Extruder Musings

[EL Cuajinais]

I’m tired of playing around with retraction distance, retraction speed, coasting at the end of a loop, and nozzle temperature, all in an effort to get rid of PLA stings. I’ve also played with lowering the current setting for the extruder stepper in the configuraition.h file. This helped, but it is still not enough. My steppers are all “Automation Technologies” brand. It may be that my PLA is has soaked up moisture but if that’s the case, that will be my typical situation anyway so I need to be able to print with it. (I stored it in a sealed bag with silica baggies, but I live in the tropics so it is exposed on top of the printer for however many days I am using it.) I also tried MHackney’s PLA settings and they did nothing for me. And I don’t see myself going the canola oil route.

The issue is I have an upper limit on retraction distance and speed since high values here result in a hot stepper motor that eventually chews-up the PLA. So to deal with the extruder motor temperature I have a few options:

1. Attach a fan to the extruder motor – The obvious choice. I would need to find a suitable size 12V fan and mount. Also possibly add heatsinsks to the motor while I’m at it. And I'm not hot on the idea of tapping into the PEEK fan wires. Any suggestions for going this route would be welcome.

2. Buy a geared stepper – If I understand correctly the gearing is to lower the speed and increase the torque. Which means if the motor overheats because it is trying to punch above its torque this would help, and I expect the quality of the prints would improve due to increased resolution in the motor steps. But if it is overheating because of the long and speedy retractions, then it would be worse off as it now needs more/faster revolutions to make retracts. Then again, if my Automation Technologies motor is overheating simply because it is a crappy motor, then any higher quality motor will result in an improvement anyway. I'd need to deal with printing or designing mounts and having to find suitable fasteners.

3. A more aggressive hobbed gear – Like the canola oil, this does not make sense, but I would love to see what effect it has. It would have certainly helped with a cheap ABS I was using for which I had to add a spacer on the spring to increase the spring tension. I wonder if this would be a drop-in replacement for RMV2 hobbed gear.
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I’d love to hear the community’s thoughts.

[DITAmech01]

I'm also having problems with PLA stringing. Installing an extruder fan won't help that problem - I've got one installed for a different reason.

I was having problems with PLA getting too warm at the EZStruder and fouling around the hobbed gear. The fix was to install a 12V fan so it blows air across the EZStruder motor. Nothing fancy here - I used a couple of Zip ties to suspend it from a few of the unused holes in the MAX top cover and it solved that problem right away. So I don't believe I need heatsinks in this case. I did patch this fan into the PEEK wiring with no ill effects so far, and a couple of people here on the Forum said that the available power for the PEEK fan should be able to handle this extra load.

This doesn't fix the stringing problem, but does seem like a good idea if you're using PLA.

[EL Cuajinais]

Thanks very much for the reply and picture. In the end this is probably what I'll end up doing. However I do think this fan will help avoid stringing. The reasoning is this: In my experience, long and fast retractions heat the stepper motor much more than short/slow retractions. When I do long and fast retractions, the extruder motor heats so much that the PLA gets chewed up in the extruder/hobbed gear area. When I do slow and short retractions, I never experience this issue. So having this fan installed would allow my to do long/fast retractions, and long retractions in my experience has been the most important factor in avoiding strings. And going fast on retractions also makes the prints finish quicker.

I need to try a new roll of PLA first though. I suspect it may be the moisture on the filament that is killing me. If the new roll works, I'll probably get vacuum bags to store the filament.

[Jimustanguitar]

I like the look of the HobGoblin drive wheels. I think I'm going to try them on my next build.

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[DITAmech01]

Can you define your length and speed for "fast" retraction? I tried doing a 20 mm retraction during a test (not sure what the speed was, but I think it was the default) and got a clogged hot end.