Commercially available bending irons are acceptable but leave plenty of room for improvement. After having the heating element fail in my unit, I decided to give the whole unit an upgrade to produce more consistent bending with less chances of burning ribs.
I kept the aluminum ‘iron’ and discarded the rest. I rebuilt the base from maple in a similar fashion to the original. The cartridge heater was replaced with a 250 Watt unit. A PID controller and thermocouple replaced the old-fashioned stove element controller. This allows for accurate temperature setting, with a clear digital display. The PID controller keeps the temperature on target.
The aluminum ‘iron’ was hollow, meaning that the outer surface of the ‘iron’ would cool if it was bending wood, particularly when using a wet cloth for steam. By filling the head with lead free solder, the amount of heat held by the head increased significantly. The temperature stability improves but the initial time to heat-up to bending temperature is increased.
I’ve very happy with the performance of the rebuilt bending iron. I’ve found bending temperatures of 160ºC (320ºF) to 170ºC (340ºF) sufficient.
Very nice rework. I assume you bought the iron new and you haven’t really made that many instruments. I am concerned about the durability of these units. What kind of PID did you use? Looks like you set the set point and then allow the iron to match. NICE!
Aluminum has excellent heat transfer but that works both ways. I often work with stainless, esp. 304 and have considered milling out a solid bending iron. Been thinking about how to power the beastie and how to control it.
How hot is a good question. Lignum is God’s original hot melt glue. Its what holds wood together and its heat sensitive. Soften it and wood will bend and take a new shape when it cools. But, maple like many north american hard woods, contains a large amount of natural sugar. Tally one second at the table saw and you have burn marks! So you want a balance between enough heat to soften lignum but not so much as to carmelize the sugars. Being able to fine tune the bending iron temperature is a true and wonderful luxury. Good Job!
Thanks! I had only used it for two instruments when the element burnt out, so you may be right about the durability. With a replaced heater cartridge it should last a while now. The Heater fits in a cylindrical hole in the head of the bending iron, you could fabricate the place for one by simply drilling a hole (1/4″ I think) in your steel. My heater came from Omega. The PID controller came from eBay. For simplicity, it should have either a solid state relay (SSR) or traditional relay output capable of handling the amperage required by your heater (ie a 250W heater running on 120V requires a 250/120=2.1A relay or larger). Some are sold with the thermocouple included. This I bolted to the inside top of the aluminum frame, you can see the nut holding on the top of the iron. Cheers, Stephen.