Paper Cutter Light
This project is a modification to a standard paper cutter that uses transmitted light to clearly show the cut location. It should work with most paper cutters provided they have enough empty space on the bottom to mount some components. It's important to look for a model with some clearance between the frame and table (below the blade) so you can mount a strip of LED's. The paper cutter used here is a 12" Swingline with a wooden frame and lots of empty space underneath.
This started with one of those "even I can build something better" moments. I chopped the edge off one too many lab notebook graphs and finally decided to do something about it. Some paper cutters have a laser line (or maybe nothing) to indicate the cut location but it's never aligned very well and can be 1-2mm thick making it almost impossible to make exact cuts. An obvious and failproof solution would be to shine light up through the paper from the bottom and use the blade edge shadow to mark the cut. With this modification it's easy to cut the dot off a 12 pt lowercase letter i. However, it doesn't work for cutting a lot of sheets simultaneously as you need to be able to shine light through the paper stack.
Most of the work on this project was in customizing the body, mounting the switch and power connector, and mounting the white LED strip. All you need is a DC power supply and a set of white LEDs with appropriate resistors. I have a strip of 15 bright white LEDs and a 9V power supply (could be battery powered). If you want a temporary solution with no work just throw a flashlight under the edge. The prototype shown here uses one of my PWM Power Supply PCBs because I thought it would be useful to dim the LEDs (it isn't). If I do this again I'll use a Single Output Supply PCB and run the LED's at full brightness. You can skip the circuit board completely if you trust your wall wort to provide stable voltage or you're using a battery.
I mounted a power switch and DC power jack on a metal plate and slipped it into an appropriately sized hole on the back left corner.
DC power was fed to the PWM Power Supply and PWM power was sent to the LED strip.
When mounting the LED's try to get the maximum amount of light directly at the stationary blade edge, that's where the action is. Make sure your LED strip doesn't extend out too far or paper scraps will lay on top of the LEDs and diffuse the light. I soldered the LED's about 0.5" above the proto board so I could bend them to evenly light up the blade edge.
When you turn it on you'll know exactly where it's going to cut all the way along the edge.