Houston we have a problem

[Slackshot]

Well guys I have a problem with my Recurves, they all are breaking on the bottom limb. They can be new or a year or two old and that is three so far also my Takedown Longbow did the same but so far with a new limb it hasn't broken. Greg and I cannot work out what is going wrong.

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This break is typical in all of the limbs ,the overlay splits and delaminates from the fibreglass. More pics

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So any thoughts and questions will be answered as this is giving me the willies

[longbow steve]

To tight on the limb bolts, not enough taper in the lams, timber not up to the task? Perhaps use a layup of glass/thinner timber and or phenolic on the pads. Steve

[Slackshot]

Hi Steve...we have not changed the design of the limbs in anyway and the timber is the same as Greg has used for many years and many bows,, Remember it is only happening on the bottom limb
Gary

[Mick Smith]

If you shoot 3 fingers under, it would add some extra stress on the lower limb, but not enough to do that, I would imagine.

In the photos, in the area around the bolt on the bottom limbs, the timber looks to be very weathered and dried out. I don't know if this would have anything to do with it.

It's a weird one alright!

[greybeard]

...we have not changed the design of the limbs in anyway and the timber is the same as Greg has used for many years and many bows,, Remember it is only happening on the bottom limb

Have you changed the riser dimensions / shape such as length and limb mounting angles?

It would appear that something in the bow geometry is over loading the bottom limb and causing limb failure.

All being equal and if Greg's bows aren't failing the archer may be the problem.

What method do you use to string the bow?

Daryl.

[Flatliner]

It looks to me like the glue has failed between the back glass and veneer. What kind of glue are you using? The limb and particularly the edges of the limb don't appear to be sealed too well which could allow moisture into the timber and create a lot of expansion and contraction (given our extremes in weather) and help the glue to fail.

Rob.

[toz]

Hi guys the riser angle is 18deg glue is smooth on , what pressure is everyone using in their airbags when they glue up?

[Flatliner]

I use 65 psi, but that should not effect the bond strength unless the join is starved for glue, the high pressure is more about minimizing the size of your glue line.
What length is your draw? If it's very long, perhaps the limb/bow design is being over stressed.
I also noticed the glass on the back of the limb looks very thin compared to the belly glass, perhaps a little too thin and is being over powered by the belly,,,, just a thought.

Rob.

[Slackshot]

Length of draw is 28/29in and the fibre glass is 40 and 50 th. Greybeard might be onto something we think,,,, maybe the limbs are loading up too close to the riser on the bow and exerting that much pressure in the fadeout area that it gives out if you follow me. This can be fixed by adding more taper in the area that the limb should be working and not so close to the fadeouts. What do you think?? seems like a plan?? thoughts gratefully accepted
Gary

[toz]

Hi again 50thou on the back 40 thou on the belly,I think that I had about 60 lb in the bag?

[Flatliner]

Greybeard might be onto something we think,,,, maybe the limbs are loading up too close to the riser on the bow and exerting that much pressure in the fadeout area that it gives out if you follow me.

The best way to determine if that is the case would be to take a photo of one of the bows that are still working at full draw and see if it is hinging a bit in the problem areas. Kind of like the final tiller on a self-bow.
That is sort of how I designed the limb shape for my recurves, through trial and error and three redesigned forms. Basically made a bow, looked at it at full draw to find how it was bending, then adjusted the form to improve and even out the loading on the limb when it was at full draw not at brace. Which goes a long way to explain the odd little kink my bows have near the fades at brace. The curve looks very even at full draw and you can see that the whole limb is sharing the load fairly evenly.

Cheers, Rob.

[Slackshot]

Hi Rob
Ha ha none of my bows are in working order now.. but yes I see what you are getting too. We have looked at the tiller and dismissed it as every thing is right there, still looking at the fadeout area and why it is failing . We have looked at bows that are many years old and cant see much difference ,Yet !!. But the thinking is the taper has somehow altered in time over the last few bows, That's the next check and thanks for your input Rob
Cheers Gaz

[longbow steve]

Hi Rob
Ha ha none of my bows are in working order now.. but yes I see what you are getting too. We have looked at the tiller and dismissed it as every thing is right there, still looking at the fadeout area and why it is failing . We have looked at bows that are many years old and cant see much difference ,Yet !!. But the thinking is the taper has somehow altered in time over the last few bows, That's the next check and thanks for your input Rob
Cheers Gaz

The heavier the bow the more taper you need to add, the lighter bows can be reduced. What weight bow were they modeled off? Steve

[rodlonq]

Gary,

I have more questions than answers sorry. That is a nasty problem you are faces with for sure.

