gr5

The spring is overly strong in the extruder so everyone is supposed to loosen the screw as much as possible so the sprint is compressed as little as possible. People who have tightened this spring had problems with grinding filament. I posted elsewhere how to modify the current to the extruder but I haven't messed with that for this particular test. I doubt anyone has. Supposedly if you increase the current much more to the extruder it will grind the filament instead of slip (skip steps). Slipping is strongly preferred. Although the alternate story I heard is that increasing the current any more doesn't make much difference. I kind of doubt that.

I reposted my data, Nicolinux's data, and IRobertI's data regarding pulling force of extruder here: http://umforum.ultimaker.com/index.php?/topic/4222-pulling-force-of-um-extruder/ Please post any test results there and I will continue to refine the summary at the top of that topic (although IRobertI is a moderator and welcome to edit my post directly if he has new data).

gr5 um2: 4.9-5.5 Kg (48-54 N) IRobertI um2: 4.5-5.75 Kg (44-56 N) Nicolinux um2: 5.7 Kg +/- 5% (52-62 N) (Bertho's UM Original can pull about 4.8Kg) I will update the above values if people post more data below. Here is my test setup: I used prontrface to slowly extrude the filament. The weight on the scale slowly decreased until suddenly the extruder stepper slips backwards ZIP! I repeated the test several times at different points of the filament and things were repeatable within 1%. I extruded about 50mm at a time at 200mm/min (3.3mm/sec). Pronterface is the perfect utility for tests like this and a very easy to use GUI. It gives you much more control over your printer (although you have to heat the nozzle to 170C for the extruder to run). Originally I got 5.5kg very repeateable. But I repeated this test a week later and wasn't able to get more than 4.9kg force because the filament would grind up. See graph in post much further down. printrun/pronterface download: http://koti.kapsi.fi/~kliment/printrun/ Nicolinux data from this post: nicolinux post #26 below IRobertI data from this post: http://umforum.ultimaker.com/index.php?/topic/3976-almost-always-missing-layers-underextruding/?p=34885 Bertho UM Original data came from here: http://vinland.com/Extruder_Drive_Force.html

I rebuilt my test jig just now so I could take a photo (I should have taken a picture originally). The bungee is critical so that you can tell the printer to extrude 50mm and it slowly reduces the weight on the scale until suddenly - ZIP - it falls back many steps on the stepper - maybe 100mm. Let me know if the picture isn't visible and I will upload it to the forum instead.

Well then you should DEFINITELY get prontrface. It's free and very helpful for this test. You can set the extrude distance and speed. I think I used 50mm for the distance and 200mm/minute for the speed. prontrface is a gui the connects to your UM2 (or UM Original) through a USB cable. It gives you SO MUCH MORE CONTROL over your printer which is especially useful when doing tests: printrun/pronterface download: http://koti.kapsi.fi/~kliment/printrun/

the screws are almost all standard M3 screws (I think that means 3mm diameter). The lengths are all in mm. Typically 5mm, 10mm, 12mm, 15mm and so on. Someone recently posted what you have to search for in mcmaster carr to find them with the same screw head - they have a weird name.

There should be a "next error" button where you click the button and it zooms and centers the view on the next internal plane. However be aware that you can also have "holes" in your model - like tiny windows where two edges don't quite meet up. I am only able to detect these in layer view where it won't fill a particular layer due to a windows over on the side. Cura can't detect these because it's hard to tell if the holes are on purpose.

So your problem with extrusion looks pretty good to me - the print you did at 80% looks fine to me. So does that mean you are all set? If you want to get another 20% speed increase you can probably just raise the temp by 10C or 20C. Is it possible that your problem was simply a change of filament that needed a different melting temperature? You said the gray filament is brand new so this might be the problem - maybe you just need hotter temperature. However if you are able to get your nozzle off, I would recommend heating it over a flame (not too hot) until everything inside turns to carbon and can be cleaned out with a paperclip on the inside.

