In my shop, I have a constant need to notch the protective carboard corners we use for shipping our wood return air filter grilles. The need comes from needing to get around our filter housings and I have not found a stock one that fits this application, so we modify what is available. This has typically been done simply with a pair of heavy duty scissors or tin snips, but it can be strenuous on the hands if you have to cut a lot of them, the notches are inconsistent which does not affect their performance, but doesn’t look as professional as I would like them to and it is very time consuming to cut them by hand.
The solution to was to create a machine that would notch the corners consistently, much like a table saw. The operation is foot activated leaving the operators hands free to manipulate the cardboard easily, quickly and comfortably. There are corner notchers for cardboard on the market that operate like a shear, but they are designed to simply round the corners. I also investigated corner notchers intended for use with sheet metal, but they are expensive, heavy and I theorize, unlike metal, the cardboard would act like a very fine sandpaper wearing down the expensive blades over repetitive use. That led me to pursue using electric scissors which do a great job of cutting cardboard, they are inexpensive, and the blades are easily replaceable. It just requires a few modifications and a table built around it to suit the needs of what you are cutting.
In this case, the table is specifically set up for consistently notching cardboard corners and as you can see in the cover photo, is part of a larger system used in our shipping room that utilizes a manual shear to cut strips of MDF protective packing material to specific lengths, notch the cardboard corners and trim shipping labels to the proper size. In this article, we are going to focus on the cardboard cutting machine part of the system. Incidentally, the table and stops could be configured and/or resized to suit your specific application and it would work equally well for most types of fabric or other soft sheet materials.
Researching cardboard cutting led me to electric scissors. I found essentially two types. One has an oscillating pair of blades more like a traditional pair of scissors. The other has a rotating decagon or circular blade. After testing both, I found the latter worked best for carboard not only because it cut faster, but it did not deflect the cut off side downward which would tend to bind against the table surface in my design. The cost was less than $30. (fig 1)
Several modifications had to be made in order for my design to work. As it comes from the factory, the electric scissors have 3 cut offs. If it is plugged into the charger, no power can be delivered to the motor. Fortunately, this one is an electrical switch and not a mechanical switch so it can be operated by cutting off power to the charger entirely. More about that later.
The second is a safety switch on the top that must be depressed before the hand switch on the bottom will turn on the blade. My best guess is that it is too easy to accidentally depress the large hand sized trigger and that necessitates the safety switch on top. Since we will be removing the large trigger and operating a protected foot switch, I decided the top safety switch was unnecessary and bypassed it by removing the switch and soldering the wires together. (fig 2 & 3)
I then soldered two 5’ wires to the contacts for the main trigger. Now when these two wires are connected, and there is no power to the charger, the cutting wheel will run. (fig 4 & 5)
The main operating connection utilized a momentary push button switch in concert with a foot petal in order to free the hands of the operator to manipulate the cardboard. The foot switches I found online were not terribly expensive, however, they were intended for higher voltage uses so I decided to just build one. I started with 2 pieces of 1/8” x 2” right angle aluminum cut to 6” and 2 pieces of 1/8” x 2” aluminum bar stock cut to 5 ½” I put the 2 pieces of right angle aluminum back to back and drilled a 3/8” hole 2 ½” from the front and 5/8” from the edge. (fig 6)
The holes are to accommodate the 3/8” threaded rod that the pedal will pivot on. Therefore, after cleaning the metal, I clamp them to the 2” flat bars to form a square base making sure the holes are opposite each other on the vertical leg of the angle bar. Using a propane torch and aluminum brazing rod, the base was brazed together. (fig 7, 8 and 9)
Several more parts needed to be cut and prepped for assembly. Since I was building a foot operated switch, I needed a pedal which I acquired with a quick stop by the auto parts store. This clutch pedal was Ideal because It had predrilled and countersunk holes for mounting. I simply used it as a template to cut down a piece of 1/8” aluminum bar stock and bore the matching holes. (fig 10)
