5 1/4 Floppy Disk Notcher

With the current pricing of vintage floppy notchers on eBay these days, I decided to reverse engineer mine and build a 3D printed modern equivalent. I've tried to stick with inexpensive parts available at the hardware store.

Examining the vintage notcher, we see only a handful of parts:

Top and Bottom halves of case

Cutter with attached knob.

Spring

Cotter pin

Screws

The cutter is ground across the diagonal of the face creating a V shape. This creates 4 cutting edges to punch out the notch.

3D Printer and Filament of choice

1/4 x 1/4 inch Steel Keystock (such as SteelWorks 0.25 in. W X 12 in. L Steel Keystock - Ace Hardware)

#4 x 1/2 Sheet Metal Screws or similar size self taping screws (Qty 2)

13/32 x 11/16 OD x 1 inch Compression Spring or Similar (I found one in the spring drawers at the local Ace, similar to Cox Hardware and Lumber - Compression Spring, 13/32 In x 11/16 In x 1 In)

3/32 x 1 inch Cotter Pin

5 Minute Epoxy

Disk Sander

Bench Grinder

Vise

Hacksaw with metal cutting blade.

Drill Press or Hand Drill

3/32 Drill Bit

Print the knob, top, and bottom from filament of your choice. The top is printed fastest when the top surface is oriented to the build plate as that will minimize supports. If you want a cleaner top, print with the bottom to the build plate but the necessary supports will increase the print time. Print the bottom and the knob with their bottom surface to the build plate.

First, the end of the keystock needs to be ground to 15 degrees along the diagonal of the face. I used a disk sander with a miter gauge set to 75 degrees to give the 15 degree face. Since we are grinding along the diagonal, place a corner of the stock on the sander table, not a face. Gently grind the desired angle by sliding the bar against the disk while applying steady gentle pressure. Repeated passes are required to fully grind the face. Don't jab the bar into the disk and don't hold it in one place.

Second, a shallow curve is ground into the face to create the cutting edges. While the vintage cutter has a v shaped grid, the shallow curve from a bench grinder will be easier to create. I used a slow speed bench grinder with a white wheel. To help maintain the necessary angle, I placed masking tape on the tool rest and marked a line at 15 degrees to help visualize the proper angle. As before, the keystock will be held with the corner on the tool rest, not a face. Adjust the tool rest so that the cutting end is perpendicular to the wheel and meets in the middle of the face. Grind using the same approach as with the disk sander. Gently press the bar end into the wheel and slide against the wheel, using multiple passes. Be careful to maintain the marked angle and the bar upright on the edge. Holding in one place can grind a groove into the wheel.

If the resulting face is not even or otherwise flawed, just go back to the disk sander to restore the flat face and regrind.

I used the keystock as it is inexpensive, readily available at the local hardware store, and the proper 1/4 x 1/4 dimension for the cutter. However, it is low carbon steel and zinc plated. Heating zinc plated steel to the necessary high temperatures will release dangerous fumes. Additionally, low carbon steel is not suitable for heat treatment. If you can get a high carbon tool steel bar suitable for heat treatment in the necessary 1/4 x 1/4 dimension for your cutter, then heat treatment is an option to increase the lifetime of the cutting edge.

Place the cutter so that the highest point of the face is on the left. Measure 18 mm (a bit less than 23/32 inches) from the highest point of the cutter face and mark the center of the 3/32 hole. Its best to punch the location to drill so the bit doesn't wander. Drill the 3/32 hole through the keystock.

Cut the cutter from the keystock 42mm (1 5/8 inches) from the highest point of the cutter face. I clamped the keystock in a vice and cut it off with a hacksaw.

Insert the cotter pin into the cutter with the closed end on the face with the highest point of the cutter. The cotter pin will be a tight fit. Insert the cutter into the base with the closed end facing away from the nearest edge. This will orient the highest point of the cutter at the back corner of the notch to cut from the diskette. Place the spring over the cutter with the smaller diameter against the cotter pin. Place the bottom on and hold in in place. The high point of the cutter should stop just short of exiting the bottom and the entire cutting face should extend past the slot for the diskette. Remove the spring and cotter pin from the cutter.

Epoxy the knob to the end of the cutter. Allow the epoxy to fully cure.

Insert the cutter into the top. Insert the cotter pin and place the spring over the cutter. Attach the bottom and screw into place.

Try it out on a floppy diskette. The quality of the notch depends a bit on the diskette case. The Kao shown cut a nice clean notch. Some other generic disks had a bit thinner, more brittle case. The notch was not as cleanly cut but still functional. On those disks, even the vintage notcher left a rough edge.