Maple-Birch laminate woes!

[Loa]

Hello,

By reading Tim Baker's list of bow woods, I decided to  try and make a maple-birch laminate pyramidal flatbow (2 inches at the flares and 1/2 inch at the tip.

I gave the first one a decent perry reflex (about 4-5 inches), and kept the second one flat. The reflexed one has a very nasty propeller blade in one limb, and flat one broke during tillering. (included a few pics of the one that blew.)

My first guess is that my back (maple) was too thick.

Are these woods a bad combination, or have I just been unlucky?

Thanks

Loa
 
   
   
   
   
   

[PEARL DRUMS]

Looks like the glue let go?

[Loa]

Hello,

Well, I hope not. It was TB III, and I know how to apply glue.

Loa

[vanillabear?]

[don s]

did you round the edges of both back and belly? the pics looks like your edges are a  sharp 90 degrees. don

[4est trekker]

Here's a few of my observations (some repeated from above) for what it's worth that I think led to the bow's failure:

1) Judging from the first pictures, the grain runout on your BELLY lam looks like the one of the likely culprits (although I think the others below contributed as well).  It's pretty severe and the limb appears to have sheared right along that plane.

2) Birch is not very well suited to bow making.  So, too, is soft maple (commonly sold at home improvement stores), assuming you used that for the back.  If not, then you used a much harder maple, which definitely would overpower that birch, especially at that thickness.
 
3) Your maple backing is too thick.

4) You need to round ALL edges or your bow more before beginning the tiller process.


Hope that helps.

Regards,

Curt

[Loa]

Hello,

It's hard (at least with my limited experience) to confirm your ideas about grain runout. I certainly don't see a "spike" of wood that looked like it straight-up peeled.

I did fear that the maple was too thick, but I didn't know I had to round my edges. I've made a couple of self-bows without a hitch without rounding any edge. I'll remember this when I'll try my next laminate.

Thanks for the inputs.

Loa

[Pat B]

I agree with what was said about. My first thought was the grain of the backing ran through the backing too steeply. I think that was the main problem. Also rounding all edges will help to prevent splinters from lifting and causing a break.
  I think you put too much Perry reflex in your stave. It was more stress than the backing could handle. 3" or so Perry reflex should be plenty without over stressing the wood.
  The reason(s) it twisted was eiother the wood grew spiraled in the tree or your glue up was twisted or the backing and/or belly wood wasn't consistant thickness.