Primitive Archer
Main Discussion Area => Bows => Topic started by: sleek on October 26, 2017, 06:36:45 am
-
Can a torges belly patch in the working limb be done with only CA glue, or is another glue required? I hinged a limb and have made it deeper a little and a lot longer, so now I want to laminate a belly slat in place and rwtiller it, tapering it out to a feather.
-
I have only done a couple of these patches and used Urac for both. I found that these patches fail over time, one lasted a few months, one lasted a couple of years. Both patches failed with the patch wood developing stress cracks, none of the patches came loose.
-
Both CA and fast curing epoxy will probably crack in working areas, I tried both and it did not work. I used smooth on for another and that bow still shoots after thousands of shots
-
I don't think that CA would give you enough clamping time and it tends to be a little brittle.
-
Laminate a belly slat? I thought we were talking about a Torges patch. A Torges patch isn't a slat or lam. We need more details, or pics.
-
Thanks for the replies, i suppose I will just cut the messed up limb off and save the good one.
-
Thanks for the replies, i suppose I will just cut the messed up limb off and save the good one.
Try a long gently curved patch, it gives more glue area. You have nothing to loose trying if your are thinking of cutting it off anyway.
Del
-
the nothing to loose suggestions sounds positive (SH)
-
Totally agree Del. The Torges style patch is too short, in relation to the depth. Still need to used the best tried and true glues for saftey, and durability.
-
From a stress standpoint, you want 25 times longer than deep.
-
I doubt Dean would be comfortable with this patch being named after him. ;)
-
Lol, its the idea of the patch he developed, but i am of course, modifying it to fit my circumstances.
-
I mean he did not develop the patch. He just brought it back to our attention.
I think Del mentioned seeing a bow collection from the Victorian era with this type of patch.
-
From a stress standpoint, you want 25 times longer than deep.
For a compression patch, you would want more depth and less length, If you had a router that would cut a nice flat spot with square edges you could barely squeeze a patch into it would be better than one that tapered off slowly.
-
Well, i guess that makes sense. Im used to thinking about tension stresses. But good reference for next time. On this one, im either going to cut and splice a new limb in, or grind the belly down till its real thin, and laminate a new belly on. Honestly, I really like the idea of a new belly. Alot.
-
My favorite Osage shooter many years ago developed a hinge mid limb In the upper. I band sawed a small piece of Osage to match the dip in the limb where the hinge developed. Mixed up a batch of Resorsinal and clamped it up. Re-tillered that Bow shot hundreds more Arrows and was going strong when it was retired. Go for it, think it thru - but I wouldn't use the CA. Resorsinal leaves a dark glue line, but is still My favorite :OK. Bob
-
From a stress standpoint, you want 25 times longer than deep.
For a compression patch, you would want more depth and less length, If you had a router that would cut a nice flat spot with square edges you could barely squeeze a patch into it would be better than one that tapered off slowly.
Indeed, that would be fine and wouldn't even need glue!
IMO the deep semicircular style patch combines the worst of both worlds! It has angles that will make it try and "orange pip" out and a small glue area.
Del
-
Circular has angles? Not any patch I ever did, which were radiused patches in fully radiused bellies.
Small glue area? It's ALL glue area, and the glue line stresses are better distributed than square or rectangle patches with ends and corners within them..
I've used the patching method Dean described only a few times, but with great success... in fact, without a failure. It works good in the right application.
-
I tried a tight fitting square patch, it didn't hold up for any time at all.
-
I tried a tight fitting square patch, it didn't hold up for any time at all.
I never actually tried one, the Torges type is the only type I have actually tried and it did work. I just don't like patches in a bow, I never feel the same way about them once they have been patched.
-
I'd grind the belly flat on both limbs, add a new compression strong lam(osage, ipe) to each and retiller. I've done this on a few bows that fretted with good success.
-
Circular has angles? Not any patch I ever did, which were radiused patches in fully radiused bellies.
Small glue area? It's ALL glue area, and the glue line stresses are better distributed than square or rectangle patches with ends and corners within them..
I've used the patching method Dean described only a few times, but with great success... in fact, without a failure. It works good in the right application.
Hmmm,
1. Have you never squeezed an orange pip or cherry pit and had it shoot out across the room? (they are roughly circular in cross section).
