CNC Router Parts no longer offers the original 5-Start ACME nut. They do however, sell a replacement nut. Get the new nut here.
The problem is that this new nut us a little larger than the original and if installed it will come in contact with the Y-beam.
To solve this problem you must add a 1/8 shim when assembling the Y-carriages.
Chapter 5, Step 7
Here you are asked to attach the supports to the main frame components. You still do this but you need to place a 1/8" shim between the supports and the frame components. The shim is made from piece of 1" x 2" x 1/8" steel.
Use the supports as a guide to drill the two holes needed. You will need four shims for each carriage. That's eight shims total.
You can also make the shims out of aluminum.
Y Motor Mount Changes
Chapter 9, Y Motor Mount Section
Since you have effectively moved the Y-carriage ACME nut over 1/8" towards the outside of each side of the CNC, You need to do the same with the motor mounting holes, bearing, and clearance holes.
The following contains the new Y Motor Mount drawing files.
While the X and Z axis don't require shims, you should make the following changes to the X and Z motor Mounts.
For more information on the KRMx01 build, check out the following forum at CNCZone: