Does shimming my build surface compete with spending a bunch more money and time on an auto-leveling system?

Question

I've had my Ender 3 for almost three weeks, gone through about a kilogram of PLA filament (printing a mix of upgrade parts for the Ender 3 and stuff I actually want to use) and made one PETG object, generally with good results.

I've noticed however, as seems relatively common (per YouTubers, anyway), that my bed isn't flat -- that is, the build surface isn't a good approximation of a geometric plane. If I adjust the bed to have correct clearance (good adhesion and correct single-line width) at the corners, I'll get adhesion failure in the center, and if I adjust to give a correct center, the extruded filament will be squished into the build surface texture; the nozzle may even lightly scatch the surface at the corners. That indicates the corners are high, relative to the center, by roundly 0.1 to 0.15 mm.

I'm aware of BLTouch and its clones, but in order to get full use of that system (which automatically compensates for the non-planar bed) I would need to not only install the surface sensing hardware, but flash my printer's firmware (potentially after removing the control module cover and plugging a cable and adapter into the mainboard). As a longtime builder/upgrader of my own computers, this is certainly within my capability, but I'd prefer to make my build surface flat instead of applying software corrections; I see this as upgrading from a 386 to a Core i3 because the computer is overheating -- that is, the problem will go away because of all the other stuff you have to do, but you haven't really solved the problem.

My general idea more or less mimics the self-answer on this question in terms of measuring the excursion and applying shims under the build surface (I've installed the Creality magnetic sheet surface, so shims would be applied between the magnetic base sheet and the removable build surface). I plan to use household aluminum foil, standard weight, which is generally close to 0.63 mil (= .016 mm), applied with repositionable spray adhesive and laid down in layers, using a combination of feeler gages and single-layer test prints to determine where and how much foil to apply.

I've "test flown" this option by putting a single Post-It sheet under the center of the removable build surface, and now I have a much closer match between the center and corners, and can (depending on my nozzle standoff) actually see the outline of the makeshift shim in the first layer where it prints over the edges of the Post-It.

Is there anything I'm missing that would prevent this shimming method using aluminum foil from resolving the warped bed to allow me to depend on an even thickness and correctly adhered first layer?

Answer 1

I may be biased as my question/answer is the one I believe you're asking this question in reference to, but I would say that yes, it not only competes but is a far better solution. "Auto-leveling" systems do not level your bed. They just partially compensate for poor adhesion by adjusting the bottom layer(s) of your print to conform to the bed's errors. This of course messes up the dimensional accuracy of your prints; in a worst case it can come out rather absurd. They also do not compensate for the change in volume (which would require differing extrusion amounts) due to changes in Z height to compensate for the non-level bed.

The right solution is always to get your bed level and flat. Ideally if the bed/print surface is warped, you replace it with one that's not, but shimming is a reasonable alternative. ABL systems (not talking about real 3-point leveling with 3 Z motors here, but "ABL" stuff like BLTouch) are a gimmick for making it easy for beginners to start printing without all their prints failing due to non-adhesion from poor manual leveling. They're not a solution.

Answer 2

So, the difference between the shimming vs. auto-leveling is that auto-leveling goes around in a 4x4 grid taking measurements of the bed (you do need to set the Z calibration first, as you know) vs. the shimming method where you go to 4 corners on your build plate where you stick a piece of paper or something under there and you adjust the knob at the bottom until you can feel tension on it. What I've found to be the best for me at least is to use both. This is my method for printing every time:

1. Clean the build plate. I will take my scrapper and scrape everything off, then I will run it under some hot water and wipe all of the residue off that is still remaining, then I might take some glass cleaner or something and wipe it down.

2. Set the Z calibration.

3. Do the shimming leveling (I would normally go through all of the corners again plus the center/Z calibration just to make sure that I didn't mess up any of the other corners.

4. I will run the auto-calibration (I use OctoPrint so I just run it through there)

5. Smear Elmer's glue over the print bed. I do this for a couple of reasons:

   1. I use the glass side of the bed, just because I've gotten better results this way, and
   2. it just makes your prints stick better. I also do this after the Z calibration and bed calibration because you get better results this way.

6. Start the print and watch the first couple of layers. If you notice that when you are printing and the brim looks stringy, like you could pick apart the individual lines, you should cancel the print, and go back to your slicer and bring your line width down my 0.1 mm, I typical print with the lines 0.1 mm or 0.2 mm below what the nozzle prints at, so a 0.5 mm nozzle I will print at 0.4 mm. And if your print messes up here I'd scrape everything off so the filament and the glue off (I'd keep the bed hot and the tip hot just so I don't have to wait 10 min. for it to heat up again) then apply more glue and reprint.