I quess you have what you have and until you upgrade components BC can help improve accuracy.
The best approach is finding just what each component adds to the backlash.
One needs to isolate the component, and test each, adding the numbers should approx the total backlash.
Usual mechanical items that cause some degree of backlash:
- Motor coupling - anything other than hard coupled will add to the BC, it's just a matter of how much
torque is applied to it.
- Thrust bearings - Can approach zero play, but will never be "zero"
- Screw - lost motion can be anywhere, vary, and linearity different along the screw and may not be
the same in the oposite direction
- Screw Nut - it is what it is
- Older Machine - One could fix / replace all of the above but conditon of the different machine surfaces
can affect accuracy.
Just some comments:
I hard couple the motors to the screw shaft. Requires good alignment, but, have found that over time the
bellows and rubber type can cause problems in repeatability of movement.
Thrust bearings are something that a lot of folks just don't pay attention to. They need to be preloaded
properly such that they minimize play with the least force / torque required for movement. I measure
the installation to confirm.
I have never used the screw mapping in Mach so don't know how well it works for a worn screw.
To profile a screw can be a PITA, rather easy on my end because I have the equipment to do it
opticaly and very accurately in rather short order. What would you do if you found that linear tolerance
spec is not over the length and is all in a small section of the length? OR Accuracy is different in the
travel directions?
For "hobby" use adjustable ball screw nuts are an option such that it is easy to minimise any play.
You pay for good quality screws and nuts. The accuracy of your machine is only as good as the components
used. For a lathe I recommend the best quality screw one can rationalize buying for the X axis ( the smaller
the more expensive they seem to be ).
Practicaly speaking on a retrofit, one can replace the axis components and find that the a machine surface
causes inaccuracies or even installation problems.
Just some thoughts,
RICH