Glass Flatness

[jdacal]

I've been curious about how one glass plate various from others, since I occasionally like to switch to another plate instead of cleaning the one I just used.

I setup the dial micrometer and put a dot exactly in the center of the metal base to use as a reference.

I then took a measurement at the center, moved to the left edge of the glass then the right edge of the glass. Here's the measurements I got.

Glass Left Center Right
#1 .270 .273 .270
#2 .269 .273 .271
#3 .268 .272 .269

Variance .002 .001 .001

My concern was that there would be enough variance between different glass plates to possible effect the quality of the print. I think .002 variance is probably safe enough? Would .002 cause any noticeable issues in a print?

These number would only be accurate if you take individual columns into effect. Since I can't presume I have the bed perfectly flat comparing left and right readings wouldn't be accurate. But comparing all left reading should be pretty close, as well as all right and all center.

I have the micrometer mounted next to the drive. I set it to 0.00 and then raised the bed until the tip touched the glass surface and those are the readings shown. In other words the bed touches the tip of the micrometer which at that point would be 0.00 then I keep raising it until it touches the tip of the nozzle then write down that reading, which are the one's shown on the chart. Then I just look at the variance between the readings.

EDIT: One other thing I do is I use an etcher to etch "L" and "R" on the front corners of each glass. That way I'm sure to always put the glass in the same position so that the high side is always on top.

[ednisley]

Once you start getting fussy about leveling, there's just no end to it! [grin]

With a layer thickness around 0.20 mm = 8 mil, the ±2 mils you're seeing should be fine: adjust the platform height so the middle of the plate is at 0.16 mm = 6 mil and the outer edge will be Close Enough on the other end of that tolerance.

That assumes you've aligned the platform to within that tolerance across the entire surface, of course. The M2's rigid frame will hold that alignment (as long as you don't abuse it), but you can put steel balls under the heater plate to eliminate the squishiness of those rubber pads:

http://softsolder.com/2013/07/16/makerg ... ort-balls/

I routinely measure the skirt around each object to check the platform alignment; its thickness should be very close to 0.20 mm (or whatever your layer height may be) and that value shouldn't vary by more than ±0.05 mm from one side to the other. After a bit of experience (pronounced "screwing up"), you can tweak the platform alignment based on the skirt thickness, without going through a full-scale alignment drill every time:

http://softsolder.com/2014/07/16/m2-platform-leveling/

At least in my shop, the M2 alignment remains stable for weeks or until I haul it off for a show-n-tell session: it's that good.

[jimc]

i have to agree with ed. my original glass plate was high in the middle and when i first got my m2 it was driving me nuts then suddenly it didnt bother me anymore because it still actually printed fine. i make my first layer in s3d at 150% then adjust the z height to give me 100% plastic contact at the lowest point. the plastic gets a little squished where any high spots are but its no big deal and goes away after the base layers are down. i really dont think about it anymore.

[jdacal]

Yes. I had already gotten to that point with one glass. But my concern was switching from one glass to another. This kind of put my mind at ease along with both your comments.

[jimc]

as long as you have good contact of the plastic to the bed between both the plates then dont sweat it. if one is thinner than the other and you notice your first layer extrusion lines are more round than flat and not sticking well then jon the fly just crank your bed up a click.

once again....an idle printer is an unhappy printer

[Capt. John]

jdacal,

Did you perform the measurement with the dial indicator on the M2?
You cannot assume the top 1/4" steel flat stock gantry is perfectly flat,
or the top grooved rail is a tad off.

I have 3 build plates that all read thick in the middle when I level
my M2 with the dial indicator installed where the extruder drive normally is.

I attribute this to a very slight bow in the top of the frame, not the glass
build plates all having high spots. This don't seem to matter, cuz my M2
keeps kicking out parts.

[jdacal]

Good point! That's why you're the Captain!