Bowing/Sagging X Axis and Bowing Aluminum Heating Plate

[ChrisERAU]

I've noticed ever since I got my M2 a couple months ago that no matter how hard I try leveling the build plate, the left and right edges of the bed are always "lower" than the center. I printed a 1 layer thick, 2 perimeter wide grid across the entire bed, and I saw that the entire center section front to back prints fine - no gap between the perimeters. But the left and right sides (again, front to back) are barely laid down, with a noticeable gap between the perimeters.

I searched the forums for this issue, and it's identical to this thread: viewtopic.php?f=7&t=2486 I just started a new thread because I didn't want to necropost...

So obviously, either the glass bed is warped upwards or the x-axis is bowed downwards or both. I figured the glass was just warped, so I flipped it upside down and clipped it, then checked the gap. The left and right sides were still lower than the center. I checked the flatness of the glass with a stiff metal straightedge and (carefully) laid it edge-wise across the bed at multiple locations and angles. I put a light behind it to more easily spot any gap between the glass and straightedge. I found that if anything, the center of the glass was actually bowing down, not up.

Next, I placed the straightedge across the printer's x axis rail. Sure enough, there was contact at either end, but there was about a .1 mm or so gap in the middle. If I knew nothing about the precision necessary in this hobby, I'd have thought it was nothing to worry about...

I've thought about putting shims underneath the x-axis rail and/or loosening the x-axis belt tension (which I haven't touched since I got it - the x and y belts have roughly the same tension).

Also, I've noticed that the aluminum heating plate underneath the glass bed is very noticeably bowed downwards by 1 to 1.5 mm. The axis of bowing is perpendicular to the x-axis bowing - that is to say, it's as if the y-axis of the aluminum plate itself was bowing downwards. However, the y-axis of the printer is perfectly fine. Anyway, the glass only fully contacts the heating plate at the front and back edges. I can physically press the aluminum and glass plates together back and forth along the center where the M2 logo is. With the bed clipped at the front and back edges, I can slip 3 index cards between the glass and aluminum at the left and right edges . I had to chuckle a little bit when I read in the thread above that some of you guys meticulously clean the heating plate before putting the glass back on! Still, the glass does get hot enough to keep PLA bonded at what S3D calls 70C. Is this a common issue? Is it possible to get a replacement?

[3dPrintingMD]

Hang on the boss....let me ask a few questions and you let me know what you think.

What is the heated build plate sitting on right now ?
(Going to assume the stock rubber corners. Each of them are a different thickness, go ahead, take them off, and measure them.
You might end up finding that each one is slightly different, which as you might have guessed by now, will make it impossible to level.]

The bed levels the spider, but doesn't consider anything above the spider, meaning, how to adjust for the differences in height of those corners.

Report back and let me know what you find.

[ChrisERAU]

Hang on the boss....let me ask a few questions and you let me know what you think.

What is the heated build plate sitting on right now ?
(Going to assume the stock rubber corners. Each of them are a different thickness, go ahead, take them off, and measure them.
You might end up finding that each one is slightly different, which as you might have guessed by now, will make it impossible to level.]

The bed levels the spider, but doesn't consider anything above the spider, meaning, how to adjust for the differences in height of those corners.

Report back and let me know what you find.

Thanks for the reply. Yup, I have the stock rubber pads. Not surprisingly, they aren't exactly the same thickness:

Near RH pad: 2.94 mm
Near LH pad: 3.14 mm
Far RH pad: 3.07 mm
Far LH pad: 2.97 mm

I also checked the flatness of the spider arms by putting the straightedge across it diagonally both ways. There's no noticeable bowing up or down to speak of.

Anyway, I'm pretty sure even with perfect 3.00 mm pads, the left and right sides of the build plate will be lower than the center. What else should I check?

[jimc]

The heated bed plate is never 100% flat. Its not a milled piece of mic6. Its just an 1/8" piece of aluminum that will warp a little as it heats up too. It doesn't need to be flat and have 100% contact with the glass. It wont make a bit of difference in the flatness if the glass. Its not uncommon though for the x axis to be bowed down a touch.

[3dPrintingMD]

Don't check all that much more. Print out some corners in PETG, or ABS, print a bunch of them and find 4 that are the same.

Many of us are running MIC6 aluminum build plates, they are flat as can be.

[ChrisERAU]

Unfortunately, I only have PLA at the moment. I went ahead and put paper shims underneath the x axis rail at the 5 middle-most spots between screws. I checked the rail with the straightedge again, and there's no bowing to speak of. I printed the 1-layer grid to check, and the left and right sides are finally at the same "level" as the center.