gaps appear as print gets higher/bed gets lower

[greens83 5]

Please help !

Suddenly my ultimaker after months of successful printing has started to show gaps as the height of the print increase/the bed moves down. The first layers print very well but at about 10mm upwards the print deteriorates.

I printed a small cylinder to show the problem.

http://s7.postimg.org/qzgn4fbob/20130715_203100.jpg

I have tried different slicers to check it wasn't a software problem.

Both slicers had problems at the same height.

Does anyone have any experience with a similar problem ?

X and Y axis seem to be fine, all belts are well tensioned. Bed is level. extruder seems to be working ok.

Any suggestions would be appreciated.

Thanks for reading.

J

 

[illuminarti 18]

What speed, layer height and temperature are you printing at? Is this the same filament, or different?

Have you checked that your extruder mechanism looks ok? Do you have the version with the spring on the back, or the thumbwheel?

When the print fails, is the plastic in the Bowden tube chewed up? Be sure and remove all the damaged plastic before restarting the print. Does clean, fresh plastic slide ok into the Bowden tube when pushed in by hand, or can you feel any friction?

 

[greens83 5]

Thanks for the reply.

Ive tried various speeds and temps. The print in the image was printed at 190 deg c,0,2mm layer height at 75mm/s perimeter and 125mm infill (Kisslicer) I also tried Cura with the same temp layer height and 75mm/s, the print was slightly different but still had gaps the higher the print got. I have successfully printed with these settings before.

Its the same filament which I have had many successful prints with at similar temps layer heights and speeds.

I did add an additional fan recently but I've had quite a few successful prints with that working fine. I took it off anyway, it made no difference.

The extruder looks to be working fine, Its the version with the spring (bought November 2012)

There are no signs of slippage in the extruder when I examine the filament.

The Bowden tube appears clear.

What I don't understand is why does it only happen once the print is above 7mm in height ? All layers below this height are perfect. Could there be a problem with the Z motor ? I checked the height of the final print and its very close to the correct height.

Im very very confused!

 

[gr5 2,172]

That is damn damn fast printing volume of plastic. 75mm/sec isn't too fast, but at .2mm layer and 190C I'm amazed you haven't had problems before.

A second fan, if it adds even a slight breeze to the nozzle tip could be the main problem. Make sure air is directed away from nozzle tip. Or raise your temp. In fact raise your temp anyway. Or cut your speed in half. You can't have your cake and eat it too. At 240C you should be able to print just fine at that speed and .2mm layer. But at 190C I would keep it under 50mm/sec or under .15mm layer height.

I had a similar problem last night because the filament on the spool was tangled. Could that be your problem? I don't always think to look at the spool.

Anyway, you are definitely underextruding. Either your feeder is too weak, your print volume of plastic too high, or you nozzle has a clog or isn't hot enough. Lot's of possible causes. You need to eliminate each cause.

 

[illuminarti 18]

Yeah, as George says, up the temperature, and/or slow down. The higher you go above 8mm³/s, the more likely you are to have feed problems (where the volume is speed x layer height x effective nozzle width). This is especially true when the plastic is cooler, and the second fan you added may well be cooling the tip of your nozzle, lowering the extrusion temperature even more, and so making it even harder to push the filament out of the nozzle.

 

[greens83 5]

Thanks guys, Ill do some testing tomorrow with your comments in mind, I think I may not have taken into account the extra volume when printing at 0.2mm. I've been mostly printing at 0.1 with the successful prints.

I'm still puzzled as to why the problem only seems to begin happening at a certain height, why do the bottom 30-40 layers print fine ?

 

[gr5 2,172]

>why do the bottom 30-40 layers print fine ?

I think you are on the edge of printing too fast. I think with some tuning you could achieve these speeds. Perhaps once you start to grind the filament, it never recovers? Or maybe it *is* a tangle in the spool (like I had last night). Sometimes if you raise the temp to 240C for a few layers, then lower it back down again it prints good for a while before having problems again.

 

[illuminarti 18]

It's a fairly common pattern that I see... prints start ok, and gradually degrade... a little under-extrusion at first can be hard to detect, but it gradually gets worse until you reach a tipping point. Looks like you're on the edge of what's sustainable, so it takes a while to kick in. Lower layers are usually printed slower, and without the fan (which may be cooling the tip of your nozzle slightly) so those put less stress on the extrusion system too.

 

[greens83 5]

Thanks guys, you make some good points, Ill slow down/heat up until its back to happy printing !

 

[greens83 5]

Could this be the problem ?

http://s2.postimg.org/3v7atr32x/20130716_193445.jpg

A big dent in the delrin wheel in the extruder ?

 

[gr5 2,172]

That certainly *was* a problem. It wasn't turning. Does it turn now?

You should get a steel one. Someone a few months ago posted a replacement steel ball bearing that fits perfectly where that delrin ring is (which is currently already around a smaller ball bearking). Having two ball bearings around each other is redundant but it was a nice inexpensive solution. I don't know the part but you only need to know the dimensions and you can order online.

 

[greens83 5]

I'm not sure If it turns or not, I have a theory that it probably turns some of the time and intermittently gets stuck in the groove and causes friction which would explain why the gaps in the prints appear quite suddenly in bands as the friction causes slight under extrusion ? Anyway Ill replace and see If it fixes the problem. I've tried slowing down and increasing temps but the problem persists. I'm 99% sure its a hardware problem now. Ill try to find the post your talking about. Thanks.

