T-Rex Internship Project Report

Company: T-Rex Arms, Centerville, TN

Internship Duration: 7/21/25 – 9/19/25 (8 Weeks)

Intern: Brant Drayer

Department/Team: Engineering

Project Title: Redesign of Electrical Control System for Kydex Molds

This report documents the work completed during my engineering internship at T-Rex Arms. T-Rex Arms, founded in 2013, is a holster and other small arms accessory manufacturer based in Middle Tennessee. The things they are best known for are making the original Sidecar holster, and their use of kydex, a hard thermoplastic, as the material for their products.

Accessories are made by heating up a sheet of kydex to a specific temperature before placing it on a former where it is vacuum sealed to a custom mold, and allowed to cool and re-harden in a specific shape.

The purpose of my internship was to help on a project redesigning the electrical controls for the kydex molding stations. I gained valuable experience working on a project as part of a team, as well as knowledge of AC and DC electrical systems, PLC programming, and helped with the physical assembly of all the new control box.

The project was important from a maintenance standpoint because it greatly simplified the job of troubleshooting and making changes. The previous wiring system (pictured below) was not ideal as none of the wiring was labeled and therefore not very traceable. With the new box we aimed for more simplicity with labeled terminal blocks, and less redundant wiring.

Another reason for the redesign was package protection for controlling a mold cooling setup that the team was working on, as well as a few other features that will be added in the near future.

In our new design we decided to alter the setup a bit. Each molding station has 4 formers or “cradles” where the Kydex is pressed into shape. Previously there was one box housing all the controls for all 4 formers. We added 4 junction boxes (one at each former), which all run back to a main box with all the PLC modules and power supply. This setup makes it easier to trace the wiring for individual components between the PLC’s and sensors, and allows for simpler diagnostics and troubleshooting.

I used Fusion 360 to create a 3D model of the box before we committed to a certain design. This was a good opportunity for me to learn 3D modeling for the first time. I learned to create and constrain sketches, and use tools like extrude, cut, fillet, etc. to create precise objects. I also learned the importance of using a bottom-up modeling approach. Bottom up basically means you begin by building each object in a larger model in it’s own file, before adding it to the main design. If objects are not constrained properly by themselves it can cause problems when multiple components interact together down the road.

We designed the main box to be simple and tidy. 3 Din rails for all the components to mount on surrounded by 1in raceway to run all the wiring through. We continued with the old designs use of CLICK PLC’s for the CPU and I/O modules. The finished back plate with a few components installed is pictured below.

The junction boxes were assembled in much the same way, but with no raceway due to their simpler wiring.

In my first few weeks at T-Rex I took a deep dive into learning the basics of PLC programming. I learned basic ladder logic and used it to build a program that could be used to control a traffic light, using basic timers, inputs, and outputs. There were not many changes to be made on the ladder logic for the existing control box, so I analyzed it to better understand how it was set up.

We greatly simplified the wiring through the use of the junction boxes and terminal blocks. I traced out several diagrams from different parts of the old system to help us figure out the new wiring. Nearly all of the sensors and modules ran on a 0-24v DC system, with a couple exceptions using 110v AC.

Sinking vs. Sourcing is an important concept to understand when it comes to wiring PLC modules. It has to do with where the field device/load is located in relation to the module. For a sinking type, the field device is placed between power (24v) and the PLC module, basically making the PLC a “sink” to receive the 24v signal. The opposite is true for sourcing: the field device is placed between the PLC and 0v, and the PLC “sources” the 24v signal to be run through the device. In the image below the Proximity (Prox) sensors and the Fan Switches are both wired in a sinking type, while the Vacuum (Vac) Solenoid is a sourcing type.

Unfortunately, my internship ended and I was not able to help install all of the wiring for the new box. However, I feel that my work on the diagrams, and hands on experience building the new box greatly increased my knowledge of basic AC and DC circuits, as well as PLC input and output types and configuration.

To recap, helping with this project has been a great experience and I left with a greater understanding of many valuable concepts and skills. Here are a few of my key learning points summarized:

Many thanks to T-Rex Arms for allowing me the opportunity for this internship. I hope that the work I was able to complete would be a blessing to the company. I learned many technical as well as practical skills, and I look forward to using them in my future career.