Hot Box made from scrap materials.

ribanett · Mar 2, 2010

I made this hot box from scrap materials I had in the shop.
The old toaster oven I have will not hold enough blanks for post-cure
The sides were made from an old Dish Barrel Box I had. (from U-Haul) This box is double thick corrugated and it retains the heat very well.
Size 16 X 14 X 14
If you have to buy new materials (dish barrel box, bulb bases and hinges) the cost should be right around $10 to $12.

Heat is from two light bulbs.

Had to insert this shield to prevent overheating one end of the blanks.

This is the rack I made to hold the PR blanks I post-cure. I cure 40 blanks at a time for 1 1/2 hours. It will hold more but I make 40 at a time.

This is the simple support framing I made from .75" square pine

With two 60 watt bulbs I get over 150 deg at the top of the box. Room temp was 60 deg.

145 deg at the top shelf of the rack

130 deg at the middle rack

Took me about 1 1/2 hours to put it all togeather.
With only one light bulb, the temp is 105 deg. Just right for drying my painted tubes and blanks.

Pioneerpens · Mar 2, 2010

I love it! I may have to borrow this set up! Way to think outside (inside) the box

Jennifer

Dorno · Mar 2, 2010

Very Very Clever

Great idea could save us a fortune and also alot of time you have my thumbs up:drink:

Cheers Ian

jeffnreno · Mar 4, 2010

Great looking box - thanks for the idea

Padre · Mar 4, 2010

Newbie question: What is this used for?

ribanett · Mar 25, 2010

Padre said:
Newbie question: What is this used for?

I use it for a number of things:

With one light bulb: drying painted blanks and tubes, curing epoxy glue,
warming PR before adding MEKP

With two light bulbs: post-cure PR blanks

DurocShark · Apr 1, 2010

How much heat is lost through the cardboard? I'm curious to see what more insulation does...

(Like I need yet another project... LOL!)

Mark · Apr 1, 2010

I like that a lot. Way to go..

I hope you don't mind me making a copy. :biggrin::biggrin:

larryc · Jan 23, 2011

They say that imitation is the sincerest form of flattery so consider yourself flattered, Larry

I just finished my version of your hot box and here are the pix.

Since the dish box size you used (16 x 14 x 14) is no longer available at U-Haul, I used the 18 x 18 x 29 box. This resulted in a lower overall temperature (100 deg vs your 130 deg at the middle of the box)

I only had 60 watt bulbs on hand so I will get some 75 or 100 watt bulbs tomorrow to obtain the desired temperature.

Thanks for the idea Larry

titan2 · Jan 24, 2011

larryc said:
They say that imitation is the sincerest form of flattery so consider yourself flattered, Larry

I just finished my version of your hot box and here are the pix.

Since the dish box size you used (16 x 14 x 14) is no longer available at U-Haul, I used the 18 x 18 x 29 box. This resulted in a lower overall temperature (100 deg vs your 130 deg at the middle of the box)

I only had 60 watt bulbs on hand so I will get some 75 or 100 watt bulbs tomorrow to obtain the desired temperature.

Thanks for the idea Larry

Put a rheostat in there to vary the light bulbs and control the temp pretty good.

Barney

ctubbs · Jan 24, 2011

If you can find a VAriack (variable auto transformer) to use instead of a rheostat it will give better control and longer life with less heat load.
Charles

larryc · Jan 24, 2011

The rheostat will only cut the voltage down so you have to have the larger bulbs to start with. The same thing with the Variac except you can increase the voltage slightly (which may result in shorter bulb life).
I am up to 100 watt bulbs and am still not getting the 150 degrees that Larry experienced. 150 watt bulbs are next. Of course I may run up against the barrier of CFL bulbs which put out little or no heat.
I do not feel any heat on the outside of the box so the double cardboard construction of this box seems to do a good job of insulation.

G1Pens · Jan 25, 2011

Put it on a timer and you wont have to worry about leaving it on.

ribanett · Jan 25, 2011

larryc said:
The rheostat will only cut the voltage down so you have to have the larger bulbs to start with. The same thing with the Variac except you can increase the voltage slightly (which may result in shorter bulb life).
I am up to 100 watt bulbs and am still not getting the 150 degrees that Larry experienced. 150 watt bulbs are next. Of course I may run up against the barrier of CFL bulbs which put out little or no heat.
I do not feel any heat on the outside of the box so the double cardboard construction of this box seems to do a good job of insulation.

