I have my newest Tiertime Cetus, I call Big MamaCatus, doing some prints I never thought I would do on a Cetus FDM printer.*
The Cetus printers do not have any mechanical leveling of the build plate. It is bolted directly to the linear bearing with three small screws with no method of adjustment. What you have for level is fixed.
The leveling is done by using a four-layer raft and a four-layer base support on top of the raft. The first layer of the raft is 300% over-extruded and squishes out broadly. This heavy first layer and the buildup of the raft and support eventually results in a build surface that is parallel to the X and Y axis. Then the print is started on top of this level surface.
The result is the use of a lot of filament material to build a flat working surface. With a Cetus printer, one throws away a lot of raft leveling material at the end of the print.
The raft and support do not provide a nice polished build surface for the base of the print. The print bottom is always ruff like about #80 grit sandpaper. I usually “flame polish” the bottom to remove the little sharp points, but the surface is still quite a bit grainy.
I have installed a 3mm thick sheet of borate glass 200mm x 200mm using binder clips on the Cetus build plate. I simply tolerate the bit of non-level of the build surface. It is a bit larger than the 190mm x 200mm Cetus bed. I can live with a bit of overhang as well as the level issue.
I have to remove the ~5mm excess nozzle calibration height to get the nozzle low enough to print without the raft and support layers.
What I get is perfectly smooth bottom prints from Big MamaCetus! (*Read the first line above again.) I can stick some thin Build-Tac on the glass for TPU and PETG.
I am exceedingly pleased to be able to print without the raft. Some prints may still need the raft if I run into serious leveling issues on a big print. I have had no serious issues with prints up to 100mm diameter so far. First layers may be a bit thin on the high side but as long as the low side will stay attached to the build surface, the second layer evens out the height. I can not see this slight deviation in any of my finished prints.
Big MamaCetus is a MK3 with a heated build surface and the auto level probe. Early electrical problems have been resolved. (See previous posts.) I still consider the flexible power ribbon connected to the heated bed a weakness in design of the MK3. Careful protection of the cable must be maintained. I know to be careful.
The picture shows BMC printing a PETG cap and the glass build-plate with build-tac surface. Nozzle temp is 240C and the bed is 85C. 55mm/s speed. The print is excellent.