Extruder motor getting awfully hot

I just had a large print fail because the grub screw came loose from the extruder gear. This is the second time I've had a print fail for something similar to this. The last time, the gear was held on merely by friction and it worked loose, but this time it was held my a screw that I'm certain was tight. I noticed that when I was tightening the screw back up that 1) the gear was somewhat soft and 2) the motor was VERY hot - much hotter than the others. This motor is very busy, especially since I added retraction, but I was surprised at how hot it was. I'm now thinking that the screw didn't just work itself loose; I'm thinking that the PLA softened and that compromised the tightness of the screw.

I'm using RAMPS 1.4 with pololu drivers. I'm thinking of turning down the pot a bit to see if that helps. I don't have equipment (or know-how) to measure the amperage - I just followed some instructions I read on-line to turn them all the way up and then back them down about 25%, so I'm sure there's some adjustment in there somewhere.

Could this be the problem? Are there any other suggestions that people might have? I was thinking that maybe I should print my gears out of ABS because of its higher melting point, but I was specifically advised to print them out of PLA because of its hardness.

Thanks

There is a lot of vibration when printing, screws will work loose, locktite is your friend for things like the extruder gear grub screw.
If the extruder motor is getting overly hot, turn the pot down a bit.

Edited 1 time(s). Last edit at 08/29/2012 08:30PM by Polygonhell.

I had this happen a few times too. Loctited the set screw and also loosened up the tension on the extruder arm so the motor doesn't have to fight unecessary friction at the hobbed bolt. Took awhile to figure out how much tension was to much and get'r right in that sweet spot.

Thanks. I'll try the locktite. I already trimmed the pot down a bit, but I haven't really tested it yet. I heated up the extruder and extruded/retracted a few times to make sure I wasn't dropping steps, and it seemed ok, but it was hardly a stress test. The next large print will tell.

Another thing that may help reduce some stress on the motor may be adjusting the extrusion multipier and the heat of the hot end. When I was first expirmenting with extrusion temperatures, the lower I went, the the higher my extrusion multiplier had to be. I dunno, just a thought. On longer prints it could add up but just thought I'd throw that out there.

Sounds like you might need a fan on the motor - I certainly need to use one. Either print a fan holder from thingiverse, or just attach it behind the stepper with the same bolts (the holes have the same spacing for 40mm fans) and with some washers as spacers. Fixed the problem for me.

fiveboltmain Wrote:
-------------------------------------------------------
> Another thing that may help reduce some stress on
> the motor may be adjusting the extrusion multipier
> and the heat of the hot end. When I was first
> expirmenting with extrusion temperatures, the
> lower I went, the the higher my extrusion
> multiplier had to be. I dunno, just a thought.
> On longer prints it could add up but just thought
> I'd throw that out there.

The only reason you'd have to increase extrusion multiplier when you decrease temperature is if your motor is skipping steps because it's having to work harder. The temperature doesn't affect the amount of plastic being extruded.

I would turn the pot down significantly, run a print, and turn the pot up just until it stops skipping steps, then just a little bit more.

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You might want to also look at a stepper motor that is a higher holding torque like in the 50 N.cm range. If your stepper is to low in torque then you have to power it with more power to get the torque you need. This would make the stepper get very hot which might cause the pulley to melt which would cause the screw to loosen.
It is not just the torque it is also the amps required to drive the stepper.

I would try either this stepper form lulz bot

[www.lulzbot.com]

or this from Ultimachine

[ultimachine.com]
From experience they both will work well and not heat up a lot.

Make sure you adjust the pot on the driver like mentioned before this is where I would check first..

Bruce Wattendorf

I'm actually already using the UltiMachine motors. I think I have my amperage too high, but I have no way that I know of to be certain - its just hit and miss.

It sounds to me like you have the stepper motor driver turned up too high.

The instructions I saw, indicated that I should turn the trimpots all the way DOWN and then turn them back on 25%, then to increase 1/8 of a full revolution until the motor is working smoothly.

But that said, my printer isn't even finished yet, so this is just a guess

You're right about the instructions. I misquoted them because I was just going on memory. Initially I turned them all the way down and then up 25%, but since then I made several adjustments when I was trying to solve what I thought was dropped steps, and who knows where I left it, so I am starting over with the pot setting to see how it goes.

Incidentally, I found a couple of extruder gears on thingiverse (here) that have a 6mm nut - into which a 3mm tapped hole has been drilled into the side - embedded into a tight nut-trap at the base of the bolt. It was designed expressly for PLA gears used on extruder motors that run hot. With this, the lock bolt is engaged in a metal set of threads, and of course the hex shape of the nut will engage the gear, so it should be much more robust. I am going to give this idea a try.

Here's an update.

I finally got home from my long weekend and tried this out.

First I printed a medium sized object and noticed that the extruder motor was getting quite warm - not to the point of compromising the gears, but enough that I thought that if the job was any bigger they WOULD be in jeopardy.

After the print finished, I warmed up the hot end again. While I was waiting, I dialed the trimpot down to its minimum setting. After the hotend was up to temperature, I pressed the extrude button. Of course nothing happened. So I increased the trimpot minimally - it's hard to gauge, but I'd say no more than 15%. I pressed extrude, and this time it extruded with no apparent missed steps. I repeated several times going forward and backwards and everything worked flawlessly.

Knowing this was not a real stress test, I repeated the print job I had tried earlier, and it succeeded without the motor even getting warm. So I repeated the print and again, the motor was not noticeably warmer than room temperature.

So I'm feeling good about having licked this one. I am still going to put some locktite on the bolt, but I'm not going to go so far as to drill and tap a nut like I suggested above - unless of course, the problem recurs.

Glad to hear you got it sorted jberbardis,

I will be keeping this in mind when I start my first prints some time this week

this is an amazing thread. im guessing anyone who switches from a normal extruder to one with a hobbed bolt will have this problem. I mean the whole point is to get high torque on the filament. Wade's gets to like 15lbs/inch or something like that? I didnt have any problems when i switched until i did my first big print with wade's. Small gear melted right off after being held perfectly without a screw. Going to trim my pot waaay down and test for new temp. THANK YOU