Hobbed Bolt Clogging & Filament Stuck

The hobbed bolt keeps getting clogging and the filament gets stuck within the first few minutes of a new print. I keep cleaning it but it keeps clogging. I am using PLA. Any suggestions? See attachments.

Hi FitzNYC, let’s check a few things. Does the filament seem to be extruding well into the air when you clean off the filament and the hobbed bolt? If the filament comes out at and curls up it could be that there is a partial clog there. If it comes out nice and straight then it could be something simpler like filament tension. A little secret on that is to use this extruder latch jig (http://devel.lulzbot.com/mini/daffodil/jigs/extruder_latch_jig_0.3.stl) to tension your idler perfectly. It should be around 4mm spring length. Then use a standard Cura profile and give it another shot.

Thanks 3dprintdaddy! I will give it a shot.

@3dprintdaddy, The filament does not always come out straight. It does curl sometimes. I am not sure how to use the extruder latch jig and make the spring length 4mm. I have definitely been experimenting with the spring tension but don’t know how to set it to 4mm. Is there any documentation on-line that would help me figure this out? Thanks you for all of your help.



That jig is 8mm wide. you stick it down sitting on the springs, then tighten the screws until the springs are compressed to the width of the Jig.

Thank you piercet!

Issue resolved. It was a combination of a partial clog and idler tension. I use the latch jig that 3dprintdaddy uploaded which worked like a charm. To get rid of the partial clog, I use the the suggestion at https://www.lulzbot.com/support/unclogging-tips , “If there is flow but it seems partially blocked, thin, or is “pig-tailing” out of the nozzle:”.

Thank you all for all of your help.

I’ve had the same problem today and have been trying to clear what has to be a partial clog using HIPS. The last things I printed were with PLA and I’m now printing the idler jig in PLA without issue. With HIPS and ABS (which I originally was switching over to) I get pig-tailing and then the hobbed bolt chewing into the filament. I haven’t had any issues with this before, successfully printing with HIPS and ABS many times.

Only thing I can think of that is different may be that I had a failed print yesterday that ended up coating lots of the hot end in PLA. I cleaned it off with it heated for PLA with tweezers. Given PLA printed fine just after that failed print I don’t think it had anything to do with it.

I got tired trying cold pulls, but will go back to that again. Was varying the temperature, but getting the idler tension right seemed a thing to knock out if I could print with PLA which seems to be fine.

Any thoughts or suggestions beyond “keep at it with cold pulls” are appreciated! Thanks for all the earlier comments.

Here is my maintenance check list for when the Mini isn’t printing properly. I hope this helps.

  1. Clean platform with alcohol and sandpaper, typically 2000-2500.
  2. Cold pole nozzle at 65 degrees (Up to 8 times).
  3. Clean hobbed bolt with dental pick and wire brush.
  4. Calibrate springs with latch jib (http://devel.lulzbot.com/mini/daffodil/jigs/extruder_latch_jig_0.3.stl).
  5. Clean cooled nozzle with acetone.

I haven’t had problems with the platform (other than one area, unrelated issue). What type of filament are you pulling at 65 degrees? Where do you use the wire brush on the hobbed bolt? If it’s just cleaning the bolt, I feel I’m OK with the pick. For cleaning the nozzle, do you remove it? I haven’t looked into how specifically yet, but any recommendations would be appreciated. I think I’ve read of others having problems with that.

Thanks for the list!

I have been printing and pulling with PLA for the most part. I use the pick and then the wire brush to make sure I get everything cleared. I don’t remove the nozzle but make sure it is cool first.

Try this out with ABS… and see if it helps with your clogging issues?
ABS_Mini_Profile.ini (12.6 KB)
Extruder_Idler.skp (1.35 MB)

You just can’t un-screw the nozzle and clean off the machine? Not sure how its put together, but un-screwing the nozzle and then setting the heat at the material temperature would seem a logical way to clean.

Removing the nozzles on a Hexagon nozzle is not recommended because they are nicely torqued on at 30 in-lbs from the factory. Removing the nozzle can risk damage to the nozzle or potential leakage if not reattached correctly. The safest method of clearing the hot end is described here:


Some users including myself have found that this method is very effective using Nylon filament as well. Give it a shot!

Well mine has not plugged yet but I will try the suggested method first. I have worked around some pretty expensive and complex machines and would not have a problem removing and re- installing an extruder nozzle. Yes I can re-torque to 30 inch pounds. I have seen a lot of things screwed up by DIY folks so I imagine that’s the reason for the warning. Thanks for taking the time to reply.

Torquing the head back on isn’t the problem. Stripping the threads off the head when someone tries to remove it is the problem. molten plastic works as a very effective semipermanent glue. Brass nozzle threads aren’t all that structurally great to begin with. Even if you heat it to the reccommended removal temperature, you still have a very good chance of leaving the threads behind when you remove the nozzle.

I’m pretty sure that everybody can torque down a nozzle to 30#… But with this machine, you have to pretty much take allot apart to do that, otherwise you risk breaking other stuff at 30 flbs while mounted…

If you consider and comprehend the working mess, you’ll find that it’s kinda funky(design)…<-- basic No-Nos…

Either way… it’s a fast printer…

I thought it was 30 Inch-pounds. I have been around “real” extruders they are usually all stainless steel. Not brass with threads that strip.

Get the heate block above 165C. Thread the nozzle back on slow (thread in reverse until the threads line up) and stop if there’s resistance. Heat it up to extrusion temps and check its tight.

Piece of cake… use some common sense. :slight_smile:

Stainless is good for abrasive materials in filaments like metal coloring and especially carbon fiber shards… Otherwise, brass is fine for the relatively soft plastics.

Thank you, for a great a common sense answer, but if your not prepared to follow directions don’t remove. And gee its going to be working with hot parts, so perhaps using caution. So is TAZ purchasing these nozzles from someone as off the shelf or are they made in house or with a CNC shop?
I have a metal lathe and milling machine so I could do a one off if needed.