Curing Oven

[Mad Max]

[Shredd]

   I have been on bow making forums and groups for a few years now... The subject of curing epoxy with heat comes up all the time... I have never heard one person say that my bow failed because I did not get it up to temperature (all being over 70 to 75*)... Matter of fact I here of people having problems with raising the temp too high too fast... I tried different curing methods and never noticed a difference in performance or structural integrity...  I talked to a very experienced composites engineer... He said, you are dealing with one thousandth's or less of thickness of a glue joint, don't worry about it, just give the epoxy ample temperature to cure correctly and all the way... Heat distortion comes big into play when you are laminating f/g where the epoxy is relatively thick and is now structural and needs to remain ridgid which is completely different when compared to a glue joint..   Another well known bowyer said high heat is hell on riser wood, and I think we can all agree to that...

    My conclusion: I just use common sense...  I cure my bows at mostly at 110 to 120*...  Its plenty enough to get those molecules moving around to get a good cure in 4 to 5 hours...  My hot box is now a wood drying kiln and I use an electric blanket to cure my bows... Anything over 90* is plenty to cure that epoxy well...

   My 2 cents...

[Roy from Pa]

I agree 100 percent..

[Flem]

I agree 100 percent..

I agree also. But thats a snapshot perspective. Where I live and my shop heating circumstances dictate a fast cure cycle. I prefer to heat 4 cubic feet to 200deg for one hour, rather than 5000 cubic feet @ 70deg for 24hrs, or either one for 6hrs @ 120deg. Matter of fact I would prefer a fast cure in any climate.
As far as damaging the materials from heat is concerned, 1hr @ 200deg=200 degree/hours, 6hrs @ 120deg = 720 degree/hours

[Shredd]

  How do you measure cu. feet on a electric blanket and a sleeping bag???   

   I guess whatever works for you...  More than one way to skin that cat...

  I do have some questions though...

What is your rush in heating up something to 200* and curing it in one hour??  What are the benefits??  Are you in large scale production where time is a big factor??  Don't things expand and contract and gas off at fast temperature changes??  Did you know that extreme temperature changes over time can warp your form??  5,000 cu. feet?? That's one big hot box...   

[Roy from Pa]

I dry my bows at 85 degrees.

Never had one delam, and they get pretty hot after I put bout 20 shots through them..

[Crooked Stic]

So exercising yur  bow makes it sweat PFFT!! 

[Shredd]

I dry my bows at 85 degrees.

  How wet are they???   

[Flem]

   I have been on bow making forums and groups for a few years now... The subject of curing epoxy with heat comes up all the time... I have never heard one person say that my bow failed because I did not get it up to temperature (all being over 70 to 75*)... Matter of fact I here of people having problems with raising the temp too high too fast... I tried different curing methods and never noticed a difference in performance or structural integrity...  I talked to a very experienced composites engineer... He said, you are dealing with one thousandth's or less of thickness of a glue joint, don't worry about it, just give the epoxy ample temperature to cure correctly and all the way... Heat distortion comes big into play when you are laminating f/g where the epoxy is relatively thick and is now structural and needs to remain ridgid which is completely different when compared to a glue joint..   Another well known bowyer said high heat is hell on riser wood, and I think we can all agree to that...

    My conclusion: I just use common sense...  I cure my bows at mostly at 110 to 120*...  Its plenty enough to get those molecules moving around to get a good cure in 4 to 5 hours...  My hot box is now a wood drying kiln and I use an electric blanket to cure my bows... Anything over 90* is plenty to cure that epoxy well...

   My 2 cents...

Damn, thats a lot of questions Shredd, you sound incredulous!

The epoxy I use will cure at any temp, but it attains max heat deflection when cured for 1hr@200deg
No hurry, just optimizing.

I don't use a form and my shop is 5000cuft

[Stagmitis]

No stagmissy..


I had a good friend who had several authentic Hill Bows built by a very well known bowyer who let his bows cure at room temp- All eventually came apart and after a while the theme that developed was they all failed in the summer months during high temps- The bowyer started using an oven with higher temps and the de-lams went away. He used either Urac or Recorcinal for the cores and not sure which epoxy for the Glass-

So I always wondered if a cure is only as good or close to the highest temp it gets cooked at.  Guess smooth-on is different.

[Flem]

Smooth-On is no different. The higher the cure temp, the higher the heat deflection temp.

[williwaw]

what is heat deflection?


https://www.westsystem.com/instruction-2/epoxy-basics/epoxy-chemistry/

[Roy from Pa]

Those glass bows sound a little dainty to me.

 

[Buemaker]

I have an old tube heater placed on the bottom of my box. Heat it up to 50 C-120 F.

[Crooked Stic]

Google EA 40 the site will tell you exactly what you need to know about the curing of the glue for best results.

[Mad Max]

It's at the top of this page stickypops

[Flem]

what is heat deflection?


https://www.westsystem.com/instruction-2/epoxy-basics/epoxy-chemistry/

Heat deflection is the temperature that a rigid piece of material will start to bend under load.
Glass transition temperature is when it starts to melt.

[Mad Max]

A hot box is good to have.
I have used mine to warm up the room over night while a glued up bow is clamped to the work bench form.
Drying out staves slow.
Warming up your epoxy before glueup.
Drying out old dead Osage crooked limbs I want to make canes or walking sticks.
And for fast curing multiple lam, striped  risers that need 3 or 4 glueups.
Always good to have

[Roy from Pa]

Yup it's hard to beat a hot box.

[Shredd]

what is heat deflection?


https://www.westsystem.com/instruction-2/epoxy-basics/epoxy-chemistry/