What could cause this regular drop in extrusion rate? I’m running PLA at 200C. It seems to be getting worse. It started as a thick/thin pattern in large fills. I experiments with many extrusion rates and temps but that makes no difference (until temp is on low edge).
Thermal shot down of the stepper driver? Does the motor stop during the empty patches?
Poor PID tuning - possible temperature fluctuations to the extent where the hot end get’s so cold the filament stops flowing.
Hobbed bolt slipping (tighten your idler).
Why so focused on temperature?
I’d suspect the filament drive or the filament itself…
Motor turns the whole time. There is no crud on the teeth of drive. BTW it’s a printrbot simple.
PID seems to be working because temp chart show only tiny 0.1 degree fluctuations. I can manually push filament thru (drive disengaged) at probably 10mm/s. So seems like PID is ok.
I wish I could relate the pattern to the size of the hobbed pulley because I suspect something in the drive., like maybe the set screw is working loose.
@Matt_Kraemer1 thanks for 105c tip. I was printing at 185 before but printrbot has suggested 200. The extruder is one piece ceramic afaik. I’ve seen that blob before when yanking filament out of cooling extruder about 100 at the time. There was a burnt looking blob at the end. Definitely worth a try at 150.
If it’s a printerbot then it will be an Ubis hotend - quite likely that the Ubis will have a different temperature/heating profile to a j-head, so you may have to experiment a bit.
Do you have insulation around your hot end? That was an issue for me once while printing with PLA that caused similar trouble. PLA needs to stay up to temp all the way until it is extruded.
Drop your temp down to 185. Is that the first layer?
I agree that 200 seems high, and I’ve seen high temps cause gas bubbles to form (steam perhaps?) that could interrupt flow.
That said its probably worth checking the stepper current as well, could be as simple as skipping steps in the extruder drive…
Looks to me like the pla hasn’t stuck to the bed and is being dragged around
Just measured the extrusion nut/ pulley and what a full revolution extrudes. Extrude 33mm in equals one rev. Output for one rev about 432mm. Then measured across fill area in photo and counted threads. It screws up once a revolution, reducing the flow at tip, then picking up the bits it’s extruding.
If i was doing it i would scale back to 180 and add a fan. Then go from there.
Have a fan. Going to try a test plate at 180/
I had a similar problem getting weird artifacts 1 rev of my extruder gear apart. What my issues was, the set screw on my extruder gear was too long. Every lap, it would swing and hit the 608 bearing that was on the other side of the filament in my extruder. When it hit the 608 bearing, it would deflect the motor shaft, but still maintain rotary motion. The result is that every rev of the extruder gear, the filament would slip while the set screw was prying out the 608 bearing. When I finally figured it out, apart from swearing loudly, I replaced the set screw with an appropriately sized smalled one, and the problem went away.
The odds of you having the same problem are very slim, but hey, worth a shot, right?
@Alan_McNeil Great i want to see what happens.
it is a heat problem. The head of your extruder is melting the plastic that is on the surface. Try to lower the temperature.
200 degrees for pla is probably too high. Recommended is 185 degrees.
I agree that the nozzle temp is too high, but why is the banding perfectly periodic, and the period just happens to be a revolution of the gear. Sounds too perfect…
Still did gaps at 185C. I put a mark on the knurled nut and watched the print. It screwed up with pointer at 6 o clock every time. So I’ve pulled the nut to look with the jewelers loupe and find some folded over teeth in bad area. Looks like it was cut some what off axis and some had the material from cutting was in the groves.
Have cleaned all the teeth and groves but bite is much less at the bad point. Tightened up the idler pulley about three full turns and am getting a decent print with plaid appearance.
Probably need a better knurled nut.
Posted a follow up with pictures.