N451BX

Homepage/Builder's log for Cozy MKIV S/N: 1671

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Ch 3 - Practice
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Epoxy Box


Chapter hours:  TOO MANY                                      Total Hours:    0





The Epoxy Box:  I decided to use MGS L335 epoxy for my aircraft.  Epoxy has an affinity for moisture, which will ruin it.  As such, most folks keep their epoxy in a heated box, to help keep the moisture out, and to keep the viscocity of the of the epoxy low, as lower viscocity epoxy will "wet-out" the fiberglass better, making for easier, faster layups, and lighter parts. 

A few different ideas have surfaced over time with regards to keeping epoxy warm and dry, and being able to dispense it with ease.  I chose to forego the epoxy "pumps" used by some and instead use a gravity feed system like some others have done.  Pumps have a tendency to clog and/or entrain air.  Any dispensing system I have seen has its pros and cons.  Pick your poison.....

My epoxy box is constructed of plywood, with "R-board" insulationInside are three paint cans, unused from Home Depot.  There is one gallon can, and two quart cans, to hold the MGS L335 resin, and MGS H335F and MGS H340Sepoxybox1 hardeners (catalyst), respectively.  I made holes in the bottom of the paint cans to fit 3/8" size tubing bulkhead fittings.  The bulkhead fittings pass through both the bottom of the can, as well as the bottom of the box.  A flat washer under each paint can around the bulkhead fittings takes up the space created by the bottom seam of the can.  Another flat washer on the bottom of the box gives the bulkhead fitting something  solid to compress against to create a good seal.  A 1/16" gasket was cut and placed between the shoulder of each bulkhead fitting and the can to ensure a good seal. 

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Beneath the box, attached to the bulkead fittings are short lengths of 3/8" copper tube, which is connected to a 1/4 turn ball valve.  All three fittings were arranged as close to the center as possible such that all three valves will come together within reach of a mixing cup positioned on a scale below the box for easy dispensing. 

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To provide heat, a 25W incadescent light bulb is mounted inside the box.  Control of the heat is threefold.  A differential temperature controller monitors the temperature and triggers the lamp on and off.  A dimmer switch controls the intensity of the light.  Additionally, a fan circulates the air inside the box to keep the temperature uniform and regulated.

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At first I planned to build the epoxy box as a stand alone shelving unit that could be easily moved around.  Over the years I have learned to appreciate ergonomics though.  I have designed the shop thus far to fit me, meaning that epoxybox7as much as possible, I don't have to squat, bend over, lean or otherwise contort myself to work on something.  To pull this off with the epoxy box meant that it needed to be mounted 56" off the floor so I could dispense epoxy onto the scale without stooping down and peering at it.  Given the overall height of the unit this would create, it would also create a pretty unstable structure, so I opted to just mount the entire unit to the wall with a shelf under it for the balance. 

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The differential temperature controller was actually a last minute add-on.  I was originally going to just adjust the dimmer until I found a setting that would maintain temperature close to what I was looking for.  I've used similar DIN-style controllers for years in industry, and they are a perfect fit for this application, but usually cost prohibitive at several hundred dollars.  Just for fun, I searched for them online one day to see what they would cost.  Surprisingly, I found this one on Amazon for $16.  There are a handfull of them available there, cheaply made from Aisa.  This particular model was private labeled by a company called InkBird.  It includes a temperature probe, and the contacts are rated 10A.  The controller maintains temperature within one degree F.  They also offered a PID unit with solid state variable external SCR output relay for $45 that could control even tighter, but I'm building an airplane, not a reactor, so that finite of control is unnecessary, so I reigned myself in and saved that extra $29 for more epoxy.  I might, however, obtain one later for a composite post-curing box that I am considering........

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Temperature controlled epoxy boxes were not mentioned in the plans.  They are one of the ingenious improvements developed by the experimental builders community over the years through collective intelligence and problem solving.



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