I just finished my build of a Blv Cube and want to get the height sensor working as well as possible. This is my first try using a height sensor and I'm curious what others do to get reliable results.
My bed is a not-flat aluminum 3mm (CR10) bed and on it there's a silicon baking sheet and then a borosilicate glass bed (Creality). The glass bed has a taped PEI sheet on one side and I'd like to put a Garolite sheet on the other side but haven't yet (I have the G10 sheet and tape).
The printer has 3 Z-axis motors/leadscrews so I could level via the motors.
The glass bed has a black dotted surface on one side (the side with the PEI sheet).
Things I've found...
After using the PEI for a while I've depressed parts of it - you can see the dips visually in a reflect-light - and those seem to affect the infrared sensor. If I do a G29 mesh scan on the PEI sheet I see all sorts of minor anomalies - I assume caused by the PEI refraction or physical imperfections or something. I tested to see if the anomalies were related to the dotted bed and didn't find a correlation.
If I flip the bed to the glass side and do a mesh scan it's almost perfectly flat.
My current work-flow is to now-and-then flip the bed over (to the glass), do a mesh scan and ensure the bed is level, then clear the height-map and flip the bed back to the PEI sheet. Once it's set to PEI I do a single G30 in the center before each print.
I'm worried that if I put the garolite sheet on the other side, over time I'll have the same effects as the PEI and I won't have a flat surface for reference.
I would rather not have to flip the bed over to do a height map.
I'd like to use the 3 z-axis leveling but that seems to require the glass surface for consistency.
I'm thinking about putting 4 "dots" on the bed corners like Lulzbot and having those produce a reference for the bed leveling. The bed is larger than I need currently.
Does this make sense? Is there a material for the "dots" that would be flat and be a reliable infrared reference point on the glass bed? Am I missing obvious anything?
One other question. I see @dc42 comments on-line about mounting the infrared sensor near the hot-end for accuracy but when I looked up the processor on the sensor it has a very limited temperature range so I don't see how this doesn't fry the board.