repeated EA-40 failures

[Alchemist]

Hi all.  I've been around here a few months, reading a ton, making to date backed bows and some laminated limbs.  I'm having issues though.

It started horrible, over clamping at totally starving a couple handle joints when using EA-40.  I cleaned, roughed up, and reduced the pressure and got a good hickory backed cedar bow....until the handle started delaminating at the fades.  I cut it off, rinsed and repeated and have a fine 68" 42#@31" d/r bow I've been shooting.  I went to repeat the process (to increase the bow weight) and ran into the handle issue again and the reglue is holding but I'm dealing with cracks on the hickory backing.

Trying to back off and 'do it right' I've started an 63" Ipe/boo bow with about 2" reflex, no deflex. Currently 50# only at brace height.  I was tillering yesterday and heard a pop.  The handle popped clean off, pretty as you please.  I could see epoxy residue on both ends but pretty much nothing in the center.  See above about rinse and repeat - sanded flat, cleaned, toothed and glued again with EA40, hardly clamping at all.  So far so good.....but....after coming out of the heat box and cooling I am now seeing glue lines opening up between the boo and ipe.

I should say I'm curing in a heat box at 160-170 with forced air, 12 hours or so, and unclamping after cooling.  I'm applying pressure with inner tubes and clamps to hold it on the form.  I'm really trying no to over clamp or wrap too tight.

Does anything jump out at anyone as to what I seem to be systematically doing wrong?  I'm trying really hard to not to apply gorilla pressure.  I guess a few questions too. 

1)  Can you safely heat treat a bow in a heat box multiple times? 
2)  Is there a good way to judge clamping and inner tube wrapping pressure?
3)  I'm thinking about band sawing off the back and trying to glue up yet again.  Thoughts?  Or just keep tillering until failure?

Thanks in advance.

[DC]

Pictures please How thick is the bow where you are gluing the handle? If that makes sense to you?

[Alchemist]

I've read over how to post pictures.  Need to do that.  What specifically do you want the pictures of?  The delaminations in the limbs?

The ipe is 0.75" at the handle.  I left it the full thickness of the ipe board trying to make it a completely stiff handle.  The cedar were 0.5".

[bownarra]

Firstly it isn't the glue that is the problem. 100%
Handle pieces 'pop off' and gluelines fail at the termination into working limb when your belly lams are too thin. Eg. the blank without handle piece is flexing too much. Look up powerlams. Or simply make your belly lam 3/4" thick so that the 'extra' for your handle thickness is at least halfway up the fades. They won't come off then because you aren't asking a glueline termination to bend.
your limb lams opening up are because a) your wood isn't dry enough to stand the heat you are using b) your heat is too high for wooden bows, your temps are more suited to glass bows made with very dry wood and very thin lams.
Clamping pressure when using innertubes for me - I pull the tube until there is no more strecth and wrap at that. I use mountain bike tubes not cut. With my glass bows, air hose two part forms and EA40 I use 70psi in the tube. Never had a delam with EA40 stick with it, it is excellent glue.
Traditonal Bowyers Bible vol3 (?) has an excellent chapter on lam bows.

[Alchemist]

I 100% agree it isn't the epoxy itself.

Sorry, the first bow whose handle came off had a power lam 2" longer than the handle and fades. 

That is the first I've heard about not curing at 160-170 F for wood bows.  Could the forced air heater be part of the issue and drying the wood more?  What temperature would you recommend?  Might further drying the wood be a reasonable step or move to incandescent lights for heat?

That is exactly how I'm doing the inner tubes.  Pull until there is no more stretch.  So it sounds like I'm not pulling too hard.

I have the TBB V3 (and 1 and 2).  I'll reread it on laminations.  I did a couple months ago and honestly found it not very helpful but maybe with a question in mind.

[DC]

  Need to do that.  What specifically do you want the pictures of?

Just a shot from the side. I was looking for limb thickness compared to fade thickness like Bownarra mentioned.

[Alchemist]

Ok.  I can't show you the actual fail but there is the 2nd glue up of the ipe/boo.



This is the cedar bow.  You can see the hack job I did adding in another fade piece.  So far it is holding.

[buddyb]

I cure my epoxy at 120 degrees for about 3 hours and let it set overnight.

