[SOLVED] Restricted extrusion problem, need help troubleshooting

Apologies to those with deja vu. I asked a similar question in the FolgerTech thread, but figured I would reach a wider audience if I simply opened a new topic over here...

I have a new printer (FolgerTech 2020 Prusa). It has been churning out excellent prints for the last few days, with probably 32 hours total use so far. However, things changed last night...

About half-way through printing a really nice horse in ABS, the flow rate became restricted to about half, with ugly results. I removed and reinserted the filiment, with the flow rate going back to normal, but after about 15 minutes it was restricted again.

My first thought was that the nozzle was partially clogged. I removed the nozzle, soaked it in acetone for 30 minutes, and then hit it with a blowtorch for a minute. The nozzle was as clean as if it had never been used. Tried it again and... same thing. A few minutes of normal flow, and then restricted. I repeated the cleaning procedure just in case I missed something (I know I didn't!) but the repeated cleaning didn't help.

The stepper motor is calibrated correctly. If I remove the hotend and ask the machine to extrude 10 cm, it extrudes 10 cm. But if I put the hotend on, it only extrudes 5-6 cm. (It used to extrude 10 cm here too!) I have taken off the fan and heatsink to watch the motor as it extrudes. It looks like it is struggling to turn, and missing steps. It looks like the drive gear is getting a good grip on the filament, so it appears there is just not enough torque. Aha, I thought! I'll just increase the motor driver voltage reference to increase the motor current. I increased it from 0.7 V to 1.0 V (or 1.25 Amp current limit). It didn't help. I also thought that perhaps something was wrong with the motor driver itself so switch it out with the spare, but no luck. The motor itself is rated for 2.6 kg/cm torque, and is successfully used by other FT 2020 users.

I also thought that perhaps adding a little more heat would help. I've been printing ABS at 230, so increased it to 240. No luck! One other thought I had is that perhaps the thermistor in the heatblock wasn't measuring the right temperature. I attached my multimeter's thermistor to the heatblock and it measured exactly the same temperature (240), so that's not it.

I'm about out of things to try. As far as I can tell, the hotend is in pristine condition. No clogs in the nozzle, completely clean and possible to see daylight through the hole. The PTFE tube looks fine, and allows the filiment to pass smoothly to the nozzle. If something physically changed, I can't tell. Still, I'm willing to replace it if anyone thinks that might still be the problem. The only other possibility I can think of is that the motor torque has degraded somehow (I've already concluded the driver is fine). It's rated at 2.6 kg/cm, but maybe it isn't putting out as much torque anymore. Possible? I suppose I can try switching that motor out.

Has anyone had to troubleshoot a similar issue? If so, any ideas on how I can get out of my rut here?

Edited 1 time(s). Last edit at 11/08/2015 04:42PM by elkayem.

Solved it! It turns out the set screws attaching the drive gear to the stepper motor had come a little loose. Good thing to add to one's troubleshooting list.