one limb took set..what now?

[Zradix]

Hey guys.
I've been very slowly tillering a r/d  tri lam.

I had the limbs bending what I thought were pretty evenly.
I've only had it on a long but taught string so far and am just getting to the point where I'm going to brace it.

Maybe my eyes are failing..I swear the bends looked pretty good.
BUT..I have one limb that has taken some set.
Basically that limb has lost some of the curve it had in the mid limb.
The other limb has retained shape just fine.
One limb's tip is about 1.5" lower than the other when unbraced.

I must have over taxed the limb that took set...and I'll have to really look at why/how there. And do what I can to make sure it doesn't get worse..by weakening the rest of the limb that didn't take set.

...but what to do about the other limb is the question.

Should I try to get the other limb to take set to match the one that did?

Should I just keep going with it? Just keeping the hook following the line. If I do this I'll probably end up with a bow that has more deflex in one limb than the other.

One thing I did notice while scraping/faceting the limb that took set, is that the osage belly on that limb seems much softer. The scraper almost wanted to gouge out/into the wood especially when doing the facets.

I was really surprised when I noticed it..lol
Everything was looking so good on the tree.
Following the line really well.
Took it off the tree to scrape a bit more and..WTH is this!?..lol

Thanks for the help.    

[Pat B]

Pics will help.
  Is it a selfbow or lam bow?

[Zradix]

It's a tri lam.
Hickory back, maple core, osage belly.
I don't have any pics that really show what's going on.
I'll try to get one sometime today if  can get a chance.
Just one limb lost a good part of the mid limb reflex.
The tips are still holding decent reflex as they were flipped prior to glue up.
Thanks

[LittleBen]

Originally posted by Zradix:



One thing I did notice while scraping/faceting the limb that took set, is that the osage belly on that limb seems much softer. The scraper almost wanted to gouge out/into the wood especially when doing the facets?

Thanks for the help.      

Seems like your problem right there. If the belly on one side is softer, it's going to take more set. If you have calipers you could check the thickness of the limbs. If the one taking more set is thinner, then it's probably your tillering is not as even as you think. If the one takin set is thicker, then the belly wood is weaker, and it's just going to take more set.

Personally, I would tiller the bow so that it has 1/4" positive tiller, and make the limb that's already taken set the bottom. That's assuming your bow is symmetric. If you do that then the top limb will do a bit more of the work, and that should help to even things out a bit.

Only other thing I can think is that one belly lam is dryer than the other. If you have a moisture meter then check. If you don't I might just let the bow sit for a couple weeks to make absolutely sure both limbs have the same moisture.

[Zradix]

Thank you Ben.
I'm fairly sure the belly has the same moisture content throughout as it is one piece and sat on a roller bench thickness tapered for about 2 weeks prior to glue up. And it's been in the tillering process for a couple weeks now as well. So I THINK it's all the same...lol

The belly lam on the limb taking more set is thicker.
The bow is symmetric.

...I'm having thoughts of putting the bow in a jig to get some bend back into the set limb and gluing a thin strip of osage to the area taking set in order to help keep it's shape...

I feel you're correct about the softer wood just taking more set.
Never ran into this before...always something new to learn I guess..lol

I've seen some experimental bows with one recurve limb and one longbow limb tillered out that supposedly shot well.

I might be ending up with something along that line.

Thanks for the input!  

[Roy from Pa]

Were these Osage lams that you z spliced together? Do they both have the same growth ring patterns? Are they sister billets? How wide are the flares and rest of the limb? This is the biggest reason I don't remove hardly any wood, until I get the bow to a 6 inch brace. I'll only remove wood if I see a major problem. Tillering for limb timing will make one limb have more bend than the other.. Pictures John..

[Zradix]

nope..it was a single osage board.

the limbs are the normal 1.25" wide for a few inches out then tapered to 1/2" tips.

I had to take some wood off before brace.
darn thing was waaaaaay stiff. like just to flex the limbs back about 2-3 " was taking 45-50 #'s...lol

Can't get a pic right now.

I'm just putting too much of a bend in the limbs at glue up.
..I need/will stop doing that..it's killing me.

back is 1/8" with .002 taper.
Core is 5/32 with .002taper.
belly was 3/8" with .004 taper.
Tapers all started 7" out from center.
12" riser piece stuck between the core and backing.
66" slats.
Limbs were faceted 1/4" in at 45˚starting gradually about 2" from riser then gradually faceted less far in going towards the tips.

Here's a pic of it after I tillered abit.
This was before the set took place...just to give you an idea of what I have...
I just really need to go with a more relaxed form.

 

[Pat B]

I'd say you have too much reflex already. It is going to be a bear to brace with that much reflex plus you are overstressing it just trying to get it to brace height.
 If the bow is symmetrical just make the limb that is taking the most set the top limb. The bottom limb usually gets more stress anyway.

[Zradix]

I agree.
Won't be doing it this way again.
just takes the fun out of it.
Gotta take a more laid back route.

[Roy from Pa]

I would say you reflexed it way too much... My bows come off the form with about 3 inches of reflex at the tips. After tillering they will have about 1.5 inches of reflex. Your bow looks nice but that isn't very practical for a wooden bow.

[Zradix]

agreed.

[Zradix]

Roy..
How are you measuring the 3"?
..just laying it belly down on the mid limbs and measure up from the bench?

...tip distance in front of/ forward of riser's back?

or some other way?

Thanks

[Zradix]

let me roll this by you guys....
the limb that has taken more set actually looks better ( not as much reflex)
now...what if I scraped the non set limb too much and actually hinged it slightly so it did take set in order to match the other limb.
..then added a strip of osage to the belly in that area to stiffen it back up?
Then finished tillering it out.

..do I deserve an       just for thinkin this way?

[Pat B]

just tiller the stiffer limb to the one that bends more. I wouldn't intentionally add a hinge.

[Roy from Pa]

Roy..
How are you measuring the 3"?
..just laying it belly down on the mid limbs and measure up from the bench?


Yes that way it will have about 3". After the riser is on and it's sitting in the tree cradle, it's about 3.5". Just depends on where I place the mid limb posts at glue up.

Your bow looks nice, John. But just cut the reflex in half on the next one and it will be much easier to tiller. I wouldn't scrape the other limb to hinge it. You should scrape it evenly to weaken the whole limb. Anyway you could take a video of it in action on the tree?

[Zradix]

I will take some pics and vids when I get a chance to work on it again.

I'll be cutting the reflex waaaaay down next time round for sure.
It's way too counter productive to have so much.

...I'm slowly comin round to the "take it easy" approach.

[Roy from Pa]

Atta boy..  

[LittleBen]

Honestly after seeing the pics I think you're in a good place. Just tiller the limb with less set as the top limb like I mentiond and you're in business.

Doesn't look like more than maybe 4" of reflex .... It's not too unreasonable. Usually just requires a slightly wider limb.

Keep on trucking and downs sweat it too much.