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Modification to the hot end for ABS printing

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ABS can be a bit challenging for the Ultimaker sometimes, mostly due to the hot end design, which is primarily for PLA. When printing ABS, the upper part of the tube inside the PEEK gets over 110C, partly melting the ABS filament in a location where it should not yet melt, causing a plug or under extrusion or grinding.

The problem is the temperature gradient: printing at 240C can be fine for weeks, or forever, depending on your luck, it can be fine in winter, but become terrible in summer. printing at 250-260C, especially black ABS wants to be hotter than natural ABS, brings the system over the critical point, sometimes right away, sometimes after a couple of minutes.

Lars has been talking about this theoretically on the google group for some time, but there are some real world aspects to it that affect UM users.

The trick is to prevent heat from rising up the tube: this can be done with gentle air cooling (unreliable, because ABS printing requires very careful and modest fan speeds), or with a heat sink/radiator.

I have been bantering with Cal over the last weeks, and we both went for a heat sink solution that solved our ABS printing problems at 260C.

The fix is only possible with parts from the V1 hot end, or additional parts from Makergear.com, specifically the 36mm brass barrel tube (M6) and either the original UM nozzle, or the (awesome) makergear nozzle set.

Heat sink 1


I added an old MOSFET heat sink after cutting off the bottom half of the radiator fins, and tapping it with M6. It is important to pick alu, mostly for the heat transfer rates, since we want to get the heat away from the tube as fast as possible.


Heat sink 2


For the last 15 months I've been using a silicone foam insulator which wrapped all the way around previously, but with the new heat sink, I had to remove the top.


Silicone Foam Insulation


And this is how the whole hot end looks now:


Hot end installed

This setup is running now for 2 months without a problem. I believe this fixed the same problems Cal had.


please ignore some of the additional mods to the hot end, they are not relevant in this context: I have a http://www.daltonelectric.com/cartridge-heater/index.htm installed (hot tip, which is why I had to close up the end of the alu block), plus the above mentioned Makergear nozzle (0.56mm)


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This setup is running now for 2 months without a problem. I believe this fixed the same problems Cal had.


Yes! I'm up to 275 C for Ultimachine black now and the results are better than ever (stronger parts with better finish quality). I've printed several 35 hours jobs that were printed fairly slowly (under 5 mm / sec filament feed rate) and I still had no trouble with heat migration or jams. Though my aluminum heatsink is smaller than Joergen's FET sink, my new PEEK also shows no sign of overheating, as did the old PEEK before I made changes similar to what Joergen describes here.

I'm also using no fan, except for a light fan on the very smallest areas (less than maybe 5-10 seconds print time) due to inadequate cooling time and my bubble wrap tent is yielding 65+ C!


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5mm/sec filament is about 31 mm^3/sec volume, about the max what you can squeeze through a 0.5mm nozzle per second reasonably.

I just want to add that heat migration upwards is not really an issue with such a massive volume of plastic getting pushed downwards through the tube, the problems start with low extrusion volumes and tons of retraction.


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Oops--I forgot to divide by 60 (minutes to seconds conversion factor).

This is a very slow 80 micron (40 micron perimeter "half-layers") / 40 mm/sec head travel nf print with a 0.5 mm nozzle. The netfabb menu numbers could be wrong too (though I think I've correlated them to some of Joergen's numbers in the past and found them to be reasonable) and I'm too lazy to measure the actual feed rate or do the arithmetic on the actual gcode. Regardless, it's a slow print and heat migration can be a problem at this rate, rather than the rate I misreported.

Also, these slow 35 hour print jobs used the nf default 2.88 mm of retraction. I capped the firmware at 25 mm / sec maximum E-speed and I built the firmware using the recent Marlin retraction fix source tree. There is no significant stringing across valleys and my nf settings do not attempt to restrict the print head to completing jumps only over the printed part (an nf option).


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Shouldn't it be possible to add a heat sink + isolation to the V2 hot-end? Although it may be necessary to cut a few mm of the PEEK to fit the heat-sink.


yes, of course, you can cut down your PEEK by the exact thickness of your heat sink. PEEK just happens to be a ridiculous hard plastic, not easy to cut without proper tools/machines, and you want to make sure you keep it very perpendicular.


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Dear Paul,

I just built my Ultimaker last weekend (I would consider myself a "capable novice") and I was printing White ABS straight out-of-the-box, so to speak. I haven't ventured down the "Black ABS" road just yet, but so far so good. Now, all that being said, I do like the look of:


Just seems more appealing than having the Peek or PTFE, which other users seem to have issues with.

Just my two cents to not get discouraged.



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The point is I was lead to believe that a heated bed was the answer to all ABS problems and now its not? just wonder what will be the next gadget I have to buy to make it work properly?




it's complicated.

the heated bed helps a bit with warping of large prints, in the same way a heated chamber will help a bit. there is no real generalization, other than the UM is primarily made for PLA.

The hot end problems can also not be generalized. Cal and I are doing industrial level production printing on our machines, with a lot of throughput and insane requirements. normal users may as well print happily all day long, without any problems. as mentioned above, 250C seems to be a threshold temperature for the standard UM design, below it's almost always fine, above it gets a bit iffy, YMMV.


