1. Metal Sheet
2. Flash Firmware
3. Edit Starting Gcode
1: About the Metal sheet
Since the bed on our printers only have designated areas for the PINDA to trigger the 7×7 wont work without a metal sheet. Prusa uses the fixed triggerpoints to calibrate Skew and I would strongly recommend a removable metal sheet since you never know when a new XYZ-calibration is required.
I ordered my sheet from a great AliExpress with PEI on it. 3D Energetic even notified me that the first sheet was without PEI and asked if i wanted to change my order into one that included PEI. I ordered a big sheet for my Raptor 2.0 as well and they shipped it with DHL Express super fast.
AliExpress Steel Sheet
Not decided yet how to keep my sheet on the bed for large and fast prints, but i think i will use paper clips. For now I just used a couple of magnets under the bed, but its not an ideal solution.
2: Flash Firmware
Slic3r version 1.4 and newer has a built in tool to flash the firmware, but before you can use this you need to pick the right HEX-file. Use the Prusa guide to select the correcet HEX-file for your machine, I added 7×7 in front of the original HEX-names to make it easier.
PS! The file you download is a zip-file, you need to uncompress it before you can flash the hex-file that is inside the zip.
3: Edit Starting Gcode
With the new firmware you can change from 3×3 to 7×7 grid by editing your Starting Gcode. In Slic3r select “Printer Settings” and “Custom G-code”
In the “Start G-code” section scroll down to “G80” and simply add “N7” behind it to enable 7×7 grid. Your new value on that line should be:
G80 N7 ; mesh bed leveling
Simply remove the N7 to go back to 3×3
All i did was copy into the original fw 3.1.0 from the great work done here:
The buildfiles and Hex-files are based on the Prusa 3.1.0 original FW buildfiles with added 7×7 based on the work done for MK3:
If you need a different version, there are a few more available here, if you cant find what you need download the source and compile it.