After a couple month hiatus, I’ve finally returned to working on my mill.  About two months ago I tested the backlash and was sorely disappointed.  Both X and Y axes were in relatively poor shape.  I got back in touch with the company that I ordered the original parts from and ordered extra ball nuts for the X and Z axes and oversized balls for the Y axis.  Along with the balls and nuts, I also ordered HeliCal couplers (zero backlash) and new, higher quality thrust bearings.

So, I got started the other night.  Yet again, I found myself carefully repacking ball bearings one at a time.  There were actually extra balls in the kit, which is good, since I have a demonstrated ability at losing balls.  When I started packing the balls I actually said to myself “I should do this sitting at a table, with my magnetic bowl.”  Of course, that isn’t what I did.  And I lost a ball as a result.

Having gotten the Y axis repacked with oversized balls, I was pleased to notice a significant reduction in “slop” when I moved the nut around on the screw.  Tonight I took on the X axis double ball nuts.  When I unpacked the parts I noticed a set screw and wondered what it was for.  There turned out to be two set screws, one hiding the other.  Too bad it took so long to figure out!

The reason for the set screw became clear once I threaded the second nut onto the screw.  There are three sets of threads that need to be synchronized: the ball screw, the left size of the nut adapter, and the right side of the nut adapter.  The set screw helps fine tune the threads together, which makes it possible to set the tension to whatever you please.  With a little work, I was able to get the double nuts set almost perfectly.  They don’t roll quite as easily, but there is absolutely no noticeable movement when moving the screw.