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mmacrobert

Filament keeps grinding

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I'm struggling with my Ultimaker. I've spent more time trying to get it to work than actually print anything useful. I'm not happy at all.

Ultimaker provided me with a new PFA tube with a larger internal ID, but I'm still seeing a large amount of friction in the Bowden and Hot End to the extent that nothing I do with the feeder can overcome it.

I've built Bertho's travelling feeder clamp only to realise that the principal source of friction is downstream of the feeder.

I keep grinding filament and all of my printing fails.

I'm not seeing any Bowden plugs in the PEEK when I disassemble the feeder head.

I've tried tightening the regular feeder clamp even up to the point where the feeder-stepper skips.

I thought it might be an extrusion temperature problem, but I raised the temperature to the boiling point of the PLA and I still see the same behaviour.

The friction of my filament against the tubing is way too high.

I need some advice on how to continue. My Ultimaker is non-functional - I'd like to remedy this as soon as possible.

Thanks,

Martin

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Just a couple of quick thoughts.

- Have you cleaned the bolt?

- TOO much tension on the thumbscrew may cause the filament to deform and make it harder to get through the system. Tight enough that you can't yank it out by hand should be enough.

- Have you checked the filament to see that it isn't too thick?

- When you tighten up the hot end too much tension on the four thumbscrews might put enough pressure on the end of the bowden to make it squeeze together at the connection to the brass so that the inner diameter gets too small. (I don't think this is likely though)

- This one happened to me once but I think it's very uncommon. Check that the nozzle isn't clogged.

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Have you measured your filament? While I think they no longer are shipping bad PLA, there are rolls of PLA with 3.2mm sections in them. The 3.2mm is too large for the hotend and thus will cause the problems you are seeing.

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I've measured the filament many times to check. It is 2.90mm. I calculated an average variation on diameter to 0.002mm i.e - 2 micron from 10 sample points per meter, measuring x any y directions to see any sort of elliptical cross section. I was impressed at the consistency.

While slightly larger than the Ultimaker filament average dia (2.88), the Ultimaker-filament showed an averaged max variation of 46micron (on diameter) per meter when calculated in the same way. This filament is also jamming in exactly the same way.

I'm cleaning the V3 bolt every time I have a jam.

There is no Bowden plug in the PEEK-PFA interface. I was hoping that it would be that simple to address. I took time to eliminate the possibility. I used a dremel tool to make an internal cone which makes a good seal inside the PEEK as it touches the brass tube.

I've stripped down the head to inspect and clean everything more times than I would like... I know the nozzle is clean - I've figured out a way of cleaning out a blocked nozzle by raising the temp to around 125C then pulling on any filament in the nozzle. It comes out clean and the nozzle hole is also visibly clear.

I don't know how to quantify "too tight" for the long thumbscrews though this might be partly responsible. I do them up "three fingers" tight. No tools required.

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At which temperature are your printing?

You have cleared the issues:

-Plugging

-Bowden tube jam (because of bad tubes, wrong filament)

So the only issue that I can think off is, stressing the extruder too much, this can be done by printing at a too low temperature or a too high speed (or a combination)

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Printing at 220C indicated. Just printing at the default Cura setting. When I take the temperature to around 240C the nozzle sputters a lot so I take that roughly as liquid/boiling for PLA. I tried 225C but it had the same outcome.

I'm wondering if it may have something to do with the spool causing a curl on the filament thereby increasing friction on the PFA, but I have no practical solution to experiment with this.

Again, any further ideas are welcome. Thanks.

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I'm wondering if it may have something to do with the spool causing a curl on the filament thereby increasing friction on the PFA, but I have no practical solution to experiment with this.
I think that is highly unlikely. A bit of extra friction from the curling of the spooled filament is nothing compared to the force needed to push the filament trough the nozzle.

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Hi Robert,

It sounds like the problem lies not in your Hot End.

If you have received a new Bowden tube and with the measurements you have

taken on your filament it sounds like this is not the problem either.

Are you printing with filament received from Ultimaker? There are different types of PLA available, so the behavior

could be different when you heat it.

I also didn't see a reply on the comment if you put to much pressure on the Adjustment screw.

This could and probably will deform your filament.

Have you tried feeding 'fresh' filament through the bowden tube? Like when it hasn't been through the feeder yet.

Is this different from the filament that has been through the feeder?

I am looking forward to your findings,

Sander van Geelen.

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I'm seeing the same outcome whether I use Ultimaker filament or from another supplier.

Whenever filament started to grind, I would have to chop off the entire length of filament because the ground area would have a large lip on both edges where the bolt was. It was clear that the lips would rub against the PFA if it were forced into the tube. To restart I'd be using fresh filament.

With the regular Ulti-feeder clamp I'd try to set it as light as possible so I'd get a reliable feed. If it started to grind again, I'd increase the pressure incrementally. That strategy didn't make a difference because soon I was hearing the feeder stepper motor skip.

