Getting a good first layer is crucial and it's the most common question I see from beginners. The problem is that everybody is showing you how to do it with a piece of paper! I mean, it's good as a rough guide, but there's a better way that's much more reliable and just as simple.
Printers with manual bed levelling
We'll start with a printer that has manual bed levelling. I'll be using a CR-10.
Most of them have a levelling knob in each corner that let's you adjust the height of the bed. A lot of them are too small though, so I recommend printing larger ones like these. You'll find plenty of them on Thingiverse.
Before doing anything, ensure that your bed is actually clean. Get a bottle of isopropyl alcohol and quickly wipe the bed. I do this before every print job.
You should always level the bed at working temperature, because it expands with heat. For PLA, I recommend setting it between 50 and 60 degrees.
Some printers have an assisted levelling function. The printer will move the head around by itself and all you have to do is set the height at each corner. If you don't have that option, then you'll have to disable stepper motors and move the head manually.
Move the head to each corner and set the initial height using a piece of paper. Keep raising the bed until the nozzle drags against the paper. This is just a starting point and if your nozzle is already close enough, you can skip this step. Do this once for each corner.
Next, we'll be using calibration squares to fine tune our first layer. You'll find links for common bed sizes below, but you can always scale them to match your specific printer.
- Bed levelling squares (300x300mm)
- Bed levelling squares (200x200mm)
- Bed levelling squares (150x150mm)
- Bed levelling squares (100x100mm)
- Bed levelling square (center)
Print the first batch and then examine each square individually. Your goal is to get as smooth surface as you can and all the squares should look the same.
Nozzle too high
If your nozzle is too high, the filament will either not stick at all or you will see gaps between individual lines. If that's the case, raise the bed slightly. You only have to adjust the closet corner for each square.
Nozzle too low
If your nozzle is too low, it will scratch against the first layer. The surface will be rough to the touch or it might even buckle if the nozzle is really low. In any case, you have to lower the bed slightly.
After you've examined every square and adjusted the corners, print another batch. Check the squares again and keep going until you get a smooth and consistent surface on all of them.
Perfect first layer
When all of the corners are set, the middle square should automatically be good as well. If it's not, then your bed is probably warped. Try turning the glass around and see if that helps. You could also print a wedge jack to raise the bed in the middle. Better still, I recommend using a mirror instead.
Mirrors have a special coating that works much better with PLA than ordinary glass. My favourite ones are from Ikea that are called "Lots" and you can buy a pack of 4 for next to nothing.
Anyway, your printer should now be ready. If you notice any warping, simply raise the bed slightly in that corner. Quarter of a turn or even less should be enough.
Printers with automatic bed levelling
If your printer has automatic bed levelling, the process is even simpler. As the printer automatically compensates for the bed surface, we can print only a single square in the middle (although that's technically not always true as I'll explain later).
Look for a setting called Live Z, Z offset, baby steps or something similar depending on your printer. Whatever the name, the setting should allow you to fine tune the distance between the bed and the nozzle.
As we did before, keep changing the Z value until you get a smooth surface. Because the square is larger now, you don't have to print the entire square with just one setting. I usually change it in the middle, so I can test two Z heights in one go.
As you can fine-tune the offset now, it might be helpful to write down the values that you've used. You can then compare them and see which ones were the best.
Because automatic bed levelling isn't perfect, most will let you adjust the Z offset for individual sides as well, so it's not just one setting for the entire bed. If you want to test for this, print the full set of squares in each corner and compare them with the center one.
And that's about it. You should now get a perfect first layer no matter which printer you're using. Let me know if you're having any issues or if your printer has different settings and I'm sure we'll figure it out.