2. Of course a circle presents angles to the compressive force. I'd drawn a diagram to explain.
3. A shallow curved patch say 3/16" deep, 1" wide, and 5 " long has more glue area than a patch 1/2" deep 1"wide and 2" long.
Hope this clarifies it
Del
-
I like the idea of grinding thinner and putting a lam,,, not really a patch,, but re designed,, -C-
-
Del, your drawing seems to have been done with a bias of preponderance to fail. Is this due to your experience, or just theory? If you'd have drawn one you were determined would succeed, as they often do, I suspect it would/should look different.
If we were to assume, as you did, that an arc/portion of a cylinder presented 'angles' by interceding with compressive forces, we would have to assume there were an infinite number of them, each at different angles, because it's a force vector interceding a portion of a cylinder(of identical material btw), and often an oblique arc/cylinder, which also helps dissipate the force in other vectors as well.
But I'm not even sure I buy all that 'angle stuff'. If the glue joint is properly done, it's at least as strong as the wood itself... and if the wood for the patch is carefully chosen from the same species and/or actual tree and ring and grain bias, then just-as-gradually-tillered and taught to resist the forces of compression as the balance of the limb was, the forces transfer into and through the patch, along the same lines as they did anywhere else in the limb. No problem. This hypothesis aligns itself more with what I've experienced in actual results. It's not a piece of polished titanium we're putting in there.
Hey, I like physics as much as the next guy, I'm just telling you guys it has worked really well for me... and is relatively quick and easy, compared to grinding the belly off one or both limbs and adding a lam, or replacing an entire limb, and reshaping and retillering the bow.
-
In fact, on the bows I've done patches on, it would have been easier to start another one than to cut off the handle, accurately grind the radiused belly away off of a bow glued into a d/r or recurve profile.... ever try that? good luck on that one... then add a lam of wood, reshape, tiller, etc. Yeah, much easier said than done.
-
Squirrels,, I get your point,, and I am sure it would be easier,, I have not tried it,, so your positive experience is noted,,
knowing how stressed sleek makes his bows worried me about the patch,, so I am leaning toward the more difficult solution,, thats just me and I understand if someone wanted to patch,, :) not saying it could not work or might not be the best solution,,,, (-P
-
Brad, I'm not saying it's the best way to go on his bow either, we haven't even seen it. Just saying that it can work well when the application DOES suit it. I've used it mostly on smaller areas, like where a fret or crack happens in an isolated area like near a knot.
-
It's a moot point since it's really only a viable option in a radiused "flat" bow belly or full D in a longbow.
A wide rectangular limb just doesn't have the cross section profile that lends itself to the scooped out patch.
That's where the whole limb patch is a better option.
-
I may as well disagree with you too, Pat. Lol. I don't see why the same thing couldn't be done in a flatter flatbow.
-
It will probably become clear when you try it. ;)
-
Del, your drawing seems to have been done with a bias of preponderance to fail.... etc
Hmmm You fall into the classic internet argument/discussion mode of failing to answer the points made.
I have no desire to be "right"... but it would be nice if you could actually say if you have ever squeezed an orange pip or a cherry pit.
Because if you have, I feel no further explanation is required.
Your comment about the infinte lines of compressive forces needing to be at different angles shows you don't actually follow the diagram.
The lines of force all run the same way (parallel to the belly)... the changing angle is from the steep curve of the patch which presents a progressively shallower angle as you progress deeper into the wood, . so near the belly the force is almost perpendicular to the glue line, and near the bottom of the patch the force is tangential to the glue line. (see pic)
I'm sure patches like this can be ok if they can be shaped accurately enough. The main point is that a longer thinner patch can be made to fit more easily because it is flexible.
Also I didn't draw it "to fail" I drew it based on illustrations in Dean Torge's published article on the technique!
As always, I just give my opinion, based on my experience and I even reserve the right to wrong.
Del
Just to clarify the illustrations show the belly of the bow at the top. They are a view on the side of the bow and not a view looking at the belly
-
as stated I have not tried one,,, on a lower stress bow,, or a bow that could be tillered as to take some stress off the patch,, leaving that part of the bow stiffer,, I think there would be higher rate of it holding,, also if the draw weight of the bow was reduced,, or if the bow was lighter weight to begin with,,,,
-
Brad, I don't construct them or tiller them in order to baby the patch. I want the patch to work like the rest of the limb. The bow pictured above is a fairly highly stressed semi-recurve design. 60" ntn and 65# @ 29". The outer limbs were kerfed with an additional osage lam slid into the recurved section, which if anything, adds even a bit more stress to the mid and inner limb areas of this bow. The patch is located approximately 3-4" outside the dips... it's working pretty dang hard... and now dyed and sprayed, you'd have to be told it was there and then hunt hard to find it. It looks as solid and integral now as it did 7 years ago.
