Makerbot Replicator 2X Extruder Drive Block Upgrade

UPDATE Jan 30, 2014

New V2 files uploaded. A few minor changes were made that should create stronger parts that require less post-finishing. Also, a remix has been created based on user comments to create a version that uses an M4 flat head screw to mount the bearing. If you would prefer to use a screw, you can find that version here:
http://www.thingiverse.com/thing:237554

Intro:

This is hopefully the last extruder drive block upgrade you'll ever need for your Makerbot Replicator 2X.

It is loosely based on the function of the official Replicator 2 (not 2X) upgrade:
http://www.thingiverse.com/thing:53125
and on the aesthetics of the whpthomas upgrade:
http://www.thingiverse.com/thing:79807

Advantages over other drive block upgrades:

1. Includes a fully surrounded lower filament guide hole between the drive gear and the entry to the hot end. This is ABSOLUTELY ESSENTIAL when printing with flexible filaments to prevent bending and kinking of the filament. Almost all of the other 2X upgrades are lacking this critical element.

2. Has a deeper filament guide tube hole than many others, which prevents the guide tube from slipping out while printing.

3. Requires no extra hardware for mounting the bearing. The mounting pin is included in the design, as it is in the Replicator 2 upgrade.

See the Instructions section for required hardware, notes, and details for a successful print and assembly.