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I'll second everything Joergen has said here. I mostly print black and yellow ABS and Joergen's estimate of roughly a 20C nozzle temperature difference is what I've found between the two colors too. The problem with black is the 20 C sometimes pushes you into problematic territory with a stock Ultimaker! Fortunately, both Joergen and I are running similar simple hot end mods and I think we are both happy with the results. I was planning a major stainless steel rework of my hot-end but may never do it, because my simple changes are working very well. I print Ultimachine black at 275C with no visible effects on the PEEK or Teflon hot end components. PEEK and Teflon are both limited to 260C for long term service, BTW, but a small additional heat sink and heat isolation (PEEK air gap) can keep them cool.

Joergen is also right that "it's complicated" and there's no general rule that works for every print, with every plastic (or every color, per the above).

For small parts, I'm printing on bare glass, like Joergen does most of the time too, I think. It's just too convenient (also for PLA at lower temps than ABS).

For big, thick, blocky parts that must be as strong as possible, I pull out all the stops and use every trick I know. I set aside my glass build plate and I tape-up my Mic-6 aluminum heat spreader plate with Kapton tape and wipe the Kapton tape with "ABS juice" (dampened paper towel rubbed on ABS). I start the print with a hot bed (120C or better) and, as soon as I know the first layer is going well, I erect a bubble wrap and blue tape enclosure to heat the build chamber. A 120 C bed produces 75C+ ambient temperature at the same height as the bottom of the print head, which I've actually found to be too hot for the entire print (results in areas with shrinkage and dimensional inconsistencies) so.....

1. I reduce the bed temp to 90 C after four layers. I've found this to be better for Kapton to bed adhesion too and it prevents Kapton tape lifting.

2. Use a slow fan for about layer four to 5 mm or so. This is after the initial layers are well bonded but while the bed and ambient air temps are still dropping from the bed temp reduction. Without a light fan, the part is usually slightly shrunken in X/Y in this region.

3. Fan off at 5mm and it stays off, except when needed for very fast print layers (small area layers).

4. Turn off the heat and remove the bubble wrap tent after print completes, When fully cold, I power-up the bed for about 20 sec (my bed heater is 1100W and AC wall socket-powered) and wait for the part to warm a bit on the bottom.

5. Work like hell to pop the part off the bed (sometimes requires resorting to using a razor blade and putty knife wedge, which isn't good for Kapton tape life usually).

The above may not work for you at all (no generalizations, like Joergen said) but I find that it results in no curling, no lifting, and minimal internal signs of stress (partial layer delamination or dimensional excursions) in the print.

In general, (and there are no generalizations ;)), I've found that a build chamber that is too cold results in delamination or partial delamination between layers. This assumes the part remains fully affixed to the build surface. If the part warps and separates from the build surface at all, this relieves the internal cooling stress in the part and you may not see any delamination effects or they may be minimal. I consider any separation of the part from the bed (lifting) to be a print failure and it's a failure I never see when following the steps above. Sometimes I'll accept a small amount of lifting when printing ABS on glass but, if it's excessive, I pull out the Kapton tape! By the way, Kapton tape on glass works too, but it doesn't stick as well to glass as aluminum. Kapton tape on glass offers a compromise between the convenience of printing on glass (hot swapable glass plates) vs. the delay of waiting for a Kapton-taped aluminum bed to cool after a print completes. Glass plates can easily be broken when removing large parts from an ABS-juiced and Kapton-taped glass plate though. I speak from experience; I've broken two!

If the build chamber is too hot, you will see "waisting" or shrinkage in some areas and the part will have excessive dimensional errors.

Partial delaminations are easy to spot in dark ABS colors (like black, which is most prone, due to its higher temp requirements). Any lighter striations along the layers is a partial delamination and it means the part is not as strong as it could be!

When it comes to the issue of stress and strain associated with cooling, I always say "the plastic has to cool sometime!" The trick is to make sure it cools in a manner that distributes stresses (spatially and over time) such that the strain is minimal and evenly distributed too.

I just received five 12" x 12" sheets of PET tape from Lulzbot but have not tried PET (polyester film tape) yet. It's thicker and looks tougher than Kapton but will have to prove to be tougher to be worth the price!


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Calin made excellent points outlining my "it's complicated" and I think nowhere in the UM literature it says that ABS printing is easy, nor does it say that anywhere on the internet :-) it is not only the hardware, but also the software (slicing) that affects the print. and it takes quite a bit of research and practice to get a really good ABS print out of the ultimaker, or any other printer.


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Sorry to re open an old post-it I just moddedmy uomo hotend and finally start to print Abs without Heather bed.

I changed my umo female Umo nozzle from 2011 with an e3d 0.6mm n ozzle. To do that I unscrewed the trheaded barrel for about 6mm, just to obtain enough female screw in the heatblock to screw the e3d nozzle.

this way the heatblock is a little bit away from peek, keeping it colder.

I covered heatblock with kapton just to keep it steadier hot and until now (2 weeks) I had very good results.

Perfect with pla from several sources, perfect with hdglass, with copperfill and finally printed my first (small) parts with abs, no heated bed, buildtak, no fan.

very happy indeed

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