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Main Boards => The Bowyer's Bench => Topic started by: EzellH93 on April 22, 2021, 08:08:10 PM
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How hot does it really need to get? I can’t seem to get mine over 145 degrees. 4 200w bulbs and it’s lined with foil. Any ideas?
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145 is plenty.
I would think 4 200 watt bulbs should do better though.
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Try foil backed foam board for insulation.
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2 more bulbs
go to the Lowes and buy a Twin-Socket Lamp Holder Adapter $3.00 each
That's how I did mine
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I got rid of bulbs and went with ceramic, they seem to get a lot hotter than bulbs
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Well if 145 is enough, I guess I'm good? Ultimately, the heat just speeds up the curing of the epoxy right? Or is the temperature necessary for a more solid curing. In other words, could the epoxy not cure at room temp over a longer period of time?
My box is pretty crude. My lid isn't built the same as they do at Bingham (concave lid with lights recessed)... it's just a flat piece of wood that is hinged. Bulbs are installed on that piece of plywood. Never understood the necessity for the complex lid design that I've seen on many oven... perhaps I was mistaken?
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You were mistaken. Insulation and a good seal is how you will get more heat out of that box. The first incarnation of my box had 2-25w and 3-15w halogen puck lights and would get to 200deg easy. That and spend $20. on an axial fan.
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The epoxy will cure at 70 degrees in 24 hours.
However heat speeds up the curing and has been said to make the epoxy more heat resistant.
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@Flem.. so the lid is my problem?
I should note that I'm using a meat thermometer stuck through the hole for my wires as my gauge. Could be massively inaccurate... maybe.
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I have used a blanket over mine :thumbsup:
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Without seeing a picture of your box, I would not venture to get too specific about your problem.
If your house is uninsulated, its going to be hard to keep warm. If you leave the window open, your heat will exit said window.
Meat thermometers are usually in the ball park, but you can do better for only a few $$
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As mentioned above a cheap moving blanket thrown over bow oven will help out a lot. Slightly lower temps are fine too.
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I just skipped the box and went straight to the blanket... :laughing:
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The epoxy will cure at 70 degrees in 24 hours.
However heat speeds up the curing and has been said to make the epoxy more heat resistant.
Roy you suppose that means if your`e hunting in a desert you might have a de-lam if temps hit 100 Degs +?
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If your going to use a blanky, be sure to get a nice Teddy to keep your bow blank company.
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I am thinking smooth on needs to be about 160 before it starts to delam.
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If your going to use a blanky, be sure to get a nice Teddy to keep your bow blank company.
My forms get 2 Teddys... Sometimes 3.... :goldtooth:
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Sounds like a three dog night.
I am thinking smooth on needs to be about 160 before it starts to delam.
Thats only if you do the post cure, which includes 2 hrs at 250deg
They don't give the distortion temp for a room temp cure. My guess it would be similar to some of Smooth-On's other epoxy's; 120-140deg.
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No stagmissy..
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I have placed a cheap sleeping bag over my heat box and put it on a couple short pieces of 2x4 to get it off the concrete in my garage. 150-155 no problem with 5-150 watt bulbs. But I live in deep southeast Texas too, we are a little closer to the sun.
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(https://i.imgur.com/QQPbsY2.jpg)
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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...
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I agree 100 percent..
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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
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How do you measure cu. feet on a electric blanket and a sleeping bag??? :laughing:
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... :)
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I dry my bows at 85 degrees.
Never had one delam, and they get pretty hot after I put bout 20 shots through them..
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So exercising yur bow makes it sweat PFFT!! :bigsmyl:
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I dry my bows at 85 degrees.
How wet are they??? :laughing:
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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
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No stagmissy.. :laughing: :laughing:
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.
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Smooth-On is no different. The higher the cure temp, the higher the heat deflection temp.
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what is heat deflection?
https://www.westsystem.com/instruction-2/epoxy-basics/epoxy-chemistry/
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Those glass bows sound a little dainty to me.
:laughing:
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I have an old tube heater placed on the bottom of my box. Heat it up to 50 C-120 F.
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Google EA 40 the site will tell you exactly what you need to know about the curing of the glue for best results.
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It's at the top of this page stickypops :thumbsup:
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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.
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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
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Yup it's hard to beat a hot box.
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what is heat deflection?
https://www.westsystem.com/instruction-2/epoxy-basics/epoxy-chemistry/
https://www.youtube.com/watch?v=mNTn9RoPFaU&t=329s
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Agreed on the hot box... I have three for different uses...
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Good information there Shredd :thumbsup:
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Yeah that was a great promo video for Instron HV3s.
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The epoxy I use will cure at any temp, but it attains max heat deflection when cured for 1hr@200deg
No hurry, just optimizing.
Flem, is that max deflection for system 3? I would be interested in reviewing the spec you are reading from.
Does this claim seem to indicate a heat treat will improve final stiffness irreguardless of cure time?
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Thats for Smooth-On Epoximite. Not sure about the specs for any System Three epoxy's.
It's a general rule that an epoxy will achieve its maximum potential for desirable properties, including heat deflection, glass transition and molecular cross linking (strength)with the highest temp the components were formulated to cure at.
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Ah, epoximite. I have never used it. guess I was seeing the clear coat you posted a pic of a while back. (I use it quite a bit), and though have not researched lately, can only recall time and temp relating to the speed of cure, but not the ultimate strength neccesarily.
thanks
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Huh