I modified lwilder's Parametric Pulley Assembly (http://www.thingiverse.com/thing:571542) scad file to allow you to change the radius of the pulley, added a guide to help keep the rope in place, and modified the dimensions of the mount. What I use it for is supporting the gantry with a counterweight. Just attach the pulley to the top with double sided tape and string it up. The current size of the pulley is sufficient for allowing a rope to go over the top without rubbing against anything, but if the weight you are using is large you may want to customize this to make it larger. For a counterweight I started with a small pill bottle filled with coins, and then added large steel washers to the string.When I was printing the mount my X-axis got nudged out of alignment so I killed the print early. If you use the skate bearing pulley you can cut down on the amount of plastic this uses as well as print time.You can specify your bolt size in the SCAD file. If you use the STL file then use a M8 bolt and nut. For the skate bearing pulley you'll need a 608 skate bearing.Tape the bottom of the pulley mount to the top of the cross support to the right of the bolt on the right side. With the gantry all the way up tie a string to the top wooden support of the gantry. Run the string over the top of the pulley and tie the other end to your counterweight so that it just barely hangs in the air. For the counterweight you'll need something small and heavy. I initially used a pill bottle filled with coins, but then ended up adding a bunch of steel washers in addition.The ideal weight of the counterweight is probably the amount of weight necessary to support the gantry at level with the extruder in dead center of the build plate. Remember that the X axis extends past the build plate and attempting to support the weight of the extruder in this area is likely unnecessary. For me gantry sag wasn't that big of a problem to begin with so using less weight seems to be working fine (although I reserve the right to change my mind later!)