I made something similar out of wood and a marble when I was a kid so I know the theory of this works - so hopefully my 3D modelling does too!
Within the 3D model there is a 12mm 'ball'. You could use a marble of a similar size if you wanted to...
Date Made: September 2013
Approx Cost: (Cost of printing?)
Approx Time: 3 hours modelling (plus printing time)
Step 1: How It Works
Once printed, the ball (or marble alternative) needs to be inserted inside the 'runner'... This should just pop in (as long as the 3d printing material isn't too brittle!?!).
It is the pressure from this ball that will 'grip'.
The angle of the top runner means that 'grip' is adjustable - depending on the thickness of the paper inserted.
So to get the clip to grip, you insert the paper between the bottom (flat) runner and the ball. Then let the ball drop down to the narrowest gap (between top and bottom runner). Then slightly pull the paper back out - this will tighten and jam the ball between the top and bottom runner, holding the paper in place...
Hopefully that makes sense!?! I have done some sketches to try and help the explanation...
Step 2: The Model
This was done using tinkercad and can be found on their website by searching for "Money / Paper Clip" or here:
Step 3: Optimization
If this model does not work very well (I don't see why it wouldn't), the next step is to analyse, evaluate and adjust the model.
Depending on whether the paper is not clipping or there is not enough room or something, then a number of alterations can be made to alter the design:
1. Make the ball bigger/smaller
2. Make the channel that the ball runs in deeper/smaller
3. Make the channel longer/shorter
4. Make the angle of the top runner bigger/smaller
5. Make the length of the runner longer/shorter
6. Raise/Lower the top runner compared to the bottom runner.
7. Make the arms thicker/thinner
There are lots of ways this could be personalised too; The aesthetics could easily be changed, adding patterns or designs or anything really.
The other thing to consider could be a way of mounting the unit (if you wanted to) - you could put a hole in the back so that it can be screwed to a wall, or you could put in a recess to allow a magnet to be glued in? Or you could just leave it on your desk or in your pocket...