Building the Block Heater

As part of rebuilding the extruder I thought it would be a good idea to build the block style heater, rather than than the original heater. I made a couple of modifications to the build, we'll see how they work out.

The basic components of a block heater.

I followed the mechanical drawings and plans on the RepRap Site. It did require me to buy a drill press, metric drills and a metric tap and die set, but I do enjoy having new power tools!


I used a 3/8" ultra-machinable brass bar from McMaster. Cutting and machining it was fairly straightforward. The new drills and drill press did their job well.


I haven't tapped anything since I was at school, but the technique came back quite quickly. A quick test fit showed that everything went together easily.


I used 1mm PTFE tubing I found at Frys to insulate the leads for the thermistor.


To increase the thermal conduction between the thermistor and the resistor and the block I used Biostar Nano Diamond thermal grease. It is good up to 240c and is an electrical insulator. I filled the thermistor hole with the grease before pushing it home. The resistor was coated with the grease before sliding it in to its hole. 

With all the parts inserted.

While I was shopping for the fire cement I found a Rutland caulk good to 600F at Ace. It doesn't require heat curing and is flexible. I'll give it a try and see how it works out. It was a little messy to apply but should be better than fire cement.


After wiring it up and waiting for it to cure first tests appeared to be promising. It heated up quickly to the specified temperatures.


First tests with filament did not go so well. The filament did not feed very well and the output from the nozzle curled up! - Not sure why?


Then catastrophe struck again, the nozzle appeared to seize up. It appeared that molten PLA had backed up the PTFE and solidified.


It was another late night dismantling the nozzle and cleaning it out and drilling out the solidified PLA out of the PTFE. After it was all clean I checked the nozzle opening in case there was something stuck in there causing the curling.

Complete and back on the extruder. Note the new sprung loaded mech.

Using another thermistor as a temperature probe inside the nozzle it I checked the temperature inside the nozzle. There appears to be a significant difference between the block temperature and the nozzle temperature. The block has to register between 250 - 260c for the internal temperature of the nozzle to register between 205 - 220c. This may have been the cause of the feed problems. At a block temperature of 220c the internal nozzle temperature was only at 185c.


Cranking the temperature up to 260c and trying some manual filament feed tests shows this temperature setting was much better. Tomorrow I'll try rebuilding it completely and testing it with the motor feed.