Torges patch question

[Del the cat]

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

[bradsmith2010]

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,,,,

[Dances with squirrels]

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.

[bradsmith2010]

good to know , thanks

[Eric Krewson]

This patch lasted a couple of years;



This was a radical attempt to save a friends failed ELB, it didn't work and failed after a few shots.

[mikekeswick]

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.

[Del the cat]

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.
 

[Hamish]

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.

[Marc St Louis]

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

[PatM]

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.

[Dances with squirrels]

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.