You need pronterface - it's a wonderful GUI utility that will connect to your ultimaker through USB and allow you to do all kinds of things for example move the extruder exactly 10mm at 10mm/sec. Or whatever you want. It's all very simple. printrun/pronterface download: http://koti.kapsi.fi/~kliment/printrun/

So Nicolinux - while you had the head apart - I hope I hope you did two things: 1) Heat the hot end in a flame to burn out any ABS in there. Or soak in acetone for an hour to dissolve any ABS. 2) Drill out the nylon piece with a 3mm drill and make sure the filament slides through there with less than a few ounces of force. I suspect there is a little piece of ABS in your nozzle tip sticking to the wall of your nozzle but not clogging the tip directly.

Brilliant! Make it out of clear or natural PLA so that it also doesn't leave a blackish spot in your print. Daid says he has the STL for a printable version of the extruder.

I can't wait until you get your own printer so you can get a better feel for these things. First of all the pressures in the nozzle are pretty high. 8 to 12 pounds force are common over surface area of 3mm meaning about 1000 psi. That's a lot of pressure! Also if you play with PLA and heat it in boiling water and bend it around you will see that it gets very soft like gum. Glass temp is around 50 or 60C where there is a rather sudden transition. Melting temp is closer to 180C where there is another transition. Those temps (50-60C) may be occurring up in the nylon. Or maybe colder. In either case it takes a bit of force to get coolish PLA around this "lip". Maybe. Certainly not a "swirling" issue. It would be easier to swirl cold honey in a jar. PLA's viscosity is similar to honey I'm guessing around 240C. In the area of the nylon it should be much colder and more like the viscosity of modeling clay (plasticine). Around 170-180C the viscosity is closer to toothpaste.

@chrisp - I don't think the bearing ever touches the drive gear directly so I don't think anything bad happens when there is no filament in there and the drive gear is rotating. But the drive gear chews up the PLA a little bit making for sharp areas. As that goes in and out (retraction) it could potentially grind the black PLA. Although I would expect all the grinding to happen on the drive side - not the bearing side so maybe you are right.

What I think is happening is that with retraction, the sharp pieces of PLA can rub against the black ABS housing shown in Chrisp's photos above. This rubbing breaks off pieces of black ABS, some of which make their way to the nozzle and cause a clog. Having straight filament pulled from straight below the UM might keep the PLA from rubbing on the ABS. Although I'm not certain that will help. Maybe the extruder needs some stainless steel parts or something much more scratch resistant than ABS? I don't know what the solution is.

I usually do fan on around 5mm up which I think is the default. Cura will turn them on gradually a little more each layer until it gets to the layer that is at 100% fan. The gaps in your brim are not good. This cube does not need brim but many of your other prints will. The gaps are either underextrusion, or more likely a leveling issue. I would re-level but only adjust the rear-most point and I wouldn't touch any of the 3 screws - I would do it only with the front panel control. Make it a little tighter than you did last time. When it asks you to check the front to points just click immediately claiming it's fine. The great thing about the UM2 versus the UM Original is leveling tends not to change. So once you get it perfect you may not have to level again for weeks or months.

And the bottom of the part looks warped kind of. This is caused by temperature issues most likely. 75C is a bit hot for PLA - I like 70C. And the fan comes on gradually over the lower 5mm or so. Not sure exactly what is going on here though - my cubes don't have nearly as much distortion near the bottom. Your bottom layer seems a bit thin. An initial layer thickness of .1mm is very difficult to achieve unless you relevel a few times. If the bed is .03mm too high (1/3 width of paper) then it will build up pressure gradually in the nozzle until finally the extruder skips steps and slips backwards quite a bit and you will get almost zero extrusion for quite a while - possibly why there was no brim touching the cube - just a coincidence. I recommend .2 or even .3mm for the bottom layer as you then don't have to level so precisely. At least until you get very good at using the printer - some day you can try to get accurate levelling to .01mm and then do .1mm bottom layers.

Several times I have been able to continue a print after a nozzle clog. In fact I did one today. It works quite well. I've done it on both UM Original and UM2. You have to know exactly where the print failed and where to continue it after cleaning the nozzle. Usually I can tell because I was there when it clogged and look at the Z height on the ulticontroller or there is something distinctive on the layer that I can compare to the layer height view in cura but today it was too difficult to do that so I Homed the head and platform and connected to the printer with pronterface and set the Z to verious heights with the G0 command: G0 Z23.3 I used pronterface to move the head in X and Y until it was right over part of the print and was able to figure out *exactly* which layer it was printing when it failed and I started at the next layer up. To continue where the print left off - the short answer is you delete the gcode up until the layer you want but in reality you have to keep some begining stuff and also add a G92 e.g. G92 E7876.1 sets the extruder to 7876.1 mm as the *current* position so that when it moves to E7876.2 it only extrudes .1mm of filament and not 8 meters of filament.

