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Chapter 04: A/B Drives and Idlers

The A/B drives and idlers form the corners of the CoreXY motion system. These components are responsible for transferring motor movement to the gantry belts. This chapter covers the assembly of these four critical corner pieces: the A-Drive, B-Drive, A-Idler, and B-Idler.

Overview of the A/B drive and idler components Overview of the A/B drive and idler components

An overview showing the four fully assembled corner components: A Drive, B Drive, A Idler, and B Idler.

Section 1: Preparation

Before starting the assembly, prepare all the necessary printed parts by installing the M3 heat-set inserts and M5 hex nuts into their designated slots.

Preparing the printed parts with inserts and nuts Preparing the printed parts with inserts and nuts

Various printed parts for the drives and idlers with heat-set inserts and M5 nuts being installed.

Section 2: Idler Assembly (A and B)

The A and B idlers are mirror images of each other. The assembly process is the same for both.

  1. Create a bearing stack using an M5 bolt as a temporary alignment aid. The stack consists of an F695 bearing sandwiched between two M5 shims.
  2. Insert this stack into the main idler body.
  3. Slide the tensioner arm into place.
  4. Secure the tensioner arm with an M3x40 SHCS and an M3 washer.

After assembling the A-Idler, repeat the exact same process for the mirrored B-Idler parts.

Exploded view of an idler assembly Exploded view of an idler assembly

An exploded diagram showing the components of an idler: printed body, tensioner arm, F695 bearing, shims, and screws.

Section 3: Drive Assembly (A and B)

The A and B drives, which house the motors, are also mirror images of each other. This is the most complex assembly in this chapter.

Do Not Overtighten

Some M5 bolts are threaded directly into the plastic parts of the drive assembly. Tighten them until they are snug, but do not overtighten, as this can strip the plastic threads.

  1. Bearing Stacks: In the lower drive housing, create the bearing stacks on the integrated posts. These stacks consist of multiple F695 bearings and shims.
  2. Motor and Pulley: Mount the GT2 20T pulley onto the NEMA17 motor shaft. Ensure you use thread locker on the set screws.
  3. Combine Housings: Attach the top motor housing to the bottom bearing housing using M3x30 SHCS screws.
  4. Check Alignment: Before fully tightening, ensure the motor pulley is perfectly aligned with the bearing stacks. The belt should be able to travel in a straight line without rubbing against the flanges.

After assembling the A-Drive, repeat the process with the mirrored parts to build the B-Drive.

Exploded view of a drive assembly Exploded view of a drive assembly

A detailed exploded diagram showing the two halves of the drive housing, the motor, pulley, and the complex bearing and shim stacks.