Saturday, October 30, 2010

Making the extruder work

Today I spend most of my time making my extruder work. I must have assembled and disassembled it about 100 times. But its working now. I changed the place of the thermistor a few times, but that didn't help. I think it is just reading too low values. At room temperature it reads 13°C, which is also too low. So now I just set the temperature to 265°C and the ABS comes out. It isn't bubbling or brown, so I assume its just an incorrect value that is being read. I don't have any accurate thermometers that go that high, so I can't see if my assumption is correct.

I tried printing a few lines without a heated bed, but of course that didn't work. I got some extra nichrome wire to add under the bed and I can isolate it with kapton tape. I hope that will work and I don't get myself electrocuted. As my PSU is really old, I think it will just blow up when I attach the heated bed to it. So I was thinking about using a single long nichrome wire with a resistance of about 160 ohm. That way I'll have 330W of power. My nichrome wire has a resistance of 19 ohm per meter, so I'll need 8.5m of it. That will also make sure everything is heated evenly.
I also have an old thermostat from an oven. That will be more reliable than the one I tried to make myself.

The only thing I'm not sure about is whether kapton can isolate the nichrome wire enough if 230V is going through it and it is being heated. But as it is being used in airplanes, it won't be that bad.


  1. I really wouldn't make a mains driven heated bed with nichrome and Kapton, it's far too dangerous.

    My mains driven beds use 9 22 ohm AL clad resistors rated for 240V. I use high temperature PTFE insulated wire and heat shrink over the joints. I earth it, include a thermal cut out and a 2A mains fuse.

    Even that would not pass any safety regulations!

  2. I was planning to earth it, add a 2A fuse and use electrical tape over the joints. Is that really that unsafe?
    I think some of the Chinese stuff they sell on ebay would also fail at those safety regulations if your heater doesn't pass.
    So there is no way to make a safe heated bed without attaching it to a psu?

  3. Well to make it completely safe it would need a second earth in case the movement broke the first one off. Also anything one could touch would need double insulation.

    The trouble with nichrome and Kapton is that if the nichrome is not in good contact with the bed it may well get red hot and burn the Kapton. Then you have live red hot wires dangling under your moving bed!

    You can buy stick on silicone heaters which are rated for mains. They are not cheap, but should be safer. I would still always include a thermal cut out.

    And yes a lot of Chinese stuff does not pass any safety regulations. There is a company called China Electric that has a company logo the same as a CE mark. Also there is a China Export symbol that is identical as well.