Working on my first trilam.
I was just getting it to a low brace.
I had to get the midlimbs moving a lot to get the tips into position.
Things were looking very good. no obvious hinges..other than the midlimbs were bending a lot more than the rest to bring the tips around.
The break was instant. No pops, creaks nothing..just pow.
The woods are hickory back, walnut core, osage belly.
I noticed the hickory didn't splinter at all. Just broke pretty clean as the pics will show.
I purposely broke a small piece of hickory that I had and it broke the same way. Is it normal not to splinter?
Noticed the osage is the only lam that didn't break through.
Here are my thoughts...
The design may be more than wood can take period.
The backing may have just gave way..too much pressure in too small an area.
The walnut being much thicker than than the belly or back was actually doing too much work and broke. Just too thick to bend that much.
I'm leaning towards the core being too thick for the amount of flex.
Maybe walnut just doesn't bend like that...too brittle?
If the core is what gave... I'm pondering the notion of using 2 thinner core layers and/or a different material..maybe action boo.
Here the pics..
Let me know what ya think..
Thanks. :thumbsup:
Here's the unbraced profile...you can see how the mid limbs needed to go a long way to get to a braced position...
(http://i748.photobucket.com/albums/xx121/Zradix/Tri%20lam%201/CIMG0001.jpg)
Here's the breaks..
(http://i748.photobucket.com/albums/xx121/Zradix/Tri%20lam%201/CIMG0002-1.jpg)
(http://i748.photobucket.com/albums/xx121/Zradix/Tri%20lam%201/CIMG0001-2.jpg)
(http://i748.photobucket.com/albums/xx121/Zradix/Tri%20lam%201/CIMG0004.jpg)
just looking at it, and seeing how far the mid limbs had to move- and no splinters-looks like it just pulled the hickory apart.
seems like there might be something amiss with that hickory, can you clamp that bow in a vice. and pull on the other limb( with a rope from a safe distance) and see what happens to it.- maybe video it!?!
If you had the mid limbs bending more than another part wouldnt that be a hinge? Even though it may still be reflexed at a point of the draw?
That was my thought too Eric.
But I don't know of any other way to make the tips come around for brace. I'm fully open to the idea that this bow was just too curvy.
Sorry double post. Maybe that design would require the string to lay against the belly at brace like a recurve
You needed to facet the Osage belly right to the glue joint between the Osage and walnut. Your belly edges are too square. I round the belly off to a radius belly. Also there is a hinge where the belly was too thin.
You should not have thinned the midlimb to "get the limb tips to come around". Doing so made it weaker there than elswhere, and I think it's obvious now why that should be avoided. If it was too strong to get it braced, you should have reduced it's strength by removing wood evenly along the limbs' length in thickness and/or width while maintaining an even thickness taper.
I would have been especially meticulous about the thickness tapering of the limbs. As long as it is accurate, the bow will try to reveal to you what its basic strung profile should look like. Listen to her. Go with her. Don't try to make her something she's not.
With that unstrung profile, it would likely want to show a braced profile that still shows some reflex. Following that, it will then show the limbs straight at partial draw, and "come around" sometime a little later in the draw... but never come around as much as a straight limbed bow.
A common mistake of folks who are new to d/r bows is trying to make their profiles resemble those that stand straight or with gentle reflex when unstrung.
I have one going now that looks much like it. It is just now ready for the tree... hasn't been bent at ALL yet. I'll take pictures when I get to working on it again... not sure when that will be though :(
John, when tillering these d/r bows, you want the entire limb to bend a little. The last thing that should be bending is the area just outside of the dips. As you pull the bow down, watch the limbs. Look to see where it is flexing. If all the bend is at the end of the riser, then that is not good. You need to watch the limbs as they react when pulling the bow on the tree. The heavy reflex in your bow is going to make those outer limbs really stiff. Even at full draw they will still hold some reflex. At a brace the mid limbs will be pretty straight looking. As you work it down the tree, the mid limbs should begin to bend, and some of the reflex will come out, but not all of it, and at the end of the riser you don't want the limb bending at all. That area will take on some bend as you get farther down the tree. It's hard to explain, but think about it like a wave rolling in on the ocean. Take a wooden yard stick and hold it at arms length, then bend both ends down, it will have an even arc. Add in the reflex and the outer 1/3 third of the limbs will still be reflexed. But most of all when pulling the bow on the tree, see how it's bending. It should be an equal bend so to speak along the entire limb, Not one area bending like a door hinge. I know, this doesn't help:)
Good luck Jeff!
