Drive Belt Replacement: All Current CMC Models

Remove the cover from the gantry by unscrewing the screws that hold it in place and set aside.

Remove the 5/32” Allen screws and washers from the lower gantry plate.

These were placed here to assist in loosening the belt tensioner.

Look for Red Dots (only these screws are to be adjusted).

Locate the 3/16” Allen belt tensioner screw that’s located on the right bottom side of the lower rail and marked with a red dot.

Loosen this screw one turn only so that there is some movement in the belt tensioner.

The tensioner springs should be visible.

Locate the belt tensioner hole on the end of the belt tensioner.

Place the 5/32” Allen screw and washer we removed from the lower gantry plate into the belt tensioner hole.

Tighten the Allen screw until belt tensioner is flush with the rail and the springs are not visible.

Go back and tighten the 3/16” Allen belt tensioner screw on the right bottom side of the lower rail marked with a red dot.

Lift the drive belt end out of the belt tensioner slot.

Pushing the drive belt end to the right may assist in getting a hold of it.

Repeat the last six steps with the upper rail.

Move the gantry to the left to loosen the slack and free the belt anchor from the end of the rail.

Unscrew the 1/8” Allen screw on the clamp that holds the belt to the belt anchor and remove the belt end from it.

Work the drive belt back through the gantry wheels and remove it from the gantry.

Remove the drive belt with the drive end still in place.

Take a strip of matboard about ⅜” (9mm) wide and 7” (18cm) long, and insert it on the inside of the bottom right pulley.

Angle it to the right so that it slides out into the belt channel below.

Locate the replacement drive belt and place the free end, teeth down, onto the strip of matboard on the belt channel.

Push the free end of the replacement drive belt to the left so that it goes up the matboard guide under the right pulley and over the drive sprocket.

Gently pulling the strip of matboard may assist the movement of the drive belt.

Remove the strip of matboard and insert it in the same manner on the inside of the bottom left pulley and into the channel below, angling it to the left this time.

Place the drive belt over the drive sprocket, onto the top of the matboard strip and under the left pulley and out onto the belt channel.

Gently pulling the strip of matboard may assist the movement of the drive belt.

Remove the strip of matboard.

Note that each belt anchor has a different orientation.

Make sure to arrange the belt anchor so that the curve faces toward the inside of the rail.

Line up the last three teeth of the drive belt to the three teeth of the belt anchor.

Secure the Drive Belt into place by tightening the 1/8” Allen screw on the flat lock plate.

Lightly pull the drive belt toward the right to take up the slack and pull the belt anchor into place flush with the end of the CMC.

If necessary, rotate the drive pulley so that the red mark is on the top.

Line up the red mark of the drive belt to the red mark of the drive pulley; this may require moving the gantry a bit in either direction.

Pull drive belt to the right to take up slack.

Do not move the gantry after red marks line up.

Make sure that the drive belt is not twisted and that the teeth are facing down toward the board into the rail channel.

Slide the screw of the belt end into the belt tensioner slot.

Click the screw of the belt end into the slot/recess on the end.

Go back and make sure red lines are still lined up.

Remove the 5/32” Allen screws and washers from the belt tensioner.

Place the Allen screw and washer into the holes provided on the lower gantry plate.

Place them so that the screw protrudes only slightly from the back of the plate.

Loosen (one full turn only) the 3/16” Allen belt tensioner screw from the right bottom side of the lower rail marked with a red dot.

The belt tensioner should spring fully into place.

Go back and snugly tighten the 3/16” Allen belt tensioner screw from the right bottom side of the lower rail and the right bottom side of the upper rail marked with a red dot.

Repeat steps 1 through 13 with the upper rail.

The Drive Belts have been replaced.

Reinstall the gantry cover(s), replacing the screws you removed earlier.