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Issue at same point each time


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Posted · Issue at same point each time

A print speed of 40mm/s seems quite fast to me, for such a big nozzle and layer? If I had to print it, I think I would rather go for 25...30mm/s.

 

At least, that is my experience with PET: print as cool as possible, well below decomposition temperature, and then print slow and in thin layers to give it enough time to melt and bond well to the previous layers, and to cause not to much ringing-effects due to speed.

 

These below were a couple of tests with PET.

 

Top row speed: 50mm/s.

Bottom row speed: 10mm/s

Layer-height from left to right (mm): 0.4, 0.3, 0.2, 0.1, 0.06

Temp: 215°C, except 0.06mm @ 10mm/s: 210°C; and 0.4 + 0.3mm @ 50mm/s: 225°C

Nozzle: 0.4mm

Material: transparent PET (brand: ICE)

 

Printing slow and cool in thin layers gave by far the best results. But there was a bit decoloration (browning), so it was still close to decomposing temperature. I could have gone lower to 200°C for these thinnest slowest prints.

 

block_geert_1b.thumb.jpg.7fad8a5326c68526dcc30ccb58666dd9.jpg

 

DSCN6014.thumb.JPG.6048c647bd1b456f5146ffa114b83051.JPG

 

DSCN6016.thumb.JPG.34c84f7029de80f9e26ea5e3e778fe0a.JPG

 

dscn6020.thumb.jpg.21bd5e7778868e4014e264253ecc0044.jpg

 

DSCN6022.thumb.JPG.a72e3faf1f92cb1f2b61ed08edd6a101.JPG

 

DSCN6025.thumb.JPG.ffc1547d179f793f396731beba704792.JPG

 

 

 

 

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    Posted · Issue at same point each time

    thanks for that Geet, very interesting...

     

    In what we are are trying to do, we need to churn out parts quickly and in ABS, and visual quality is mostly secondary in this case. I have had very good results the last 2 days with my revised settings and as we want to print quick 40/45 seemed the obvious way to go on it and frankly the results were almost bang on so im reluctant to change them now. I have just tried to pull one apart and i basically couldnt. Once spare time is available i will do some more testing but im really very happy with where i am at now.

     

    Cheers gents.

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    Posted · Issue at same point each time

    Basically the higher the fan, the better the quality of the part but the worse layer adhesion is.  The lower the speed of the fan, the better layer adhesion is (stronger part).

     

    For PLA you want that fan at full speed.  Beyond 100%.  For ABS you want that fan down to a minimum speed.  It depends on the air temp.  Ideally you want the air temp up around 80C and then you can have the fan near 100% but this would destroy your printer as the stepper motors can't handle that (55C air temp is about the limit - that's what the Ultimaker air handler uses as it's highest allowed temp I think).

     

    So that's why I suggested the test with the breakable part.  Do it with different fan speeds from 0% to 100%.  Do a binary search - start with 50% and if part is weak try 25% (else 75%) and if part is strong at 25% then try 37.5% and so on.  But you measure adhesion strength by seeing if you can get it to break along layer lines.

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    Posted · Issue at same point each time

    In my further research, the "internet" suggests the fans won't run unless they are at least 25%. I have mine set to 8% in Cura and 100% on the material profile and they start and run at 8% perfectly fine... 🤷🏼‍♂️ I mean they are moving very slowly, but they are running.

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    Posted (edited) · Issue at same point each time

    I printed a tower and couldn't physically destroy it... So at this point im very happy, seems I am good for my material now and the results are as good as when I was using PLA only now with the added temperature resistance I need. Thanks for all the help guys.

     

     

    Edited by Super_paulie
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    Posted · Issue at same point each time

    In my experience not. (But other people may see things differently of course.)

     

    Because then the nozzle is sitting there and just waiting. The flow is stopped, the filament spends time in the nozzle, heating up more, thus getting hotter than before and more liquid. It may ooze, and it will surely have different flow characteristics than before, which will show up as horizontal lines. Also, the heat accumulated in the filament, still has to "evaporate" after printing. Thus if it gets hotter due to waiting, then that extra heat also needs to get out of the print. The only advantage is that the nozzle does not radiate its heat directly onto the model.

     

    For small models, best is to keep the layer-printing time and flow-rate as constant as possible. So that the printer spends an equal amount of time on each layer. This gives each layer the exact same cooling time. If there are huge differences in time per layer, e.g. when a model suddenly goes from a very huge area to a tiny area, that often creates faint horizontal lines in the print: not much, but you see it.

     

    What I often do for tiny models, is create a dummy tower that has the inverse shape of my real model. Or better: the complementary shape. And then of course, the tinier the model, the slower and cooler you need to print, and in thinner layers, to get maximum details, and the least amount of heat in the model.

     

    See these pics for "inverse dummies": the first is the concept, the second is part of a real model, otherwise the top does not solidify well and deforms.

     

    dummy_inverse_block6.thumb.jpg.2bdb2396588983363b48127ee12d8174.jpg

     

    dummy_cutout2.thumb.jpg.750722bab5fa1c22a5e38d2a5717ab5b.jpg

     

     

     

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    Posted · Issue at same point each time

    That is incredibly interesting, thanks for that. Id never have looked at it that way and I enjoyed thinking it over!

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    Posted · Issue at same point each time

    @Super_paulie your part is big enough that I don't think your issue is "small part cooling" issue.  Not certain.  But you can print two at once.  The catch is that you may get some stringing between your parts.

     

    I get stringing with certain filaments but not with others (not even a tiny bit).  I don't pay all the much attention though to which types string as the small amount of stringing I do get clean up pretty easily.  But keep this in mind.

     

    Anyway I don't think you have too little cooling - you can always increase fan speed if you do.

     

    I'm glad your fan kicks on at 8%.  You should try stopping the fan with a finger and see if it can restart but don't worry.

     

    That 25% number isn't all that helpful as all fans are different.

     

    As far ask breaking the part - put it in a vice or something.  come on - PLA isn't that strong.  It's no stronger than wood.  I can break a pencil in my hands.  You should be able to break a print of the same dimensions even easier but it's okay to use tools.  You want to stress it like a bridge is stressed - from 3 points.  Rest it horizontally on a fulcrum (like another pencil?) and then push down on the ends.  Ideally it will not break on a single layer but shift over a few layers indicating that you have reasonable layer adhesion.

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    Posted · Issue at same point each time

    Yes, to me too your part looks big enough not to worry about layer-time. Except if you would have tiny features protruding from the top. I wrote that reply because you asked it. But it is more for very small items. Very often I have models with a tiny top surface of ca. 10mm x 10mm with very fine details (as in the blue thing above). And then it becomes a necessity. And even then I often give the dummy a very crude shape: just hollow below the top area, and filled as soon as the tiny features are reached. Just to get the nozzle away, let that cool, and keep the flow going steadily.

     

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    Posted · Issue at same point each time

    Thanks guys. I am content with my original part with my settings. But it was just out of interest on the cooling time. We produce 3 distinctly different products and one of them goes from very large to very small at the turn of a layer. This is the part I was looking at layer time on, but I print towers currently and its good. See attached for the part in question. It's either experiment with a layer time or use these "cooling towers", which I know works.

     

    Also GR, this is in ABS and I literally couldn't pull it apart with 2 pliers. I'll have to print a bigger tower to get that leverage.

    IMG_20201125_130521.jpg

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    Posted · Issue at same point each time

    Sounds like it is more than strong enough for your particular need for these particular parts.

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