A behind the scenes blog covering the goings on at ESTechnical. Expect my ramblings about R&D, CNC, fixing machines, reflow and wave soldering... Ed Simmons
Frankengluegun: Making a low cost temperature controlled glue gun
Until recently, the Bosch glue gun has served me well - it's now 3 or 4 years old and has started to get hotter than it's meant to.
I think these glue guns have some sort of positive temperature coefficient heater, this regulates the temperature just by changing its resistance according to temperature. However this has stopped happening recently and the glue is getting dangerously hot.
Hot glue is used in the ESTechnical reflow controllers to support the display as it is only soldered onto the controller PCB at one corner (this is done is a specially made jog to ensure everything is help in the correct spacing). After being on for several hours during a production run of Reflow Controllers, the glue was boiling and smoking. Something had to be done about this - someone was going to get burned - it was dripping from the nozzle and smelled awful.
At this point I searched for temperature controlled glue guns and was horrified by the cost of them. I decided that since they were so expensive and 'normal' glue guns are not designed for the kind of abuse we give them during a production run of controllers, that I should make my own temperature controlled glue gun.
Since the glue gun wasn't drawing far more than it's normal heating up current, I thought I should try fitting a thermocouple to the heater barrel assembly and powering the glue gun with a cheap PID temperature controller from ebay. I had a few of these lying around so I got straight to it.
Inside the glue gun I found that the heater is a cartridge in hole in the glue barrel casting. I was able to slide the heater out, cover the inside of the hole with thermal paste and slip the heater back in. There was a convenient hole in the casting at the full depth of the heater tube, I covered the tip of a thermocouple in kapton tape and slid this into the hole with more thermal paste.
I also managed to fit the thermocouple cable neatly through the rubber cable glad in the handle of the glue gun, then cable tied the thermocouple cable along the length of the power cable.
I cut off the plug of the glue gun and connected fork crimps to the end of the wires. All the connections were made to the back of the controller using crimps fastened in the screw terminals. A short section of cable with a plug was used to supply power to the controller. Until I fit the controller into a box, the connections are covered in lots of electrical tape.
The end result is excellent, the PID controller means I can set it to 140°C and it stays there even when pumping lots of glue through it in regular bursts. 140°C is perfect for our application, I'm sure it was slightly hotter than this when operating normally originally. The glue runs less and is easier to work with as it is firm enough to hold very quickly.
Due to the great level of interest in the temperature controlled glue gun, please contact us for a quote if you would like to order one (or more!).