For a left handed version see: https://www.thingiverse.com/thing:2031054

Version 0.9: 6 January 2017
I finally got around to redesigning the slider. It holds its spring a lot longer than the one in version 0.8. Although eventually it tends to come to loose. The only way I found to solve this is to put a small spring in the button. So the two flanges are pushed outwards. It's also just one part now instead of two. With that I had to slightly alter the upper and lower body. So these parts are not compatible anymore with version 0.8 parts. The first slide in and out could be tough but it should be fine after that.
I'll leave version 0.8 online for people who want replacement parts. The knife stand of version 0.8 is compatible with all versions so also with version 0.9.
It works reasonably well right now so I will stop calling it a work in progress. Although I would consider Version 1 to be a final version I am not sure I will have the time to ever get there. So lets consider 0.9 a final version .... for now ....

Version 0.8.1: 13 July 2015
As promised I uploaded the adjusted knife stand.

Version 0.8: 12 July 2015
This update removes the end piece. It was an overly complex way to hold the upper and lower body together. With that the blade snap off option is gone but soon in version 0.8.1 I will also update the knife stand and include a snap off in the base. The stand is a bit tight so will fix that too while I am at it.
I removed the assembly video since it is no more applicable to this version. The pictures are still of version 0.5 but the files have been updated.
For the next version I will address the slider. I am not happy the way it works.

Version 0.5: 31 Aug 2014
Finally a version that might be worth putting online. I designed this cutter as an exercise in 3D printing. We use cutters like these frequently in the workshop so it is quite useful too. It is also often used as a general utility knife in the office, in craft projects, etc. The little stand makes it an enjoyable icon on the shelf or desk.
It prints without any support. At 0.2mm layers and below it shouldn’t require any post processing.
It holds standard 18mm segmented blades which you can find in any DIY or hardware store.
The slider may be tight at first but should settle to the correct thumb pressure after sliding it up and down a few times. I found out that PLA (and ABS for that matter) doesn’t hold its initial spring. Let me know if you have problems with that. I can always upload a slider version that slides easier at the start.
Be careful these blades are sharp, use them with care.
In the 'end piece' you can find a slot which can be used to snap off blunt sections of the blade.
Enjoy,
PS: if you make one please share a picture.