ERC as a core?

[toomanyknots]

I have been hyped up lately over using erc as a core. It is beautiful and light weight. I have some of it. Everything seems to be falling into place,  . I have recently made a hick, erc, hick trilam. It was really nice, and wasn't wanting to give up a tiny bit of the 2" of perry reflex. I had it bending pretty good on the long string, the bend was looking good. And BAM explosion. Now, it was feeling like a bow would feel, that would eventually end up at 90# to 100# @ 32" if tillering went smooth, maybe a bit less. It did have a good 2" reflex. The back did break, but so did the core. I don't know which one went first! I mean, I have no idea how the core could go first, but I don't trust erc.  The lamination didn't seem great either, but it seems the erc is just brittle and hard to get a good lamination. The joints were perfect, I don't think it was glue starved. But it might of been. It did have a good amount of reflex, which would of been hard on the back. But if was freaking straight grain riftsawn hickory! The core was 1/4", the backing was 1/8". I have read of erc being used as a core in elbs, and making record breakingly fast bows. I just don't like big heavy dense longbows either. They are not my cup of tea. I would love a lightweight core to use, that is also as beautiful as erc. But I am starting to hate erc.  Btw, it was a completely clean knotless piece. I thought, with the erc being samwiched, there wouldn't be nothing to fear except set, which clearly was not happening either. AHHHH!

[ionicmuffin]

I would think it would make a nice backing, or even a belly because the ERC bow i had been working on failed in tension not compression. I dont see how the core could go first, as far as i understand, the core does very little work in comparison to the back and belly, so if you can make a backed ERC normally, then this should be no different. Did you see what caused the back to go? bad grain in that area? knot? ect?

[mikekeswick]

Without having it in my hands it's impossible to tell how/why it broke.
Cores are not in tension or compression however they do feel shear forces.
Light weight cores are not really the way to make the fastest bows perfect tillering, weigth distribution along the limbs, thickness to width ratios, bend tests to check the elasticity of the particular wood you are using etc are the way to go.
If the back broke then the core would break too unless the glueline was terrible.
If you don't trust erc then the way to find out wether that lack of trust is justified is to do some bend tests with it and then make some miniture bows. Make the widths/lengths to scale and it will act exactly the same as a bigger bow.
If a wood survives being a mini bow it will survive as a big un.

[toomanyknots]

I am guessing (hoping I guess) that the back failed from being over tensioned, it did have a steady 2" perry reflex. But I am thinking the erc has something to do with it... whenever a bow blows up, and erc is in the area, I am a little suspicious,...  . Maybe the belly and the core came unlaminated, and this caused the back and core to break at once, as the belly was in one piece. Like I said,it blew up pretty much, the core was broken here and still intact here and there, etc. The backing was straight grain rift sawn hickory, almost perfect with very little run out, and the bend was perfect at the time. Just made a heavier bow with an identical piece from the same board. No clue. It doesn't seem the easiest thing to get a good glue up with erc, yet I see everyone else do it fine. I am guessing I am the failing factor here,  . I will try it again, but without the reflex, and maybe come down a bit in weight, and hopefully it will work out. I was surprised to see it was taking no set at the time, and there was very little hickory towards the outer limbs. It was nice and light in the hand, and didn't wanna give up a smudge of reflex, man it was coming along nice before it blew. Has anyone else on here tried erc as a core in a heavier bow?

[toomanyknots]

Here are a couple pictures I took before it blew:



It's about 3" (maybe 4"?) perry reflexed, the belly was tapered to give an even reflex profile. When I took it off it had about 2" stay in:











 

[DarkSoul]

If you ain't breaking them....

The bow seems a bit narrow for a projected draw weight of roughly 100#. How wide is it exactly? And how far was it bending at what draw weight when it blew? A picture of the break might also help in getting an autopsy. But as Mike explained, a break can start in the backing, taking the core with it. As long as the belly is still in one piece, the break must have started in the back(ing). It could have been something as pathetic as a sharp corner at that drawweight...
Personally, I'm not liking anything over 1½" of reflex. I always get problems with lateral stability. My dream bow would have 2" of reflex glued in, ending up with 1½" after tillering. Especially with such a narrow ELB, the chance of getting stability issues with the reflex is very real. Although this most likely did not kill the bow, it might still be better to reduce some of that initial 3-4" of reflex in your future attempts. But it could also just be my own inability to deal with some reflex!
Another word of advice would be to taper that ERC core a little bit. Although I do think 1/4" thickness is adequate for this design and estimated draw weight, it is evident you were running out of hickory on the belly near the tips. I would taper the core, starting at midlimb, from the initial 1/4" to 1/8" at the tips. Again, this did not kill your bow, but it might still be an improvement for your next bow.

