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eldrick

Tweaking the UM2 nozzle for better extrusion

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My UM2 has roughly 1000 hours of use now, printing both ABS and PLA.

I've had some recent under-extrusion issues, even after cleaning the nozzle with acetone and applying all of the known "fixes". (Roberts extruder, increasing extruder motor current to 1500, better-fitting clips on the Bowden ends, etc.)

So I took the dam thing apart again, and this time I resolved to do the job right.

First, I soaked the brass nozzle in methyl chloride to remove any trace of PLA, then in acetone (Note: both are fire hazards and have the potential to poison living things).

Then I swabbed out the inside with Q-Tips repeatedly with acetone, cleared the orifice with a needle, and inspected the nozzle again. I wasn't satisfied with the condition of the opening (slightly out of round), the flat on the outside of the tip (not much flat there), or the inside of the barrel (coated with black crap).

So I raised the ante:

- I got out the Brasso (metal polish with rouge in it) and used it with a half-dozen Q-Tips to polish the inside of the barrel until I could see bare metal again. I don't know what the black stuff was, but I believe that being smoother and fresh metal should considerably reduce friction and back-pressure in the nozzle.

- Then once it was all reassembled and the bed re-leveled, I put a piece of 1500-grit sandpaper (very fine, used for polishing paint on car repairs) on the print bed, with the nozzle just touching it with light pressure. I manually moved the paper a few inches under the tip in circles. This left a very thin streak of metal on the sandpaper as evidence that it was lightly sanding the tip flatter.

The result has been a noticeable improvement in extrusion and print quality. When extruding a few mm prior to a print, the plastic no longer curls up against the nozzle, and outside periphery layers are visually better-aligned and smoother.

My UM2 is now pretty-much back to its original level of operation and print quality.

Of course a new nozzle would have been a lot less work, but UM2 parts still don't seem to be available here in the U.S. (If a replacement nozzle had been available, I'd have bought one and drilled it out to .5mm, as .4mm is just too fussy and clog-prone for me.)

 

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Thanks for that report, it is good to know things can be (laboriously) fixed.

>My UM2 has roughly 1000 hours of use now, printing both ABS and PLA

Is there any reason to suppose that if you print exclusively in one material, the gunk buildup inside the tip would be reduced? In any event, a ready supply of replacement nozzle assemblies would certainly be welcome.

 

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My guess is that the stuff was carbonized PLA. If you let PLA sit in the nozzle without extruding for even a few minutes at temps over 180C, it tends to turn into something like burnt sugar.

It wasn't really that much work - maybe spent 20 minutes over and above removing/reinstalling the printhead and nozzle.

While in the shower this morning, it occurred to me that if the drawings are available, I'd consider having a local high-grade machinist do a run of UM2 nozzles in several orifice sizes: maybe .35, .4, .5, and .65mm?

 

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Hi EldRick -- thank you for passing this along. It answers a lot of questions, I think.

Seems to me the gunk inside could also be forming an insulating layer and lowering effective nozzle temps.

When I get to the point of needing to do this myself, if spares aren't available yet, I might try shipping the .stl to shapeways and having them print a blank for me -- it would cost about $25 in raw brass. I would still need to manually drill and thread to finish it, but labor-wise that sounds comparable to what it takes to recondition one. Given shapeways' lead time, I might order the blank sooner, as a contingency. (The .stl looks like it might need a little tweaking first, to get thread diameters right.)

The drawings are at https://github.com/Ultimaker/Ultimaker2/tree/master/1301_Integrated_nozzle_heater_block_3mm_filament_(x1). I would use freecad to import the .step and export the .stl.

 

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Actually I just posted a comment about the .skp file, which is not remotely of engineering-drawing quality. You could try sending them the .stl for printing, but good luck finish-machining a nozzle from that.

One tip on reassembly: use a little anti-seize compound in the holes for the heater core and the thermistor (as well as the aluminum heatsink). It will make them a lot easier to remove and insert without damage if/when you have to take them out again, and might even improve thermal conductivity a tad. I discovered when removing the thermistor that it slips in 1/8" further than it had been, because it was tight in the hole without the lubrication of the anti-seize.

 

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EldRick, thanks for sharing.

I'm curious as to whether/how many times you tried the Atomic a.k.a. Cold pull method before doing the disassembly/chemical cleaning?

