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Monokote Sealing Iron Handle Repair

Repaired Monokote sealing iron handle w/splint installed - Airplanes and Rockets

Repaired Monokote sealing iron handle with splint installed.

Fatigue crack in the handle - Airplanes and Rockets

Fatigue crack in the handle.

Disassembled Monokote sealing iron components, with splint - Airplanes and Rockets

Disassembled Monokote sealing iron components, with splint.

Handle splint cut from 1/16 inch metal - Airplanes and Rockets

Handle splint cut from 1/16" metal hanger strap.

Cold chisel used to create curve in splint - Airplanes and Rockets

Cold chisel used to create curve in splint to conform to Monokote sealing iron handle. 

My original Top Flite Monokote Sealing Iron, purchased in the mid-1970s, lasted until the late 1990s, when the heating element burned out. A quarter century of use was not too bad. To replace it, I bought a Tower Hobbies iron, and the first time I used it the handle started to bend where it transitions from a hollow round shape to a flat shape. The metal was noticeably softer than the Top Flite handle, which never even hinted at bending. For two decades I have had to be very careful not to press too hard on the iron lest it bend. After many times of bending and straightening the handle, a major stress crack had formed, and it was pretty evident that the handle would not last much longer. I would either need to buy a new Monokote sealing iron, which in all likelihood would be equally cheaply built since Top Flite does not make them anymore, or come up with some kind or repair for this one.

Living by the World War II era philosophy of "Use it up. wear it out. Make it do, or do without," attempting a repair seemed like the right choice.

The first order of business was to disassemble the Monokote sealing iron. A hex wrench is used to loosen the heat adjustment knob set screw and remove the knob. Remove the single retaining screw in the wooden handle and slide it off, then remove the four bolts from the top of the flattened portion of the handle assembly to release the shoe.

Carefully pull the heat shoe away from the metal plate while feeding the A/C power cord into the handle, in order to keep tension from building on the heater element wires.

Cut the two crimp connectors from the power cord and heater element as close to the connectors as possible. The crimp connectors should not be re-used. Replacements are cheap (Walmart and auto supply stores have them). You might be able to getaway with not cutting off the crimp connectors, but drilling and tapping the handle would be more difficult and you risk damaging or breaking the heater element wires.

For the metal splint, I used a hacksaw to cut a 3/8" wide by 1-1/2" long piece from a section of surplus 5/64" thick perforated metal hanger strap (bought at Lowes). The edges were filed smooth, then a cold chisel and hammer were used to create a lengthwise curve to closely match the curvature of the sealing iron handle. It doesn't need to be perfect.

Two clearance holes for 4-40 bolts (machine screws) were drilled in the handle, and then the metal splint was laid in place on the outside top and the hole locations were marked on the splint from underneath. Location is not critical. Tap-sized holes were drilled in the metal splint and then a 4-40 tap was used to cut threads. Note: The photo showing a cold chisel to form the curve was made after this step because I forgot to take it before drilling and tapping the holes. Forming the curve afterward would distort the threaded holes too much to be useful.

Monokote sealing iron handle with metal splint installed - Airplanes and Rockets

Monokote sealing iron handle with metal splint installed. Screw heads flattened to provide clearance for heater element wires.

The heads of the 4-40 bolts were flattened a bit with a file and were used to secure the metal splint to the outside of the Monokote sealing iron handle. Then the bolt was pounded with a hammer along its axis to compress the threads to prevent loosening. Continued heating and cooling cycles might otherwise allow the bolts to loosen. Flattening the bolt heads provides extra clearance for the heating element wires and insulating tubing - it's a pretty tight fit even without the bolt heads inside the handle. 

Push the A/C power cord back through the wooden handle and through the rounded metal handle. Use the two new crimp connectors to re-attach the power cord to the heater element wire. Being A/C there is no polarity to be concerned about.

Next, carefully feed the heater element wires all the way back into the handle while making certain that the insulating tubing completely covers both wires all the way back to where they connect inside the heating element foot. The wires are bare and could easily short out otherwise. You will need pull the A/C cord while pushing the foot into place to keep it from bunching up inside the handle. Install the four bolts back into the top of the heating element foot, and reinstall the thermostat adjuster knob.

Plug the Monokote sealing iron in and verify that everything is working properly. If all went well, then from now on you will be able to apply covering without needing to worry about bending the handle!

 

 

Posted March 28, 2020

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Kirt Blattenberger
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Even during the busiest times of my life I have endeavored to maintain some form of model building activity. This site has been created to help me chronicle my journey through a lifelong involvement in model aviation, which all began in Mayo, MD ...

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