
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Your handle belly I would fill in with strips or slivers of wood or maybe even combed flax with smooth-on.Extend fades a little if possible.I then would wrap handle with sinew or nylon and smooth-on.Then sew a wet piece of thick rawhide around the handle too.I would feel pretty confident of that holding together.Bomb proof!!!
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It's strictly an appearance thing. I am quite confident using those cracked handles. I have filled them with Bondo which has almost zero strength and had no problems. I just don't want them to look like a cobbled-up piece of crap.
PS the piece of crap I was referring to was the bondo not your idea Ed. Sorry if that came across wrong.
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I know you are using a stave but wanted to show this handle was glued and clamped with just spring clamps(http://i623.photobucket.com/albums/tt320/bubncheryl/build-a-long/Picture017.jpg) (http://s623.photobucket.com/user/bubncheryl/media/build-a-long/Picture017.jpg.html)
(http://i623.photobucket.com/albums/tt320/bubncheryl/build-a-long/Picture016.jpg) (http://s623.photobucket.com/user/bubncheryl/media/build-a-long/Picture016.jpg.html)
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Nice joint Bub
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DC, V cuts were such a pain in the rear, I just went to a squared up kerf by using the table saw. easy to slip a cut slat in to. Works best if you have a way to clamp it the same for each pass, but maybe 4 hacksaw blades bolted together on the ends would clean up the cut enough?
Anyway, other than that it's all been said EXCEPT..... I have had a lot of trouble with some woods cupping a lot more than others when using water based glues, even TB III. Thinner belly slats do it more, like a 3/8" thick belly lam would cup more than a 1/2" one. Goncalo alves was the worst for me, but other woods will do it, too.
I would check my fit, and be really happy. Then, when I wet the surfaces with sizing or applied glue, the whole slat would cup, turning the edges down and the glued side convex, bulging uip lengthwise in the middle. It's amazing how strongly this would defy the clamps, especially rubberbands, creating a tiny gap all along the edges between the backing and the core. Then I'd have to mess with adding more glue to the edges and reclamping here and there, or trapping the limbs to see if it would go away.
I started wetting both sides and waiting a few minutes to see what the wood was gonna do, then gluing when the surfaces were mostly dry.
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Thanks DC