Wednesday, August 10, 2016

DIY Hot Box for Drying Leather

I decided to build a hot box to speed up the drying time between processes during leatherwork.


Dwight and some other kindly leather working souls are engaged in a thread over at the leatherworkers.net forum and it finally inspired me to research and create one of these little time saving devices of my own.

The following will provide you my results and insights into the process.  Bear in mind that this is a work in progress and things are subject to change as the hot box moves from concept to reality.

I'll update photos as construction proceeds.


LED Digital 110V Temperature Controller MH1210F

150W 110V Ceramic Heat Emitter

110v AC to 12v DC Transformer (2 Amp)

Pulse Width Modulators (Fan Speed Control)



Hot Box Wiring Schematic w/MH1210F Thermostat and Optional PWM Fan Controls

Hot Box Dimensions Front
Note: Width dimensions of opening are to accommodate lighting panel grid.

Hot Box Dimensions Back

Cut sheet for a 24" x 90 panel (modified cabinet depth to 11 3/4" to use what I had on hand)

The following photos show the plywood assembly.  Note the holes cut into the face panel for the controls.



Used a length of 1/4" Pex toilet fill line cut into 2" lengths as stand-offs.  Tapped the plywood and mounted the CPU fans with 4" 8-32 round head screws.  Had a couple of old porcelain medium base lamp holders.  Ceramic heat lamps installed.

View of the sub-top with holes cut for wiring.

110V AC to 12V DC transformer wired up.

Doors cut and mounted.

3/8" plywood back panel glued and nailed.  Note access panel for wiring.

Pulse Width Modulators installed and tested with fan... works like a charm.  Here you can see the thermostat being wired.  I used 18 gauge stranded wire throughout.

Single gange cut-in box installed which will house the timer.  Colored tape was used to mark the hots, neutrals, and grounds.



Here, 10-24 tee nuts are epoxied onto the back of the cabinet.

Came up with an idea for my pegs using 10-24 all thread cut to 6" lengths, covered them in heat shrink tubing, then installed brake bleeder caps on the ends.  NOTE: I had tried to epoxy wood dowels sections to the heads of flat head screws, but the glue failed.

Shelves cut to size... Can't remove without flexing the shelf or removing the door.  I may add some extensions to the shelf cleats to solve this problem.

 The holy grail has been reached... 140º F...!!!


Some testing results:
  • Changed to all-thread pegs... working great now.
  • Shelves can't be removed without flexing or removing doors.  Will glue some extensions to the shelf cleats.
  • Thermostat read out is consistent with oven thermometer.
  • 120º F - 15 minutes
  • 130º F - 22 minutes
  • 140º F - 30 minutes
  • Thermostat interval 140º to 137º - 2 minutes
  • Reheat to 140º cut off - 3 minutes
I may change the cycle interval from 2 degrees to 5 degrees to reduce wear and tear on the thermostat.


Hope this helps,
Mike

4 comments:

  1. which amp model transformer did you use?

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  2. Thanks for posting this info Michael. This will be my next project for the shop for sure. What is the top switch with two dials? I don't see that listed in your parts list. Thanks.

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  3. Added the PWM switches to the list. These are used to control the speed of each cooling fan. I wanted to be able to control the fan speed independently from the heat lamps. Too much air flow will negate the heat being generated by the heat lamps. These controls also have an off position which will allow either fan to be turned off if not needed.

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