Glass delaminating issues

[djschwartz90]

Hey everyone, I'm a relatively new bowyer (and new to the site) with a couple laminated longbows under my belt. Sorry for the length of this post, however I am having a persistent problem achieving what I feel to be an adequate bond between my glass and core wood... here is what is happening:

I just glued up a Hill style longbow two days ago. After cutting the limb profile on the bandsaw, I am able to peel the black fiberglass off of the core wood (on the narrow strips removed from the limbs) relatively easily and cleanly. The wood core laminations do not do this, they tear and break.

When I noticed that the glass could be pealed away from the core wood like this several bows ago, I began to worry about about shooting them. None of my bows have ever delaminated while shooting, however I sacrificed one of them and used a razor blade at the tip of the limb to try and pry the glass off of the core wood. Sure enough, once started, I was able to "zip" the glass off of the entire limb fairly easily, leaving a clean, smooth surface!  At the time, I was using thickened West System epoxy for my laminations; thinking this was the problem, I just switched to Smooth On as I have not heard of anyone else having this problem. Unfortunately, I saw no improvement with my most recent Hill longbow, as noted above...

As for my general gluing procedures, I grind my limbs with a drum sander using 100 grit paper. I wipe down my fiberglass (the rough side) with denatured alcohol, blow it dry with compressed air, and let it sit for 10-15 minutes. I apply epoxy to both mating surfaces of each lamination, use C-clamps and wood/rubber pressure strips to hold the lams to my form, and am careful to tighten the clamps only moderately tight (as tight as I can get it with my thumb and two fingers). Based on what is occurring, it seems like I am getting a starved glue joint; I just don't see how my clamp pressure could be more than the 60-80 psi that guys using the air hose method are producing. I feel like if I use any less pressure, my glue lines will suffer.

Has anyone else had this problem? Again, I have never actually had a bow delaminate, maybe I'm just worrying about nothing, but this just doesn't seem right to me. Any suggestions would be very much appreciated, thanks!

[djschwartz90]

Here is a picture of the glass peeling away from the core wood:  

[djschwartz90]

[djschwartz90]

Sorry, here's the pic. I'm learning lol...
 

[ianpc]

I had one bow do that to me a while back, I used the microwave to heat the epoxy that time and I think I got it too hot... I mixed the epoxy and by the time I was clamping it the left over glue went solid and clumpy... After curing the bow when I took it out of the form the glass peeled off like that.

I stopped heating the epoxy in the microwave and haven't had an issue since.

[Archer Dave]

Bummer man. Hopefully someone will have some good advise for you, but that someone is not me as I have yet to make a laminate bow. I only have experience build selfbows. Hoping to do my first R/D soon so I will be interested to see what happens.

Dave

[Bowjunkie]

Sure, starved glue joint. You could try to use coarser sandpaper to grind lams, I use 40 grit, and use less pressure on the clamps.

When I clamp, I use a thumb and one finger and it is nowhere near as tight as those two could make it. Perhaps half as tight as they're capable of.

Also, I don't blow off with air, I don't want to risk introducing any moisture.

How far apart are your clamps?

[snapper1d]

What temp are you curing at.If its too high it will do that.Been there and done it.Its not starved of glue using SmoothOn.100 grit is also plenty rough for sanding.

[djschwartz90]

My clamps are 2-3" apart. And I didn't bake it, I  cured it at a little higher than room temp (the heat set at 80) for 48 hours.

[jess stuart]

Did you wash your glass with acetone?  Sometimes glass can have some residual oil, dirt etc.

[cunruhshoot]

The only time I had glass peel up was when I mistakenly glued up the glass smooth side down. Is there any chance that this could be the issue?

[Crooked Stic]

Is your core wood the correct moisture? Glue mix correct. Stir the smooth on 5-6 mins. and it don't hurt to have more resin in the mix (white part)I never clean the wood with chemicals. Glass either unless it has oily smudges on it.

[djschwartz90]

I did wipe the glass down with denatured alcohol, but I let it dry for 10-15 min. Glued it rough side down, glue was mixed well, 1:1 by volume. As Bowjunkie said earlier, it seems like it is related to too much clamping pressure even though I thought I was going pretty light. How tight should C-clamps be when gluing up a bow?

[snapper1d]

SmoothOn will cure at room temp but it improves a lot with heat up to 150 degrees.If you thought you were going pretty light on your clamp pressure you probably were.Cold thick SmoothOn is harder to push out.When it gets hotter and it gets thinner your clamp pressure will get even lighter and more glue will ooze out.A bow with 60# air pressure on it and is put in a hot box will squeeze out most all of the glue.Epoxy works on a molecular level.

[mikkekeswick]

Yes I also doubt whether it's a starved joint. You have to really cinch those clamps up to do that.

[Robertfishes]

When you peeled the glass off did the glue stay on the wood or on the glass? Do you have a oil and moisture filter on your air compressor line?

[Buemaker]

I vacuum the lams instead of blowing off with air. The small brush on the vacuum I wash sometimes in dishwashing soap and rinse it to make sure it is clean.. Bue--.

[Pheonixarcher]

Also, make sure your denatured alcohol is not contaminated. Instead of using the compressed air, try just using a stiff bristled nylon (or similar) brush to clean your lams and glass. Try mixing the smooth on at 2 parts A: 1 part B. Make sure that your form and lams are perfectly flat.

Are you clamping directly to the glass, or do you have some sort of pressure strip?

[snapper1d]

I was thinking the same thing.I wonder if the denatured alcohol was contaminated or if it penetrated deep enough that it just appeared to have dried.I quit years ago trying to degrease woods and glass.On oily woods you just seem to keep drawing oils up to the surface by dissolving them.Just a good sanding is all thats needed.

[Bivyhunter]

I have a bit of a different take on your issue, I think the sandpaper the manufacturer is using to prep the glass is getting to dull and not etching the glass well enough. I've had several limbs come back to me from random batches the past several years where there will be pea to quarter sized spots on the limbs where the glass has started to separate from the veneer. I grind all my veneers, (except veneers I'm going to dye) with 36 grit to make sure I'm getting lots of surface for the glue to stick to. I've started hand-sanding my glass now with a piece of 60 grit to increase quality of the gluing surface. Hope that eliminates the problems in the future.
If I were you, I would go with a rougher sandpaper for your laminations than 100 grit, at least 60 grit. It would also be a good idea to rough up that glass a little more as well. my $.02 for what it's worth.