Deformed Glass Build Platform

The attached photo shows a calibration print of one .1mm layer on my glass build platform. As you can see the four corners seem to be laid down well AND level with each other but the center looks as if the glass is actually higher there? Am I interpreting this picture correctly?

Regards,
Wisar

Yes I think you are. Also, the skirt around each of the corner squares is of an uneven height, suggesting that the glass is lower at the top and bottom edges than elsewhere.

First, you need to find out whether the glass is bowed, or the printing head height (if the head moves from top to bottom) or bed height (if the bed moves from top to bottom) is varying along its travel. Hold the edge of a metal ruler on the glass. Does it contact the glass all the way along the edge, or can you see light under it?

If the glass is bowed, then check whether the surface it is clamped to is also bowed. If it is just the glass, then the clips holding the glass at the top and bottom edges may be distorting it. Thicker glass will help. Stiffness increased with the cube of the thickness, so 4mm glass should be more than twice as good as 3mm glass.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Flip if you can the glass, if bowed you will have the reverse effect. If it doesn't change and prints the same (which I think will do) then the problem is like in my printer and in any other printer "makerbot style" with 8 mm rods. The rods bend downwards due to it's own weight plus the weight of the carriage and extruder(s) if direct drive, so you will always have less gap between the nozzle and the bed at the center of it. some new printers have 10 mm rods now and that solves the problem.

I flipped the glass and was able to get pretty uniform squares printed. I was hoping this would be the case as I really did not like the idea of the warping rods on a brand new printer...though obviously I can see the potential for that happening. Not related to warped glass but I wonder if mechanical end stops are really good enough for the z-axis when trying to get a good 1st layer down on a .1mm resolution print. I wonder if an upgrade is in my future?

Thanks for the pointers,
Wisar

Your first layer should be thicker than your layer height to ensure good adhesion.
It should also help with minor differences in nozzle height across the build plate.
So if you can get that first thicker layer down it should even out for the later thinner layers.

On my prusa i2 i use a 0.08mm feeler guage to set the nozzle height on my ikea mirror tiles.
And i think the first layer is 0.3mm with 110% squish, sorry cant remember the correct term or box in cura.
I can get a layer height of 0.06mm with my 0.3mm nozzle.

Gordon

Gordon, good point on the thicker first layer. I am not used to printing at .1mm, or with ABS for that matter, and have not had to use a thicker 1st layer when printing with PLA and layers of .2mm or higher. BTW, I wonder why more people don't use a feeler guage? A piece of paper seems a little primitive. I had not thought about it until your post but have ordered one.

Cheers, Wisar

Not everyone knows how to use one. Theyre called feeler guages for a reason.
You need to get the feel of the gap with just the right resistence/lack of resistence.

I also got fed up of tearing of bits of paper and the litter.

Gordon