If you're having trouble with getting your prints to stick to the bed, there are a couple of things you can try, depending on the shape of your print, and the material type.
For all materials, I would suggest no faster than a 20mm/s bottom speed layer. With some shapes, as explained in detail here, you may want to consider 10mm/s bottom layer speed, or including brim. You can set the bottom layer speed separately in Cura from the rest of your print speed.
PLA should have no problem sticking to the bed as long as:
1. It is heated (60 C)
2. The nozzle is the right distance from the bed
3. Your glass is clean
4. The printhead isn't moving too quickly
If you're printing something with a solid base, you generally don't need any form of glue to help it stick. If the print has a very large surface area, you may want to turn on the Brim option in Cura under Platform Adhesion to help make sure you don't get warping in the corners. 90 degree angles are particuarly prone to this over rounded corners.
If your bed is leveled to the right height, the first layer lines should touch and appear flat, rather than rounded. The picture below shows what the first layer should look like; this outline has had 2 passes by the printhead.
If you're doing a print that has a lot of small, disconnected parts on the first layer, you may want to use glue. You can use the glue stick that came with you machine. Put several passes of it over the print bed, and then use a wet paper towel to smear it around the plate until you have only a thin, almost invisible film remaining, with no clumps. Any excess water will evaporate during the heating process. For more information about using glue with your prints, see here.
ABS is notorious for the high degree to which it shrinks as it cools. This can cause warping, and, if severe enough, cause the print to come off the bed part way through.
Like PLA, you want to make sure the bed is leveled the correct distance from the nozzle; the filament should appear flattened on the bed plate, with the lines touching one another.
Unlike PLA, the temperature of the bed alone, is frequently not enough to keep ABS stuck to the bed. Here are a few things you can do to improve adhesion with ABS:
- Raise the default bed temperature. The default bed temperature for ABS is 90 C. You may have better adhesion at 100 C, or 110 C, though it will take longer to heat up. You can either adjust this in the Tune menu as you're starting your print, or go into Materials --> Settings --> Customize --> ABS --> Build Plate Temperature, and adjust the temperature and confirm that you want to use that as your setting for ABS.
- Turn on the brim setting under platform adhesion in Cura. For ABS prints, absolutely turn on brim. If you use brim, any warping that occurs should only occur on the brim, rather than on your actual print, and the increased surface area should help it stay on the bed.
- Use hairspray or a glue stick on the glass plate to help with adhesion. If you use hairspray, take the plate out of the printer before spraying it, to avoid getting hairspray on your belts or other sensitive parts. If using a glue stick, put several passes of it over the print bed, and then use a wet paper towel to smear it around the plate until you have only a thin, almost invisible film remaining, with no clumps. Any excess water will evaporate during the heating process.
- You may also want to consider some sort of heat shield on the front of the printer to help keep the ambient temperature inside the machine higher. I would not recommend totally enclosing the machine, but a piece of plastic or poster board lightly attached to the front of the machine can help.
- You can also turn off the side fans to help the print cool more slowly.