High spot on the glass...

[jereywolf]

I was just leveling my bed today, after doing it six months ago, and it seems that there is a high spot in the center of the glass. I mounted my indicator to the drive gear housing and got the midpoint of the corners in X within .002" of each other and the same for Y. The readings for X and Y were about .005" off from each other. But with the indicator in the center, traveling from the top point in Y to the bottom point I got about a .006" increase in the center. So when I set my Z stop, the nozzle is .006" closer to the glass in the center than it is at the edges. The glass is clean and there is nothing underneath ii to lift it up. I also flipped the glass over and rotated it, with the same results.

So the short version... high spot in the center of the glass... problems with first layer when the nozzle gets too far from center.

Anyone else had experience with this?

[jsc]

If your glass is bare and clean, you can actually SEE the doming if you bring your nozzle nearly to the glass. Put your eye down parallel to the glass and move the X and Y axes back and forth, looking at the reflection. You will see the gap between the nozzle and the reflection shrink and grow as you do so.

I think it's fairly common, and shouldn't be an issue. Level your bed to work perfectly at the center, where most of your small prints will be, or optimize for an average of the center and the edges to use more of the bed.

Are you using clips to hold down the glass on the bed? What happens if you leave them off, does the doming decrease? I have been running without clips for some time, have not had any issues, and my hypothesis is that you should see less doming without them.

[Dale Reed]

jerrywolf, If you flip the glass over, does it do the opposite (more gap in center) or the same (high in the center)? If it's the same (high center), it might be the clips, or something else higher in the center supporting the glass. If it's the opposite (low center), it might be the glass... and flipping it might (perhaps?) let it "flow" down on the edges. (Glass, after all, is ever so slightly fluid. I know this well, owning an 87-year old house!)

Just a couple hypotheses and a quick way to check....
Dale

[jereywolf]

Jsc, you're absolutely right, you can see the doming! I have never seen it like that before. And Dale, yes when I flipped the glass over it was exactly the opposite! I guess for now I will avoid small objects far from the center...maybe I will look into glass with a tighter tolerance for the thickness, and flatness. Thank you guys for replying! You two are always so helpful to everyone on here.

[jimc]

my first glass was like that. its not uncommon really. try flipping it over so the dome is down then put a clip on each corner. the dome will hit in the center and the clips MAY be enough to pull the corners down so the plate is flat. a perfectly flat plate is actually hard to find. a couple thousandths off shouldn't make much of a difference. you can compensate in your slicer. as long as you are somewhat level. if your using s3d you can set your first layer height to print at say 150%. over 100% s3d will print a thicker layer and push out more material so that it will straighten out any minor deviations. if you get another piece of glass, stick with the original borosilicate from makergear. its thicker and fairly durable.

[jsc]

Actually, Jim, that's not quite correct. From what I recall from the S3D forum, the first layer adjustment under 100% will keep your first layer height but push out more filament, and over 100% will extrude the correct filament amount for your layer height but raise the layer height. It is very confusing.

[jimc]

huh really, i swear i read somewhere that in one of the recent releases that they changed something with that and over 100 would now increase the filament to extrude the correct amount for the higher layer. i could be wrong though. i cant keep track of what they change and what they dont.


jin, goto the s3d website and look at the change log for 2.1.0. they mention something there about it. it seems like that is what they are saying but it is a little vague.

[jsc]

Ok, that does seem to indicate it now works as you said. My mistake.

[jdacal]

I'm seeing similar with my glass. Heat at 70C, at the center of the glass I have it gapped at .005" but near the left and right edge from there the gap is at .007" at the edges. Is that, as they say, close enough for government work? Not sure what else I could do since both edges are at .007" so no sense in tilting the bed. Would a .002" difference between center and edges be acceptable to most of you?

EDIT: Took a couple of more measurements, on the "Y" axis the difference is much bigger as shown in the picture. Again, not sure if that variance is considered acceptable? Measurements are approximate based on feeler gage just barely touching extruder tip. I ordered a spare glass with the printer and switched to the spare after the first day since I noticed the center was higher, but the spare is the same way. I'm assuming its normal but that .010" seems kind of a big difference from .005". Maybe not though, I don't have enough experience with these printers to know what is acceptable.

Thanks


.

[jimc]

Glass in general is not perfectly flat. .005" is pretty small and not uncommon. I have one piece of glass the same as you have pictured and one that is pretty close to being flat. I think its just by chance you happen to get one thats perfect. A .005" variance as a beginner can be annoying but you can work around it with s3d by printing a thicker first layer.