For when your prints warp on the build plate
Although PLA is not as prone to warping as ABS, it can still warp, typically when printing wide rectangular objects. Small objects don't experience the stresses of the cooling filament as much as large objects, and round objects don't have the corner concentrations of stress that objects with angles have. That being said, it's not impossible to print large rectangular objects. There are many factors that affect warping that can be mitigated by various means. This article attempts to describe these factors and provide solutions for them.
The speed at which the PLA cools plays a major role in warping. You generally want the PLA to remain as close to a uniform temperature as possible. This can most easily be accomplished by printing with the cover on, and with the handle cutouts covered with masking tape. The hot end generates a lot of heat, and the fan will circulate that heat within the build chamber. Blocking the holes in the cover will trap more of the heat inside, and keep the PLA at a more even temperature. As an additional measure, if you are doing your own slicing, you can pre-heat the build area by adding the following GCode to the end of the "Start GCode" in your slicer:
Note: The last "S210" sets the temperature back to the build temperature. If you're not printing at 210C, then change this to the value you are using.
Reducing the infill percentage as much as possible will help keep your prints from warping. New Matter Store designs print with 20% infill which, while it makes for a stronger part, is more prone to warping than a 15% or 10% infill. Depending on the shape and use of your part, you may be able to slice with no infill at all, which will help prevent warping.
The square infill pattern used by the New Matter Store is a good compromise between speed and strength, but tends to warp more than the honeycomb pattern, which prevents long stretches of filament from contracting the part, and warping. If you need infill, see if your slicer supports the honeycomb infill pattern.
If you have the ability to modify the design that you are printing, then there are basic things you can do that will improve the "printability" of the part.
Sharp, square corners are much more prone to warping than rounded ones. If you can round the points off to a nice curve, then the print will adhere better. Warping pretty much always starts at one or more of the corners, and works its way in. Eliminating the sharpness improves the strength of the corner.
Warping is more likely to occur if the bottom layer is completely solid, as this causes the most stress within the material. If you don't need the bottom to be completely flat, you can improve the printability, and save yourself some filament, by poking holes in it. Some people like to use pyramid or cone shapes to create indentations near the corners that relieve the stress that is experienced there.
A Tale Of Two Parts
I printed the gray block first, and then decided to use natural filament for the second one, in case there was a problem. Being able to look inside a prototype is useful in determining how to optimize it. The second attempt turned out a perfect part.