 

[greens83 5]

I found the post If anyone else reads this and wants to replace their Delrin wheel:

http://umforum.ultimaker.com/index.php?/topic/1676-modification-of-upgraded-extruder-drive/?hl=%2Breplace+%2Bdelrin

 

[gr5 2,172]

Great! I saved that in my tips file for the next person who has the same problem.

 

[greens83 5]

A quick note on the bearing solution. The bearing sizes specified in the above post is 4mm wide, this size doesn't fit in between the two ply walls of the extruder, it needs to be 4mm internal diameter, 8mm external diameter and 3mm width not 4.

 

[illuminarti 18]

Greens83 - I wonder if perhaps you have the wooden sides of your extruder clamped too tightly? That may explain both the groove that wore in your Delrin wheel (because the small bearing in the middle couldn't rotate either), and the fact that you can't get a 4mm bearing to fit. You may want to loosen the bolts that hold the sides together a little bit?

I know that a 8x14x4 bearing fits ok in general, because I just upgraded my own worn-looking Delrin ring to an 8x14x4 bearing, and it fits fine, rotates freely, and still prints well. (The smaller bearing was a bit of a tight fit inside the new one, but I chilled it with a can of compressed air turned upside down, and that made it shrink enough to fit).

The original Delrin ring looks like it's 15mm diameter, not 14, but the fractionally smaller diameter doesn't seem to cause a problem.

 

[mostlyatomicbob 34]

I was having the same sort of problems and after much head scratching solved this myself yesterday!

Luckily for me I have access to a lathe and Delrin. 2 mins later problem solved!

 

[greens83 5]

The 4mm bearing fits fine into the removable part of the extruder as you have shown above. Its the part of the extruder attached to the back of the machine, where the filament fits in between the two plywood sides which the 4mm bearing doesn't fit between. I could try loosening it. I'm not sure it'll be enough though. I have contemplated sanding a little off.

 

[illuminarti 18]

Hmm, interesting. You're right. The central plywood spacer is 3.75mm or thereabouts, in my standard extruder. Still, it fit ok, and worked fine for me, it seemed like.

I actually upgraded a couple of days later to Maxy's Quiet Retraction extruder body (http://www.thingiverse.com/make:42264) and that has more space in the middle, so it works fine there too.

 

[greens83 5]

I modified the extruder to accomodate the bearing. Unfortunately it did not solve my problems.

I am convinced that it is a hardware problem, I am printing G-Code that I know 100% printed fine a few months ago.

 

The problem is under extrusion. I have checked the nozzle and Bowden for obstructions - all clear, although I did notice a very slight resistance when the filament gets to the white connection piece at the extrusion end of the bowden.

 

The extruder itself seems to be working fine.

 

I am at a loss as to what to check next. Could the extruder motor have been damaged ?

 

Any suggestions welcome.

 

[illuminarti 18]

It's possible that the white teflon coupler has gotten damaged. That might be causing extra friction in the feed path, as you noticed, and causing under-extrusion. Might be a good idea to disassemble the hot end and check that piece for obvious damage.

Also, did you ever try printing the same pieces with significantly lower layer heights and speed (0.1mm layers at 50mm/s, for instance), and see how that affects the results?

 

[greens83 5]

Ill disassemble and have a look at that. Im also going to try pushing a pin/drill bit through the nozzle at temp, Ive read a few threads where this has solved sudden under extrusion.

I have tried slow speed & low layer heights and the problem still occurs. I am 100% sure this is a hardware problem. Im using archived g-code I know printed absolutely problem free a few months ago.

I just want my old UM back ! :(

 

[gr5 2,172]

So many possibilities... Here's a thought:

What if the amplifier for the thermocouple is reading high. Many people have been complaining about this. Some people have even modified their firmware temp tables to fix this. People who were printing fine but now their nozzle temp has an offset.

So if your nozzle is much colder than you think, it might actually be at 150C even though you think it's at 190C. This would explain how your delrin wheel got damaged (too much pressure). The quickest test is to just raise the temp to 240C (I often print at 240C anyway - I print anywhere between 190C and 240C depending on a few factors).

Also I recommend setting the nozzle to 190C, turning the extruder by hand to feel the resistance. Try turning the big gear slowly and then quickly. Then raise to 240C and try it again. Try turning slowly, then try a quick half-way-around rotation. Does it come out differently?

 

[greens83 5]

Hmmm, thanks for the input, before I go off on this tangent why would the thermo couple suddenly start reading wrong ?

 

[gr5 2,172]

I don't know but if you google ultimaker and thermocouple there are all kinds of failure modes. The most common failure mode is the wiring at the head if you don't use the strain releif properly. Everytime the head moves, the wires move and the strands in the wire break one at a time. When they are all broken you still have intermittent contact but the temp bounces around.

Also the amplifier board which is located on the print head can go bad and add some kind of voltage offset to the signal.

Also people have reported problems that the temperature changes suddenly when the fan or heater on the hot end are turned on. It will go from 210C to 230C instantly. This I think is caused by signals getting from one wire to the other (through radio waves or magnetic induction or cross talk or whatever you want to call it). Keeping the fan and heater wires farther away from the temperature wires might help but they typically all get stuffed tightly together.

There's just too many failure modes. YOu have to measure the voltage before and after the amplifier and again at the UM circuit board to figure out where the problem might be. But a simpler test is just to raise the temp to 240C and see if it helps or not. If not then you can probably eliminate this as the problem.