Re: [CAD_CAM_EDM_DRO] Just How Accurate Is CNC?

Hi John;

While I hate to bail out with a catch phrase the answer to your question
is that it depends. There is also a huge difference between
postiional accuracy and repeatability.

For many applications REPEATABILITY should be far less that 0.001".
In fact a CNC machine that can not repeat is virutally useless in my
opinion.

Positional Accuracy is a wholly different ball game. Here you have
far more physical issues affecting the concept. In the end it really
does depend, for some applications 0.001" positional accuracy could be
terrible. For some applications such tolerances are for all practical
measures impossible, or at least not within the budget of most machine
shops.

In the past I've done a bit of work within the optics industry. For
practical matter the machine that repeats well can be a very good
performer, the issues with absolute position can be addressed outside
the machine. That is a bit of work with some regressions and metrology
on the production stream can provide you with information needed to
tweak a machine so that the parts are coming out with the right
precision. In other words you take the precision requirement out of
the machine and rely on its repeatability. Do realize that this is a
continuous process. This works good in a production environment but in
reality would be useless for one off production.

To obtain acceptional accuracies for one off machining requires some
pretty expensive hardware. It is not impossible but the number of
factors that come into play can be fairly huge. Even the act of
machining the material will change its size.

Dave


softtechinit wrote:

>
>What sort of repeatability and positioning accuracy should one
>expect from a CNC mill? Would you call 0.001" typical or
>unacceptably sloppy?
>
>Regards to all.
>John
>
>
>