New heatbox built
Posted: Thu Oct 16, 2014 7:07 pm
Good evening everyone.
Recently I asked about the value of Techniglue, and after some investigation, I ended up getting some Smooth-On EA-40 from John McDonald in Sydney. Impossibly good service by the way. Ordered it over the phone Friday late morning, and it was on my doorstep Monday morning (Had been away for the weekend).
So anyway, while EA-40 cures at room temperature in 24 hours, I needed to hurry the process along for the sake of the bowmaking courses I run. The best way to do this is with a heat box.
I had deliberated over heaps of different options. One was to use a fan heater that you might put under your desk. Another was to use ceramic infrared lamps. In the end I settled on old-school halogen lamps for reptile enclosures. I got six ceramic light fittings and six 75 W lamps from the local reptiliary.
I had toyed with the idea of using a reptile enclosure thermostat. They cost about $50, but only went up to 50 degrees, generally. I found some thermal circuit breakers for under six dollars from an electronics supply place. It turns out these are tremendous, especially for the value. I got a breaker that shuts off at 60, and one at 70 degrees C.
I insulated the box with polystyrene insulation boards such as go under house slabs and in walls. Two sheets at $16 each were enough. Then over that went some aluminium faced bubble wrap which was about $45 for about twice the amount I needed. I might have gone overboard with insulation, but I was keen for the unit to be efficient.
Enough chatter! Onto the pictures!
Here's the whole:
Here's the circuit breaker:
It's tiny. The base is 16 mm diameter. Rated for 10,000 cycles, so should be good for a good long while. I bolted it to a short piece of right angle aluminium. I heard Al is a terrific conductor of heat. Holding it while cutting it, I found this to be true. The thermostat is set at the same height the bow staves will rest.
I was worried six lamps would not be sufficient. However the box got up to temperature in a few minutes, and once up to temp, only needs the lamp on for about 30 seconds at a time.
I make backed wood bows mostly, as do the students on my course. This requires much less space than a glass bow in a large form. To the frame of the box, I screwed two pairs of right angle metal. Across these will go removable bars, and onto these go the glued up staves.
Here, a few bows and a board stave play proxy for a class full of laid up bow staves:
I saw someone else did this on theirs, but theirs looked better. It's a tip from a broken bow attached as a handle:
I set it going with the 60 C circuit breaker. I put a meat thermometer through a crack in the lid for a few cycles. Not in the same place as the circuit breaker though. Once up to temp, the box goes from about 56 to 60 approximately twice in 90 seconds. I'm yet to test the 70 C circuit breaker.
There is no fan in this box. But I left a board stave in for a while and felt it all over and couldn't find anywhere hotter or colder than anywhere else. The lamps are fairly close together and have a wide angle of radiation.
I've not yet tried it for real, with a glued up bow. But very soon I will. I suspect I will have some success cooking it for four hours, based on others' reported experiences. I'll try five just in case.
Overall, so far, I'm very happy with it. I need to put some handles on it to make lugging it around a bit easier though.
Recently I asked about the value of Techniglue, and after some investigation, I ended up getting some Smooth-On EA-40 from John McDonald in Sydney. Impossibly good service by the way. Ordered it over the phone Friday late morning, and it was on my doorstep Monday morning (Had been away for the weekend).
So anyway, while EA-40 cures at room temperature in 24 hours, I needed to hurry the process along for the sake of the bowmaking courses I run. The best way to do this is with a heat box.
I had deliberated over heaps of different options. One was to use a fan heater that you might put under your desk. Another was to use ceramic infrared lamps. In the end I settled on old-school halogen lamps for reptile enclosures. I got six ceramic light fittings and six 75 W lamps from the local reptiliary.
I had toyed with the idea of using a reptile enclosure thermostat. They cost about $50, but only went up to 50 degrees, generally. I found some thermal circuit breakers for under six dollars from an electronics supply place. It turns out these are tremendous, especially for the value. I got a breaker that shuts off at 60, and one at 70 degrees C.
I insulated the box with polystyrene insulation boards such as go under house slabs and in walls. Two sheets at $16 each were enough. Then over that went some aluminium faced bubble wrap which was about $45 for about twice the amount I needed. I might have gone overboard with insulation, but I was keen for the unit to be efficient.
Enough chatter! Onto the pictures!
Here's the whole:
Here's the circuit breaker:
It's tiny. The base is 16 mm diameter. Rated for 10,000 cycles, so should be good for a good long while. I bolted it to a short piece of right angle aluminium. I heard Al is a terrific conductor of heat. Holding it while cutting it, I found this to be true. The thermostat is set at the same height the bow staves will rest.
I was worried six lamps would not be sufficient. However the box got up to temperature in a few minutes, and once up to temp, only needs the lamp on for about 30 seconds at a time.
I make backed wood bows mostly, as do the students on my course. This requires much less space than a glass bow in a large form. To the frame of the box, I screwed two pairs of right angle metal. Across these will go removable bars, and onto these go the glued up staves.
Here, a few bows and a board stave play proxy for a class full of laid up bow staves:
I saw someone else did this on theirs, but theirs looked better. It's a tip from a broken bow attached as a handle:
I set it going with the 60 C circuit breaker. I put a meat thermometer through a crack in the lid for a few cycles. Not in the same place as the circuit breaker though. Once up to temp, the box goes from about 56 to 60 approximately twice in 90 seconds. I'm yet to test the 70 C circuit breaker.
There is no fan in this box. But I left a board stave in for a while and felt it all over and couldn't find anywhere hotter or colder than anywhere else. The lamps are fairly close together and have a wide angle of radiation.
I've not yet tried it for real, with a glued up bow. But very soon I will. I suspect I will have some success cooking it for four hours, based on others' reported experiences. I'll try five just in case.
Overall, so far, I'm very happy with it. I need to put some handles on it to make lugging it around a bit easier though.