This is an derivation of the "Spring-loaded Replicator 2 Drive Block" by MakerBot to make it compatible with the Replicator 1 (single and dual extruder). Only minor changes has been made, as outlined in the list below. Based on the work of Thingiverse users MakerBot, whpthomas, emmett and whosawhatsis.

It is the same spring-loaded arm used to squeeze the filament between the drive gear and a bearing with a constant amount of pressure. Minimizing the chance of skips due to variance in filament thickness. Both normal and mirrored models are available to fit either side of the carriage. The models are offered as STL and STEP files.

A simple spring height adjustment part is included to easily increase the spring rate if needed. This piece fits over the stub on the base part.

Changes:

• Cut upper-left corner wall from the lever to fit the Replicator 1 extruder mount carriage
• Changed the lever and base screw hole to accept a regular countersunk M3 hex screw (easy to find find)
• Cut a slight piece off the cover to avoid resting on the drive gear
• Decrease the bearing bolt stub diameter to fit the readily available 623ZZ bearing (3 mm vs. 4 mm ID)

Instructions: Follow the excellent instructions by MakerBot: http://www.thingiverse.com/thing:53125

Parts:

• 1x M3 x 16mm Flat Head Cap Countersunk Hex Screw
• 1x M3 x 8mm Flat Head Cap Countersunk Hex Screw
• 1x Ball Bearing, 3mm ID x 10mm OD x 4mm Width, typ. 623ZZ bearing
• 1x Compression Spring, 0.360"OD 0.276"ID 0.630"-0.900"L (9mm OD x 7mm ID x 16-22mm L), 32lbs/in spring rate

Suppliers: I used the following webshops to get the needed parts: http://www.a2stainless.co.uk (Socket Countersunk Screw DIN 7991 - M3 16mm, 8mm) http://myworld.ebay.com/bearingoptions (Bearings 6000 Series - 623ZZ) http://myworld.ebay.com/switchedkwb/ (2x Compression / Pressure Springs - 31 x 10 x 1mm)

Notes: The hex screws has to protrude 3 mm behind the base to properly secure the base and lever, any longer and the screw will hit the stepper motor mounting bolts. Cut the screws down to length if needed or loosen the stepper motor bolts.

After mounting the lever and base to the stepper motor, make sure to leave enough slack/space to allow the lever to move freely up and down. Add some medium thread-lock if needed.

The compression spring should have enough force to squeeze the filament fairly well. If rated on a scale from 1 to 10, where 1 is super soft and 10 massively hard, the spring should be in the 6-7 range.