First attempt at laminate longbow-help needed

[Erik]

Hi
I'm in the process of tillering my first attempt at a laminated longbow.

I'm at the 2. stage and have it braced to approx 6". The top limb (left) is 4 cm longer than the lower limb. To me the lower limb seems to be bending more at the first 8 inches from the fade, compared to the top limb! Any help on the further actions regarding the tiller is greatly appreciated.
     
Also when drawing it to 15" it gives me ruffly 11#, which is a bit low, since I was going for 40#@27". Of course I'm not sure, but assuming the force/draw length to be overall linear, I would end up with around 25#@27".

I'm thinking of shortening the bow from 67 3/4" to 64", in the hope of adding some poundage, but how much can be expected?

Also I'm thinking of adding 1 mm of power    glass laminate to the back, but again how much added poundage can be expected?

In advance thanks
Erik

[KenH]

Cutting an inch off each end will gain you 5# of draw weight

[Erik]

Thanks Ken, I'll start by shortening it and see where it takes me.

\\Erik

[Wolftrail]

Dont grind the fades at the start concentrate more on mid limb area first.  Most of the shooting power comes from the fades not the outer limbs.  11# at 15" is wimpy.  Shorten it to 62" you may get to 36# .
 "I'm thinking of adding 1 mm of power glass laminate to the back"   I have not done that so can't comment.

[mikkekeswick]

Do not add glass - it will overpower the belly and give you a load of set - thus dropping your weight further from ther breakdown of the belly cells.
The best way to make weight is to start again!
You havea large hinge on the right limb in the worst place. Forget trimming the ends of this bow as you have a load of weight to lose still before you fix that hinge. That bow in it's current state isn't ready to be braced at all. a bow must not have any large weak spots even when only braced at 1 inch in early tillering.

[Nezwin]

Without recurving the tips, a 64" 'straight' bow will probably start to stack at full draw. I don't know if shortening is a solution.

What about a bamboo backing?

[Erik]

Thanks Dean, I'll be concentrating more on the mid limbs.

Mike, just to clarify, the bow is ash back and jatoba belly, so if I added glass laminate on the back, it would make the belly to weak compared to the the back?

Just so I'm sure I have identified the hinge I have marked the spot on the picture.
   

I'll go back to the longer string, and see if I can fix that hinge, it'll give me some experience at least.

Neil I thought of bamboo, but it's quite expensive and difficult to get hold off.

Thanks again
Erik

[Wolftrail]

What wood is the bow....?  "in the hope of adding some poundage"   before going any further and I repeat dont tiller any more just glue on a lam on the back about 3/16"  ~ add another 1/8" 12" lam on the back. The hinge will be gone.    :p   I have done this with success.

[mikkekeswick]

Yes you are correct. Wooden bows need to have roughly balanced resistances to stretching and compressing for the bow to work well.
Glass is so much stiffer than wood that you would be building in a huge difference in properties and you will end up with a lot of set. The reason is that you will end up not stretching the glass so the wood has to work overtime in compression = bad idea!
Seriously forget the weight this bow will come out at just concentrate on getting the tiller perfect.
Then your next one will work out much better due to you being better at tillering.
Sure you could shorten it or add a belly lam but like I said earlier the best way to make weight is to start again with FRESH wood and never oeverstrain it. Easily said but hard to do!
Good luck.
Also post pics early on before it is bent much at all.

[Erik]

Dean the bow is ash back and jatoba belly, but I'm unsure whether I should spend any more money on this bow.
Mike, thanks for the advise, I'll concentrate on the tiller and hopefully I'll learn from this.

\\Erik

[Wolftrail]

Yep no doubt, and most of us learn the hard way.  When you have a few bows under your belt you will develop your own way of doing things that are unique to yourself and building bows will come easy.
   :cool:

[Erik]

Hopefully it'll be easier the next time Dean.

Couldn't help myself and took off 5 cm from the top and 4 cm from the bottom limb. Went back and used a string 1 inch longer than the bow (now 64"). Been concentrating on that bottom limb and would appreciate others opinion on the tiller at 6 inch limb end bend. Just discovered that the string is out of the nock groove on the top limb on the picture, I should go recheck the tiller tomorrow    :(    
   

Also tried to trace the bend by overlaying a circle, and it seems to me that they are bending reasonable even, but then again, please tell me if you see stuff that I don't
   

In advance thanks
Erik

[Erik]

Also played around in Gimp, doing some overlaying of the limbs. Here the overlay has been skewed in order to make the limbs align from the fades and not from the center of the bow, as the riser is not positioned dead center, but 1 inch off towards the lower limb.

Green string is the original and the red string and black limbs is the reverted overlay, and I think it looks alright?
 

\\Erik

[Wolftrail]

Mid and outer limbs are not doing much.  Like others say you are better off starting over to reach your desired weight of 40# and having a well tillered bow.

[Erik]

Yeah Dean, it's just hard to let go, invested a good amount of time in this bow already.

But with a loose string it's the inner of the limbs working right? and I should expect less bend in the mid/outer limbs?

\\Erik

[monterey]

Just carefully bring the bow to the best tiller possible and accept the weight you end up with.  It will prepare you to build a better next bow.  There is always a "next bow", even after your " last bow".

Relax and have fun.  

[Erik]

I'll give it my best shot at the tillering, just looking for others opinion on the tiller. Well dunno if it's gonna be the last bow from my hand, but at least it's gonna be a while before I take on to build another.

\\Erik