It might even be useful to try cold pulls with different materials such as pla, abs and nylon. I got out some black stuff with nylon on one UM2 where PLA did not seem to catch on to it.

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...how many times you tried the Atomic a.k.a. Cold pull method...

I've been printing a two-month-long project with white PLA. I've used the atomic method dozens of times, and recently got into the habit of doing it after every multi-hour print.

I often got some brown stuff with a few flecks of black, and keep repeating cold pull until it comes out clean. I'm damned if I know where the black flecks come from, as I use only high-quality filament, keep it clean in sealed poly tubs, run it through a piece of poly foam as a wiper in front of the extruder, use Roberts extruder made of white PLA, and I can see nothing in the Bowden tube.

Before this extreme cleaning, I had done the cold pull several times until clean, and the nozzle was still lined with black stuff when I removed it. The atomic method is better than nothing, but not by a lot, IMHO.

Very frustrating.

 

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Hmm, yes frustrating I can imagine. I can also imagine the particular colorant playing a part in how hard the perhaps carbonized plastic sticks to the inside.

Did you try cold pull with Nylon?

Bukobot recommends Nylon 618 and the article is excellent:

http://bukobot.com/nozzle-cleaning

Could it be also that nylon sticks better to carbonized pla?

The quest for as-clean-as-possible-nozzles continues :)

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Ultimaker uses it between nozzle, the metal collar, and the aluminum heatsink (the copperish stuff you can see smeared on the heatsink around the collar), and recommends that you use anti-seize with copper in it, to avoid multi-metal corrosion. This was from another post on the Forum somewhere - someone asked what it was, and whether it should be removed.

Pretty much any hardware store anti-seize will have copper, and often aluminum, in a lubricating base. Usually available in a small tube of thin paste.

To apply, use a toothpick, and wipe a very small amount around the female inside threads and in the holes, so that putting the parts together pushes the stuff in, instead of just wiping it off the outside of the male part or thread. You don't need much. Don't put any inside the nozzle barrel.

A Ferrari-certified mechanic once told me that you could tell how good any auto mechanic is, by whether he always puts anti-seize compound on all the metal parts that fit together.

 

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When I get to the point of needing to do this myself, if spares aren't available yet, I might try shipping the .stl to shapeways and having them print a blank for me -- it would cost about $25 in raw brass. I would still need to manually drill and thread to finish it, but labor-wise that sounds comparable to what it takes to recondition one. Given shapeways' lead time, I might order the blank sooner, as a contingency. (The .stl looks like it might need a little tweaking first, to get thread diameters right.)

 

Okay, I decided to put my money where my mouth is, and have ordered a first-draft nozzle blank from shapeways; $30 including shipping. I think I have the dimensions right for drilling and tapping, but won't know until I try it. All I've done so far is increase the nozzle OD where the external threads go -- it looks like the original STEP had the thread minor diameter instead of major, although I might be completely confused.

Files at https://github.com/stevegt/Ultimaker2/tree/master/1301_Integrated_nozzle_heater_block_3mm_filament_(x1).

 

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I've given up on reproducing the nozzle, and now I'm trying to order a new one from Ultimaker, which is also proving to be difficult.

I've received one response with a steep price (€ 69,59 excl. VAT and shipment) from sales@ultimaker, but have not been able to get Zenalda Furtado to tell me how to actually order or pay for it.

Ultimaker still seems unwilling or unable to provide post-sales hardware bits. I'm hopeful that illuminarti can provide a nozzle here in the US.

 

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For what it's worth, I recently had to disassemble the brass heater block for a sensor repair...I removed the temp sensor probe and heating element. I went ahead and blasted the brass block with a propane torch until nothing was left to burn. I did a quick scrape down, nothing fancy. I reassembled ( it still had black oxidation on the inside of the extruder nozzle because I didn't have time to Q-tip polish the darn thing) and I must say, I noticed a remarkable difference in extruding...no curling, clean extrusion rates, etc. I usually use the "atomic method for quick cleans"

Just thought I'd pass that on.

EDIT: I've since had to clean the nozzle, and this time I did polish the inside with a widdled down q-tip stick, a drill and some "Never Dull" brass cleaner. Worked awesome, and is a real confidence booster knowing the inside is so smooth and shiny :)

 

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