Where to begin? I have been 3D printing for about 6 years. I have printed over 1500 parts on FDM type printers alone and another 700 on SLA printers. I have owned and worked with about a dozen different printer models. So most of what I am sharing here is from personal experience and what I have gleaned from research online.
In summary I suggest you try the following: Make sure once again the bed is level while it is warmed up. (The paper trick works well enough for this to get it level.) Like Jeffeb3 said use 60 for the bed temp. (I might even go down to 50 or 55 but never above 60). Adjust your Z homing height to be a little higher off the bed after the paper tick. Make sure your print bed doesn’t have cold spots. Make sure there are no drafts of air blowing onto your print bed. Or you could try my solution I explain at the end.
Now for some details on WHY bed adhesion fails or succeeds.
PEI is some really good stuff. I have had pretty good luck with it. However, I had better luck with it when I was using ABS. PLA I always had more problems with the first layer. Like Jeffeb3 mentioned PEI gets more sticky as it gets warmer. Problem with PLA is it gets more loose and melty as it gets warmer. At about 70 c it is soft enough that it can change shape if pressure is applied. So even it is “Sticks” some pressure could still pull or push it off the bed. So I don’t let the bed get hotter than 60 with PLA. As a contrast ABS doesn’t get soft until about 170 c. From my experience ABS stuck better on PEI for the first layer. ABS suffers from shrinkage so it could pry back up later in the print job. So bad news either way. I have tried dozens of other solutions like hairspray, glue sticks, tapes, slurries etc… I could speak to the pros and cons of each but I won’t waste our time. PEI is the second best solution I have found. The best is explained near the end.
Level bed is huge problem for many people. Use the paper trick to make sure the bed is all the distance from the nozzle. But then you need to set the nozzle distance from the bed as a different step. Here is my reasoning. There is no one size fits all for correct nozzle height when you switch filament types. PLA and ABS need to have the starting Z height just a little different to get best results. I don’t have a science reason for this but I know from experience that I needed to reset the z homing height every time I switch filament type for best results. So the paper trick is great at getting a level bed but not for setting the nozzle height.
Aluminum is more likely than glass to warp as it gets hot so the center of your bed may be higher up when it is hot. 200 mm x 200 mm at 60 c this shouldn’t be a big problem. But still I would do the paper trick while it is warm. When you are doing the paper bed leveling make sure you level the corners in the correct order.
Correct Order? If your bed is leveled with 4 screws (one in each corner) then do this order. Front left then back right. repeat this several times until they are both level. Then start working on Front Right and Back left. When they are level do the Front left and Back right again. keep repeating this until all 4 are at the same level. it can take time.
If your bed is held in place with only three screws this is a lot easier. Start with the edge where two screws are closest. For example if you have two screws in the front two corners of the bed and only one screw in the center back then start with the front. level the front left and then the front right. Stay in line with the screws don’t be checking the very front of the bed unless the screws are right there at the very front. If the screws are set back about an inch then check an inch back so you are in line with the screws. Go back and forth until they are equal. Then go to the back center near the rear screw. After that test all four corners. Last you can check the center of the bed to see if it is warped up or not. I primarily use a TAZ 5 with a huge print bed something like 270 x 270 (I don’t remember exactly). It does warp up in a little in the center when I get it up to 90 c or higher. I have a solution for that near the end of this.
Flow rate vs nozzle height. This is a big problem for many people that they just don’t realize. I hope I can explain it well enough to be helpful. If the nozzle is too high off the print bed it won’t physically smash the plastic into the print bed. So it won’t stick well. If the nozzle is too low it will smash it so flat that it oozes to the sides. It will stick a single bead to the bed pretty well but the next bead that tries to lay down next to it will either have problems sticking or it will push the first bead sideways and make it peel off. You can see this happen early with a brim sometimes. When you pull a printed part off your print bed you can also see the beads that made up the first layer. If you see the beads have small gaps between each other then the nozzle was too high. If the beads are all messy and overlapping then the nozzle was too low and too much material caused the beads to run together. But nozzle height isn’t the only factor here. Flow rate is the other side of this same coin. It is possible for your nozzle height to be perfect but your printer could push out too much or too little plastic at any given moment. This is more noticeable when you have a Filament that isn’t a consistent thickness. Some brands are better than others.
Here are some photos that show these problems. This first one shows the messy lines from too much plastic getting smashed down into too small of a space. You can also see how the bed wasn’t level because the plastic is even more smashed together on one side than the other.
This one was about perfect. Printed on PEI with some damaged spots perfect flow rate and homing height. Almost all perfect lines with a few spots that you can see the filament diameter was inconsistent so there was more or less plastic extruded. This is about as good as you can get without a raft.
Briefly I will say that air moving across your print bed can cause problems. Cold drafts especially. Do what you can to minimize these. It is possible but not likely that your print bed can have cold spots. Aluminum usually normalizes this so you probably don’t need to worry. I have had some heat beds that are hotter in the back than the front or there is a dead spot near a corner.
Moving onto my best suggestion for solving print bed adhesion. I have been doing this for over a year and 99.9 % of the time my prints stick to the bed first time and stay stuck through out the print. Larger ABS prints still tend to warp a little but most of that is reduced as well.
In short I use these printer bed adhesive pads and I also print using a raft every single time. Before you buy any of these I hope Ryan can do something so he can get a small kickback if you click the link and buy it. I don’t know how that works but I would prefer to have Ryan get a kick back for a product I recommend on amazon. Here is my review of this product on amazon.
So this stuff works great for bed adhesion. But you still have to get your Z homing height correct. Too close you can stick so well that you actually rip these pads. Too far and you still have problems. Again different material types still need a slightly different z homing height because of the flow rate vs nozzle height issues. So this is how I solved the problem. I use a raft for all of my prints now. The raft lays down a few really Thick beads that get smashed down onto the print bed so they stick well. But then it leaves a space between each of them so they don’t knock each other loose. This means my z homing height has more flexibility or tolerance. I could be a little off (too high or too close) and it will still work. My bed could be slightly out of level. My bed could be slightly warped. I haven’t had to level my print bed or adjust my z homing height in over 8 months and I switch between filament materials all the time. Now there are some settings for the raft that you may need to adjust. I am using CURA as my slicer and some settings can make it create a space between the top layer of the raft and the bottom of my printed part. But usually the default settings are good so I don’t have to mess with them much. If you have questions feel free to ask.
Here is a picture of a part that was printed on a raft. The beads are all just about perfect. I used a black marker to make them visible on the light colored plastic. The small circle of plastic is actually the bottom of the raft for another part I just printed a few minutes ago. You can see the thick smashed beads and the space between them.
There are so many things that I have tried and learned from. This is the best solution that I can recommend. I mostly use ABS, PLA, PETG and HIPS but this has also worked well with Laywood, t-glase, Nylon, N-Vent PVA and a more that I can’t think of at the moment. Nylon did damage these pads a little as can be seen in the pictures attached to my amazon review.
Thank you for your patience. I have tried to write this over about 5 hours but I keep getting distracted with other tasks that require my attention.