To Heat Box, or Not

[D.A. Davis]

I've read on here that there are a few bowyers that do not use a heat box.  I konw that some use the heat strip, but I've read where some don't use any heat source.  They just let the adhesive cure naturally without heat.  What are the pros and cons of using this method?  Is room temperature important when using this method?

[Moen]

I use WestSystem Epoxy, with and whitout heatbox. But i dont glue if the roomtemp is under 21 celsius. I never have failure. Never seen delamination on my bows. And i talk about bows up to 130#. With SmootOn i dont know.
Good luck

[Jason Jelinek]

I've heard the glue cures stronger using heat.  I read the G2 instructions and all I could tell was that it cures "faster" using heat.  Maybe it is for convenience?

[Moen]

UHU Endfest 300 cures stronger using heat. Up to 90-100 celsius. WestSystem also, but not much. And you never feel/see the difference if heat-treated or not. Try a glue test like the test from TBB..

[D.A. Davis]

So, if using Smooth-on I need to use heat.  I was planning on it, but was just curious of the other processes.

[Jason Scott]

You don't have to use heat with smooth-on.
I do use heat, but, I do know that my mixing cup and stirring stick is hard as a rock the next day and it just sat out at ambient temp all night. I had to chisel a glob off the garage floor several times.

[BOWNAERO]

Its been several years since I built bows-( the bow building bug is biting again). I would believe that the heat process not only helps the "cure", but thins the epoxy as well which in turn should assist it in saturating all the various lamination pores creating a better overall bond. For example spread a small batch of epoxy and hit it with a hair dryer, the thick epoxy basically goes to soup. Imagine what happens with the addition of the pressure hose!!
Again, its been a few years since I built and adhesive technology is ever advancing.
                                GOD Bless,
                                      Terry

[Roy from Pa]

Good point Terry. I use smooth on also. It dries just as well without heat as it does with heat. Just takes  a little longer to dry without heat. Never had a glue joint come apart yet, with smooth on or urac 185.

[BOWNAERO]

Just my curiosity, but are there any major commercial bowyers not using the heated cure process for the limbs? I could possibly see no need for heat in some types of riser laminations, but the limb and all of its dynamic flex is a super critical adhesion joint. Binghams, and Old Master Crafters had advised me-(years back) to always use heat, even as far as glueing limb tip overlays.

[Dick in Seattle]

I use the oven.  I was told that in addition to speeding up the process, using heat helps with the glue distribution,i.e. keeps the glue thinner and lets any excess squeeze out more evenly, giving you thinner, lighter glue lines and possibly better penetration into the sanding lines on the lams.   Also that it helps to protect the bow should it later be subjected to heat, like being left in a hot car or something.  I guess the idea is that if it is exposed to heat greater than what it was cured at, delamination is more likely.   Don't know of any solid scientific studies or anything, but that's the way I was taught, so that's the way I do it.   There's also the fact that that big wood oven on wheels in the shop is a great conversation starter with visitors 8^)

[Swissbow]

I don't use a heat box with my bows and never had problems. But I only glue up a bow if the temperature is over 20 degrees C and I warm up the epoxy with an electrical oven so it gets a bit more liquid. The epoxy I use is mainly used in construction of glider planes and boats and cures very good at room temperature ( according to the manufacturer ). BTW has anyone of you ever tried to put a sailing boat into a heat box ?

-----------
Andy

[rbbhunt]

From what I understand, a lot of epoxies will be able to endure higher temperatures without any softening when cured at elevated temperatures.

[rbbhunt]

And here is an interesting excerpt from Smooth-on's tech bulletin:
"Apply to prepared surface and let cure for 24 hours. Applying mild heat will cure EA-40® faster – 150°F/65°C for 6 hours.
Post Curing – After EA-40® has cured at room temperature, heating the epoxy to 150° F (65° C) for 4 to 8 hours will increase physical properties and performance"

This tells me it might be best to let it set at room temperature for 24 hrs and then put it in the heat box.

[Bob Barnes]

this is all interesting...I recently glued a nice hickory backing over a glass backing...I did it to pick up some draw weight and also because the bow had an osage belly with no glass.  The wood lams were all glued with urac but I used smooth on for the glass to wood joint...and didn't use the hot box...after finishing it and getting it tillered to the intended 50@30... it only lasted a couple of days before the hickory snapped mid limb and it can apart for most of the limb that gave way...no indication of any damage other than the broken and separated hickory backing...???

I plan to take the backing off and add either another piece of hickory or a piece of bamboo...but want to figure out why it happened.

thanks.

Bob