This is a remix of Talon V2 Utility Knife by HallPrecision found on Thingiverse. His is a great design but I wanted to remove the logo from the front, the website address from the back and get it to lock in place more securely. I found myself having to hold the blade portion when cutting things or it would slide back in. I tried a few different designs, ended up with this. The flexible locking pin hasn't been changed, but you now slide it up a ramp into a notch. I made the notch long enough to stick your fingernail in and push in to release it. It does take more work now to slide it back and forth than before, so if you liked the non-locking fast sliding mechanism I'd stick with the original.
I also split the two halves into their own stl files and made them each 1% bigger. My printer is dimensionally accurate but my razor blades were just a little too tight at original size. It could be my blades, who knows, but people can always increase/decrease in their slicer as needed for their personal preferences. Last thing is I put a little extra width on the knob that holds the blade in when retracted to make it a little tighter against the blade.