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extrusion, layer hight, feed rate, what to do?

Posted by cat.farmer 
extrusion, layer hight, feed rate, what to do?
December 02, 2013 02:01PM
I have been trying for a week to get my printer calibrated, but have had just tons of jamming issues.

I got down to the bottom of my jamming problem last night. turns out my head is digging into the print after printing 7 to 12 layers and is causing the filament to back up and jam, it is repeatable, I printed an open cube last night and you can see it in the columns of the cube, 8 layers and jams, then 8 layers more and jams.

I checked my z-travel - it was all good, no missed steps, 15 runs to 80mm and they all measured the same, and correct height.
checked my E feed rate, and it was all good.
printing 1.75 PLA @ 185 (have tried higher temps also, up to 210)
.4 print head
Using slicer - set to .4 print head, layer height .4, extrusion multiplier at .95
my extruded filament is measuring .48
I don’t believe it is my Z axis falling during printing, as the jamming is repeatable. I just think my layers are too tall or I am extruding too much.

so now I turn to you for some help..

what is the proper way to adjust for this problem?

increase the layer height to better match the extruded diameter?
somehow decrease flow rate to make narrower extrusions?
more heat?

If I print a narrow wall object such as the .5mm calibration test it turns out looking nice, but anything with a thicker wall seems to jam.

Edited 1 time(s). Last edit at 12/02/2013 02:03PM by cat.farmer.
Re: extrusion, layer hight, feed rate, what to do?
December 02, 2013 09:26PM
Usually, the layer height must be lower than the nozzle diameter. I print 0.25mm layer height with a 0.5mm nozzle. You might want to try this.

Also, play with the retraction, both speed and distance. I've found that slower retraction will cause less jams, in my case.

What hotend are you using exactly?
Re: extrusion, layer hight, feed rate, what to do?
December 03, 2013 01:00AM
Thank for the reply. My hotend is peiced together off of ebay parts.. PFTE insulator,stainless barrel, aluminum heat block and a brass nozzle,heat sink and a 40MM fan.
I did figure out my problem tonight... my extrusion rate was off. I had calibrated originally using only a20mm feed... tonight i used 900mm and ended up with 969, so with the proper extrusion setting things are working much better. I still am having jamming problems, but I am much closer to getting things working. I will try a slower retraction rate, as it seems to jam more offten after it retracts..
Re: extrusion, layer hight, feed rate, what to do?
December 03, 2013 07:20AM
I must say, hotends are very tricky part. I consider it one of the toughest mechanical part of a 3D printer.
You jamming may occurs because of your hotend inside surface roughness is bad. Stainless steel is very hard to drill and the plastic will stick to it. I suggest you drill a larger hole (4mm) and you put a PTFE liner like most hotends currently uses (2mm id). This will greatly help your custom hotend.
Also, you might want to get an e3D or a J-Head from the originals sellers, these will solve all of your problems!
Re: extrusion, layer hight, feed rate, what to do?
December 03, 2013 07:41AM
The extrusion process is fairly simple - if the extruder is calibrated and the X,Y,Z is calibrated, you don't get to much plastic with the settings you have. Making the whole thing work - not so simple at all.

1) Never rule out bad filament until you have used a lot of it (material as well as diameter variation)
2) Suspect any hot end that did not come directly from the people who designed it
3) Hot end cooling can make a lot of difference with some hot ends
4) Double checking the X, Y and Z is never a bad idea, they all get into the extrusion process
5) Extruder slipping (bolt tightness, gunk, bad parts) is a real issue

I have had jams with the head down on the glass. That's pretty common. Bed height is the issue. I've never seen a jam from over extrusion on higher layers. The stuff just seems to get pushed around and makes a big mess. That's not to say it can't happen.
Re: extrusion, layer hight, feed rate, what to do?
December 03, 2013 10:10AM
I have thought maybe it was bad filamet, but i don't have any experience with this stuff, so I'm not sure. I think my jamming is from too much heat creep. I had tried a bigger fan but i couldn't get the hotend to hold temp very well, something i think i have corrected with insulating the heat block, but I stopped short of testing it last night.
Is there a link that explains what to look for with bad filamet?

You are right Uncle Bob.. nothing about this is as simple as it seemed when i started my build.. of course i did it the hard way, by designing and building my own. I am pleased i can get it to work and very surprised at the definition i can get, even when it is not completely calibrated yet.
Re: extrusion, layer hight, feed rate, what to do?
December 03, 2013 12:39PM
I wish there was a simple "is this is bad filament?” sort of test? What works for me may not work for you. Yes filament with rocks in it will not work for any of us, but that’s not usually the issue. The only real test is to get some from a couple reputable dealers and try it out. If two out of three work fine, the third is (by definition) bad filament in your setup.

Hot end design is tricky. Heating profiles and tapers are not at all easy to figure out. Some very successful designs go from room temperature cold to hot in a very short distance. Others seem to warm up over a bit wider range.

If you are printing a spiral vase, the filament feeds all the time. There’s no (or almost no) start/stop. There’s pretty much no retraction either. In a more complex print there is start stop and may be retraction. That’s more of a challenge for the hot end than continuous feed. I can set up my hot end with “bad” (as in Uncle Bob’s improved design) cooling and it will continuous feed filament like crazy. Meters and meters of the stuff are no problem. Put it on a complex print and it jams up. Go back to the “factory” cooling it does fine.

I also have a spool of “cheap” filament that will feed for about 3 to 5 meters. It prints fine. At some point the hot end fills up with little black chunks of crud and that’s it. No more printing. Time to shovel crud out of the hot end before it will print anything…. That’s not your problem. It might not be a problem with a different hot end, it could be rocks in the filament. Who knows …
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