- Joined Mar 24, 2008
First step is to get the sheet metal. I got a .01” x 12” x 12” sheet metal and used the following pattern to cut 6 metal spacers shown in the .png file (print this pattern using M$ Paint and the individual sheet is to scale). You will also need a piece of ¼ thick aluminum for the top of the hot plate. I countersunk and tapped the holes for a #6/32 screw. This is important, as it will simplify construction later. Also drill a 0.1” hole in the side of the back of the top plate as deep as you can to immerse the thermocouple into. I used high temperature RTV to make it stay in place. So after cutting and drilling the spacers to spec I started assembly. The 1.0” x 1.0” notches give the square bumps on the heater spaces to go when stacking the heater elements (Qty 4). You will also need a separate unnotched bottom plate. Assemble as shown.
After you are done stacking the metal plates (spacers) and heater elements (Quantity 4 of each) unite the hot assembly the with a #6/32 nut, this will form a space between the wooden base and the heater assembly (which will char the wood less later).
Do yourself a favor and crimp the lugs on before starting the stacking phase and if you are real adventurous cut the lead lengths too (I’m chicken and used the entire wire length). I labeled each lug with the resistor number matching the terminals shown on the schematic. I also labeled the terminal holes on the base block (hidden hidden below the lugs) for easy reference. Take the time to add spacers as needed to level the total hot plate assembly and match the heights of the wrap around wooden frame. Mostly this is for appearance.
SchematicThen wire the hot plate as shown.
A quick note about the power supply, you can use a 24VAC transformer and a commercial proportional power controller in lieu of a variable power supply. Since I do have a variable DC power supply that is what I used.
When I turned it off in 1hour 10 minutes the hot plate cooled to 60 °C. In 3hours it was 28°C. Now you know why the timer was in the picture.
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