After reading some of the other posts, I decided to take a stab at building a cure box.
Goodwill supplied a microwave with turntable. Purchased 20W UV light from Amazon, and a small ceramic heater from Walmart.
I was able to remove the transformer and microwave emitter from the microwave.
I then cut a hole in the side of the microwave to mount the light, making the hole a little smaller so the cut edges are hidden by the bezel of the light.
I cut the bracket for the light, and bent each side into an L shape, which snugged the lamp to the sheet metal when tightened, see photo.
The Walmart heater was $14 for a 350W ceramic heater, meant to be mounted to an outlet, this thing is small.
I removed the case, and extended the wires to the control pad. A 1-3/4" hole was perfect to mount the heater controls. I drilled a hole on the top of the microwave case in a clear area. The fan at the back of the microwave turns on when the unit is operating, and contrary to my expectations, blows into the case. So I mounted my heater assembly near the vents in the wall of the heating chamber, so the heat would blow towards them. I sealed the top and bottom of the microwave with non-flammable pink fiberglass insulation, so the rear mounted fan pushes the heated air into the cure chamber, then exhausts the heat on the far side. The insulation prevents the heat from traveling around the outside of the chamber.
The maximum setting on the heater is 90 degrees F, but I’ll have to check the temperature inside the chamber. I may add a different temperature controller to allow me to heat the chamber further.
I wired the UV light and heater to the wires that used to feed the transformer for the microwave. The timer works fine, and powers everything up no problem. A better microwave might be able to sense a fault in the transformer, but this one worked fine. I was pretty happy to get everything neatly in the original case. Cost for used microwave was $25 (local dump had just shipped out their electronic waste), heater was $14, and UV lamp was $37.99
If you get a free microwave, you’d be into it for $52.
I like the ceramic heater because it should not overheat, and isn’t as dangerous as a regular heating element. The heater also includes a fan and solid state temperature control.
That’s slick! Where in the circuit are you drawing power for the light and the heater?
Probably not necessary, but it occurs to me, were I to build one, that I’d be inclined to line it with mirrors. Really get into all the nooks and crannies.
Hi. Sorry, didn’t see your replies right away.
Yes, two power leads went to the transformer that powered the microwave emitter.
Just hooked those up to the UV lamp and the heater.
I have since removed the original heater control (only went to 90 degrees F), and stripped the heater down to just the heating element and its support/shroud. I drilled two holes in the shroud, and screwed the heater to the mesh of holes where the light used to be, and the fan blew in fresh air.
Now the big fan at the back of the microwave blows air into the side of the microwave, but the only way out is through the heating element into the curing chamber. A set of holes on the far side lets the heat out. All original to the microwave. I secured the new heater control sensor to the back side of the outlet holes, and it maintains the temperature around 137 to 140 degrees F now. I had to throttle down the fan a bit so it would get hot enough, but it works like a charm now.
If you use this control, just follow the included directions. The trick is, the unit needs power to work AND you need to route one wire of your heating wire through the relay terminals to control the heater. The relay does not provide any power, just makes/breaks connection to maintain temp. I have everything hooked to the original transformer leads, so program the timer on the microwave, and turn it on. That powers up the rear fan, the UV light, the controller, and the heating element all together. The controller keeps it’s setting when powered off, so this works well. When the timer reaches the end, everything shuts off.
I retained the two over-temperature switches on the microwave (in the original circuitry) and the thermostatic safety switch on the heater shroud. Given the that the inner and outer microwave cases are metal, I feel pretty good about the unit being safe. The beauty of the ceramic heating element is that it should never get hot enough to cause a fire anyways, the heating element is self-regulating by design, so there are multiple layers of safety in place.
The metal inside of the microwave is painted white. Is it worth the effort to install aluminum, mylar, or mirrors, or is the 20W light with a turntable plenty already? What material is the most reflective to UV light? Does polishing matter?
It’s up to you - it would just cure much faster than without it. Polished aluminum/mylar is like 95% reflective for UV - so it effectively bounces between walls many times. The walls are likely steel and polishing them would not be anywhere near as reflective to UV as aluminized surfaces (not to mention much more work).
