I cured a longbow at 150 degrees for 4 hrs then turned the power off in the shop and let it cool down overnight. Next morning power back on but forgot the bow was in the hotbox and it was still plugged in. 6 hrs later I took it out and let it cool overnight. Total of 10 hrs at 150 degrees. Well the bow delaminated after just a few shots. Any thoughts on this failure?

Thanks

James

My opinion is the second time is what caused the problem . Now i am not a professional builder but that is my take on it

Same as leaving a glass laminated bow in a hot car I suspect.

Good question, but I wouldn't be too quick to blame it on a second heat session. I know a guy that due to how he builds up his bows, runs them through multiple heat sessions in the same hot box. He's a good bowyer and has made a lot of bows that way, some heavy draw weights too. I don't recall a single bow of his delaminating.

So, I'd reevaluate all other relevant factors before I assigned any blame. Was the pressure maintained through to the end of the second session? What type of press? I'd also assess things like glue type, glue age, glue amount, adequate mixing, all gluing surfaces fully wetted, amount of pressure, same pressure everywhere, surface prep(smooth, rough, etc) wood type(oily or not?), were lams free of contaminants, degreased or not, any dyes or stains used? Where did it let go relevant to the design.... Etc. Much to consider.

Always sad to loose a bow build. I have a circulating fan in my oven, keeps temp even. I always unplug oven and open lid. I don’t trust switches. Leave overnight under pressure.Lots of good bow builders on this sight that have there way of cooking bows.

Seems odd to me if it never gets >150°.Im assuming you've made bows before and off this form before? Seems like cured is cured unless it got hotter than the initial cure.Bummer though.

Yeah, if it got hotter the second time but wasn't under the same pressure, then maybe.

What glue was it?

Post curing is supposed to be beneficial but surely time starts mattering when it's too much of a good thing.

Id say type of glue used and moisture content of the wood used may be a factor. but.... i wouldn't make a habit of cooking a bow that long. That's a bummer loosing a bow.

Personally i lay my footed risers up with no heat at all using smooth on epoxy 65-80 degrees room temp over night, then I use a heat strip system to cook the limbs both one piece and take down bows. With heat strips 160 degrees for 30-40 minutes does it.

Kirk

I use to do 185 for 1 hour and let it cool. The second time you cooked it you ruined the properties of the epoxy.

You know i have several risers i used epoxy that are several lams on then shaped the riser and in the box for 150 degrees and they are is still together one is 30 years old still shoots good. Look at the wood maybe it was just some bad lams .

After close inspection, I think the problem was a starved glue section at the fade ramp. Thanks guys for all comments and evaluations of this failure. Lots of information to consider.

James

I have my oven on a timer and have forgotten it many times some bow more than twice and its never made any difference .

The problem with using a hot box to cure bows is that you are cooking your form to death while you are at it. To get the heat needed to cure the epoxy inside those limbs requires about 5 hours at 180 degrees.

i know its a pretty common way to cure bows using a hot box, but if you are building a lot of them it doesn't take long for your forms to start twisting from all that heat. Once a form is twisted, you are building a bow with a twist in it from the start, and it turns into a nightmare to adjust tracking.

Building a heat strip system isn't difficult, and it takes all the fight right out of it.... Kirk

Or go with the big boys and use metal forms.

I'm with Jeff Durnell. I too cure multiple times. The more ornate the bow, the more times it goes in for a cure. Never had a delam.

I have forms that are thirty years old and they have never twisted, some get used every week. I have heated bows as many as four or five times never a problem . 150 degrees is enough to heat a bow and a long slow cure is the best .

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