Managing Steel Sheets on Prusa 3D Printers

The Prusa MK3, MK3S, and MINI all use removable steel sheets as a printing surface. Removable sheets have several advantages over their older non-removable predecessors: by removing and flexing the sheet inwards or outwards, parts pop off much more easily, and when the sheet wears out, it is easily replaced. They're held down to the heat plate with rare earth magnets, so they don't move around during prints but are very easy to swap.

Sheets come in two flavors: smooth PEI sheets, and textured power-coated sheets (I personally use the smooth sheets for PLA, and the textured sheets for PETG). Since I basically manufacture WLAN Pi cases on my small farm of three Prusa MK3S printers, I have several sheets running around (three textured, one smooth).

To be clear, this is Joseph Prusa's print farm, not mine, but it was cool to visit with one of my printed WLAN Pi cases.

One natural attribute of spring sheets is that they vary slightly in thickness, so they each require a bit of tuning; the nozzle must be calibrated the correct distance from the sheet. Too far from the sheet, and the plastic won't stick on the first layer. Too close, and the part will have an "elephants foot", or worse, the nozzle will scratch and destroy the bed.

As a cumulative result, it would be very easy for me to mix up which sheet goes with which printer, all of which need unique first layer height settings for each sheet. Settings could look like this:

Printer 1

• Textured Sheet 1: -0.625 mm
• Textured Sheet 2: -0.895 mm
• Smooth Sheet 1: -1.100 mm

Printer 2

• Textured Sheet 1: -0.645 mm
• Textured Sheet 2: -0.912 mm
• Smooth Sheet 1: -1.118 mm

Printer 3

• Textured Sheet 1: -0.600 mm
• Textured Sheet 2: -0.870 mm
• Smooth Sheet 1: -1.027 mm

While you could keep track of this manually on a notepad, you'd have to manually set the numbers each time you swapped a print, and you could never know whether your settings are already correct before a print or not. That's where sheet profiles come in! Sheet profiles allow you to configure and store unique first-layer height values on each printer, for each sheet you plan to use with it.

To create a sheet profile, go to Settings > HW Setup > Steel Sheets on your printer's LCD screen, where you can create, rename, and calibrate sheet profiles. Keep in mind that you'll need to create a unique profile for each sheet that you plan to use on any given printer, so for example, if you add a new sheet to your collection of three printers, you'll need to create a unique profile for it on each printer. The values from one printer won't work with your other two.

There's an additional layer of complexity here that I haven't discussed yet, which is the first-layer heights themselves. When I print WLAN Pi cases, there are two halves: the front orange half, which prints on it's face (which is visible to the user), and the grey back half, which prints with the inward-facing part down on the bed. 

These two parts require different first layer heights. For the orange front, I want to "smash" the plastic firmly into the textured sheet, so that you can't see the individual lines. For the grey back, I do not want any elephants foot or "smashed" plastic, because the first layer isn't visible when the WLAN Pi is assembled, and any elephants foot would keep the parts from going together nicely (although a tiny bit of elephants foot does make the case snap together nicely).

So how do we handle this? For the most part, I dedicate one printer for backs, and one printer to fronts. But what about the third printer? It regularly needs to be repurposed to the other color. That's where sheet profiles come in! Now, my profiles look like this (numbers totally made up):

Printer 1

• Textured Sheet 1, Close: -0.831 mm
• Textured Sheet 1, Far: -0.625 mm
• Textured Sheet 2, Close: -0.761 mm
• Textured Sheet 2, Far: -0.598 mm
• Smooth Sheet 1: -1.100 mm

And similar for printer 2, and so on.

Since the printer's 8-bit board can only store 7 characters to identify a sheet, I need to come up with a naming convention. Here's what I came up with:

• TX 1A C: Textured sheet, sheet 1, side A, "close"
• TX 1A F: Textured sheet, sheet 1, side A, "far"
• TX 3B C: Textured sheet, sheet 3, side B, "close"
• TX 3B F: Textured sheet, sheet 3, side B, "far"
• SM 1A: Smooth sheet, sheet 1, side A

To identify sheets, I write "1A", "2B", or "3A" in the upper-left corner with a silver paint Sharpie. That area is unprintable, so it's immune to cleaning and... uh... printing. Whether the difference between Side A and Side B will really matter, I'm not sure. I'll find out when my textured sheets wear out and need to be flipped over.

What about the Prusa MINI? It's super new, and the firmware is in the "basically functional" stage, so it currently does not support multiple profiles. I am looking forward to when they add the ability to differentiate between the smooth and textured sheets for it, but for now, I'm happy with keeping those values written down on a notepad.