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Extruder head refuses to go above 86 degrees C.

Posted by mimarob 
Extruder head refuses to go above 86 degrees C.
September 17, 2008 06:00AM
So I got a spool of ABS plastic.

Having before extruded CAPA successfully (extruded not printed since I had to roll the filament myself)

Now I tried to extrude some ABS. The motor feeding the filament seems to work good enough, but as mentioned before somewhere the PTFE barrel pops out of the clamp. That is ok I belive there was a fix for that somewhere.

My problem seems to be that the temperature is never reached.

After a loong wait the temperature (~86 C) is high enough that I can manually push the ABS filament out through the barrel.

I meassured and calibrated the thermistor, it should be the one reprap recommends (mouser).

I then meassured the voltage over the heater in steady state, it was 2.5V
Also I removed the connector and meassured the resistance while the barrel was still hot, I got about 6 ohms.

This gives me about (2.5^2) / 6 => slightly above 1 Watt.
Is this enough?

Reading some more into the instructions I saw that you should adjust your hb/hm if the temperature was to low.

What are the hb and hm? Are they parameters for the heater profiling?

Is the difference really that big between individual heaters or are the defaults set very low?
Re: Extruder head refuses to go above 86 degrees C.
September 17, 2008 07:19AM
ABS melts at 105C so if you can extrude it at 85C I think your thermistor reading must be wrong. Which electronics are you using?

1W is also way too low, but measuring a PWM waveform with a voltmeter is not straightforward. If you are using a Darlington the on voltage is probably about 10V. If your meter is displaying average then you have 25% PWM so the power is actually 25% of 10^2/6 i.e. ~4W.

I extrude ABS at 230C using about 14W.

Re: Extruder head refuses to go above 86 degrees C.
September 24, 2008 10:26AM
The way I've heard is good to see if your heat calibration is off is to get a small cup of water, and touch the water surface to the bottom of the extruder (not too deep or it'll hit the electronics etc). Odds are, the extruder will cause the water to bubble and boil at some low temperature, when in reality it should bubble at somewhere in the 100-110C range (because of insulation around the heater). So if it boils at some temperature like 50C or something, you know for sure your calibration is off.
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