Colorfabb nGen

Discussion in 'Calibration, Help, and Troubleshooting' started by Spoon Unit, Mar 16, 2016.

  1. Spoon Unit

    Spoon Unit Well-Known Member

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    Looking for ideas on how to print this thing. I've tried a variety of temps, all on UHU glue, and by about layer 4, my print detaches. I've played with first layer thickness too to try to get more material down, but I'm wondering if nGen and UHU is just not a good combo.

    Have you printed nGen successfully before? On the BB? What sort of setup?
     
  2. Paul Seccombe

    Paul Seccombe Well-Known Member

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    I'm only on my second ngen print but haven't had any issues. I used the standard Simply3d settings (from the latest dual Profile), 235 on the extruder, 80 on the bed with UHU, about 30% fan on layer 3 or so. Still getting a little stringing but apart from that it looks OK.

    I did a 19.5 hour print with generic PETG with a temperature of 240 and it looked perfect again except for the stringing (which is why I knocked the temperature down to 235 for my latest ngen print).

    Have you tried adding a raft? I did this on the smaller parts.
     
  3. Spoon Unit

    Spoon Unit Well-Known Member

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    I've never tried a raft. On my last printer that was just a hideous experience so I never considered it here. I don't get the logic behind using a raft?
     
  4. Mike Kelly

    Mike Kelly Volunteer

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    Rafts are good for ABS because it distributes the internal stresses better and increases the first layer bond strength.

    If the raft removes easily it's great. If not it's worthless. Just depends on your slicer and material
     
  5. Spoon Unit

    Spoon Unit Well-Known Member

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    Finally figured nGen out on the BB. Print at 215, bed at 95.
     
  6. Rob Heinzonly

    Rob Heinzonly Well-Known Member

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    The Colorfabb documentation said :
    • Processing Melt Temperature 210-240°C
    • Heated Bed Temperature 60°C
    • Cooling 0 to 100%

    I noticed before that there is a difference between the set temperature of the heated bed and the glass temperature of the glass surface. Maybe that explains the difference.
     
  7. Alex9779

    Alex9779 Moderator
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    What do mean with that?
    I know the "glass transition temperature" but that is a filament specific unit. It is the temperature when the material gets soft: https://en.wikipedia.org/wiki/Glass_transition
    It generally defines the max temperature at which a material begins to loose its form...
     
  8. Rob Heinzonly

    Rob Heinzonly Well-Known Member

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    @Alex9779 : Sorry, typo. I meant the surface temperature of the borosilicate glass.
     
  9. Alex9779

    Alex9779 Moderator
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    So what is the difference between the temperature of the heated bed and the temperature of the glass surface?
    Ya I know there must be a difference because the thermistor is UNDER the glass and what for us is important is the temperature ON the glass but in practice this should make not much of a difference.
    Ok ok don't bother me with heat transition theory, I might have to get into my lectures and books and get the heat transmission coefficient of borosilicate glass to calculate the temperature degrade from the heated bed to the glass surface with air convection on the top surface but I still think in practice this should not matter...
    I know myself that the values are a bit off, the sensor reads for example 70° C but if you touch the glass it is not that hot but until the prints starts the top surface may reach that temp...

    So back to my question: you think we have to set the bed to a higher value to get the needed temperature on the glass surface? Then by how much?
    That's what I read between the lines when you start to differ between those two temperatures...
     
  10. Spoon Unit

    Spoon Unit Well-Known Member

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    I found with a lower temperature on the bed, nGen just peeled off as it was printing and seemed to warp. So I put my thinking cap on and started to think about the how and why of the heated bed temperature. It could be completely wrong as a result, as I used no theory, just logic. So I'm just waiting here to be corrected in my thinking, but here was the end result:

    Bed temp = Tg(Material) + 10

    The thinking goes like this. Bed temp is probably not quite bed temp as theorised above a little, and the base layer of the print is not going to be bed temp due to a reasonable large surface area, regardless of having the part cooling fan on. So choosing something higher should get the base layer to some sort of level of softness where the action of gravity can fight warping a little; not a lot but hopefully enough to keep the base layer fixed.

    Having come up with that, I looked up Tg(nGen) and found it to be 85, so I set the bed to 95. Result - 3 perfect prints in a row.

    OK. Tear away.
     
  11. Alex9779

    Alex9779 Moderator
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    If I would take your formula for ABS then 105 + 10 = 115.
    I tried printing ABS with 110 to 120 as recommended even from E3D with this result:
    IMG_0543.JPG
    I did some research, on the guides I posted are explanations, and from this point I printed ABS with 90° C bed. This was the result, other settings all untouched (!):
    IMG_0544.JPG
    Has to cancel that print because of some other issue but you see the difference...
    Did some more tests, no parts left of those but with the same results.
    I never got a good print with the recommended values...

