From clean to blobbing stringy mess

[hakanai]

So I get everything calibrated and had a few good prints out of my Max when I decided to try and print a large part (the reason I got the machine) It was an eight hour print so I kept an eye on it for an hour or so before going to bed. A few hours later my wife gets up for work and takes a peak at the machine and tells me "it still thinks it's printing, but it's not". i go have a look and the hobbed pulley has chewed through the filament, so no more filament going to the hot end. The print looks very good until the last few layers where it looks starved for material. The remaining filament in the bowden tube shows signs that the pulley had been slipping before it finally ate through the filament. Ok so it seems like it jammed and needs to be cleared. I didn't know why it jammed, but a jam seemed apparent.

Stock seemecnc hotend EZ truder cold end - ABS - 222c 10mm/s first layer - 220c 40mm/s other layers

I bring the temp to 235c and extrude some fresh filament in, nothing comes out a first, then a rush of charred filament comes out and after a few cm it extrudes clean. So now I think I have my clog solved. I print again and it is a blobby mess. Excess filament everywhere. It doesn't seem stringy anywhere. I also see the stepper lose grip on the filament and slip forward occasionally. So i check my extruder calibration. All looks good. I try agin, same thing. The hotend seems to require excessive force to extrude. So I take the thing apart and check the PTFE lining. The inner tube has in fact contracted a tiny bit at the nozzle end. So I ream it out slightly and flip it around so the clean end is at the nozzle. It didn't feel perfect when I just slid some filament through by hand but it did feel better. Now I am getting stringy/blobby prints. The attached photo has the calibration pyramid I did just before the big print failure and the last little fan cowling I tried to print.
I have a E3D hotend on the way as well as some new PTFE tubing. I have messed with the stepper current settings, no help. I have measured the extruded material (in air) and it actually turned out to be .7 from my .5 nozzle, so my nozzle setting may be wrong but if anything it should be easier to extrude through.

I figure it must be either the PTFE or the nozzle causing the problems. I did not have a PEEK fan at the time of the original failure. So I suspect that is when the PTFE lining was damaged and now is too snug to be free and easy flowing. I don't know how the nozzle would become a problem from simply sitting at 220c for a few hours. That's what it does anyway. Oh and I measured the filament diameter after the failure so that is current. I do think my filament was relatively damp. I have since baked it and tried extruding into open air and the extruder still slips (even at 235c when the pyramid was done at 220c). Everything ABS.

Thoughts?

[kbob]

What happens when you push filament through by hand?

I'd take a look at the extruder. Mine has enough grip to stall the motor instead of slipping.

(a) Is the gear tight on the motor shaft?
(b) Is the gear aligned with the spring loaded bearing?

[grasshorse]

Something similar is happening to my machine. I am also using the EZ Struder. Prints were looking marginal but complete. Note that I am still learning how to calibrate the machine and a n00b. I too have been running hot end temps between 230-240c. Now all of a sudden halfway through printing the extruder can no longer push the material out through the tube and the hot end. Tried to feed the filament through by hand and it challenging. I notice that there is significant filament dust that is aggregating in the EZ Struder and that some of that is getting into the Bowden tube. So much so that when I clipped off the filament at the extruder and pulled it out of the hot end and Bowden tube it had a significant amount of resistance. After doing this about three times I don't have any more answers. I was about to post about this issue when I saw your post. I thought I would just post my experiences as well.

Steve

[lordbinky]

Maybe put some sugru around the hobbed roller, it might be able to keep traction and reduce wearing the filament.

[grasshorse]

I solved my issue. Turns out that the EZ Struder was not getting a good enough grip on the filament. If I pushed the button the other way and added more pressure it started to work. I tightened all of the screws into the stepper motor and it started extruding again. I thought it might be a voltage issue in not having enough power. It was just a mechanical grip issue in my case. I also wanted to note that I have the top mounted spool and cold end. Not sure if you do or not. I had wondered if it was due to more resistance of the bent bowden tube. I hope that helps.

Steve

[grasshorse]

Hakani, when you added your EZ Struder to your Rostock, did you change the EXT0_STEPS_PER_MM to something close to 92.667 in the Repetier Firmware or EEPROM config? That ended up being my ultimate problem. The EZ Struder was trying to pump out 6 times as much filament as my machine could actually handle. It worked at first and just just took it out on the filament chewing it up. Soon I had such a bad problem with the dust from the chewed up filament. I was introducing a lot of resistance to filament passing through the Bowden tube making the problem even worse. Now things are looking MUCH better.

Steve

[Flateric]

Maybe put some sugru around the hobbed roller, it might be able to keep traction and reduce wearing the filament.

That's neat stuff, makes me wonder if it could be extruded itself. Similar to silicone extruders.

Would be a neat new material.

[ApacheXMD]

cheaper DIY alternative to Sugru is Oogoo, basically plain old silicone caulking/sealant/adhesive mixed with cornstarch.

[lordbinky]

Unless that's the only one that works in making oogoo, you'd want to avoid silicone caulk that uses the Acetoxy catalyst which has the acetic acid component that corrodes metals. ( Oxime is the catalyst that doesn't).

edit: also the component of sugru (3-aminopropyltriethoxysilane) that gives it it's adhesive property is an allergen to some people. After the sugru cures there is none left and it's no problem. I wasn't allergic, but I got it approved at my work and it was a pain to get our safety to approve it without obtrusive PPE requirements.
MSDS
Data Sheet

[hakanai]

So after some time replacing parts of the hotend, which helped but didn't solve the issue, I went through the whole calibration process again (3rd time). I had calibrated my EZstruder to 92.67 originally but after going through calibration again I ended up with 86.34. I don't know why the relatively big change, but I did learn a few things about calibration. 92.67 moved exactly 100mm of filament past the hobbed pulley, but it was producing walls on a calibration cube that were too thick. Now 100mm extrude doesn't get me exactly 100mm past the pulley but my wall thicknesses are spot on and my 100% infill is just barely 100%. In other words, it's exactly 100%.

[kbob]

That's neat stuff, makes me wonder if it could be extruded itself. Similar to silicone extruders.

Whaddaya know? 3D Printing Sugru!