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Tool Review: NEMA 23 Stepper Motor Covers

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Tool Review: NEMA 23 Stepper Motor Covers


Over the last year I have been finishing a project to convert my X2 manual mini mill into a fully enclosed 3-axis CNC milling machine. Once I had the stepper motors mounted and running, I worried that the wire connection at the base of the motors might be a potential weak point in the design. Eventually I want to use mist coolant when machining parts but I do not want to run the risk of shorting out the wiring due to spotty connections. At first I though of a few ways to fix this issue and sketched out a few ideas on paper, but the designs were large and bulky and looked like over-engineered boxes. I wanted a simple and practical solution that would securely anchor the wires to the motor while preventing liquid damage from mist coolant.

While searching the online CNC forums for ideas, I stumbled across these professional looking NEMA 23 Stepper motor covers. These plastics covers incorporate a threaded panel mount pin connector to secure the motor wires to the side of the motor case and only cost $13.50 each. Intrigued, I printed out the motor sizing guide to see if my Probotix stepper motors would be compatible, and emailed Jeff Birt at to inquire about the different options. In no time, Jeff responded with the following:

“A NEMA 23 [motor] frame has a 57mm square profile. There are some 60mm motors out there which get labeled as NEMA 23 as the mounting boss and hole pattern is the same, but the regular NEMA 23 covers will not fit.

The covers come in two basic flavors, with or without a sealing O-ring (IP40 or IP65). Unless you have an IP65 rated (sealed) stepper motor than there are still ways that liquid can get inside the motor. The O-ring will help to prevent the cover from filling up with coolant. To really seal the motor you have to buy a sealed motor, use the O-ring style cover, and use a water tight gland nut or connector.

In reality you are better off to fashion sheet metal covers that will cover the area over the stepper coupler and the stepper motor. This will keep out the majority of the mess. The other trick is to face the connector hole downward.”

After a few emails back and forth to verify that my motors would fit, Jeff recommended the standard IP40 covers (since my stepper motors were not sealed) and offered to send me three covers to test and review. Before I could begin the install I had to source my own eight pin connectors for wiring up the unipolar stepper drivers to the motors. If you are using bipolar stepper motor drivers, then you can purchase the optional 4 pin connectors when ordering the motor covers from Soigeneris. Since my motor drivers from Probotix are unipolar, I had to use eight pin connectors. (awesome quick MicroChip video on Unipolar vs Bipolar). You can find these connectors online or at a local surplus electronics store. Getting all eight wires in the connector is a challenge, but with some patience and a fine-tipped solder iron it is possible.

Designed by DY Engineering in Israel, these covers were originally made to meet the functional and aesthetic demands of the inventor and DIY CNC hobbyist Daniel Yosefi:

The idea came after I fitted stepper motors to my first machine and at first I soldered the wires and used isolation tape on top. It looked awful, not safe and not professional and I hated it. I started looking on the web and forums for some solution. I believed there ought to be some solution that people were using since there are literally thousands of DIY CNC machines being built, but I was so disappointed to find that there was no neat ready solution. I decided I wanted something more professional and safe so I gave it some thought… lot’s of actually, (I scraped several alternatives till I got to this one) and came up with this solution.

I machined them out of Delrin and mounted on my motors. I was very satisfied with the look of the machine, but I had no plans of making it a commercial product at that time. Some time later when a few friends saw the photos of the motors with the covers mounted and told me this was a great idea, I realized that I was not the only one putting attention to detail when building a machine and others may also benefit the idea.

The first commercial ones were still being CNC machined and after I was confident the demand could justify an injection mold’s cost, it was made and now they are injection molded.

Besides wiring the pin connectors, the installation is extremely simple and the instructions are well documented and available for download. The covers mount to the rear of the motor using the threaded screw holes in the end of the motor case and come predrilled with center marks for drilling out the mounting holes. During installation you may need to shorten the machine screws that secure the motor case together. This is easily done by removing each stepper motor screw one at a time and grinding off a few millimeters at the end to allow adequate clearance for the shorter motor cover screws that are included with the cover.

These covers are also compatible with stepper motors that have a rear shaft. The design incorporates an internal sleeve for protecting the rear shaft of the motor from interfering with the wiring during operation. After following the instructions and soldering all the wires to the pin connector, simply wrap the motor wires inside the cover and use the four machine screws to secure the cover to the back of the motor. An overhanging lip completely covers the gland where the wires exit the stepper motor.
Even without the O-rings installed, these covers protect the stepper motor wiring from flying chips while the overhanging lip provides protection from oil and lubricant spraying inside the wire connections. With the addition of the panel mounted pin connectors, the motor’s wiring harness is securely fastened to the side of the motor covers and ensures a strong connection during operation. These NEMA 23 stepper motor covers are the perfect finishing touch to any CNC project.

6 thoughts on “Tool Review: NEMA 23 Stepper Motor Covers

  1. J.Morlen says:

    Awesome find!!
    I’ve been looking for something just like this too!

  2. DragonPhyre says:

    A printable version will be coming in about a week… This is how these things go.

  3. Dave says:

    i want these. tell me how to get them please.

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