Ed, pretty simple, but first let me say that the tapered bearings are usually bought in a matched set. Those bearings from McMaster are not matched sets, though they aren't too bad for the price. When you rip it apart you will notice that the factory bearings most likely weren't matched sets, since they (or at least ours did in the 2axis I've done so far) were shimmed.
Basically a matched set when placed back to back will have no backlash. These bearing need up to a three thou shim in the center to eliminate the backlash. I think this is why Fadal trys to sell you a whole carrier, they buy cheap bearings then pay some guy $6 dollars an hour to shim them, then stiff you with a high bill for crap.
I know for sure there are more surefire ways than what I'm going to explain, but it seems to work for me pretty well. First check what your backlash settings currently are. You can set it back to zero or just add what the settings are to what your getting. Slap a test indicator in the spindle and come down on some surface, 1-2-3 block, gage block, ground angle plate, something nice and flat. Come down on it slow in .0001 increments, until you hit zero on the indicator(or pick a random number if there is "zero" fanatic standing over your shoulder), then crank it back up and keep track of how many .0001 bumps you give it until the needle starts moving again. I know its not the Fadal way of doing it, but it will get you in the ballpark. Try it at a couple of different heights just to see how your ball screw is doing.
I would say if your over .0008, then you need to add a shim to tighten up the bearings a bit, or you have a crappy ballscrew, your current backlash settings should let you know were you are at.
Just be thankful your working on the Z, thats the easy one, the X doesn't look too bad, but the Y is a *****.  |