2 HLD failures

[Onebowonder]

Too bad about the bows. 

My take on this design is that, although interesting, it is not a viable method of making a reliable wood bow.  Sure you may get some that will survive, for awhile, but unless you are using wood that has a very high elastic modulus then the bow is sure to develop problems, sooner or later.

I haven't built any HLD's so, what do I know, ...but nothing that I see in the work presented here would lead me to conclude that HLD is not a viable method for making a reliable wood bow.  I know you have a very high degree of bowyer expertise, and I do not mean to call that into question.  I'm just curious, - - - What are you seeing here that causes you to suggest that?  It just seems like a very broad leap to a very distant conclusion.

OneBow

[PEARL DRUMS]

I concur with Marc, but boy I don't want argue my feelings. I completely respect Simons work just as much as Marcs. But I have my own feeling on high and low points working and HLD bows. I think Simon needs to trademark that "HLD" term btw!

[Smokedancer]

I'm still getting my head around this whole concept of hollow limb design - it blew my mind when I first saw it on here... seemed so counterintuitive to have so much compression force acting on two narrow ridges of belly, but I kinda get it now that the force is absorbed by the flattening out of the bow's cross section.

Could one explanation for these failures be that the walls of the HLD weren't sufficiently thin to allow enough of this flattening out effect?

[rossfactor]

Both these woods are low density, and probably not very elastic.  I wouldn't throw out HLD as a viable option based on failures with these wood types. It is probably a design that favors highly elastic woods, considering that there are additional force vectors (not simply compression and tension) which factor substantially in this design.

Gabe

[IdahoMatt]

Both these woods are low density, and probably not very elastic.  I wouldn't throw out HLD as a viable option based on failures with these wood types. It is probably a design that favors highly elastic woods, considering that there are additional force vectors (not simply compression and tension) which factor substantially in this design.

Gabe

+1

[Carson (CMB)]

Thanks for sharing these failures rather than just sweeping them under the rug.  I am surprised to see members dissing the hld design because a non-bow wood and borderline bow wood blew up on you. 

I always enjoy your bows simson.  I am working on my first HLD, and of course it is from a highly reflexed low-density bow-wood, cascara.  working towards brace now, and it is quite clear the design allows a stiffer limb with less mass.  It is also clear it is going to take study and practice to properly execute.  Just as a square limb cross-section has an optimal width vs. thickness for given bow length, weight and wood type, so does the HLD have a optimum, but it is more of a wall thickness vs limb depth relationship you are working out. 

[simson]

Some guys obviously didn't read my first post. To say it clear:
The sumac gave up because it was a high stressed  no-bowwood.
The elder blew up because I had it at 30" for some seconds while struggling with the scale, it was tillered to 28" but had potential for more.

Yes the failures are the important ones! They tell you for sure what you only surmised before.
The chrysals are the most interesting to me. Yes they go right across (great!) but they appear from the photos to be worst at the edges? Am I right here? The tension break is also a good thing in my eyes it shows that the wood is being made to work properly with reference to it's properties. As in bows normally fail in compression due to (most) woods being stronger in tension. To be fair I haven't done many bend trsts with elder but I would presume its a tension strong wood. On a side note have you ever hada compression fracture with elder?

Mike, the chrysals go around the ridge, think on a cross section - the fractures appears on the entire belly and the outer third of the limbs. And yes I'm with you elder is a tension strong wood and very elastic. I never had compression fractures with elder.

Too bad about the bows. 

My take on this design is that, although interesting, it is not a viable method of making a reliable wood bow.  Sure you may get some that will survive, for awhile, but unless you are using wood that has a very high elastic modulus then the bow is sure to develop problems, sooner or later.

I'm convinced this is a great design to save mass and it has other properties too. Meanwhile I have made at least twenty  bows, some still in my possession and still in use. They are very fast and save. But we should work on that and share the experiences.
I'm waiting on your HLD.

I concur with Marc, but boy I don't want argue my feelings. I completely respect Simons work just as much as Marcs. But I have my own feeling on high and low points working and HLD bows. I think Simon needs to trademark that "HLD" term btw!

.... trademark .... LOL

I'm still getting my head around this whole concept of hollow limb design - it blew my mind when I first saw it on here... seemed so counterintuitive to have so much compression force acting on two narrow ridges of belly, but I kinda get it now that the force is absorbed by the flattening out of the bow's cross section.

Could one explanation for these failures be that the walls of the HLD weren't sufficiently thin to allow enough of this flattening out effect?

examined the bow (the pieces) once more - I don't think so Smokedancer!

Both these woods are low density, and probably not very elastic.  I wouldn't throw out HLD as a viable option based on failures with these wood types. It is probably a design that favors highly elastic woods, considering that there are additional force vectors (not simply compression and tension) which factor substantially in this design.

Gabe

Sorry Gabe, but especially elder is a very elstic wood.

Thanks for sharing these failures rather than just sweeping them under the rug.  I am surprised to see members dissing the hld design because a non-bow wood and borderline bow wood blew up on you. 

I always enjoy your bows simson.  I am working on my first HLD, and of course it is from a highly reflexed low-density bow-wood, cascara.  working towards brace now, and it is quite clear the design allows a stiffer limb with less mass.  It is also clear it is going to take study and practice to properly execute.  Just as a square limb cross-section has an optimal width vs. thickness for given bow length, weight and wood type, so does the HLD have a optimum, but it is more of a wall thickness vs limb depth relationship you are working out. 

YES
Oh man Carson!
I can't wait to see your HLD!!!!!

[Marc St Louis]

I heat-treated an Ironwood bow several years ago that had wide limbs.  The heat did a very odd thing to the wood, it made the belly concave to the point that it was very similar to your hollow limb bow.  The first time I braced the bow one of the limbs split right in half from handle down to very nearly the tip.

Your Elder bow, even if held at full draw for several seconds would not have exploded unless there was something wrong with it.  I've lent, sold, given away bows tillered to 28" that were drawn well past that 28" yet they didn't explode.

I'm not saying that you simply cannot get a working bow using this method, I just wouldn't trust it if I had to go out and put meat on the table or defend my people.

Just out of curiosity, was it the top limb that exploded? 

[RyanR]

That top bow was beautiful. Hopefully you can get one to hold up. Good luck

[DuBois]

Man, that is a bummer Simson. Those were looking sharp. I been wondering, have you ever tried a reverse HLD with the hollow side toward the back? You got me thinking on it.

Like when a tape measure will fold over one way but not at all the other way. I wonder if a ring could be chased on a sapling from the center of the tree toward the outside of the tree and end up with one ring in a reverse HLD and then tapered somehow to the tips. Ever thought on this?

I am probably nutty as squirrel poop.

Thanks for the awesome bows you make, Marco.

[Josh B]

Thank you for posting these Simon.  Very thought provoking.  Some of the damage is what I expected, but yet not quite.  The tension failure looks exactly like I had envisioned it would.  That is to say showing a tension load across the entire outer surface of the limb.  The chrysals on the other one are not where I thought they would be.   To be more specific, I expected them across the entire inside surface, but not on the outside.  It would appear that at some point the compression load is a little higher on the outer thirds.   Your HLD appears to be pretty close to a half pipe cross section.  I wonder if a less extreme profile would have faired better, but still maintained some energy storage advantages.  For instance, say the cut away profile were only a third of a pipe instead of a half pipe.  Just sort of thinking out loud here.  Sorry for the ramblings.   Josh

Edit...scratch all that.  After closer scrutiny, I can see I need to study on this a lot more.