Prusa Mendel seems to be melting everything.

I have a prusa mendel that I built mostly from scratch a few weeks ago, and I've been working on it since. I need help adjusting the temperature on the extruder, because everything seems to be coming out in melted blobs. It's running the latest Marlin firmware on an arduino mega with RAMPS, and using Pronterface on the computer side. Does it seem like the thermistor settings are wrong and it's hotter than it thinks? What do I have to do to fix it?

Second problem, it seems to be extruding faster than it should be, where do I adjust the extrusion speed? Is that in Pronterface, or the firmware?

Thanks for whatever help you can give, everything past mechanics is pretty new to me.

You have to fix your firmware. Make sure the thermistor table you used matches the type of thermistor you added to your hot end: there are various versions and using the wrong table results in the wrong temperature (I am assuming here that Marlin uses tables like Teacup).

As a verification method you could use an optical thermometer to check the temperature. Be careful though: I ruined my hot end in the first 10 minutes after assembly because I messed up and it got way too hot (J-heads contain teflon which melts at 250 degrees Celcius).

Extrusion speeds are based on the diameter of the plastic as specified in the slicer software. If your extruder is spinning wildly you probably messed up the number of steps in the firmware for your extruder. Read the documentation carefully and measure everything: from hobbed bolt diameter to number of teeth on the gears, steps on the motors, sub-stepping used and then go back to the firmware to set it up. I usually use a marker on some fillament to verify the extruder steps after the initial calculations; leave the hotend off, just tell the extruder to go up and down a bit while being careful that you don't bumb the fillament into the cold hotend.
Just mark 10, 15, 20 and 25 mm and make sure that the extruder sucks in the same amount that you told it to using the manual controls.

Edited 1 time(s). Last edit at 07/17/2013 05:51PM by Cyberwizzard.

I'm in the firmware, and it asks for Kp, Ki, and Kd values, is that what I should be modifying? I'll keep looking for something more obvious in the mean time.

actually, I think I found what it actually is, thermistortables.h, nvm

You need to do a step by step calibration of your machine. Unless your steps are set correctly it's not going to do you any good adjusting the ttemp table. If the extruder motor is not calibrated correctly it's not going to matter at what temp you try and print. If you are using known components you can use the stock values in the firmware to get you to a point where you can print. Search calibration in the Wiki and on the forums. I use this as a guide. [richrap.blogspot.com] This is also helpful [reprap.org]

Edited 1 time(s). Last edit at 07/17/2013 10:55PM by vegasloki.

Marlin has an M code that does auto PID calibration. When your printer is cold, just enter M303. (You can add a goal temperature with the S parameter, but without the S to calibrates to 150 degrees)

Once you enter this command, you can watch the temperature go up and down a few times, as it zeros in on the PID values that you should then enter into your firmware. You can refine them if you want, but I never did that - the numbers I got have been working fine for me - AFAIK.