Inspired by the cantilevered Z stages of the Thing-O-Matic and Ultimaker I designed this upgrade for the Makerbot Cupcake CNC. It should be possible to get 140mm of z travel with a standard x/y stage.
I've designed it to fit a standard reprap extruder. There's room for any extruder, the mounting holes for the makerbot extruder are just a bit too wide.
In addition to a bunch of m3 nuts and bolts you will need a few bits of new hardware: 2 x 268mm lengths of 8mm smooth rod, 3 x LM8UU linear bearings, and an M8 Coupler. You will also need to print one of http://www.thingiverse.com/thing:9622 to couple your z motor to the z rod. For the z rod I just hacked down one of my z rods to 185mm.
You also need a popsicle stick, an m3 x 30 bolt (fully threaded) and a printed z-endstop-adjuster part.
If there is sufficient interest I've been pondering making an upgrade kit available.
Remove the z pulleys and belt from your makerbot. Remove the bolts holding the top panel in place. You do not need to completely disassemble your bot to get the top panel off. Just remove and/or loosen the bolts on the side until you can bend back the sides far enough to slide the top off. Now you can pull out your z rods.
Transfer the z-motor to the new top panel and put the panel in place on your bot. Bolt it into place.
Now's a good time to remove the bearing brackets from the middle and old top panels of the bot. The two on the right side will get replaced with two new ones. The upper has an 8mm hole in it and goes inside the bot, the lower is solid and goes in place of the old bracket.
Cut the ends off a popsicle stick. Â I can't tell you exactly how long it should be as it is dependent on your extruder. Â Drill a 3mm hole offset to one side (use the z-endstop-adjuster as a guide) Install two m3 nuts in the adjuster and bolt the popsicle stick on as shown in the cut-away of the z-stage. Run the m3 x 300m bolt through the extra hole in the top panel of the z-stage and add a washer and nut. Spin the nut til the bolt turns smoothly without slop. Secure it with either threadlock or another m3 nut. Thread the adjuster/popsicle stick assembly onto it.
Assemble the z stage using the bolts you took from the old z brackets. You'll need two m3 x 12mm bolts for the holes nearest the extruder. The rest are all m3 x 16mm. Leave all of the bolts loose until you have it assembled and then tighten them down. Make sure to drop the LM8UU's in place before closing things up. Tighten up all the bolts.
Thread the M8 coupler a little way onto the M8 threaded rod and run it through the z stage. Place the stage in it's approximate location and install the rearward smooth rod. Now install the forward smooth rod and loosely install the new z rod clamps.
Install your extruder and see if you got the endstop flag the right length by seeing if you can adjust it to zero. If not, pull your z-rods and remove the z-stage to adjust. Once you have that done tighten down the z-rod clamps.
The z-rod coupler can now be installed. You may find it helpful to slide the z-stage up off the m8 coupler so that you have more room to move things around.
Hook up your motor and give things a try. the Z motor will be inverted from standard, but otherwise all of your settings should work as normal.