Re: [CAD_CAM_EDM_DRO] Just How Accurate Is CNC?

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?
>
>

There are a whole raft of things that cause loss of accuracy. You can't
lump them all together. There are things like axis straightness and
orthogonality, which cause increasing errors as you move farther.
There are things like screw pitch error and variation, which can
be compensated for. There are things like backlash that are quite
repeatable, but can cause poor finish, out-of-round circles, etc.
.001" on a 1/4" part is pretty poor. .001" on a 12" part is getting
into the stratosphere, when you include stress release in the
part, temperature variation, etc. To hold .001" over 12", you need to
keep the part in a temperature controlled room. So, it depends
on what you are doing, and the size of the parts.

I have a Bridgeport with high accuracy screws and .001" backlash,
and it is more than accurate enough for me to make some fairly
exotic parts at times.

Jon