A lot of folks are trying to improve the flatness of their build plate. Here’s one that I happened upon by accident. But it only helps when you want to print over the full area of the bed.
I had to replace my magnetic sheet because there were some areas with weak magnetic field strength (see Build Plate Edge Lift - Check Mag Sheet Field Strength - #29 by korzenec for details).
When I removed the old magnetic sheet, I noticed the edge of the plastic frame was sitting higher than the aluminum heat plate in some areas (in my case the front of the printer). Since the magnetic sheet is cut larger than the aluminum plate its edges sit on the plastic frame. The end result is the magnetic sheet sits higher than the aluminum heat plate and it will also lift the edges of any build plate when placed on top. In my case it added 0.2mm of “warp” to the outside front of the build plate. To make matters worse, this added warp is outside the Bed Leveling test area (so not compensated for) so first layer print quality suffers on those outside edges.
When I replaced the magnetic sheet I cut it down so it only rests on the aluminum plate. FYI - Cutting the sheet is easy with a straight edge and a utility knife.
Really good you spotted and fixed that. Have you visualized the field yet?
Yes, clean mag lines on the sheet.
Might be interesting to put a strong magnet to a clean area of the old sheet (if not too damaged from removal) and see if that produces the same kind of issue you had in the corners?
Ran the experiment
see Build Plate Edge Lift - Check Mag Sheet Field Strength - #29 by korzenec for details.
Just by going by how bulk recording tape erasers (demagnetizers) work is they use line AC to demagnetize. Moving a magnet back and forth across the magnetic plate kind of simulates the same thing.
There was a joke a long time ago about somebody sticking a floppy disk to a refrigerator with a magnet. The joke was they destroyed the data by doing that - except people tried it. They could generally still read the data after sticking a floppy disk to a fridge with a magnet. I just looked for a reference for that but the web has decided any magnet will erase a floppy.
The reason why it actually did not erase the floppys is similar to what you saw after just setting the magnets on the sheet. Not a big effect and that’s the first time I’ve actually seen why. A static magnetic field may interact but it’s not the same as an A/C magnetic field or rubbing the magnets back and forth.
Rub the magnet across a floppy and then you can erase it. It’s the changing magnetic field that makes the difference.
This is really cool stuff - nirvana for nerds.