From looking at your photos a couple of things:

1 Cut your heat shield in half. The only shelf that will be effected by the radiant heat from the bulbs will be the bottom one.

2. Seal the corners of the box with duct tape. The reason you do not feel warmth on the outside of the box is because there are convection air currents thru the channels in the cardboard. These currents are carrying your heat away. Every edge should be taped.

3. Because you have about doubled the inside cube of the box. You may have to add an additional bulb.

Hope this helps.

snyiper · Jan 26, 2011

Another build option is to use old election signs for the outside, it is usually made from plastic cardboard called cloroplast I believe. This stuff is usually pretty cheap after a election!!!

larryc · Jan 26, 2011

ribanett said:
larryc said:

The rheostat will only cut the voltage down so you have to have the larger bulbs to start with. The same thing with the Variac except you can increase the voltage slightly (which may result in shorter bulb life).
I am up to 100 watt bulbs and am still not getting the 150 degrees that Larry experienced. 150 watt bulbs are next. Of course I may run up against the barrier of CFL bulbs which put out little or no heat.
I do not feel any heat on the outside of the box so the double cardboard construction of this box seems to do a good job of insulation.

Click to expand...

From looking at your photos a couple of things:

1 Cut your heat shield in half. The only shelf that will be effected by the radiant heat from the bulbs will be the bottom one.

2. Seal the corners of the box with duct tape. The reason you do not feel warmth on the outside of the box is because there are convection air currents thru the channels in the cardboard. These currents are carrying your heat away. Every edge should be taped.

3. Because you have about doubled the inside cube of the box. You may have to add an additional bulb.

Hope this helps.

Thanks for the info.
I followed your instructions about taping and reducing the size of the heat shield but still could not get enough heat so I went to two 150 watt bulbs - too much heat. Settled on one 100 watt and one 150 watt bulb and I get the 150 degrees at the center of the shelves. Sometimes you just have to play with these things.

Rangertrek · Jan 29, 2011

Great idea using the materials around the shop.

MesquiteMan · Jan 29, 2011

I built one a year or so ago to dry larger quantities of blanks before casting. I made a 2x2 frame and inserted 3/4" foam sheathing between the frame. I then covered it all with fire rated drywall. On the bottom, I installed 2 keyless fixtures and wired them to a switch and then a male plug end. I installed 2 expanded metal shelves and lined the outside with some scrap beadboard I had around the shop. I put casters on it and made a door for it.

For my heat source, I am running 1 250 watt heat lamp currently and can achieve and hold at 180 F. With both bulbs running, I was getting too hot, pegging my temp gauge which goes up to 350 F. I was worried about it getting too hot and starting a fire! I installed a sheet metal guard over the top of the bulbs to prevent small pieces form dropping on the bulb and possibly starting a fire.

My box is 34" tall, 30" wide, and 28" deep and can do a few hundred blanks at a time and works real well. I will try to take some pics and post them later.

MesquiteMan · Jan 29, 2011

snyiper said:
Another build option is to use old election signs for the outside, it is usually made from plastic cardboard called cloroplast I believe. This stuff is usually pretty cheap after a election!!!

I think I would be careful with the plastic signs since parts of them will be close to the heat source and may exceed the flash point of the material. Not sure what that is, though. I do know that wood's flash point is 525 F and should never be a problem. Not sure about cardboard either but I do know that I have a piece of fire rated drywall UNDER my light fixtures and the paper is all black and charred from the heat. Be careful and run your box outside for 24 hours the first time you run it to make sure it is not going to catch fire!

MesquiteMan · Jan 29, 2011

larryc said:
Thanks for the info.
I followed your instructions about taping and reducing the size of the heat shield but still could not get enough heat so I went to two 150 watt bulbs - too much heat. Settled on one 100 watt and one 150 watt bulb and I get the 150 degrees at the center of the shelves. Sometimes you just have to play with these things.

Were you not getting enough heat when the blanks were wet or after they were dry? In my "kiln", with wet wood, the best I can get is 145F when I load it for the first few hours. As the blanks dry, the temp goes up until it steadies out at 185 F when the blanks are dry. They is one way I know the blanks are dry and I have tested this theory with a $300 moisture meter that I have that can be set for the specific gravity of the specific wood I am measuring.

Hot Box made from scrap materials.

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