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Main Boards => The Bowyer's Bench => Topic started by: Sant-Ravenhill on December 01, 2020, 07:41:37 PM
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Years ago I built a heat box/bow oven out of plywood. It worked great but is now gone. I sold my house, in a rental and will be moving in a year. I would like to make a bow or two this winter.
I want to make another bow oven but I would like it as light and portable as possible as I will be moving it up and down stairs. I was thinking foam board, styrofoam insulation, or? Possibly a light 1X pine frame for strength? Or much better ideas? :clapper:
Thanks for your time...Brett
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Depends on your desired temps, but I have seen it mentioned here that some use an electric blanket laid over the form with a heavy comforter over that to keep the heat in. I think that will get you into the ~120F range with little trouble.
If it needs to be a box I would suggest a light wood frame with panels made from heavy cardboard. The cardboard will survive much higher temps than the epoxy will with no issues at all.
Mark
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You can build a hot box with foil backed foam board held together with duct tape and ceramic light sockets and 100w bulbs for the heat source.
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A couple of good ideas...thank you. If anyone else has some thoughts please post. Brett
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A refrigerator box? It could be folded flat when not in use.
I do a variation on the blanket trick by putting a blanket over the form with each end slightly open and blow a space heater through it. Temperature is monitored with a Bluetooth meat thermometer. I run it at about 135* for 12 or more hours then turn off and leave it overnight.
Then there's the car in the sun trick if the season and climate permits.
Another is to wrap it all up in black plastic and lay it in the sun. Just don't lay it on the grass.
Finally, you don't need any oven contraptions at all. If kept at room temperature (my definition is 72*) and allow at least 24 hours.
I've used all of the above except the refrigerator box and they all worked.
Good luck with your tight quarters building. It's been successfully by others.
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The oven is expedient, but not essential to building a durable, quality bow.
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The electric blanket with another blanket over it is your easiest way to go. And its already been mentioned that epoxy dries in 24 hours at room temperature at 70 degrees. The heated blanket will get 110 degrees easily.
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i use an electric blanket with a sleeping bag over top... i get 110 to 120 degrees... plenty of heat to cure a bow...
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Thanks to all. It sounds like an electric blanket is the simplest way to go. I have more than one old sleeping bag to cover it with. Though the refrigerator box or foil backed foam board are serious options for a more structure oriented bow oven.
I've always read that you want higher heat to cure or there is the possibility that the limbs will delaminate. Any truth to that or is it like onetone posted, expedient but not essential?
Thanks again! This is one of the reasons why I love this website.
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TTT
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Supposedly the higher heat will keep from delamming up to that temp, I haven't seen proof of that but have seen a heat delammed bow.
I had heard some big name bowyers weren't heating so I built my bro and I a pair of TDs without heat to test,
cured at 70* in the shop.
That was 4 years ago and no probs yet, but we don't leave em in a hot car or anything like that.
Mine has been left in the truck on a few warm days ,80ish, but I roll the windows down a bit.
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You can use 1/8" plywood and glue/laminate some rigid foil faced insulation to it. Makes a stiff panel that is reasonably light. Plus you can crank the heat up to 200deg if you want.
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You can use 1/8" plywood and glue/laminate some rigid foil faced insulation to it. Makes a stiff panel that is reasonably light. Plus you can crank the heat up to 200deg if you want.
Good idea. Maybe sime hinges to allow folding it up?
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I used a padded moving blanket draped over some f clamps over my bows and a small space heater placed just outside the open end with the blower on high.
My heater is the ceramic type with no glowing red hot elements. I stuck a meat thermometer through the blanket at the far end and it read 160 degrees.
Dave.
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I only use 2 electric blankets and 2 clip on shop lights to cure my bows you can go between 125-200 F the only problem is you really have to watch it tell you get your temp stabilized I usually cure between 125-150 F I have a controller kit for it I never put together , and when your done fold it up and put away ! I have room temp cured bows to with out issue !
