Well, you leveled your CNC bed with the router bit, but it’s important to remember that the flatness of the bed is now relative to the CNC router, not the 3D printer nozzle.
3D printers are generally much more sensitive to variations in bed height compared to CNC routers, and this can lead to the infamous “first layer” issue, where adhesion problems and inaccuracies in the final print can occur. For example, my Ender 5 Plus has a printing area of around 350mm square, and the bed’s level/pitch and surface height can vary significantly from one end to the other. I’m using a 0.4mm nozzle and printing layer lines at 0.2mm in height, so even a variance of 0.05mm can cause issues like poor adhesion, warping, or uneven prints. It’s worth noting that even materials like glass can have variations in surface height in the range of tens of microns.
To combat these issues, I manually adjust each of the 4 corners of the bed with the nozzle parked at each corner, and before every print, I run a 4x3 bed leveling grid pattern using a BLTouch probe to measure the elevation at each point. The machine will automatically use this height map during printing to compensate. There are other types of probes like inductive sensors that offer even higher precision but come with their own trade-offs.
In your case, given the giant scale you’re working with, and if you are using something like a Super Volcano, it has the ability to extrude a significant amount of filament quickly, and might compensate for an uneven surface to some extent. Your first layer might not look perfect, but it should adhere well and minimize warping. I personally run my bed at 75°C, which is quite hot (borderline melting) and helps with adhesion. I also use a PEX surface plate from WhamBam systems, and apply a thin layer of Elmer’s glue stick (the purple one helps me see where I apply it). This combination has proven to be quite reliable. What’s great is that the glue stick can be easily cleaned up with water, whereas hairspray can be messy and may require IPA or Acetone for cleanup.
I watched your videos and didn’t notice any obvious layering issues, but if you want to experiment further, you could try increasing the nozzle size to 0.6mm or even 1.0mm, raise the temperatures and printing speed, and possibly increase the layer height to 0.4mm - 0.6mm to see if this helps with better adhesion and smoother printing.
I look forward to seeing more prints!
