This is a remixed version of "Pen Spring DA OTF Knife" by "davinci85" with an edited blade that's still blunt and safe, but looks more aesthetically pleasing. I also added "teeth" to the switch so you can get a better grip with your thumb.
Instructions: To insert the pen spring, start at the middle of the grove where it is slightly wider. Push in one end of the spring and drag it to it's end while pushing in more from the back of the spring. Compress the rest to push in the other end of the spring to it's place from the middle. It will be a bit of a tight fit, just be careful and sand or file if needed. Adding a couple drops of olive oil dramatically helps!
FINAL EDIT: (Omg Lol) Added a new blade that's still blunt and not pointy but looks even better. Made the latch stronger, and also made the bumps on the case more dramatic so the SwitchBlade can now snap together without glue and can easily taken apart.
Final Edit (Hopefully): (Feb. 8th, 2018) I printed, and redesigned many, many times and I got it working. I believe I pretty much have the best design changes I can make to this.
Edit: (Sept. 24th, 2017) I have just printed this and am still running into multiple problems. So if you want to save filament, please wait until I fix these issues. I only have a couple to go. I will let you guys know when with one more edit to the description here when I'm done.
P.S. My printer isn't functioning properly now so it will be a little longer now. :/
EDIT!!: As of September 18th, 2017, all parts have been improved and modified, along with a few new changes.
I have checked and fixed/made sure that everything is sized properly and fits better together as I had to sand parts down to size so they could fit. I don't know if anyone else had problems with that but I did. Please note that you still have to sand the parts smooth regardless to reduce friction.
I have added spacers to the top half of the case so it is not possible to glue the 2 halves together too tight. (So the mechanism is just loose enough to function nicely.)
The part where the spring sits on the blade has little cutouts so its easier to put the spring in, but has remaining extended ledges that jut out to prevent the spring from popping out while using. This is especially helpful for stronger/longer/stretched pen springs. Please take a look at the picture of it above to see what I mean.
- The teeth on the switch have been enlarged.