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I would room temp all of mine but in the cold months I can't count on keeping the room that I'm "allowed" to use at 70 degrees minimum. :)
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Epoxy will cure just fine at 70deg. Even at lower temps, within reason. Just have to double the time for every 18deg in temp change down and half it for every 18deg up. The prime reason for cooking bows is to cut production time. If you are brave enough to ignore the EA-40 cure schedule, you can have a bow cooked in 45min @ 160deg. Of course you have to start with room temp materials and factor the cool down period. I always put a dummy wood block with a temp probe in the center, in with the bow blank to get an accurate idea of the internal temperature.
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Great information...thanks again to all that have posted. It has saved me lots of time experimenting from scratch. I will keep you posted on what I end up doing and the results.
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here is something else to consider... i call an electric blanket gentle heat... meaning it heats up slow and evenly... if you don't heat your form up evenly you could warp it... i have heard of this happening more than once... if you want to take an extra precaution you could put plastic over the form before putting the blanket over it to help maintain the same moisture content on all sides...
flem... my school of thought on temperature is to give it enough heat so those molecules can get moving and interact properly... meaning get the temperature above ninety degrees...
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Thats a really good point Rich. I should be qualifying any statements I make, because I do not use a form and don't know about any affect my heating schedule might have on one.
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Shredd I will definitely put plastic under the electric blanket. The last thing I need is a warped form. It should be pretty straight forward to get the heat above 90 degrees that way. Thank you.
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You can build a hot box with foil backed foam board held together with duct tape and ceramic light sockets and 100w bulbs for the heat source.
This works great. The insulation foam board is plenty stiff and you can move the dang thing around.
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Shredd I will definitely put plastic under the electric blanket. The last thing I need is a warped form. It should be pretty straight forward to get the heat above 90 degrees that way. Thank you.
it can't hurt... if you are on the fence about the blanket vs the hot box, i want you to do something...
i want you to take two sheets of plywood, some wire, four bulb sockets, male electrical plug, hinges, insulation, ect ect... and put them in one corner of the room... now take an electric blanket and put it in the other corner of the room... now go cut your riser, grind your lams and get ready for glue up... when your ready for glue up, look in that corner of the room and then the other corner of the room... which do you choose?? :) ;)
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And let me know when you have decided. I'll come by and get all that plywood, etc. Out of there for you. :)
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Does he get to fashion the materials into a useable box first? Also if he were to replace the inefficient light bulb heat source with one of these as small as 300w(housing removed);
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His box would be up to 150deg in about 3 minutes.
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Hey Flem, is that an electric baseboard heater that you have taken the shroud off of?
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You guys that are advocating for a solid box of some sort are forgetting OP's requirements that it be light and easily portable because he doesn't have much space to work with and is in a temporary living space. The boxes could be the best bow oven on the planet, but they don't fit his requirements for the moment.
Flem, I like that baseboard heater idea a lot for a more permanent installation. Does the thermostat control manage the internal box temps ok or do you need to do something else with it?
Mark
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Yeah its an electric baseboard element. I had the same dilemma as the OP, space and weight. My shop is congested, everything is on wheels. Even on wheels, the hot box takes up way too much real estate.
That pic was a screen shot, mine is 18" 300w. Any more wattage would be overkill for 6 cu ft of space. You can use the thermocouple that they come with, but its a pain to get it in the perfect position corresponding to desired temp. I use mine for other stuff also, so I put a PID controller together. I use this box regularly at 200deg. The fan along with the diffuser over the element, eliminate hot spots and keep the heat circulating.
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Nice set up Flem I still have my PID kit I have yet to put together , if your using the heat blanket system with out additional shop lights or heating elements it takes a good while to come to temp but it’s a good thing as it slowly warms your form ,so no warping at least I never have had it ,I also have some IR heating elements that I want to try with the PID controller & blanket !
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I put casters on one end of my hot box so I can stand it on end and roll it into a corner.