Belt Driven Z-Axis - SolidCore 3D Printer

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Belt Driven Z-Axis - SolidCore 3D Printer. This is the z-axis design for the SolidCore CoreXY printer. see https://www.youtube.com/watch?v=T9B5B61Mo4k We've been 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 pivot balls that attach the Z-axis bed mounts can be held into position by the weight of the bed or magnetic force. The dowel pins ensure that there is zero lateral play on the bed. You can only move it by lifting it. 3-Point Bed LevelingThree point bed leveling uses three independently driven lead screws to automatically level the bed and compensate for a bent or uneven plate. See Triple Independent Motors Z axis with self leveling bed or Triple Z. 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.Bed FlatnessIn 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 PlateCast 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 PlaneSince 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 MountA 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 Synchronization3 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 FirmwareAuto 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.Bed TiltA 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 MountA Kelvin kinematic mount has one reference point and allows the expanding heated print bed 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 assembly is correct.Triple Z-Axis-Belted Z-Motors The triple z-axis design used on the SolidCore Printer utilizes three independent driven stepper motors to implement auto bed leveling. Each lead screw will be constrained by a MGN12 linear rail. Originally we were working on a design that used one single z-axis motor and a belt routing the three lead screws together in sync. But after having trouble sourcing the belt that was the perfect length I decided to just go with three stepper motors similar to the HeVort 3d printer or Jubilee tool changing corexy platform.Triple Z FirmwareWith the Duet Wifi electronics board, we can drive 3 steppers and run an auto bed leveling routine using a proximity sensor or probe.Many 3d printer users frown upon the idea of multiple steppers for Z-axis motion due to syncing issues. But with the 32 bit Duet3d board and RepRap Firmware keeping the three lead screws in sync should be fine.When powered up stepper motors tend to jump to the four steps that match the phase current. Some will jump forwards or backwards after a number of power cycles.RepRap FirmwareWhile a single Nema 17 stepper motor can use a continuous closed loop belt routing to all three lead screws in sync. This can be avoided by adding code in RepRap Firmware to detect a power down moving the motors to the correct position ready for power up. The Duet WiFi has two power monitor circuits on board but it doesn't matter because the machine will run an auto levelling at start up.