CoreXY Build

Friday, June 18, 2021

Kinematic Bed Mounting

The 3-Point Kinematic Bed Mount is still in the design phase, but it will be made to level and compensate for a bent bed plate or dips. The three z-axis lead screws are used as the three points that make up a triangle and define plane of the bed can raise without binding or twisting keeping your work flat. The kinematic bed mounting system allows the bed to heat up without the thermal expansion effecting z-axis motion or bending the bed.

What is a kinematic mount?

A kinematic coupling is designed to constrain the mechanical components with optimal precision and positional accuracy. For example a kinematic coupling uses three radial v-grooves in one part that mate with three hemispheres in another part. A kinematic mount, which is ideal for bed leveling and proper mechanical constraint. A kinematic mount is a mount in which all six degrees of freedom (three translations and three rotations) of a 3D object are restrained from moving without over constraint.

How does a kinematic mount work?

A kinematic mount is a type of mounting mechanism used for positional accuracy. The movable frame that holds the print bed pivots on a ball bearing which is set into a hole in the fixed frame.

Kinematic Constraints

Kinematic constraints are constraints between mechanical components that decrease the degrees of freedom of rigid systems. The degrees of freedom or DOF of a rigid body is defined as the number of independent movements it has. To determine the DOF of this body we must consider how many distinct ways the bar can be moved. On a two dimensional plane such as a 3d printer build plate, there are 3 DOF. The print bed can be translated along the x-axis and y-axis, and rotated about each axis.

Z-Axis Documentation Drive Folder

Thursday, June 10, 2021

CoreXY Belt Routing

Belt Path Crossing

While the SolidCore 3D Printer design had a lot of influence from the Railcore's design, which also has the "x" shape belt path that some say “serves no purpose.” True, but you see the quality prints that the Railcore community is putting out. The print quality of the RailCore is AMAZING! Although the belts don't have to cross if the pulleys are at different z-levels. I originally thought that the difference between the hbot core xy design was that the corexy belts crossing segment.

We already designed and built the SolidCore with the crossed belt path so we're going to stick with it for now. Later on after many performance tests I'll try out some other design configurations to test out any changes.

Hbot vs CoreXY

The difference between hbot and corexy is that hbot has a single belt on a single plane, corexy can have either two non-intersecting planes or a single plane with pulley idlers on different levels which keeps the belts from rubbing.

While the Hypercube has the stacked belts on different planes configuration unlike the SolidCore corexy configuration "x" crossed belts.

Stacked Pulleys

Offsetting the stepper motors with stacked belt path pulleys may give the belts a clean run and simplify belt alignment. A printer's motors can be offset at different heights so that the belt routing runs a straight belt path and don't have to be twisted. But this belt routing path would also mean that on one side of the gantry the belt would have the teeth on the side of the idler wheel which wouldn't run as smooth and could lead to artifacts within printed parts.

SolidCore and RailCore Crossing Belt Segments

While many frown upon the crossed belts configuration found on the Railcore or SolidCore due to the y-axis could possibly bind if the y-axis isn't completely perpendicular to each other.

CoreXY Mechanism

CoreXY Explained

The corexy parallel kinematics mean's that the motors are the largest source of inertia within the system, and are stationary. This means rapid acceleration because the two stepper motors provide a means of moving both axes independently or simultaneously. The major benefit of the design is that the motors remain in a static position.

The corexy kinematics is a complex motion system where X or Y motors move together or opposite of each other to move the carriage from left to right or towards or away . If you were to move just one motor you would see the print head move diagonal.. If the two motors move opposite of each other the print head will move along the X-axis, If the two motors move in the same direction the carriage will move along the Y-axis.

CoreXY Kinematics

Two Motors

Both Motors Move Clockwise >> Carriage Moves Left
Both Motors Move Counter Clockwise>> Carriage Moves Right
Both Motors Move Opposite of Each Other>> Carriage Moves Toward & Away
One Motor Moves>> Carriage Moves Diagonal

Belt Path

A printer’s motors can be offset at different heights so that the belt routing runs a straight belt path and doesn't have to be twisted. But this belt routing path would also mean that on one side of the gantry the belt would have the teeth on the side of the idler wheel which wouldn’t run as smooth and could lead to artifacts within printed parts.

Mechanical Arrangement

The crossed belts configuration found on the SolidCore CoreXY y-axis must be completely perpendicular to each other to prevent any mechanical binding.

Linear Rail: Supported vs Unsupported

A crossbar made from u-shaped aluminum extrusion is used as a support for the linear rails. Depending on the rail length if the y-axis has an unsupported linear rail it could possibly lead to deflection. The load of the belt paths have to be balanced along the running plane with the pulleys. An unbalanced load can lead to the belts trying to slip off the pulleys and premature wear of the bearings.