Zat German wrote:Makerbots use cartridge heaters in their extruders but don't they have safety electronics to prevent them from running away in the event of a failure? I don't see any mention of this in the project, that is probably the only thing holding me back from one of these.
Good point. 40W at 100% duty cycle would melt any nearby plastic parts. 40W is the low side of the soldering iron wattage for typical handheld soldering irons that are actively controlled, and 25W is typical of small soldering irons that are 100% duty cycle and regulate their temperature by convection into the ambient air. With the larger surface area of the nozzle and heater block, I'd guess the 100% duty cycle temperature of the 40W extruder would be soldering iron temperatures. There shouldn't be any combustibles near the extruder, so I wouldn't think this would be much of a fire hazard. More of a self destructing extruder problem.
It's still a valid concern. You could always buy the less expensive version with the 3W resistor, or connect the cartridge heater in series with a temperature switch or a thermal fuse. Thermal fuses are used in appliances like coffee makers, and are small and inexpensive. Even better, have a temperature switch or thermal fuse open to E-Stop the machine when there is this much of a problem.
BTW - I ordered four of these extruders, so I'm betting they're going to be be good stuff.