Lifting/warping is an inherent issue due to thermal shrinkage of ABS plastic. All FMD style 3D Printers that use ABS have this challenge. The following are some tips to prevent this occurring:

  • Level - [Plus/Plus 2] Make sure the platform is completely level to the nozzle - this can be a challenge to get it level, but it alleviates the warping. Under the platform you should find three screws (with springs on newer models), use these to level the platform to the nozzle. 
  • Hot, hot, hot - For large prints, the platform must be hot to every corner, typically pre-heating for half an hour is enough, or printing immediately after another print. Also try placing one of the gloves supplied over the platform while pre-heating to create an insulating effect.
    [Plus/ Plus 2] In the maintenance window, the software reports the platform temperature of the center of the table, not the corners! These corners need to be hot! Make sure the reported temperature is ~105°C for 5 minutes before print.
  • Wind Barrier - Make sure this is closed during printing, or at least until the raft has been laid, then it may be opened. We don't want the material being deposited onto the hot platform to be cooled from above and heated from below creating uneven thermal shrinkage.
  • Draughts/Cool air - [Plus/Plus 2] This can accelerate uneven thermal shrinkage. The most effective solution here is to enclose the printer in a suitable box. The box must not be removed once printing begins as it would be like opening the oven while cooking a souffle.
  • Nozzle Distance - It is very important to have the nozzle close to the platform (0.1 - 0.2mm), too high and you'll get the raft lifting.  Make sure the first layer of the raft is squished out flat.
  • Perfboard - We find that the supplied perf board is the best platform for ABS prints. Make sure it is affixed to the platform properly.
  • Do not - wrench, pull or grab the finished printed models of the platform - doing so will affect the level of the platform and you'll have to re-level again! Always remove the platform or unclip the perfboard.

The UP further minimizes this issue by the use of a heated platform & the perforated build boards. ABS has around a 3% shrinkage but 90% or the shrinkage happens below 60 degrees . The bed on the UP 2 keeps the model warm until it is finished & the model can shrink uniformly. The shrinkage is taken into account by the software so the model is printed very slightly oversize.

The Geometry, density & size of each model can also dramatically alter the effects of shrinkage.

The other cause of Lifting that is not related to shrinkage can be the nozzle height is set too low, ie The 1st layer is not getting pushed into the holes of the perfboard so as to give a good hold. You can check this by looking at the bottom of the raft after it has been removed from the board. If you can see/feel very small or no dimples at all (that are not broken off) then it may be too low. You should have either 0.5 to 1mm dimples or marks to indicate they have broken off in the board. You do not need to clean these broken off bits from the board as the next print can bind to them.

If you are getting the dimples but not out on the corners of the model it is likely to be shrinkage.

Thanks to Andre' from C-iT for the detailed tips!