I was so annoyed, I made Bertho's clamp by force feeding the filament. It was once I had this clamp operational, that I realized that my problem was somewhere downstream.

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Can you upload a picture of your damaged PLA?

And a picture of your current feeding mechanism?

Do you have the v3 Drive Bolt?

Have you ever tried to start a print, and feed your filament manually? (open the feeding mechanism, lower the adjustment screw).

This will probably not result in a very good print, but if this goes flawlessly (no clogs, no grinded filament) it means

every part of the process works as it should and the problem lies in your feeding mechanism.

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Hi Sander, All,

I've done some experimentation and I am able to reproduce the failure on demand. I can also reproduce a remedy on demand. However, the remedy is not really practical.

Current Feeder mechanism: I'm using Bertho's rolling feeder clamp design to eliminate problems caused by changing filament diameter. Extruder_Drive

The filament is jamming inside the Bowden Tube - previously we dismissed the possibility of this type of friction, however the amount of friction generated is significant and is a strong function of the diameter of the spool used to coil the filament. The spool diameter should match the curvature of the Bowden in service to minimize points of contact between the filament and the inner wall of the Bowden.

When the spool diameter is much smaller than the curvature of the Bowden it will adopt a coarse spiral inside the tube that is pushing outwards along it's entire length. Since the spiral inside the Bowden is a significantly smaller diameter than the natural state on the spool this "normal force" can be significant. Since this normal force can be high, the sliding frictional force will also be high due to the large contact area. This is observed by a steady increase in frictional force as the filament is forced into the Bowden. With a small enough coil the filament will jam in the Bowden so tightly, that the filament cannot be moved even with extreme force.

You can check this with a simple experiment testing the potential extremes - heat PLA with a hairdryer with just enough heat to coil around a cardboard toilet roll, let it cool and try feeding the filament and get an idea of the "feeding force". It will be very high and will jam in the Bowden.

Snip off another length of filament and this time use the hairdryer to make a perfectly straight filament section. It will be very easy to slide.

Remove the filament, and add a small drop of water to the surface of the tightly coiled filament - the surface tension will show the points of contact between the filament and the inner wall. It will be pushing the inside wall along the entire length. Repeat with the straight filament - there will be random points of contact.

These observations explain happy printing at the start of a spool, but jamming as the spool is consumed and the coil diameter reduces - I have experienced this. It also explains the success of UM users who routinely "respool" their filament to create larger coils, when operating from the smaller diameter spools they experience jamming - check out google groups http://tinyurl.com/9b489ez comment by WThM de Groot. Furthermore filament that has not been wound cleanly onto the spool will have slight kinks of tighter diameter, which in turn increase the "normal force" and hence dry friction on the Bowden Id.

A partial solution (also a business opportunity for UM) is to use spools with as large a diameter and as wide as possible to ensure that the coil radius is constant for the entire length of filament. You could sell empty spools with this geometry.

Another solution is to reduce the sensitivity of the Bowden system to the coiling effect, but I have no practical suggestions on how to achieve this without eliminating the Bowden entirely.

My remedy (though impractical) is to preheat the filament to get it to "relax" so that the coiling has a larger radius. I've successfully remediated filament that I would have otherwise thrown away due to jamming. A hairdryer seems to work best, to apply the minimum amount of heat. It is possible that heating may change the filament diameter - I've measured an increase in average variation from 2 microns to 20 microns, however I can print where otherwise I would not...

I just have to respool my filament or change to a different supplier who supplies larger spools and winds the filament on without filament kinking...

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I don't know how to quantify "too tight" for the long thumbscrews though this might be partly responsible. I do them up "three fingers" tight. No tools required.

this sounds way too tight, enough to completely crush the filament. I would dial it back all the way, until it makes barely contact, hold the filament while you are turnig the large cog, and slowly tighten the thumbscrew until you need about 20-30 newton (2-3kg) force to hold the filament before it grinds/slips

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Hey Martin

Are you having this behavior on your filament when you are trying to print anything?

cam00010.jpg

I haven't found an answer neither, the only way I can print is removing the damaged filament while the printer is paused, and then continue printing (I'm using Cura 12.08) but is a pain in the ass to be checking the printer for hours.

I've tried to print the same feeder than you but i haven't had luck with it. I keep looking an answer as you. I hope some day we found it.

P.S. Sry for my english

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Hi Mastheraldo,

Do you print with retraction/destring?

With the standard feeding mechanism that is provided with the UM, this can cause trouble in your

feeding mechanism. So i recommend to print without retraction, or use this printable upgrade:

http://www.thingiverse.com/thing:26094

If you do not, please check the tension on your adjustment screw.

It could be that this is too tight, and deforms your filament causing it to get stuck in the bowden tube.

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