Adding a belly lam?

[Arrowind]

I have a bow that came in under weight and I don't want to leave it.  I'd like to increase the draw weight by adding a belly lam.   I'd prefer not to pike it.  I was aiming for about 55lbs.  I was trying to tiller to fast, made mistakes and It came in at 48.   Anyway. I figured if I am adding a lam I should probably reduce the weight further so I can ad a slightly thicker piece to give me a little margin for error.

The bow is hickory, 2" at the fades about 1.1/4" mid limb and 1/2 inch at the tips.  .    I've tillered it down to 33lbs and am planning on adding an Ipe belly lam..   

Any one have any suggestions on how thick a piece of ipe I should use?  I'd like to get the bow back up to around 55lbs or a tad more. I have a few pieces cut out that are about 3/16 of an inch thick.

Do I need to reduce the draw weight further?   I want to end up with enough Ipe on the belly to be thick enough not to crystal and yet thin enough for me to glue on and bend to follow the fades etc.   Oh and thick enough to bring the weight up.

[lesken2011]

I am certainly no expert, but if it were me, I would make sure the limbs are scraped dead flat and as close to good tiller as you can get. After that a good heat treating of the belly, pull them into a slight reflex, then glue on the belly lams. I have used TB3 for this, but got some creep and will probably use Weldwood Plastic resin (water based) or one of the epoxies next time. The thickness is difficult to determine as you did not mention the length and 2 Inches is wider than an ipe bow would generally be. I have never used ipe for this, but have used osage a couple of times. 3/16 will add a lot of weight, but after smoothing out the transitions and final tiller, who can say? All you can do is try. No guarantees about crysaling. Just my humble opinion. Maybe some guys with more experience will chime in. Here is a pick of a molle style bow I added osage belly lams to.

[Pat B]

I did the same on a 60" osage static recurve a few years ago. The bow was built less than 2 months after the tree was cut. It felt dry, worked like  dry wood but took excess set and fretted badly.
  I ground the belly flat and added an Argentine osage belly lam. I used Urac glue and, after retillereing, the bow came out to the weight I wanted and it shoots very well. It was my go to bow on my second elk hunt in Colorado. It now belongs to Eric Ward.

[Arrowind]

Thanks guys.

Lesken - looks nice -  yeah I spent time grinding it flat yesterday and checking tiller along the way.  I was also checking to make sure it was "flat" by using a very square block of wood and running it along the belly checking for gaps.

The bow is 64" but only 23-24" of each limb are actually "working" the rest are levers and a stiff handle.   

It's a pyramid front profile.  (will probably end up tillering a little from the sides too) 

Pat B - I think I remember what you are referring to...  Didn't you post it here?  I spent some time looking for it yesterday but you got a lot of posts to look through dude! 

I realized a few hours after I posted this yesterday that I should probably be focusing on limb thickness a little more... If I measure the thickness of some other hickory bows with similar or near similar dimensions I could get a guesstimate of how much to take off and how thick the lam should be... seems better then trying to guess based on draw weight.....just thinking....

[Pat B]

I generally get a stave bow to about 3/4" thick limbs before I start tillering. From there I remove wood until I get the limbs to bend evenly and together. I then concentrate on getting the bow to the weight I desire.  It is too easy to remove too much wood from the limbs by trying to thin them down ahead of time on the bandsaw. If left thick and tiller to get the limbs to bend well first you have eliminated one of the grimlins that make bows come in under weight.

[SLIMBOB]

What Pat B said.  I think some folks when new try and "short-cut" the tillering process by looking for a measurement for thickness.  Start thick and take wood off until it bends.  3/4" is a good number and that's way thick.  The number, at least to me is irrelevant on any stave bow.  It's thickness is whatever it is when finished.

[akswift]

Arrowind-

if you have the lams cut at 3/16, and you reduce the limbs by 1/8 before you add them, you will have approx left to 1/16 to tiller with. Although this is not much margin for error, you might want to consider that almost all of the compression work is done in 1/3 of the limb nearest the belly,  3/4 of the compression work in the 1/5 of the limb nearest and half the work done in the 1/10 of the thickness nearest the belly.

You seem to be taking the harder road to gain 7 lbs weight , so I will assume that you are choosing the method somewhat as an experiment in building method and materials.    Have you considered reflexing the reduced bow before glue-up to take advantage of the "perry" reflex? Laminated designs can bring multiple factors into play for added performance.

Just guessing, but if you substitute ipe for hickory, and tiller for 7 lbs additional weight, your thickness will pretty close to where you started. I would be inclined to have a good tiller before glue-up. I have heard it said that doubling the thickness will  increase the pull eight-fold. Maybe there a target weight to be figured for the back that would get you close to finished when you add the 3/16.