PETG bed temp for first layer different from other layers?
I can't understand why PETG should be printed with a different bed temperature during the first layer (typically 85C) compared to when printing the subsequent layers (typically 90C). I can only imagine that this may cause some thermal expansion/contraction in the bed itself, and the first layer of the PETG, and due to different thermal expansion coefficients of the two materials, potentially causing the first layer to unstick from the bed. We all know that if we let the bed cool after the print is done, the print peels off the bed quite nicely, compared to leaving the bed hot, due to this effect, I assume. So why not use a constant bed temperature throughout the print?
I've heard it mentioned that the first layer bed temp is lowered "to improve adhesion." Fine. So why not keep the bed at that lowered temperature throughout? I don't see how it ever makes sense to vary bed temperature during the print. Thoughts?
RE: PETG bed temp for first layer different from other layers?
To help with warping. The hotter your can keep the part without it getting soft the more you'll help with warping. That's why printing in an enclosure is beneficial with most materials.
RE: PETG bed temp for first layer different from other layers?
Hotter temperatures give additional strength as well.
RE: PETG bed temp for first layer different from other layers?
Many filament manufacturers and 3d printer makers often recommend slightly different temperatures, both nozzle and build plate, for various filaments. This almost always comes from testing, either in the lab and/or from feedback from users.
If you think about it, particularly for the build plate, when the gcode calls for a different temp for subsequent layers, it typically will not wait for the plate to come up/down to temperature, but go right ahead and let the temperature gradually come up/down to what is called for.
There's a lot of very geeky literature out there analyzing dimensional stability of various substances vs. temperature. Seeking this shall be left as an exercise for the student. 😉
Personally, I've found that the only material(s) I've used in 3d printing that have a significant expansion/shrinkage are ABS/ASA with the former being more significant.
The issues I've witnessed are in the cooling, from ca. 100C down to room temperature, not +/- 5 degrees C.
The worst I've seen is a chassis part which I glued thoroughly to the build plate with a liberal dose of Layerneer. It actually cracked when cooling rather than pulling off of the build plate!
RE: PETG bed temp for first layer different from other layers?
Thanks for the insights folks!
RE: PETG bed temp for first layer different from other layers?
I noticed that too in PrusaSlicer and the only reason i could think of was that the Fan is more likely to be on after the first layer.