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Author Topic: Problems when prints have frequent retraction  (Read 1032 times)

Milo

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Problems when prints have frequent retraction
« on: November 24, 2013, 08:41:02 AM »
Ok, so I figure I should start my own thread of issues here instead of just interjecting in other's potentially different problems.

I've been having very successful prints on my BukoBot V2 when there is little-to-no retraction involved.
However, when a job involves any sort of retraction, the printer seems to struggle to extrude enough once it returns from the travel move. I had limited success by changing my slic3r settings to extrude an additional 0.05mm after each retraction but it was just not consistent enough to eliminate the problem entirely.
It wasn't until last night however that I noticed something odd about the filament shortly after the problem begins. I stopped a job the moment I heard the extruder make a sort of skipping sound and then removed the filament and noticed this:

It seems that somewhere during the retraction process, the drive gear isn't catching into the same groove it previously created, which then leads to much thinner filament in the affected area. This would also explain why sometimes I will remove the filament only to find a semicircular groove ground out of it where the gear must've been spinning on the spot.

I've had the issue occur with 6 types of PLA, all from DiamondAge.
Bukobot v2

whosawhatsis

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Re: Problems when prints have frequent retraction
« Reply #1 on: November 25, 2013, 02:55:58 AM »
Diamond Age filament is a particularly low-temperature blend that has a tendency to conduct heat up the filament despite the cooling of the barrel and expand/soften too high, causing jams. We're working on a fix for that filament, but higher-temperature formulations like the ones sold by Toybuilder Labs work more reliably. That's what we carry in the shop.

Milo

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Re: Problems when prints have frequent retraction
« Reply #2 on: November 25, 2013, 10:32:43 AM »
Well, I have about 6 rolls of the stuff at the moment, so I guess I'll just print without retraction for a while.
So does this mean that when I've increased the temperature thinking that it wasn't soft enough to extrude quickly that it has probably made the problem worse?
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Tyson

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Re: Problems when prints have frequent retraction
« Reply #3 on: December 03, 2013, 08:41:58 PM »
I use different colors of the Diamond Age PLA, at temperatures between 180 and 200 and don't have problems.
I would get some "clicking" where the drive would slip and I would notice that would reduce in an area of reduced extruder output.
But I seem to have been able to get that to go away.

Make sure your spring on top of the extruder is tight so the drive bites hard.

Check your filament feed to minimize twisting or rotation of the filament between it coming off the spool and going into the extruder.
(I use the $10 Amazon Lazy Susan approach for the filament spool and place it about 2 feet behind for a gentle feed)

After addressing these two things the problem has gone away.


Milo

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Re: Problems when prints have frequent retraction
« Reply #4 on: December 04, 2013, 12:49:13 PM »
The BukoBot V2 doesn't have a spring tensioner, so it's either full locked or not much tension at all.

I hadn't thought too much about the way my filament has been feeding. At the moment, it's sitting on my record player just because I saw it as a quick alternative to buying a lazy susan. I'm wondering if maybe the fact that the filament sits about 80cm below the printer is affecting it. If I get time tomorrow I'll run a few tests with the printer on the same level as the filament to see if that's causing the issues.
Bukobot v2

Milo

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Re: Problems when prints have frequent retraction
« Reply #5 on: December 08, 2013, 10:19:21 AM »
Ok, so I tested a few prints with the printer basically on the same level as the filament and it didn't really help much.
I did make one observation however, that the drive gear was almost as hot at the extruder motor, which makes me think that it might by why it's chewing the filament so easily.
I've turned the extruder voltage right down so I'm going to see if that helps and I might also get a second fan in there to help ease the heat.
Bukobot v2

Milo

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Re: Problems when prints have frequent retraction
« Reply #6 on: December 08, 2013, 02:07:07 PM »
I've just had success printing a part that's failed probably 15 times previously.
I dialled my extruder stepper down to about 0.65v and it has been running a lot cooler. I think this might be key to the issue with the softer Diamond Age PLA.
Bukobot v2

jit

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Re: Problems when prints have frequent retraction
« Reply #7 on: December 08, 2013, 07:31:29 PM »
I recently made a discovery that may or may not be relevant to the problems some people have with retraction.

While doing maintenance work, I partially dismantled my extruders.  To my surprise, both of my Tatsu drive gears fell off as soon as I pulled the motors out of the extruder blocks.  They had worked themselves loose somehow.

This means that the end of the set screw had not been firmly pressed against the flat on the drive shaft.  Therefore, the Tatsus could rotate slightly relative to the drive shaft.  So each retraction was shorter than the amount specified in my Slic3r settings.  Also, there was friction between the Tatsu and the drive shaft, possibly leading to wear (and heating) at their interface.

When these were first assembled, I had firmly tightened the set screws.  But I was using a hex driver shaped like a screwdriver, not the kind with a right-angle (Allen wrench style) which can deliver higher torque.  And it's possible the set screws had not been precisely centered along the midline of the flat on the drive shaft.

Perhaps it would be a good idea for anyone who thinks that retraction may not be working properly to check that their Tatsu drive gears are not loose.
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whosawhatsis

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Re: Problems when prints have frequent retraction
« Reply #8 on: December 10, 2013, 02:47:20 AM »
We've seen setscrews work themselves loose when trying to press jammed filament through the nozzle. We switched from stainless-steel-finish set screws to oxide black ones because the rougher surface seems to offer more resistance to this effect.

Milo

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Re: Problems when prints have frequent retraction
« Reply #9 on: December 12, 2013, 01:18:27 PM »
Ok, so for anyone having problems with Diamond Age PLA on a Bukobot V2, I might have a solution for you.
Try turning the extruder voltage down, set your retraction amount to 0.5mm, I have retract speed at about 90 but I'm probably going to tweak that a bit to see how it affects things, and lastly set it to extrude an additional 0.06mm after each retraction.

Give that a shot and let me know how it all goes for you. If you have any further tweaks on it or questions go ahead and post. I'm confident that the buko v2 is very capable of using this softer PLA.
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Milo

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Re: Problems when prints have frequent retraction
« Reply #10 on: January 09, 2014, 11:41:10 AM »
After having another run-in with this problem, even after the workaround I thought was working, I looked to other fixes.
I've actually gone the other direction with idler tension, by cutting a film canister open and making little rectangular strips from the side. I layered 2 of these and put it in where the idler locks into place, which has increased the tooth bite of the extruder gear, leading to seemingly no skipping or chewing during retractions.
Bukobot v2

Milo

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Re: Problems when prints have frequent retraction
« Reply #11 on: February 12, 2014, 04:31:24 AM »
The problem here is jamming due to the expansion of filament in an all metal extruder.
The fix is lubrication. I solved this with an old film canister, which I punched a hole out the bottom of and filled it with cotton wool balls drenched in sewing machine oil.

I did find after the first couple of prints like this that the cotton balls can actually feed a little bit into the extruder causing a slight block, but adding a sponge or cloth to the bottom of the canister solves this problem.
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midoco

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Re: Problems when prints have frequent retraction
« Reply #12 on: February 12, 2014, 03:48:53 PM »
Thanks Milo!
I tried this with 3 in 1 oil and it worked pretty well.  I might try a thinner oil next...  maybe gun oil?

Milo

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Re: Problems when prints have frequent retraction
« Reply #13 on: February 13, 2014, 01:23:46 AM »
Thanks Milo!
I tried this with 3 in 1 oil and it worked pretty well.  I might try a thinner oil next...  maybe gun oil?

Perhaps. I've only used this oil because it was all I had handy at the time, but I assume thinner will be better to some extent.
Glad to hear it helped
Bukobot v2

 

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