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Hot extruder motor

Posted: Sun May 18, 2014 4:03 pm
by Steve T
I'm starting to run some lengthly prints and for giggles wanted to feel how warm the steppers got. Not surprised the "X" & "Y" are warm as expected but the extruder is hot to the touch and uncomfortable to hold. I have the filament feed tension screw set loose so that can't be the problem. The high quality green abs from MatterHackers I am running through the feed tube seemed to slide through with minimum resistance. Printing at 0.2000 layer thickness and at a reduced speed of 3000 mm. I'm extruding at 240c which is supposedly the max on these hot ends although the seller of the filament says to extrude starting at 230 equivalent to 250 on the M2. Could I be trying to push a plastic not soft enough or am I worrying about nothing and that a hot extruder motor is the norm? My finished print is coming out nice so all my settings seem to be correct. I will be trying other filaments to see if the temp rise is the same on the motor but would appreciate any feed back that might save the motor from premature failure.

Re: Hot extruder motor

Posted: Sun May 18, 2014 5:36 pm
by jimc
Thats normal. I believe mine runs at about 60c. How hot it runs is determined by the current which is set in the firmware. The extruder motor should be the hottest motor on the machine. My x and y run at about 45c and the z is cold.

Re: Hot extruder motor

Posted: Sun May 18, 2014 6:55 pm
by Steve T
Thanks jimc. All your details seem to fit my experience with the steppers.

Re: Hot extruder motor

Posted: Sun May 18, 2014 10:17 pm
by ednisley
Steve T wrote:a hot extruder motor is the norm?
A stepper motor's winding current determines the case temperature, because they operate as constant-power devices. Higher current produces more torque, but also more heat from the winding resistance; the good comes with the bad. Steppers run fine with disturbingly high case temperatures, so that's not a problem.

The M2 has good motor-to-chassis heatsinking for the X and Y axis motors and decent heatsinking for the Z axis motor (*), but the extruder motor's plastic mount is a good thermal insulator. The fan in front of the filament drive cools the whole affair, which is required because the ABS plastic used there has a glass transition temperature just over 100 °C: you can't push the motor current too high.

My rule of thumb is that if I can't force myself to keep my thumb on something, it's running just under 150 °F = 65 °C. If your thumb matches mine, then your motor is hot, but not excitingly so.

The only way to know whether you can reduce the current is to reduce it, then see if the reduced torque causes problems. If the motor begins making odd clicking or grinding noises, that's a problem: it's slipping while trying to drive or retract the filament. That won't cause any damage, other than possibly to your print quality, but it's a sign that the current is too low or the (unchanged) extruder acceleration is (now) too high for the available torque. Easiest fix: crank the current back to its original level.

(*) The original M2 Z axis stepper had very high resistance windings, which meant it had to run with relatively low currents and low torque. The newer M2s have better motors; that problem Went Away.

Re: Hot extruder motor

Posted: Mon May 19, 2014 2:05 pm
by Steve T
Thanks for your reply Ed. I have a limited understanding of motor winding and the rise in current/drop in voltage but certainly not enough to tinker with outside a breadboard environment. I'm pretty sure I'd end up with a melt down if i messed with the electronics on the M2 so I'll take the word of the knowledgeable here and accept it as a safe heat level. I have a squirrel fan booster on a heating duct that does get too hot to touch but according to the manufacturer it's normal heat rise since the fan doesn't push any air over the motor and is still working after more than 15 years both heating and cooling seasons.