Ball-bar Re: Mill retro-fit info available...

Jon,

How about using an lvdt (or is it ldvt?) as the "length" component.
Or stacked strain gauges? I didn't realise there was a rotary encoder
involved for rotation. I thought this was "pulled" from the cnc or
time based (samples/unit_time.) Wouldn't the length itself, plotted
against time, define a motion path? (assuming we know what the motion
is "supposed" to be)

Ballendo

--- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
<snip>The approved technique is a ball-bar tester. I think I could
> make one of these, although it would be quite a complex and precise
> gadget to build. You make the CNC machine orbit in a circular
move, and
> while one end causes a shaft encoder to deliver rotation around the
circle
> to the device reading the move, a linear motion detector on the bar
reads
> deviation from the length of the bar. You then plot this (with the
length
> expanded) on a theta-radius plot, and you can see axis jitter,
sluggish
> axis performance, backlash, non-orthogonality, etc.
<snip>