PRO Rack and Pinion Drive Instructions [Archived]¶

These instructions go through the steps required to assemble your Avid CNC PRO rack and pinion drive. While the majority of the photos shown are for our NEMA 34 rack and pinion drive, most of the same steps apply for the NEMA 23. Any special cases that apply differently for the NEMA 23 are shown separately.

If you are using the PRO drive with Avid CNC extended linear carriages, the first step in setting up your rack and pinion drive is actually to modify the extended carriage to which it will mount. This requires simply replacing one of the bolts through one of the fixed (non-adjustable) bearings, as shown in the photos below. Remove the 30 mm bolt, and replace it with the supplied 40mm bolt so that it sticks out the back of the carriage. This bolt provides a mounting point for the EZ-tension system included in the PRO drive. Once this is done, install the carriage on your machine as normal before proceeding with the rest of these instructions.

Once your carriage is configured, the actual R&P installation can begin. The next step is to mount the supplied pulley to your motor.

You will want to set the height of the pulley such that it aligns fairly well with the mating pulley on the drive spindle (combined gear and pulley component) when installed, and so that it does not stick out so far that it risks interfering with a rack clamp. Approximate positions of the NEMA 34 and NEMA 23 pulleys with respect to the motor boss are shown below:

Once the pulley is installed, you can attach the motor loosely to the rack and pinion drive plate. First, align the hex nuts in the slots on the back side of the rack and pinion plate, and place it on top of the motor.

Once these are in place, install the socket head cap screws into the hex nuts. Do not tighten them completely at this time, as the motor needs to be able to slide freely to install the belt.

Next, place the drive spindle spacer washer on top of the drive plate -- see picture below. Note, for the NEMA 34 system, this is a thin flat washer, while for the NEMA 23, this washer is slightly thicker.

Place the drive spindle on top of the washer, and install the belt around both the motor pulley and the drive spindle.

Next, install the drive spindle shaft using a large flat head screwdriver. Note, this shaft needs to be tightened all the way down until no more rotation is possible. For the NEMA 23 spindle, there will be some resistance to spinning the drive spindle until the shaft is fully installed, which will flatten out the lock washer.

The PRO NEMA 23 spindles use a washer near the head of the spindle shaft. This washer is not used with the NEMA 34 PRO spindles.

At this point, it is time to apply tension to the belt. A quick clamp can be very helpful here, and will allow you to apply tension to the belt and hold it in place while you tighten the mounting screws underneath.

You are now ready to mount the drive to your linear carriages or other linear bearing system. To do so, align the PRO pivot with the tapped hole in the carriage for the pivot bolt, and then insert the pivot shaft and tighten with a wrench.

Next, install the tension system brackets. Attach the drive tension bracket to the R&P plate using the supplied bolt. Attach the carriage tension bracket to the extended 40mm bolt using the supplied hex flange nut.

Lastly, install the two M8 washers and tension spring onto the tension shaft, and connect this arrangement through the carriage tension bracket into the threaded portion of the drive tension bracket.

Your completed assembly should look something like the following:

Once you install the system on your machine, tighten the tension bolt until you get solid engagement between the rack and the pinion gear. The amount of tension you apply depends on the mass of your system, the acceleration settings you use, and the torque of your motors. More tension will provide more resistance to the pinion gear popping out of the gear rack, but can also accelerate wear on the pinion, so make sure to leave at least some travel in the spring.