Prototype Mechanical Pencils

These pencils don't really work well enough to use.  They are more to share my prototyping thought process. The pencil is printed in one piece without the need for supports. Here is a link to the Google plus page https://plus.google.com/u/0/co... that shows how you load the spring and the graphite. This was printed with PLA, 2 shells, 10% infill no supports. You may need a screwdriver to pry spring off of the base of the pencil.

When I remixed the one mechanical pencil https://pinshape.com/items/282... to work for 0.7mm lead, it had issues. The moving carriage was too easily pushed back when writing, which could be remedied by making deeper gear teeth on the the rack. The pencil has awkward to hold which could easily be remedied without changing the mechanism itself. However, the graphite would break off in the carriage and get stuck; that would be harder to fix.

These pencils work with a mechanism more like existing mechanical pencils.  Ordinary BIC mechanical pencils work with a spring loaded chuck. You push the eraser on the back,  that opens the collet chuck, the graphite falls through the collet chuck , the spring  pushes the eraser back and closes the collet chuck holding the graphite in place. This mechanism is the same but I replaced the circular collet chuck with a planar gripper and the helical spring with an embedded ribbon spring for ease of printing.

These pencils don't really work because the gripper does not hold the graphite tight enough for writing. The problem is that grooves are not deep or precise enough on the gripper to hold the lead in place; even with a stiffer spring and a mechanism that pulls tighter, the graphite could slip off of the line of action.  The 3D printed gripper has much looser tolerances than than collet chuck and the grip opens too widely without a collet.  This comes back to the same problem with the remix; how do I hold and release a thin, fragile piece of graphite consistently?  I am looking into more feasible mechanisms now that I have taken a compliant mechanisms class.