Re: calibrating cnc systems

Hi,

Some thoughts about this step size calibration:

Many control software packages only offer "whole" number step sizes.
In many cases this will be fine, but for those machines using the type
of drive(s) Jon mentions below, it will often prove inadequate to have
only the choice of 999,1000,1001 steps (for example). The "true" steps
may be 1000.5467 (or some other non-integer number).

That error can/will build up and create problems if not taken into
account by either the calibration(by deciding WHERE you will allow the
error to exist) or the software.

Secondly, along these same lines, sometimes precision can be increased
by using something other than the "obvious" step size. In other words,
even when the .200 lead drive screw is driven by a full step drive
(200 SPR) for a "calculated" 1000 steps per inch (SPI), you may find
that things are better at 999, or 1001, or...

Also, you can sometimes increase accuracy for a given part (using some
small portion of the overall travel) by RE-calibrating for the area
that the part will actually occupy in the machine. That is to say, if
there IS an error which has been "spread" across the ENTIRE travel,
you can reduce the inaccuracies by "spreading the error" over the
smaller travel needed for the specific part.

Hope this helps.

Ballendo

--- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
<snip>
> (On non-leadscrew machines, the diameter of the drum pulling
> tapes, cables or belts, or the number of the teeth on a pinion
> gear are the factor in the calculation instead of leadscrew
> pitch.)
>
> Jon