[toomanyknots]

I feel you on the instability thing. That is where I feel a mirror is unmatched for tillering reflexed bows, unless you have a clamp on your tiller tree. Because with a mirror you can firmly hold the bow while you pull it, where with a tiller tree, it will just flip. It was pretty narrow, but that was what I ended up with after floor tillering. And that is considering the extra weight a reflexed bow will feel like, I thought anyhow. I wanted 80# or 90# @ 32" to start with, I just kept running low on wood at the tips, like you mentioned, so I went with it. And although I glued up 3" to 4", it only kept about 2" right after I unwrapped it. I feel this prestressed the backing, which is kinda cool, or would of been, if it didn't blow. I know the bow did not give up any of the 2" reflex, but, after it blew, and I pulled the laminates apart, the belly took a bunch of string follow, that it never had before it blew.

[mikekeswick]

That erc has some pretty serious grain violations. I've neverused it so can't comment more about it in particular but if you are using a light 'risky' core material the grain should be perfect, especially if your core is so thick.
I have a feeling the core may have sheered along the fibers which started the break.
Some tips on these sort of bows.
Make a form for your glue-ups. Use a sheet of ply cut into strips then laminated together to give enough width. You need to be able to control where the reflex is. Hanging a weight off the middle will give you too much in the handle area and not enough in the mid to outer limbs - this is important!
Either taper your cores or make them 1/4 inch thick max.
Also you should definately NOT be able to 'pull apart the laminates'. If they came apart at all without being cut on a bandsaw or something then your glue-up was not good enough. What method do you use?
I'm not trying to critise  just pass on some of the things i've learnt about elb's.

[toomanyknots]

That erc has some pretty serious grain violations. I've neverused it so can't comment more about it in particular but if you are using a light 'risky' core material the grain should be perfect, especially if your core is so thick.
I have a feeling the core may have sheered along the fibers which started the break.
Some tips on these sort of bows.
Make a form for your glue-ups. Use a sheet of ply cut into strips then laminated together to give enough width. You need to be able to control where the reflex is. Hanging a weight off the middle will give you too much in the handle area and not enough in the mid to outer limbs - this is important!
Either taper your cores or make them 1/4 inch thick max.
Also you should definately NOT be able to 'pull apart the laminates'. If they came apart at all without being cut on a bandsaw or something then your glue-up was not good enough. What method do you use?
I'm not trying to critise  just pass on some of the things i've learnt about elb's.

Critise all you want, as long as you don't criticize,  . Naw, just kidding around, please always feel free to criticize all you want, I am surprised anyone would take on the huge task of pointing out any of the hundreds of things I am always doing wrong anyway,  . Yes, I don't think the glue up went too well either. I blame the cedar honestly, although everyone else gets good glue ups with it. When I pulled the laminates apart, the cedar left like a veneer of cedar on each piece of hickory. Some pieces broke off, but most of the cedar delaminated from the pieces of hickory. It is very light, brittle, dusty wood, if you know what I mean,... it sands to very fine dust. I tried to clean off the surfaces as good as I could before glue up. The bond was definitely not "stronger than wood". (I used TB3) I wonder if I squeezed too much glue out? And I tapered the belly lam to get an even reflex, most of the reflex was in the outer limbs actually. Seeing as the hickory backing was an eighth of an inch, and the core was about a 1/4", to get a good 1/2" at the tips I tapered the belly hickory lam to 1/8" thick at the tip before glue up. It worked pretty good to get a nice even perry reflex.

[ionicmuffin]

so maybe it wasnt perfectly smooth? not sure, by your description it seems like the wood was weak. so not sure if there was some major factor there that caused that. could be the glue up.

[DavidV]

Not that I have any experience with these bows... But the grain doesn't look great on the ERC and you might not be getting enough pressure with inner tube. If the glue up DID go well, you may be able to blame the ERC for being oily.... although I've never had any problems gluing it.

[toomanyknots]

Yes, none of the grain in the erc I have is anything near perfect. I am happy enough having a couple pieces with no knots. 

[vinemaplebows]

TOOMANY,

                            Like I said on PP PLANET I think you should use a well cut quarter cut board, look for a board you would select as a unbacked board bow. Still bet Cascara would do well in this application, very similar in weight and characteristics. Sheer force on a reflexed ERC board is tearing the wood apart in my opinion. The wood is stepped through, and the sheer at the glue lines are doing their job, but the wood is failing. Think of a perry, and the stresses put on the glue lines in that design.


VMB

[toomanyknots]

TOOMANY,

                            Like I said on PP PLANET I think you should use a well cut quarter cut board, look for a board you would select as a unbacked board bow. Still bet Cascara would do well in this application, very similar in weight and characteristics. Sheer force on a reflexed ERC board is tearing the wood apart in my opinion. The wood is stepped through, and the sheer at the glue lines are doing their job, but the wood is failing. Think of a perry, and the stresses put on the glue lines in that design.



VMB

Thank you for the advice. I will definitely be on the lookout for some Cascara.  If I make another bow with a erc core, considering your advice, I will try to select the best board, and not go for reflex or a heavy weight this time.

[BillBow]

Thats a big shame Toomany, I hope your next one is a real beaut.

Bill