Extruder Temperature Control

Topics Related to the ORD Bot Printer

Extruder Temperature Control

Postby dave3d » Thu Nov 07, 2013 8:50 pm

I am pleased to say I have progressed with my Ord Bot build and I have now had some successful prints with ABS. I am still a newbie but maybe moved up to a level 2 newbie now.
One or two things still giving me grief. One of which is an occasional overtemp problem on the extruder. I usually print in stand alone mode (Arduino mega 2560/Marlin/Ramps 1.4/Slic3r) direct from the SD card. I do this because of Repetier freezing when controlling direct from the PC, but that is another problem. Printing direct from the SD usually works reliably but occasionally it goes overtemp sometimes during printing and also during the initial heatup.
I raised the overtemp limit to 245C in Marlin. I have a hotends.com Jhead and the temp limit for peek is 247C so very close. I autotuned the temp control to get the PID values. I repeated it for consistency and I put the new values into Marlin. I run the extruder usually at 230C for ABS. I would run at 235C if I could. I also altered the temp band when the heating comes on full. It was 10C originally and I widened this to 15C to help prevent the temp overshooting. All these changes helped reduce the frequency but it occasionally still does it. When it happened last time, I had the set point on 235C and it peaked at 247C and cut out. There was no thermal load on the extruder. It was during the preparation stage before printing.
Any suggestions would be appreciated.
dave3d
 
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Location: Chester, UK

Re: Extruder Temperature Control

Postby dave3d » Sat Nov 16, 2013 10:04 pm

I did not get any replies, but I have now solved the problem of hot end temperature oscillation. I fitted a fan-shield:

http://www.thingiverse.com/thing:127932

I had a simple unducted fan on the hot end before this.

I found however, using the new fan-shield and blowing cold air onto the jhead actually made it worse (the fan is wired in parallel with the heater) but reversing the fan direction and having it suck air from around the Jhead now makes the temperature very stable.

The fan shield fits a MK V jhead exactly.
dave3d
 
Posts: 64
Joined: Tue Jul 02, 2013 8:06 pm
Location: Chester, UK

Re: Extruder Temperature Control

Postby fma » Mon Jan 06, 2014 12:54 pm

Could your temperature problem come from a bad PID?
Frédéric
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