The Ember 3D printer is open-hardware. You can download the CAD files for free! Today we’ll take apart the build arm on the printer and examine how it was engineered. This is not a necessary procedure for the operation of the print, just a demonstration of how the components work.

Step 1: Remove Build Arm From Printer Body.

The build arm is attached the the vertical drive of the Ember. Unscrew these 4 bolts to remove it.

Step 2: Connecting the Build Arm and Build Head.

This t-shaped piece interfaces with a slot on the build head. It snaps into place. Magnets inside the housing of the build head correspond to magents in the t-shaped part on the build arm.

Step 3: Kinematic Coupling

On the top of the build head housing there are three spheres that protrude from the surface. They interface with these three sets of metal pins embedded in the build arm. Together they form a kinematic coupling. This coupling ensures that the build head seats on the build arm with little wiggle -- this is useful for accurate and repeatable positioning of prints.

Step 4: Degrees of Freedom and the Calibration Bolt

Notice that the joint in the build arm can move freely. It can rotate in one dimension, and rotate in another, and can also slide up and down. This freedom allows the build head to mate with the window in the resin tray when printing. Tightening the calibration bolt clamps the joint and keeps it from moving.

Step 5: Opening Up the Joint

If we unscrew these 3 bolts, we can how how the joint works. The ball joint has a split. And there is a cylinder inside the ball joint. When the calibration bolt is tightened, it clamps down on the ball joint and the ball joint clamps down on the cylinder.

Step 6: Dismantle the Lever

Unscrew the bolt at the top of the lever and you can remove the handle and slide the ball joint off. Remove the plastic spacers and slide out the inner cylinder. It’s surrounding by a plastic sleeve to reduce friction. We can now easily see the 3 magnets in the t-shaped piece -- which match the 3 magnets in the build head.

Step 7: Remove the Back Plate

Lastly we can unbolt this plate from the main arm piece. We can see that there is a large pocket machined into this hole. The hole reduces the weight of this piece which in turn reduces the torque on the vertical drive on the printer. This through hole is the slot that holds a 4mm hex key -- used to tighten the calibration bolt.

That's how the build arm works! It's relatively simple but has some clever engineering.