Thumb Screws Unscrewing

Hi… Just got the taz5 about 1 1/2 weeks ago… I have been having a difficult time getting any jobs to complete before the filament gets stuck and stops advancing…

After much trialing, I have discovered that the thumb screws are ever so slightly unscrewing which causes the hobbed nut to stop advancing the filament - which then becomes stripped…

Does anyone have an idea about how to fix this problem… Lock tight / plumber’s tape have both failed… I also noticed that the housing for the nuts poorly holds the nuts in place… They can easily be rotated…

My test tonight was to every so often tighten the screws as it was printing… That solved the problem of having a job finish successfully… However, that was an hour of nursing… Not a very tenable approach I would say.

I don’t have any proof that I’ve seen that happen to me, but I’d begun to wonder about that lately.

I’ve had a few times recently when I could swear I’d set the distance between the washers at very close to 5 mm, only to find the distance at 6.5 mm or so at the end of a 90-minute print. Looking back, it only seemed to be happening (if it really was) on prints with lots of very frequent retractions.

I just finished a 3-hour print that needed very few retractions, and the thumb screws haven’t moved.

In my case I’m not saying for sure it’s happening, just that I suspect it might be, under some conditions.

I’ve never seen the nuts rotating, but I wasn’t looking for it. Hmm…I just looked, and one nut has a flat face facing up, and the other one has a hex corner facing up…

I’d guess the nuts have to fit loosely in their pockets, so they can rotate up when the thumbscrews are loosened and the clamp is rotated up out of the way. But they wouldn’t need to be loose in the Y-axis direction, and be able to spin.

I’ll watch more closely, if the issue is caused by the nuts turning, a simple shim – a toothpick maybe – placed in the nut pockets alongside the nuts would eliminate that issue, as a test anyhow.

Regardless of how it works out, I’m glad you mentioned it. I wonder if anyone else has experienced this?

They can and do work loose sometimes. Vibration from retraction or short infill back end forth motion usually does it. Blue loctite helps in quantity if you want to go that route. Same thing with the taz bed level screws.

Thanks for the confirmation of what triggers it, that’s very good to know.

So the next question is, when that happens is the thumbscrew rotating, or is the nut spinning in the pocket? The answer to that will determine where any fix should be applied.

I suppose putting a tape or other marker on the thumbscrews, and watching the position of the nuts in their pockets, will pin that down. The thumbscrews and nuts can’t both be rotating together, or else the tension wouldn’t be changing.

I’ll try to do a high-retraction print test in the next few days and see what I can tell. I’m glad the original poster brought this up!

Hmm… Is this in reference to the thumb screws on the idler? The compression from the springs should keep them from unscrewing. Same concept as a lock washer. If they are unscrewing, then maybe not enough idler tension to accommodate varying filament diameters while printing… should be slight teeth marks on the filament when extracted from the hotend.

This should hold true for the bed adjustment screws. I’ve found that the corners may not “spring” back after wrestling off a stuck on print. Depress the corners individually to make sure the plastic mounting / adjustment bracket is not hung up on the adjustment screw thread.

The hex nut pockets on the idler are probablg well matched for the width of the hex nut. If not, the nut would spin and the screw would never tighten. :slight_smile:

Sorry if I’m off base on the screws being referenced. I can’t think of any other thumbscrews on the TAZ… Z-endstop and maybe the bed attachment are the only other thumbscrews that come to mind.

Thanks for answering…

I can positively say this is happening a lot… I don’t know what initiates the process.

I have printed about 30 times different objects and have noticed a pattern.

Long print job (e.g., 2 hours+) will definitely cause the relaxation of the thumb screws.

Also anything that involves a lot of back-and-forth short spurts (e.g., building a perimeter 3mm wall about 20 mm high - 120 mm long - think a box) starts the relaxation process…

Locktight is a bad solution — it gums up the screw and then it is hard to use the thumb screw afterwards. And strange as it may seem, it doesn’t seem to help either…

The nut is certainly spinning in the pocket – it has a very sloppy fit… My first thought is for that to be corrected or adjusted in some fashion…

Well, I printed my “problem part” with lots of retractions in it today. Same settings as the last time I tried it. This time the print completed, and the hobbed bolt showed only minor ABS accumulation on it. The two nuts didn’t move during the test, and the distance between the compression washers was unchanged at 5.0 mm. So I guess my problem isn’t that, this time at least.

Just prior to that I’d done a 5-hour print at a fairly slow speed on a group of three parts with few retractions and also had seen nothing moving or changing during that either.

Since my nuts have two different orientations – one with a hex point pointing straight up, and the other with a flat pointing straight up, it appears they can indeed rotate, but I sure couldn’t make them do it today.

I do have strong suspicions that the loading-up of the hobbed bolt I often experience as part of my “problem print” failures are due to too-high extruding or retraction speeds, but I’ll start another thread about that in a while and not hijack this one. :slight_smile:

Sorry I couldn’t duplicate the adjustment-loosening problem, but today at least it just didn’t happen for me.

You might try putting a small shim of thin sheet metal down beside each of the two nuts, using brass shim material or aluminum flashing used on gutters, which can be cut with scissors, as a way to ensure they can’t rotate. One narrow strip, bent into a “U” shape flipped upside down, should take care of both nuts. I’m thinking of doing that myself, just as insurance against any rotation there.

In the interest of completeness: I just remembered one thing that may have changed from my previous “problem part” printing effort a few days ago and this one – in between I tightened a possibly loose extruder gear. It’s the small gear attached to the extruder stepper motor that drives the large gear on the hobbed bolt shaft.

I saw a post elsewhere about that as part of a general check-up list, and the set-screw on that small gear did seem not very tight. So I loosened it and then tightened it again. The poster also mentioned verifying the setscrew was on the flat of the shaft. You can see the flat of the shaft from the side, in the gap between the stepper and the plastic gear.

It could be that that gear being loose could cause more shocks upon retraction and then moving forward again, as any slop is taken up and then things get jerked into motion again. Something to look at anyhow, It could explain why I didn’t see the tension settings moving this time but did before.

Testing settings today, I found that reducing the retract speed to 1/2 or 1/4 of what it normally is (default speed is 1800 mm/minute for S3D) greatly reduces or eliminates the shaking/jiggling etc. of the extruder assembly when retractions happen. At 1/4 of the standard speed it’s quite calm. And it doesn’t seem to significantly impact the total build time, nor the build quality.

So that may be a good workaround to at least help eliminate the loosening of the thumbscrews you’re seeing.

Hi…

Thanks for your notes…

I ended up sending in the single extruder head together with about 15 feet of pla back to Lulzbot a couple of weeks ago. I’m waiting to see them try it out with the pla to replicate the problem.

I in turn purchased another head - which exhibited the same problem… So perhaps the pla? which is lulzbot pla.

I am printing abs with no problem… And I swapped out the extruder for a flexextruder – and had no problems.

So there is something odd about the pla process…

Since you are only having problems with PLA I would suspect heat creep instead of loose idler. Now I have a TAZ 4 with the new hexagon hotend that seems to be vulnerable to heat creep with PLA. I made a 40mm fan shroud that puts out 8.5 times as much air as the tiny fan that Lulzbot uses.

I don’t know if my duct would fit on a TAZ 5 or not but here is the file http://www.thingiverse.com/thing:845113