Bed Heat ?

Discussion in 'BigBox General Chat' started by Spoon Unit, Aug 26, 2016.

  1. Spoon Unit

    Spoon Unit Well-Known Member

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    I'm looking for some input on how to think about how hot to have the bed.

    I started out just following what I read on the internet for various materials.

    Then I started to think that the bed heat should be something close to Tg for the material.

    Now I'm not so sure.

    For me, so many problems are fixed by having a good first layer and I've got that down to a fine art now. But you can still have some issues later if the material pulls away from the bed. Some of those is about understanding the model, and using infill in such a way as to not set up crazy internal stresses. But I'm wondering if some of it might also be about having the bed temp right.

    Looking through some of the settings people are using with aluminium bed, I noticed that some use a different bed temp after the first layer. So I'm curious to understand why that might help. A clear place it helps is in the speed to return to cool-enough-to-pop-the-part-off. But I'm also wondering if it can help with keeping the base flat. I'm beginning to think that while Tg might be good for first layer adhesion, we actually might not want such a malleable material at the point those stresses begin to grow. If the material is less malleable, perhaps it won't bend, and such issues might be reduced. So at this point the question turns to what temp you need to stay stuck to the bed and that will again vary depending on the bed material, the adhesion used, and the material printed.

    Anyone with any cunning observations / knowledge in this area?
     
  2. Ephemeris

    Ephemeris Well-Known Member

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    As with everything 3D printing related, it's complicated :) The temperature you WANT, and the temperature you MUST use may not be the same. In my observations, the minimum temperature you can use for a given bed is dictated by the bed not cooling the plastic exiting the nozzle so fast that it stiffens before become squished and stuck to the bed. This is one reason the temperatures for aluminum beds may have to be higher than you expect. Glass being an insulator is much less likely to cool the plastic too fast to adhere. Bottom line, do what works for the bed and filament you're working with.

    "In theory, practice and theory give the same results. In practice, they rarely do."
     
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  3. Spoon Unit

    Spoon Unit Well-Known Member

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    I hadn't even considered this aspect *blush*.
     
  4. R Design

    R Design Well-Known Member

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    The variables I have in mind include:

    - more heat gives the plastic time to better flow over the glass;
    - more heat keeps the 2nd and higher layers warmer in balance meaning less shrinkage post extrusion (after it's come out of the nozzle);

    and then on the other side:

    - I think of ice cream on a plate at a picnic!

    Given all of that it makes perfect sense to have a high temperature for the first couple of layers and then lower it to a more moderate one.

    However I've never found the need to do that.

    The low hanging fruit, I reckon, is not to work on the bed but the build volume. To install side panels, block holes, make a front panel and consider a top. At least to block draughts - at best to actually trap heat in. I bet that having an ambient temperature of 30 with no draughts is a great help.

    The best argument I can think of for a aluminium is an easy way to get a better temperature distribution over the bed (remember the photos in the forum that showed it's poor near the edges and horrible in the corners?).
     
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  5. Spoon Unit

    Spoon Unit Well-Known Member

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    All good food for though @R Design. Thanks.

    I just finished running my first couple of prints (PLA) where I played with this aspect. 70 for first layer, 50 for second onwards and another with 60 for second layer+. Both turned out well (UHU on Glass), with flat bottoms. These weren't overly stressy prints. The 4th part lifted slightly, but interestingly didn't seem to have any deformation on the bottom layers.

    50 feels too close to un-sticking temp, but I'll definitely drop the temp from now on for layer 2+ for a while.
     
  6. Old_Tafr

    Old_Tafr Well-Known Member

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    Interesting as as yet no mention of print cooling fans, or the lack of.

    Doing my PID tuning a draft from the window completely screwed the first attempt. Closing the window it worked perfectly the next time.

    I maybe benefit from a small room with door and windows now closed all the time...... except for the effect of fumes, and the steadily rising temperature of the room.
     
  7. mike01hu

    mike01hu Well-Known Member

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    All good thoughts! I use the aluminium plate and find that PLA sticks well with L1 at 70C and nozzle 210, then reduce over the next few layers to 50C similar to what Alex has done and holding the extruder at 200C. The problem I found was that if I reduced the bed too much there was a danger of unsticking smaller parts and introducing some warp on larger ones; for other filaments the rules change! As with everything 3D-printing there are caveats and none more so than filament variety, colour and filler that, coupled to bed type, bed temperature, adhesive, nozzle size, nozzle thermal performance, get together to spoil your day! :(:eek::confused:o_O
     
  8. Dr Jeep

    Dr Jeep Well-Known Member

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    You forgot Humidity, Barometric pressure, Moon Waxing/Waining, Urgency of Print, Intoxication of Operator, Star Sign and most importantly litres of goat blood split during last sacrifice. :D
     
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  9. mike01hu

    mike01hu Well-Known Member

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    . . . oh, and those too! :p:D:p:D
     

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