Thanks for the help guys.
I understand what you guys are saying.
Maybe I did try to force it.
In some ways I feel like I was pretty close to a good brace profile....following the ideas you've posted.
..in others memory says the mid limbs were bending too much.
I think part of the problem may be the unbraced profile.
when you really look at it, the midlimbs are about the only place in the limb that's really curved. Sure the outer libs have some but not much. Almost like 2 straight lines with a curve in the middle.
If I made the entire limb bend the same amount throughout it would have weird belly pointed tips and fades with this odd bump in the middle of the limb.
I think it would really help to have a more gentle arc through out the limbs.
This one was glued up with a profiled back, but the core and belly were still just rectangular slats.
If I would have profile tapered the core and belly it would probably have a more even arc....hhhmmmm
I really appreciate you all talking this out with me and letting me bounce around ideas.
:bigsmyl:
The only time I've seen hickory break in tension across the grain the hickory was infected with fungi. If it were healthy is would have splintered more.
How can you tell infected hickory?
Not saying this was in particular, but it would be nice to know.
John, I really think for you not making many bows, you induced way too much deflex and reflex. If you remember in your other thread, a few Bowyer guys said good luck tillering that thing. Deflex and reflex is nice, but too much is not a good thing either for someone who has not made many bows. That's my final answer:)
yep..
I agree.
Was a real eye opener.
also realized with actual experience how much more touchy keeping the limbs straight is when there's so much bend in them.
I've heard it was...but how much worse could it be right...lol
Still want to try to make a trilam....even worse now. like it to be made from 62" lams. can that be done in a mild r/d bow and still get 28" draw w/o too much stack?
I realized this year that I really didn't like hunting with such a long bow.
There won't be no stack.
ok.
Guess the drawing board is coming back out.
Zradix, Just the fact that it broke across the grain tells me there is a problem with the hickory. Hickory is very strong in tension and not apt to break across the grain.
I've made lots of hickory backed bows and the only one that failed was due to fungi in the wood.
I agree with everything pat,Roy,and Jeff has told you...I think your hickory is bad and if u have some of the same stuff left do some bend tests with it first before wasting anymore time with it...if the hickory is bad then no matter what shape or design you do its gonna blow...So find out first if its any good...I'm betting it isn't..as pat said its bad hickory that breaks straight across like that and good hickory will splinter...and the other problem is as Roy n Jeff says...too extreme of a shape for a novice to handle...and honestly I didn't like the shape of it having all the reflex in one small area so closer to the fades than the tips....try getting your reflex to start mid limb and then continue it progressively more in one sweeping arc to the tips...and getting your lams perfectly thickness tapered will aid in this...I dont think you thickness tapered your lams good enough on that one because all the bend happened in that one area during glue up...
Exactly, precision tapering PRIOR to glue up is a key move on bows like this. I grind mine as precisely as I grind glassbow lams, and when ya pull it down into reflex on the form, not only is the reflex evenly distributed during glue up, the dang thing pertinear tillers itself.
I saw this mentioned earlier... I DON'T have the pieces shaped at all in regards to their width profiles prior to glue up. Doing so would limit room for shifting centerline during layout. The exception to this is bamboo backing... I shape it to oversized width profile so it can be adequately thinned... since it is so high-crowned.
I agree with all of ya.
I know the biggest failure here is me.
Maybe the hickory was bad. I had one little 8" or so piece that came with the lams...for packing I think. Looked exactly like the backing.
That little piece broke w/o splinters...broke exactly like the backing.
I'm pretty sure the lams were evenly tapered. I may not have specified the right amount of taper, but I'll bet they were evenly tapered. Don't have the specs right here..but the backing was tapered 1/8 to 1/16", the core was .004 taper, the belly was .003. ( may have those flipped around) They had a 14.5" parallel center section.
Thanks for the help guys. :thumbsup:
Can you tell if hickory is bad by looking at it?
No, you have to smell it..
:bigsmyl: :wavey: :laughing:
ok..I'll bite..
What does bad hickory smell like?
Smells like ash.