Maybe but remember that you *always* get better extrusion at higher temps. There isn't some sudden melt point where extrusion stops getting any better - viscosity keeps getting lower. http://umforum.ultimaker.com/index.php?/topic/4127-um2-extrusion-rates-revisited/

I did the extruder weight test! Quick answer: 12.1 pounds or 5.5 kg. I used a bunjee cord that stretched more and more as the filament went up into the tube. I had the other end tied to weights on a scale and watched the "weight" drop down to lower and lower values as the extruder lifted more and more weight. I was at 3.3mm/sec extruder speed. The extruder can definitely hold more weight when stopped. I repeated the experiment a few times. Everytime it failed it spun backwards (I was staring at it and watched it zip around backwards). Another way to say it is it missed steps rather than grind the filament. I used the same light blue PLA from UM that I think you used nicolinux. I got a variation of only 2 ounces or 1%. So my extruder had 10% to 50% more power than yours. Not sure how relevant this is as I'm not sure how repeatable your test was and how accurate. I should have taken a picture of my setup. I'll describe it in words: I put a spaghetti pot on a scale, connected the two handles with very short bungee. inserted a 2 foot PLA. Clamped to the bottom with vice grips with bungee also going through vice grips grip. This second bungee reached both ends down to the bungee on the spaghetti pot. The spaghetti pot had 14 pounds of weights in it. After I was done I measured everything together including the weight of the vice grips. Subtracted total weight from the weight when it failed.

I'm very glad you did this test. Can you post this same post in a thread by itself? I'll post my results in the same thread. I am printing something right now but it should be done in a few hours. I will do the same test. @illuminarti - I think this says a lot - I believe the feeder has the same torque when stopped as when moving (or slightly higher than when moving). nicolinux - I think you should concentrate on your nozzle. Do you have acupuncture or hyperdermic needles or .3mm drill bits or something strong and metal that you can use to clean out the tip of the nozzle slightly? Just rub it around the inside of the nozzle hole 5 or 10 times trying to scrape out any possible gunk that is stuck to the side of the nozzle hole. Don't push it high enough up such that you damage the nylon (it's pretty far though so it should be safe). Also I think you should check the white nylon piece to make sure the filament slips through it easily.

I'm quite surprised. This is interesting. I can see the width of a piece of paper so I guess I should be able to see the gap. I always use paper. I think I can adjust to .03mm accuracy with paper. Maybe. Not sure. Are both of you doing this on blue tape? Or does this work on UM2 glass bed also?

They don't? I think they do. When Cura went from 13.04 to 13.05 it broke all the plugins. Not all of them have been fixed. The tweakAtZ plugin that works best is on the plugin page but some of the other plugins might still not work. This one works fine (but does height in mm, not layer number): https://github.com/Dim3nsioneer/Cura-Plugins/raw/master/TweakAtZ.3.0.1.py

Another solution might be to mess with the "start gcode" settings. For example you can add a sleep (say 3 seconds) and/or a pause (where you have to push on the ulticontroller to continue). That gives you more time to not burn your fingers. And while changing that code you might want to increase the E feed from 3 to 6mm of filament and decrease the speed by maybe 3X so you don't extrude to fast and potentially grind the filament.

The big lesson is pretty simple. The faster you print, the higher temp you will need to print with. Otherwise the extruder just can't deliver the needed pressure to get the desired filament out. The photos are useful because they recommend specific speeds and temps that are at the upper limit so you can stay well below those if you want prints without underextrusion.

@schafe - yes - order this glass from your local glass cutter. They will do it for very little money and they will grind the edges so they aren't sharp. mnis posted dimensions above. It's ordinary glass I believe. It's not pyrex - it's normal glass. But very thick (4mm).