Maybe the problem is in limb timing. Perhaps the bottom limb is getting home too early and then being pulled back again when the top limb gets home? Has there been much hand shock before the failure occurs? Dynamic problems may not be apparent by looking at the static shape at any point in the draw. Maybe using a high speed video camera to look at the shooting cycle in slow motion may shed some light on any unwanted dynamic effects (when you make another bow to work with).

It looks like the propagation of the failure may be between the glass and the outer lam close to the thin end of the wedge. Is the thin of the wedge fine enough not to cause a step in the thickness?

I also think Rob has a point with the finish. Is it an oil finish or something like that? Perhaps the lam material is not standing up to the stress if the moisture content gets too high or low. What is the lam material by the way?

It certainly must be frustrating to have 3 bows let go in the same way. But it does indicate the offending problem is intrinsic in the current design rather than a random flaw in the lam material.

Or alternatively - are you using heavy enough arrows to absorb most of the stored energy?

Cheers.... Rod

[Slackshot]

Steve, the tapers are made too fit the poundage of the bow, tapers have been anywhere from 50lb to 70 lb to suit ,not the same tapers
Rod,, these bows when they fire have very little hand shock if any and shoot very well until I get a smack in the mouth as the limb fails. wedges are very fine at the tapered end and the usual length as per bows that are working(old bows). These bows have not had any finishing oils or anything on them letting them see how they go first. Agreed on the design problem but what where. Another problem I just thought of is that the overlays were lifting off the fibreglass on the tapered end at one stage by a few mm.. which also indicates unseen forces . Lamination material Tassie Oak fibreglass from Binghams
Cheers
Gary

[greybeard]

they all are breaking on the bottom limb. They can be new or a year or two old and that is three so far also my Takedown Longbow did the same but so far with a new limb it hasn't broken....

...we have not changed the design of the limbs in anyway and the timber is the same as Greg has used for many years and many bows,, Remember it is only happening on the bottom limb

All being equal and if Greg's bows aren't failing the archer may be the problem.
What method do you use to string the bow?

You mentioned that your take down longbow suffered the same fate and as it has been the lower limb in all cases is your stringing technique the villain?

If Greg's bows are the same design as yours and not failing one has to ask the question is it the bow or the archer causing the problem.

I have seen two 70# longbows fail in the lower limb fadeouts because of incorrect use of the step through stringing method.

Daryl.

[little arrows]

and a little voice from the back of the room asks - are you string walking????

cheers
sue

[Ian Turner]

Hi Sue (and others),
Please explain!
Does string walking cause issues with trad style bows?
I have no idea.
Also when it comes to shooting 3 fingers under does the bow have to be specially designed to handle that style?
And while i am asking what other shooting styles etc can cause issues with trad bows?
Cheers
Ian

[Slackshot]

Hi Daryl...Greg has made only one bow in recent times ,,cause he was busy helping me,,,,, But he did make a Takedown longbowish same as mine and it broke the top limb after many shots from it same type of fracture.. My stringing technic has never changed and I would assume that if it was a bad technic they would break whilst the stringing process is taking place ?? Hi Sue I don't walk the tight rope and in answer to Ian Turner, in my opinion string walking would not make the slightest difference,, nocking point would change with three fingers under so no the bow would not be especially designed. I prefer one above and two below. The plan for the next weekend is to measure all my risers (angles etc} and carefully look at all my limbs and compare to known recurves that have past the test of time
Thanks again for everyone's input
Gary

[Slackshot]

AAH HA...would the positioning peg in the mould make a difference ?? Me thinks that it would as the curve is a lot closer to the wedge and therefore making the limb flex down nearer to the riser,, ,just a thought as everything else looks OK