19 January 2014

Temperature Controller For Safer Side Bending

I posted a topic on the Delcamp forum a little while ago about this temperature controller device that I made for side bending. Thanks to those who participated in the thread there. I've copied the same post here, but I also added some more how-to info for those who may be interested. It's not difficult or too costly to make.

The point of this temperature controller project was to make side bending safer, and more consistent and predictable. I haven't actually used it yet to bend a side for real, but it acts like it's going to work well. It's similar to a couple of products that you can buy from one of the luthier supply companies, but I wanted something simpler and more fool proof than what I saw available. This turned out costing a fair bit less than those products too.

Solid state relay and 15 min timer
The digital temperature contoller
The thermocouple, 24 gauge wire
Power cord about 4' long
So, my side bending setup has always been pretty minimal, with no timer or temperature control on the heating blanket. The temperature was adjusted by either plugging in the blanket, or unplugging it. I learned to deal with it so I didn't bother changing it. A few months ago I got distracted by a visitor a few moments after starting up my bending machine with a maple side in it. About half an hour later I came back to my workshop to find it smokey with the side sizzling and hissing away in the bender. It's scary to think what could have happened if I'd decided to eat lunch or something before going back. Sooo... that was the start of planning this little temperature controller project. 

Heating blanket cord about 3' long
6" cube thermoplastic junction box
Thermocouple attached - red is neg.
Holes marked on box cover
Corners drilled
Used a rotozip to cut openings
I wired it so that the digital temperature controller and the heating blanket don't get any power until the timer is turned on. Once it's turned on, the temperature controller reads the temperature of the heating blanket through a thermocouple and decides weather or not to let current go to the heating blanket. The controller can of course be set to make the blanket be whatever temperature you want, and it remembers its settings after the power has been shut off and restarted again. I chose a 15 minute timer because that's ample time to bend a side, but probably not enough to start a fire if I wander out of the workshop again. All the parts are easy to find online and at a local hardware store.

Mounting the components This is how the controller
is mounted
The relay is grounded - not
sure if that's necessary

Wiring is mostly done Knots are tied in the cords for yank protection Another view of the yank protection knots

About to close the box Vent holes were drilled in opposite sides of the box The red LED inside the box is part of the relay. It turns on when current is flowing to the heating blanket