Filament Drive

Today I worked some on the filament drive system.  I chose to do things a little differently than what I have seen others do.  I strongly dislike live shafts in mechanisms, and I use dead shafts whenever I can get away with it.  I also wanted some reduction, but didn't like the backlash present in the lower cost options for gearing.  Timing belts and pulleys are relatively cheap, and can be very compact.  These are MXL pitched pulleys.
I use a .25" shoulder bolt for an axle.  They come reasonably precise, and with a hardened, ground shoulder perfect for running the needle roller bearings on.  The drive roller itself is a piece of 360 brass .625" in diameter.  The center was drilled and reamed to the bearings OD, .4375", for a nice press fit.  I then bored the pulley out to fit this assembly.  This direct coupling of drive roller to reduction avoids having to fasten each one to a live shaft.

Here's a mock up of the whole setup, minus the shaft that the idler rides on.  The idler is a rubber idler roller, with a bronze bearing in the center.  I still have to make the frame for it, I'm waiting on some hardware to come in from perennial favorite McMaster.