:wavey:
:knothead:
Hey man...it's not beyond possibility that smell is how to check.
thought maybe it had more of an earthy scent or something.
but ok..ya'll got me.
LOL
I would say your design was just too radical for the materials. Too much reflex and deflex. Mid limbs get insanely thin when your try to coax them into uncurling. If the belly had been solid osage without the middle lam it might have held up better. But than again other may be right and it might have just been the hickory failing. I only use bamboo for just that reason. Not a fan of wood backings.
I agree.
Problem #1, #2, #3...ME
Here's a few picks of the left over hickory.
It's about 1/8" thick.
One end I snapped yesterday as a test...broke pretty clean and straight across.
The other end was cut.
Today I took this piece, held it between my hands and snapped it.
You can see how it broke.
Surprised it broke in 3.
I later took the long piece, held it over the edge of my desk to beak it. Just popped clean, no splinters.
When I look at it very closely it almost looks porous and has sort of a fuzzy/spongy look to it.
Don't get me wrong. I'm not blaming the wood for this fail.
Nor am I blaming the gentleman that sent the wood. I'm positive he wouldn't send crap wood purposefully.
Are these types of breaks normal for hickory?
I just want to learn what to look for.
Does the wood look normal to you?
(http://i748.photobucket.com/albums/xx121/Zradix/Tri%20lam%201/CIMG0002-2.jpg)
(http://i748.photobucket.com/albums/xx121/Zradix/Tri%20lam%201/CIMG0004-1.jpg)
(http://i748.photobucket.com/albums/xx121/Zradix/Tri%20lam%201/DSC_0064.jpg)
The porous nature of that piece supports my fungi theory. It really doesn't take long for fungi to get into any whitewood. If this hickory tree was cut and stacked in the weather before going to the saw mill the fungi has a chance to get in.
I found out about this "rot" when I was given a squared off hickory log that had been cut 2 years before and stored in a garage. When the tree was cut it sat on the ground for a week before storing it in the garage.
When I got the log I took it to a friends portable sawmill and we sawed it up into backing strips and a few staves. The first bow I backed with one of these backing strips broke across the grain. The rest was used as kindling. d:^(
This is also when I fund out about TB glues releasing at 150 deg. I called the TB folks and asked how to remove the backing strip glued with TBIII and they told me to heat it up to 150deg. I used a heatgun and screw driver to remove that backing strip, cleaned it up and re-glued a different backing strip on.
I agree. It may not have been cared for properly. Wood for bows, backings and such, due to the dynamic life it will lead, requires specific care. I too had a friend give me some hickory staves that weren't strored properly and they were no good. Dang shame too, as they were beautiful, clear, straight.... um... firewood. They didnt break, but took a lot of set very early on. It was actually kinda funny.
All hickory can look porous if you make a very smooth cut on the end.... but it shouldn't look fuzzy. Did you get to bend it at all? Did it take any set?
Hang in there man, it ain't easy being a new bowyer. I've been at it for all of a year and so far I've chrysaled walnut and cherry, cracked the tips heat bending elm, and raised splinters on hickory and hard maple backing. If not for the fact that I've managed to make a few that I like to shoot, I would have quit by now. I have yet to find the perfect board, but I agree with the old hands on here that your piece of hickory had to be inherently bad to break that way. Nothing you could have done about that. I'll bet if you tone down the deflex and reflex in your form (copy Roy's, that's what I did), you'll be back on track.
Thanks guys.
I appreciate the info.
I had just barely got the bow to a 2-3" brace.
When I pulled the tips down about 3-4" Pow.
I had previously had the tips moving about 9" on a loose string.
I just put my bow back up on the tree, the good limb is appx 1/4" lower than when I started....doesn't seem too bad to me...
...who knows..maybe just that end of the piece was bad..
I'm not going to burn this one yet.
Going to salvage the riser and horn off the tips.
I'll be keeping the backing just to compare to next time...
...and to think..I went to hickory on this one to avoid unforeseeable boo problems..lol.. :knothead:
Oh yeah t5, it can be rough..lol
this is only my 4th attempt. 1 oak board (little chrysal), bbi (no good), BBO worked and is my hunting bow now, then this..my first kaboom.
I already have some plans for tri2...
Not so radical..but still have to make it hard to do..lol