After cutting a 4 ¾” piece of 1” aluminum square tubing two holes needed to be cut. One is a 3/8” hole for the threaded rod 1 ¼” from the end, and the other is a ¼” hole drilled 3/8” from the back. I mounted the flat stock for the pedal to it at a right angle with some self boring screws. (fig 11) Then the pedal was mounted to the flat stock. (fig 12)
In order to keep the pedal from wondering back and forth on the threaded rod, I cut two pieces of aluminum tubing with a 3/8” inside diameter at 2 1/8”. (fig 13)
After cutting a 3/8” threaded rod to 6 ¼” it was mounted to the base centering the pedal assembly between the 2 aluminum tubes and washers secured by some nylon insert lock nuts to allow free movement. A 1/8” hole was drilled just to the side of the square tubing at the rear of the base to secure a small spring. A ¼ x 1 ¾” screw was inserted through the hole previously drilled in the back of the square tubing. The other end of the spring attaches to this and an additional nylon insert lock nut is placed at the end to prevent the spring from slipping off the assembly. (fig 14)
Using some 1/8” x 1” bar stock cut to 7”, I bent both ends to 90° at about 1 ¾”. After drilling a 7mm hole in the middle of the bar stock I mounted the momentary switch with the button facing down in the same direction as the 90° bends. 1/8” holes were drilled ½” from each end for the mounting screws. (fig 15)
With the aid of some vice grips to position the switch at the desired height, I drilled through the vertical leg of the base using the hole previously drilled in the bar stock as a guide. (fig 16) The primary reason for mounting the switch facing down and using a lever to press it as opposed to just placing it under the pedal was to allow the pedal to be closer to the ground and thus, more comfortable for the operator. A residual benefit is that the bar stock the switch is mounted on will flex slightly reducing pressure on the momentary switch and promoting longer life.
The completed base assembly is complete. (fig 17) However, to minimize the chance of the switch being inadvertently activated I decided to build a shroud to shield the pedal.
The shroud is constructed of a light gauge sheet metal cut 5 ½” x 18’ and notched for the threaded rod with a nibbler. (fig 18) The two sides were folded 5 7/8” from the end in a sheet metal brake. (fig 19) A quick coat of paint (fig 20) completes the shroud.
The shroud is mounted to the base with some 1/8” x 5/8” screws and the foot switch is complete (fig 21)
With the foot switch complete, it was time to turn my attention back to mounting the scissors on the table. The frame of the table was constructed of 2×4 with a ¾” laminated top to be mounted on the frame. I added two ¾” x 3 ½” boards spaced 4” apart with 3/8” mounting holes dilled 5/8 from the edge and 5 ¾ from the end of the two boards. A second pair of 5/16” holes were drilled 5” back from the 3/8” hole centers and 1 ¼” down from the edge of the board. (fig 22)
When the large trigger was removed from the scissors, two shoulder holes were left on either side where the previous trigger pivoted. Utilizing these holes as mounting points, I used a tap to cut 3/8-24 threads approximately 3/8” deep into the scissors. (fig 23)
The scissors are mounted to the table with two 3/8-24 x 1 ¼” bolts tightened gently into the plastic holes tapped earlier. Nuts with washers to distribute the pressure are tightened against the scissors. The charger cable needs to be plugged into the back of the scissors before the ¼” x 6” bolt is inserted into the lanyard hole at the back of the scissors. Nuts are again tightened against the scissors to ensure it remains stable when it is under load. (fig 24)
A hole is cut in the laminated top to accommodate the protrusion of the scissors cutting blade and it is mounted to the table. In this particular application, an aluminum fence is mounted to the left of the blade for repetitive and consistent cuts. (fig 25)
A little more wiring is required. When the charger is energized, the scissors will not run. A wall box is mounted to the back of the deck and a combination switched receptacle is wired to a generic plug in cord. The switch is mounted so the down position turns on the receptacle on, disabling and charging the scissors. (fig 26) In the up position, the receptacle is off. This is more intuitive as in the up position, the scissors are enable to run by activating the foot switch and when the switch is down, the scissors are disabled.
Finally, the main trigger wire are soldered to the momentary foot pedal button (fig 27) and the charger is plugged into the switched receptacle (fig 28).
The final result is a machine that notches our carboard corners quickly, accurately, and consistently. (fig 29)