[Alchemist]

One other thing I'm mention is that the separations are happening in the tillering process or the separation happens after a day or so.  If memory serves, it was after coming out of the heat box a 2nd time after putting on the tip overlays.

[DC]

The thicknesses in the first picture look OK to me but I've not had too many pop off so I'm no expert. Fades may be a bit abrupt. In the second picture it been modified too much for me to guess about,

[Alchemist]

Here are the limbs cleaned up out of the heat box.



And them the following day after I put on the tip overlays and in the heat box again.



There were never even tested.  They are recurve limbs.

Finally both sides of the ipe/boo out of the heat box a 2nd time after putting on the handle a 2nd time.

[Hamish]

I'd always thought bow quality epoxy had a really long shelf life, but I just checked Smooth On's website  "This product has a limited shelf life and should be used as soon as possible." So how old is your batch? Most glue companies have extensive after sales information. Contact them with the batch #, and tell them the problem you are having, they may be able to diagnose it.

The splitting of the joint (backing and belly)after initial curing could have something to do with the heat used to speed dry. You might want to let them sit around for a week or so to increase moisture content. 160F sounds from memory to be the upper limit used by glass bowmakers. I'm not sure whether that's because the epoxy in the FG backing starts to re soften, or whether the new glue can't take it?

Anyway the joint still looks starved(too much clamping pressure), and has started to open up a little at the edges because the already glued bow stave,  now unclamped  is getting reheated again, and the glue may have softened.


Your options.
                   Buy a different glue, like  urea formaldyhyde.

                    Buy a fresh batch of EA 40, apply plenty of glue and, less heat.

[HH~]

Go to Huntsmans laminating epoxy. Just way easier to work with and goes farther and it was developed for laminating wood together. Roll it on with a 2: foam roller. I did a R & D yesterday with Huntsman and a bike inner tube. I tooth my lam surfaces lightly. Gives me good results.

For doing handles I use a similar epoxy to EA40 but when it dries it will not shrink more than .0010". Glued up a finger jointed osage for a fella night. The joint was not the best as the saw blade was a little dull for the cuts but when i glued it up i told him "this is not going anywhere" he agreed.

HH~

[Alchemist]

I'd always thought bow quality epoxy had a really long shelf life, but I just checked Smooth On's website  "This product has a limited shelf life and should be used as soon as possible." So how old is your batch? Most glue companies have extensive after sales information. Contact them with the batch #, and tell them the problem you are having, they may be able to diagnose it.

The splitting of the joint (backing and belly)after initial curing could have something to do with the heat used to speed dry. You might want to let them sit around for a week or so to increase moisture content. 160F sounds from memory to be the upper limit used by glass bowmakers. I'm not sure whether that's because the epoxy in the FG backing starts to re soften, or whether the new glue can't take it?

Anyway the joint still looks starved(too much clamping pressure), and has started to open up a little at the edges because the already glued bow stave,  now unclamped  is getting reheated again, and the glue may have softened.

Your options.
                   Buy a different glue, like  urea formaldyhyde.
                    Buy a fresh batch of EA 40, apply plenty of glue and, less heat.

The EA40 is under 6 months old.  I've already contacted 3 Rivers Archery and the epoxy is fine.  We ran through a few tests.  I'll drop the heat and maybe even move to static instead of convection heat.  I looked up the temperature ratings and there are curing references to 185 F and even up to over 200 F.

I'm unsure how to apply less clamping pressure.  Seriously.  There is a certain amount of pressure needed to keep the pieces together at the handle section when doing a r/d.  The other pressure is just the well stretched inner tubes.  Can you suggest something more?  As for more, I have epoxy coming out both sides of the joint.  How can I have more?  I'm very distinctly looking at my surfaces and they are very well coated.

When you say 'let them sit around a week' what do you mean?  The individual parts before gluing or the glued up bow?

@hedgeHunter which Huntsman are you suggesting?  I see a few products.  This one?  TDR 1100-11 Resin.

So, to repairing that ipe/boo.  Any votes for or against band sawing it apart and gluing it up again with less heat and pressure.  Or trying TBII?

And thanks for the input for this newbie.

 

[HH~]

T 1100-11

What B Widow been using for years. Best to bring it up to 130-145. It will cure in several hours at that temp.

Shawn