Are there any tricks to getting the bed of the A20M to roll absolutely flat along the Y axis, rather than dipping down while it is near the middle?
The "front" and "back" extremes of the Y axis appear to keep the bed at the same height when the bed is totally cold and perfectly flat. Also, the Y axis rail appears perfectly straight (on the top at least) and level according to a good-quality level and a straightedge.
Yet as I roll the bed towards the middle of the Y axis, the spacing between the hotend and the bed varies tremendously, with a large dip as the bed gets towards the middle (e.g. when the hotend is above the center of the bed). Again, at either extreme of the Y axis, the spacing between the bed and the hotend appears consistent -- and, of course, I can adjust the thumbwheels to change it, as needed (no problem there).
I can't explain why the bed "dips" as it moves from the edge to the center of the Y axis, and then returns back to approximately the original height at the other end of the Y axis -- when the bed is cold, and has been verified to be perfectly flat when cold. (Again, heating has absolutely nothing to do with it, as I have the printer turned off during all of these tests and measurements.)
I am suspecting some sort of problem either within the Y-axis rail itself (i.e. within the gap that the rollers ride on) or in the roller/roller-assembly itself.
Anyone else find tightening or loosening things up making a difference?
Even with a BL Touch auto leveling sensor I can not use my printer, because this difference in bed height along the Y axis (dip in the middle) is so dramatic.
Thanks!
Dip in Bed Height in the Middle of the Y Axis
Re: Dip in Bed Height in the Middle of the Y Axis
hi, can you provide pictures or videos?
Maybe the bed itself is uneven?
Maybe the bed itself is uneven?
-Keep your mind and try to test it. 
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-Everything will be fun！-Support all Getech printer.
-You can ask me the questions and I will kindly reply.
-Respect others is the best way you can get help!
Re: Dip in Bed Height in the Middle of the Y Axis
As I mentioned in my post, the bed "has been verified to be perfectly flat when cold".
I used a quality level and straightedge to ensure that the bed, when removed and cold, is perfectly flat, and after being mounted, when cold, is also perfectly flat, with no dips in the middle.
The bed is not warped, bowed, or twisted when mounted.
When the bed is cold, it has no defects.
The error in the machine appears to be associated with the Y-axis rail and/or roller mechanism.
When traversing the bed along the Y axis, the distance between the hotend and the bed surface drops dramatically (> 2 mm) while in the middle of the Y-axis range of movement, and then returns to an approximately equal level at either extreme of the Y-axis.
The problem is not the bed being warped.
The problem may be in how it's mounted to the carriage. The problem may be in the Y-axis wheel assembly. The problem may be in the inner surface of the Y-axis aluminum bar that the wheel assembly rides on.
I am asking if anyone knows of any tweaks, or ways to check, the alignment of the Y-axis, its carriage, (etc.) that may have an impact on the distance between the bed and the hotend throughout its movement in the Y-axis.
Thanks.
I used a quality level and straightedge to ensure that the bed, when removed and cold, is perfectly flat, and after being mounted, when cold, is also perfectly flat, with no dips in the middle.
The bed is not warped, bowed, or twisted when mounted.
When the bed is cold, it has no defects.
The error in the machine appears to be associated with the Y-axis rail and/or roller mechanism.
When traversing the bed along the Y axis, the distance between the hotend and the bed surface drops dramatically (> 2 mm) while in the middle of the Y-axis range of movement, and then returns to an approximately equal level at either extreme of the Y-axis.
The problem is not the bed being warped.
The problem may be in how it's mounted to the carriage. The problem may be in the Y-axis wheel assembly. The problem may be in the inner surface of the Y-axis aluminum bar that the wheel assembly rides on.
I am asking if anyone knows of any tweaks, or ways to check, the alignment of the Y-axis, its carriage, (etc.) that may have an impact on the distance between the bed and the hotend throughout its movement in the Y-axis.
Thanks.