New bow gone bad....

[Tunames]

Just finished my first glass bow today. A binghams "pronounced" take-down. The riser is Cherry with maple & paduke accent. Minimul shots and strung just enough to tiller account it's righthanded and I shoot left. I drew it back for a couple of shots and creeeeeek. Tried to draw again and the same thing. closley inspected and hairline cracks along the accent stripe! any Ideas as to why? Glued with smooth-on. could it be over clamping of glue joint? poor design? bad luck?......

[broketooth]

i see it. and this is my guess look at the grain of the wood in the riser. it will be stronger if you turn the grain 90 degrees to the limbs. so when you draw the bow the riser wont have flex or very minimal at best. i dont know how to make marks on your pic to show what im talking about  but i do know if you turn the grain so it is perpendicular to the limbs your riser will be stronger    oh by the way nice choice of color woods. get you another riser block of the same woods and make another should be an easy fix@ minimal cost too

[TradBowyer]

if you are laminating your risers, you must make sure that the wood is "pre-dried" before you laminate or the wood will shrink and pop your gluelines (exotics especially). I have a drying box that I put all my riser wood in for a week or so before I'll work it. Nothing worse than having glue lines pop. Ever since I started drying my wood, i haven't had any issues....knock on wood.....

[Tunames]

I went back and forth on which way the grain should run. Do you Cherry is ok for a riser? Where the accent ends is in between the end of the bow and the bolt. effectivly giving the limb "leverage" to pry apart the glue joint. is that a problem?

[bjhaug]

Yeah, that's the weak spot.  Having the grain run the way it is in the accent strip is allowing it to fail.  If you think of wood grain like corrugated carboard - if you try to bend it perpendicular to the ribs, it's tough to do (that's the way that broketooth was saying to run the grain), but if you try to bend it parallel to the ribs, it's easier to do - that's the way the grain is running in your strip.  

I'm really bad at explaining things, so bear with me on this.  If the bolt is at the base of the limb and the bow is drawn, there is a pivot, or hinge point at the end of the riser that's opposite the bolt.  This force will act on a arc coming from the bolt, down through the limb, with the focus of the force on the edge of the riser.  That force from the draw is what caused the split.  The force found the weak spot and did it's thing.  

It's a beautiful riser though.  If you have a way of re-creating it with the grain all running the same way, it'll be a sure thing!

[Tunames]

So the general consensus is just Grain. Shouldn't the glue handle a little flex? It holds up ok in the limbs....

[Pennsyltuckey pete]

I am still learning about bow building too so take my input as that of a novice.  Tunames, did you tooth the wood and the accent strip? I can see and understand the points about leverage and the grain. I have seen glue joints hold while wood is torn apart. I am thinking it is a glue issue.  again rookie input here.

pete

[bjhaug]

Well glue isnt an issue if it is actually stronger in tension or compression than the wood can create through expansion and contraction.  Smooth-On is one such glue where you can glue perpendicular grains together and not have to worry about it failing due to expansion and contraction.  

In the case of this handle, I think the only reason why it failed is its position relative to the limb.  If a pad were to be added to the end of the riser to cover the edge grain of that accent strip, say 1/4" - 3/8" of a good hardwood, I dont think it would fail.

[Tunames]

Well good news and bad closely inspecting (with a magnifying glass) there are no cracks! in the glue line. I had finished it with Deft laquer when bolted together and drawn at about 25 inches it creaks. So there is flexing in the limb to riser joint. I cleaned it up with scotchbrite and waxed it with auto wax. I think I'll just call it "ol creaky" and stick with one peices......

[Bjorn]

Nice job and good woods! Try applying bees wax to the surfaces that mate together-where the riser and limb contact. Rub some on the bolts too and don't overtighten.

[Tunames]

My final post on this thread. I unbolted the limbs to wax them and at that time I remembered that I hadn't glued in the locating pins yet! they were just setting in the holes. A little epoxy and 24 hrs. later NO NOISE. thanks to everyone for all the suggestions. I learned alot from this build starting on a new form for a one peice R/D longbow. Im sure I'll have a few questions on that as well.....