Del, I follow your diagrams. I just don't fully agree with them. I didn't comment on your cherry pit comment because I think it's not directly relevant to our discussion, and I was trying to be brief. I understand where you're going with it, but I think the relationship of these patches to the bow limb are more complex than you believe or show in your drawings. The one I showed a picture of was ground through any compression forces, through the neutral plane and right up to the backing strip, at least along the outer edge... yet it wasn't ground across the entire width of the limb. It's ground into the limb at an angle. Why grind across the entire width of the belly if you don't have to? ... and grinding them at an angle, too, helps incorporate them. Another positive aspect of this type of repair.
Since the day this patch was tillered into this bow, it has acted homogenously with the limb. There have been thousands of arrows shot from it, and it practically looks like the day I sprayed it... other than the dye has faded a bit.
Again, if properly mated, prepped, glued in, and tillered, the joint will be strong, quite strong, which means the glue joint isn't an issue.... and so long as the glue joint isn't an issue, the 'outside' wood trying to 'spit the pit', can't.
-
good to know , thanks (SH)
-
This patch lasted a couple of years;
(https://i.imgur.com/HNQGDFu.jpg)
This was a radical attempt to save a friends failed ELB, it didn't work and failed after a few shots.
(https://i.imgur.com/f7U05Dw.jpg)
-
Del the compressive forces are only in the outer couple of mm, not all the way into the limb - so if you squeezed that pip at just the widest point it wouldn't want to go anywhere. DWS has a point about the gluejoint IF well done. This method requires perfect shaping of the parts, the concave is easy but the plug requires much more care. I suspect this and incorrect clamping pressure are where most people go wrong, also not letting/making the plug compress before blending into the limb.
I've used this method on a couple of bows years ago and they held but I gave them away in the end (haven't heard anything bad!). Personally now if a bow chrysals it is in my wood stove pretty quick and anyway I don't make hinged bows anymore ;) ;)
Eric that bottom patch doesn't look too clever, even if the patch held the rest of the wood around it wasn't up to the job anyway.
-
Yes Mike.
But the two points which have been repeatedly ignored (not by you) are:-
1. The difficulty of getting a good fit with a short deep stiff patch, compared with a longer shallower more flexible one.
2. Improved glue area with a longer patch.
Of course I've used deep short patches where appropriate and indeed I've done a double one on a Warbow repair (not one of my bows) which had two pinches. I went deep to remove the underlying knots and actually turned the plugs on the lathe to ensure a good fit. However I overlayed the deep patches with one long thin one.
It's about using techniques that are appropriate to the task in hand.
Del
PS:- You said "so if you squeezed that pip at just the widest point it wouldn't want to go anywhere" . That only applies if a patch is fully semicircular and you are squeezing across the diameter.
-
I like your belt and braces solution Del. Increasing the surface area of a glue joint and reducing the angle of the feathered exposed surface gives you the best chance of success. So much safer than the ice cream scoop patch.
-
Tried it and didn't like it.
Most modern glues are not well suited to this fix as they are a plastic (read pva and alphatic resins) and consequently have too much flexibility; might be a different story with hide glue
-
Even Dean struggled for a long time before figuring out this patch. Hr mentioned that essentially nothing but Urac was up to the task. It really does sound too fickle for most. Especially if you don't have the tools to scoop out the area and make the insert.
-
Of course we'd do well to work with the proper tools, materials, glues, and knowledge when taking on ANY task, not just this one... but it doesn't require a professional wood shop or machine shop to do. I've done these with a cheap spindle sander and didn't find it difficult at all. No, it's not for everyone or every application, neither is the patch Del showed above, but we should be mindful not to dissuade those it may help.
Good job on that yew bow, Del. Makes perfect sense there. I understand the merits of the longer, flexible patch, where applicable... but I won't be grinding most of the belly off of a tillered bow to replace a single isolated issue.