K2 Build Log Part Six: Gantry Motors and Idlers

Mar 16, 2022

Let’s build the gantry motors and idlers. There are two versions: Short Motor, Tall Idler and Tall Motor, Short Idler.

Tall Motor, Short Idler


Gantry Tall Motor, Short Idler BOM

Aligning the motor pulley

Place the pulley in the jig with the hub down:

Pulley inside alignment jig

Insert the motor shaft into the pulley with the flat aligned to one of the set screws. Move the pulley and jig up and down till the nub inside the jig is fully inside the pulley’s channel. I found it easier with the whole thing inverted. Once you’re satisfied, tighten the set screws.

Pulley aligned on motor

Now remove one set screw at a time, apply loctite and screw it back in. Place the printed part on top with the flat side on the motor and align it according to how you want the wires to end up. I aligned mine so that the wires would go towards the nearest side of the printer when installed. Apply loctite to 4x M3x10 SHCS and screw the printed part to the motor.

Printed part attached to motor

Idler stack

For the following instructions, I’m assuming that you aren’t using shaft retaining compound to “weld” the pulley to the motor. If you are, you can skip everything after the pulley is aligned since you won’t be needing flats or set screws.

Remove one of the set screws from a pulley. Insert the pulley onto the M5x35 shaft, aligning the set screw hole with the flat on the shaft. Build the rest of the idler stack as follows around the M5x35 shaft:

Bearing - Washer - Pulley with hub down - Washer - Washer - Bearing
Idler stack

Note that the second washer above the pulley isn’t in the eDrawing. That’s because the spacing for the idler pulley is designed to allow some leeway for non-standard rails sizes. However, this results in the top pulley not being fully seated in the accent part. In order to seat the pulley fully for my standard-sized Robotdigg rails, I added an extra washer.

Use a sharpie through the set screw hole to make a mark on the shaft. Remove the shaft from the stack and use a dremel to grind a flat around the mark you made. This flat will help the set screw remain immobile and prevent the pulley from rotating relative to the shaft.

Idler shaft with ground flat

Rebuild the idler stack and insert it into the bearing hole in the main printed part. Place the accent part on top and press it down till its flush with the main part.

Installing the main body

Insert 4x M4 roll-in nuts (lower in the top extrusion) and 3x M5 roll-in nuts (left in the bottom extrusion) approximately in the locations shown:

Roll-in nuts

For subsequent steps, apply loctite to each bolt.

Insert 2x M4x20 SHCS into the holes shown:

First M4x20 bolt
Second M4x20 bolt

Insert 2x M5x12 BHCS (eDrawing says M5x10 but I found them too short) into the front holes:

Front M5x12 bolts

Insert 1x M5x12 BHCS into the side hole:

Rear M5x12 bolt

Insert 4x M4x50 SHCS into the idler accent part:

Idler bolts

Using calipers and a flat surface, ensure that the body is 45mm from the Z extrusion and flat with the front extrusion:

Left alignment
Front alignment

Tighten all bolts.

Installing the motor

Place the motor with its attached plate on top of the main body.

Motor placed on top

Insert 4x M4x55 SHCS and tighten them.

Finished installation

Short Motor, Tall Idler


Gantry Short Motor, Tall Idler BOM


Insert the heatsets into the holes in the picture below:

Gantry Short Motor, Tall Idler BOM

Motor and Idler stack

Same as described above

Installing the main body

Insert 4x M4 roll-in nuts (the ones on the right in the lower extrusion) and 3x M5 roll-in nuts (the remaining ones) approximately in the locations shown:

Roll-in nuts

Place the main body in position and insert bolts in locations analogous to the previous assembly. The only difference is that the idler will use 4x M4x70 SHCS.

Align it so that it is 45mm from the Z extrusion and flat with the front extrusion.

Right alignment

Installing the motor

Place the motor assembly on top and secure it with 4x M4x30 SHCS.

Finished installation

Remaining two motor assemblies

Repeat the above process, the remaining two are identical to the ones we just built and installed.

Gantry rails

Place one of your gantry rails between the two motor parts we just installed and verify that it fits. If your rail doesn’t fit, check the distances of your motor parts from the vertical extrusions again. If they’re still 45mm, hop on the Annex discord and ask for help.

Finished assembly on the front side of the gantry, rail test fit

Using the same method as described in part two, install the rail onto the inner slot of the extrusion. Repeat this process for the remaining three rails.

Finished installation of static gantry rails