    Tg of PLA is BTW ~65° C and recommended bed temp is 55° C to 65° C...

    What I wanna say is that you can't postulate a formula, it is material, printer, environment dependent...
     
    #11 Alex9779, Apr 15, 2016
    Last edited: Apr 15, 2016
  12. Henry feldman

    Henry feldman Well-Known Member

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    Yep, that is the range of possible cooling values. Such a helpful spec... Excellent guidance from the manufacturer! :rolleyes:
     
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  13. Spoon Unit

    Spoon Unit Well-Known Member

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    I go with 75 bed for PLA and it seems to work well. Thanks for the actual physical evidence from some prints there Alex. I've yet to play with ABS.

    You are wrong on one point though :). Of course I can postulate a formula. I already did!. It could well be wrong (looks like it is), but the great thing is that I already learned a good amount from the conversation following the postulation - hehe. I'm sure there must be a good forumla too, even if it's way more complex than my first stab.
     
  14. Rob Heinzonly

    Rob Heinzonly Well-Known Member

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    @Alex9779 You got me thinking... This morning I did some measurements with the heated bed set on different temperatures, ranging from 60°C to 120°C

    As you can see in the tables below, the center of the bed pretty much follows the set temperature, so I was wrong about the offset earlier. 70 mm to left and right the temperature drops for about 8% regardless of set temperature. More to the edges of the bed the temperature drop gets more dramatic.

    [​IMG]

    [​IMG]

    Of course these measurements are strongly influenced by external factors so your mileage may vary. But my rough guess is that with some types of filament your usable print surface will be something like this:

    [​IMG]

    So from 80,50 to 230,140.
     

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  15. Alex9779

    Alex9779 Moderator
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    Touché! :D

    @Rob Heinzonly wow great analysis...
    So we see that there is a temp drop of 1-2° C right above the thermistor. That's ok IMHO as 3D printing is I some points not an exact science, more of an art, maybe a dark art ;).
    But I am surprised of the drop to the edges of the bed as E3D stated they have three different zones on the bed with different heat deposition.
    Looking at this I don't wanna see the temperature disposition on my UM2 bed!
     
  16. R Design

    R Design Well-Known Member

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    NIce job @Rob Heinzonly.

    Those are the kinds of disparity I've observed with my Flir One with the bed set at 75C. (btw. what did you use for the measurements?)

    I'm kind of worried about parts detaching the day I have a really full build tray.

    What are we going to do for the bed?

    Did anyone ever fit a sheet of aluminum before? Like, between the PCB and the glass....
     
  17. Paul Winter

    Paul Winter Well-Known Member

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    Hi,
    Yes, just replaced my glass build platform with a solid plate of 6mm Aluminium. It sits on top of the PCB, covering the screw heads of the bed levelling system, so I have had to drill some recessed holes underneath the plate to allow it to sit flush and in direct contact with the heater PCB.
    I have binned the glass build plate due to issues with bed adhesion - couldn't get prints off without pulling glass with them.
    A small technical issue to solve is to make a clip arrangement to pull the plate firmly down onto the heater PCB (to stop the plate shifting slightly backward and forwards), and given the plate is running at 90C, a printed part is out of the question.
    Because the plate is 6mm thick, the small binder clips I used to hold the glass on with don't now fit.
    For now, Kapton tape folded around the edges of the plate and the heater PCB work OK.
    The plate is easy to remove to get stubborn prints off, and because I use PVA adhesive as a bed surface treatment, I can stick the whole plate + print under the tap.
    The plate was really shiny when I bought it, but I have matted the build surface down with some Wet and Dry abrasive paper.

    Also, because I use a Prusa i3, I replaced the original perspex Y-carriage with a similar 6mm plate drilled in the appropriate places for the bearing and belt mounting screws etc. as flexing in the carriage was making levelling a constant nightmare. Between these two mods, my bed levelling has dropped right off, once set initially.

    The only thing to watch out for (it's still early days for me in this respect) is to make sure the Y-axis motor and belt can handle the inertia of trying to move the new carriage and the buildplate without missing steps, introducing ringing, or stalling the motor.

    Three plates custom cut to 224mm square cost me less than a couple of borosilicate glass plates, so the math works out.
    1 plate for the new Y-carriage.
    2 plates for interchangeable build surfaces, so I can be cleaning one while the other is in use on the printer.

    It's looking good so far.
     
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