Hotend: temperature fluctuating

I’ve spent the past few days trying to optimise the Prusa Mendel printer with respect to speed and temperature, having already  calibrated steps/mm etc. The printer however, was having none of it and very kindly gave me wildly varying prints where the top surface rarely bridged properly. I noticed that the temp was varying quite a bit so I decided to change out the thermistor which had probaby come away from the heater block. I replaced it with a different model and decided to tape it to the block with kapton tape. However the fluctuations were worse (+/- 15 degrees C around setpoint!). The new thermistor, too, was struggling to stay in contact with the heater.

I had reinforced the previous thermistor/fire cement setup with a flat brass piece so i bent this to try to pin the new thermistor in place in the (now widened) hole. This helped but didn’t solve it completely. So then i stripped some light wire and wrapped it around the brass and the heater block to hold the brass tight against the thermistor and the heater block. So the temperature is now nice and stable! However I need to set it to 300C to get the flow i used to get at 210C….. must be a temptable problem… but at least its extruding repeatibly again!

Printing from SD using sprinter firmware works well – its nice not to have blobs everytime you do something that forces the netbook to work hard 😉

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