Pressure when laminating

[Badger]

  I normally use strips of inner tubes but have been thinking of trying a new method to get just a bit more pressure. Putting a maybe 1/4" thick strip of rubber or very dense foam over the back and then wrapping it with linen thread at about 1/8"apart winds. Has anyone tried anything similar to this? I have been playing around with the tri lams lately and see a need for a little more pressure in some places on the limb.

[leehongyi]

sure it can be done. i used similar method to press horn strips to core wood and it worked!
but i think inner tuber is stronger and more average than this method.

[Pat B]

Steve, a few years ago James Parker did a demo at the Classic where he wrapped a boo backed and belly bow with cordage and used wood wedges to tighten the wrap and control the direction of the pressure ie. R/D. Someone on PA used this method not long ago so maybe they will chime in. If not, contact James for instruction.

[Del the cat]

If it ain't bust, don't fix it. Rubber strapping provides a good even pressure if done right, you don't want too much (nor too little) pressure.
Maybe a single layer of rubber wrap to hold it in position and apply initial pressure followed with a spine of rubber blocks and more wrapping to apply pressure to the centre line? I think with dead flat lams, wrapping probably exerts most force along the edges.
Del

[Badger]

  Del, I have always done a shit load of lam bows and have had very few issues. On the tri lams where the powerlam blends in to the lams I have been putting extra wraps and that seems to solve the problem. I have had an occassional issue in recurves with insufficient pressure.

[Badger]

  Pat, the wedge method is an ancient method used in a lot of asiatic designs for centuries so it is proven tried and true.

[RBLusthaus]

I use about 40 spring clamps.  Clamp on both sides of each limb.  As many as I can fit.  Works for me.  Russ

[leehongyi]

here's some pics about the chinese rod method. hope can help!
the rod go through the holes from the bottom of handle to the top. the more holes it goes through, the more tight it could be. use the tool to apply the rod and the handle works as a lever.

[leehongyi]

a finished pic

[Don Case]

Somewhere I saw a system where they used  male and female cauls with an air bladder. They clamped the parts and the bladder between the two cauls and then inflated the bladder. I tried to find an example on Google but struck out. Hopefully you can imagine what I'm talking about. The bladder was reinforced so it wouldn't blow out the side. Gives nice even pressure that you can actually measure.

[Badger]

  The bladder method is popular amoung glass bow builders, they often use firehose. A good hose to use is a silicone hose used in roller bed trailers, just the right size and they seel all the fitting needed to put it togeter. Not sure why no one uses it but I gave some to a guy and he loves it. What I do like about the form is that it supports the wood through the bends lowering any risk of breakage. I don't like forms because I never build two bows alike.

[zenart]

Is it possible to successfully use water pressure in bladders? How much pressure is actually needed? Do you just watch glue run out and say, enough, same as inner tube wrap?

That's the thing I noticed about inner tube wrapping, it's an art. It still requires a sort of feel to hand-stretch 'em to get 'adequate' pressure, not too much and not too little. And unless you're beyond just good I doubt anyone could get EXACT same pressure throughout the length of  glue up.. at least consistently. Also, rubber wraps change from source to source, not a lot but they do have differing strength from one tube to another, and they change over time, losing elasticity from drying out.

But yah, it sure would be nice to have one single form that allows for arc geometry to vary from bow to bow.. one that has flexibility to dial in small measured adjustments in precise areas of bend yet still have even pressure from above and below throughout for glue up.

[mikekeswick]

The problem with the rope wrapping method is that you need two people and it induces twist. The wedge method is just a pain in the $^&*! Try cleaning all those wedges after glue up.......
Either the firehose or innertubes for me!
Badger are the edges of those powerlams thin enough. I find if you make them an inch longer than you plan on (each end) and really concentrate on getting those last couple of inches cigarette paper thin I don't have any problems just using innertubes as standard. Sometimes I will add a normal clamp and a wood block at the ends of the powerlam just to 'make sure' i'm not going to get a shoddy glueline.

[Badger]

     Sometimes I get myself off track when I start posting. Lately I have been looking at much wider backed designs. I feel like the inner tubes put great pressure on the edges and make for great glue lines in general but may not be putting enough pressure down the center. Still I admit the inner tubes are hard to beat. Just looking for another alternative possible improvement.

[DarkSoul]

I agree that the inner tubes work best with narrow limbs. I mainly use the inner tubes for BBI's, which are narrow enough for them to work, and which have a crowned backing of bamboo. The crown seems to help in creating even pressure along the width of the laminations. Steve, let's say you want to laminate a 2" wide flatbow together, using a 1/8" thick hickory backing. How about adding an additional dummy lam of 1½" x ¼" to the back? It should spread out the pressure over the thin and flexible backing. You could even use a 1½" half round stick (we can just buy those here in the home improvement store) as an optimized pressure strip.