Glass Beds and Even Heating

[sonnichs]

OK--back at it--I ran a partial print of my 4x8" "dovetailed rail" tonight. It lifted off the be so severely that I stopped the 5 hour print. This has to be within about 0.1mm flatness because two dovetail chasers ride up and down the lands and the must be perfectly flat.I have attached a few photos-showing the print from the top (z) axis plus a side view to demonstrate the warp. Also an STL of the half image.I have played a lot with bed-leveling, speeds and temperatures now and I don't think there is a lot more to try here. A steel ruler check shows the bed to be perfectly flat, both heated and cooled. And of course I go through a lot of time leveling it.So I think this could relate to the plastic (PLA) I am using. Or perhaps a perfectly flat item that covers the whole bed is just not a good fit for this printer creality ender 5) . I went ahead and drafted the print into two 4"x4" pieces and was surprised to see that even at this size there was about 0.8mm warpage at one end-more than is acceptable for a set of dovetails running on lands. Not sure when to throw in the towel here-when I have all the material easily available I can machine this construct in metal in about 30 minutes. Fritz