SolidCore CoreXY Z-Axis Bed Leveling
We recently started working on the SolidCore 3d printer‘s bed leveling and mounting system. The z-axis uses a 3-point kinematic bed mounting with magnetic pivot spheres on each mount This properly constrains the bed at 3 points of contact. The original SolidCore Z-axis design was somewhat primitive because we only designed gantry style 3d printers via the Workhorse Printer. But after testing the SolidCore we noticed the design flaw. The kinematic bed mounting design is still a work in progress but is quickly evolving.
3-Point Bed Leveling
Three point bed leveling uses three independently driven lead screws to automatically level the bed and compensate for a bent or uneven plate. The Z-axis lead screws are used as the 3 points that make up a triangle, defining one plane. The advantage of a kinematic bed mount is that the defined plane of the bed, a kinematic mount, is that the aluminum plate can properly expand without bending the plate.
In a standard aluminum stock, as heat warps or cools down your aluminum build plate, it expands unevenly; this causes problems with the much needed flatness of the print bed as it will eventually bend under pressure. The bed can raise or lower without binding or twisting, keeping the bed flat.
Cast Aluminum Tool Plate
Cast Aluminum tool plate is a good solution because it has good thermal conductivity and heats up evenly without warp or twist. The bed needs to be flat and remain level In three point bed leveling, the three z-axis lead screws are used as the three points that make up a triangle and define a plane.
Three Points Define A Plane
Since 3 points define a plain 3 screws, evenly placed in a triangle will raise and lower that plain without imparting any twisting forces so the bed will stay flat.
Advantages of The Kinematic Mount
A mechanical bind can cause the bed to tilt over time. The advantage of a kinematic bed mount is the aluminum plate to expand and to be set in tram with the XY plane of the printer without causing anything to bend or flex.
Lead Screw Synchronization
3 points define a plane, therefore 3 screws need to be in synchronization. So the best way to achieve that is to drive them via a single motor and continuous belt. If designed correctly so that none of the screw or bed mounts can warp or twist, then the bed will remain level.
Bed Leveling & RepRap Firmware
Auto Leveling with the Reprap firmware uses this plane to make a heightmap, and adjust the lead screws to level the bed. With 3 independently driven lead screws that automatically level the bed before each print, and bed mapping to compensate for a bent piece of sheet metal used for the bed plate.
A kinematic coupling bed mount is stable, like a tripod. When you turn one leveling screw, the whole bed plate tilts on the other two screws. A kinematic 3 point mount allows the aluminum plate to expand and to be set in tram with the XY plane of the printer without causing anything to bend or flex.
Kelvin Kinematic Mount
A Kelvin kinematic mount has one reference point and allows the expanding heated plate to slide on the leveling screws in a controlled way. Setting it level the first time is fast and easy and then it doesn’t have to be touched again, assuming the printer’s frame is assembled correctly.
Internal Stresses in Aluminum Stock
Tooling plate is cast so it doesn’t have the internal stresses compared to other aluminum stock. The cast aluminum is milled flat afterwards. When heated it should expand evenly and with a kinematic bed mount it shouldn’t change shape or noticeably bend in the Z-axis.
Alternative Bed Mounting Options
The SolidCore CoreXY 3d printer also has other bed mounting options for the z-axis setup. These bed mounting options use a spherical magnetic ball to pivot the bed on three points.