Filament Stripping!!!

Hey guys,

I've been using Makerfarm's Prusa i3v 12" printer for the last two or so years. Up until recently, it's given me no problems what so ever (excluding basic maintenance, etc.) HOWever, about a month ago, the hobbed bolt in the extruder began to strip the 3mm filament. I've been using Greg's Wade extruder and a .5mm J-head Hotend for the entirety of the life of this printer. So, I figure maybe the nozzle was clogged. I disassembled, cleaned, and reassembled the hot end. The filament still stripped in the extruder. I purchased a new J-head hot end to no avail. So, I thought perhaps after two years of heavy use the threading on the hobbed bolt was a little dull. I purchased a new bolt. Still, the filament would strip in the extruder. Frustrated now, I thought perhaps this was the perfect excuse to upgrade altogether. I purchased the new E3D V6 Titan Aero extruder/hot end. It worked for maybe a 10cm's before, yep you guessed it, the filament stripped. So here is what I'm thinking...

1. The filament is bad. I've been using eSun's 3mm black filament since I started printing with no problems until this debacle.
2. There is some problem with the stepper motor. It's the only part I haven't replaced. I doubt this though since it still rotates which is all it really needs to do.
3. There maybe some problem with control board. I'm using a Rumba board. However, it was replaced about year ago, so it's fairly new.

Im bashing my head right now against the wall. If you guys have any suggestions please feel free to drop a line. I think my next (easiest) step is I'm gonna try a different brand of filament. Maybe i just got a bad batch.

Thanks for the help,

73
Fudz

Filament stripping, is caused by only one thing. There is a bearing that presses the filament against the drive gear, usually spring loaded. If the pressure is too low, the gear doesn't bite deeply into the filament and will strip it. Increase the pressure. It should almost crush the filament. The motor should start skipping steps before the filament strips.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

How old is the filament?
I read on the web and have some experience that the water absorption can make it stiff and brittle. That would make it more prone to striping.
I have used some really cheap filament from a variety of suppliers and not had any issues when new. So I am slightly suspicious that when we say bad filament its actually old filament that's the issue and not always the supplier.
I keep meaning to make a jig to measure the filament stiffness but haven't got round to it yet.

I have been seeing reports about one brand or another being terrible and causing extruder jams, etc. for years and have had literally zero problems once I figured out what it takes to extrude reliably. I have seen photos of filament that has a sudden increase in diameter that won't fit into the extruder, but those are very rare, and I have never seen it in any of the filament i have ever used.

I used to have all sorts of problems with "extruder jams" for about the first year I was printing, so I spent months experimenting, researching the problem, and looking for reliable extruders and hot-ends. The first ah-ha! moment came when I compared complaints about extruder jams between 3 mm and 1.75 mm filament. The people who were running 3 mm filament almost never complained about extruder jams and the people running 1.75 mm filament had all sorts of problems. The main difference between the extruders at that time was that all the 3 mm extruders had gears to multiply the motor torque and almost none of the 1.75 mm extruders had any gears. That was 4 years ago. Now geared 1.75 mm extruders are common, but a lot of people throw away the reliability gained by torque multiplication by using a pancake motor to minimize weight.

The basic strength of the filament is huge (unless you have old, moisture laden PLA). It's only going to strip if the drive gear doesn't bite deeply into the filament. You get it to bite deeply by cranking up the pinch roller pressure. There are a bunch of designs out there that are intended to solve the stripping problem by driving the filament from two drive gears. I'm sure it works as long as the gears are squeezing the filament tightly enough, but one gear is sufficient if the extruder is adjusted properly. Like so many things in the 3D printing world, solutions to problems often don't directly address the problem, they work around it.

The next contributing problem is hot-end design. There are a lot of stupid designs out there. The budaschnozzle, for example- what appears to be a heatsink is actually slotted aluminum rings stacked on a piece of teflon tubing! There are wood parts just a few mm away from the heater block, and there is no heat-break- a large diameter aluminum tube. It is amazing that plastic can be made to flow through it at all. For reliable extrusion of multiple filament types, you have to have a heat-break and active cooling above the break. If you want to run it hot, you can't have any teflon tubing going down to the heater block.

The combo of geared extruder and actively cooled hot-end solve 99% of extrusion problems. If you retract the filament too much and the extruder pulls soft, sticky filament up into the heat break, the torque provided by the geared motor will be able to push the filament back down anyway. I have been running a BullDogXL (one of the early geared 1.75 mm extruders, 5:1 ratio) on one printer almost daily for about 3 years with an E3D v6 hot end. There has been exactly one true filament jam that occurred because of a foreign object embedded in the filament. It has never stripped the filament. I don't use any oil or run filament through a sponge to capture dust. I can't see how dust could possibly cause a filament jam.

Recently I've been running E3D Titans with v6 hot ends and getting very reliable operation for about 1/2 the cost of the BullDogXL and v6 combo. I've only had the pair running for a few months now but so far, so good.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Quote
the_digital_dentist
Filament stripping, is caused by only one thing. There is a bearing that presses the filament against the drive gear, usually spring loaded. If the pressure is too low, the gear doesn't bite deeply into the filament and will strip it. Increase the pressure. It should almost crush the filament. The motor should start skipping steps before the filament strips.

I agree, except that you *can* have too much pressure. You don't want to "almost crush the filament"... in the extreme, that can make the filament out-of-round, create lots of dust to jam things that should slide and lubricate things that shouldn't.

My rule-of-thumb is that you should only have enough pressure so that the stepper motor always skips before the filament starts stripping.

I said "almost crush" not "crush".

When printing flexible filaments you have to back off on the pressure quite a bit, too.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Update!

Upon closer inspection, the hobbed gear in the Titan Aero was slightly off center to the filament and bearing. I disassembled and adjusted the gear. After testing, it still stripped. However, after some adjustment of the tension spring, it seems to be working correctly now. Keeping my fingers crossed. Thank you everyone for your help. I'll keep y'all updated if this continues to be a problem in the future.

73
Fudz