Re: Just How Accurate Is CNC?

<snip>

>As I said earlier, he is estimating only 0.001 on his machine.
>It appears to me that his modifications were not too successful.

Hello,

To me it appears that he is honest<G>

Have a look at the thermal expansion values for steel, aluminum and
cast iron. Then put a threaded rod in a drill chuck and run a nut up
and down it a few times. Note the heat increase, and apply the
numbers...

The typical jobshop spec on parts is +/- .005 for feature to feature.
+/- .001 for typical diameters.

As others have posted, repeatability is far more likely to be in the
under .001" category. But those who claim better than .001" using
machines without thermal management are fooling themselves as well as
you...

Read Aaron Moss's discoveries about limit switches on his industrial
hobbies website.

.0001 inch is a REALLY small amount, and I can change even a small
part by several times that amount by holding it in my hand!

As Jon E says, on a large part, you're crazy if you think you're
getting better than .001.

As Marcus stated, even a commercial machinning center costing many
tens of thousands of dollars still is really only a .001" machine,
for most items...

BTW, Rolled ballscrews are only accurate to within .003". Unless
you've got leadscrew compensation--which in the hobbyist market only
EMC has-- then you're going to get LESS than this, not more...

It literally cracks me up to see what some folks think their machine
is capable of...

Fortunately for all of us, real world parts are most often FAR more
dependent upon RELATIVE accuracy, than absolute accuracy.

ALSO most real world parts have no testosterone to deal with<G>

So getting back to the top question; I think you've found someone who
honestly evaluates his product.

Ballendo

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "softtechinit"
<JFlanigan@T...> wrote:

>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "John Heritage"
> <john.heritage@v...> wrote:
>
> > 0.001" is around 0.0254mm.
> >
> > The newest commercial machine, driven by linear motors, can
> > achieve a tolerance of 0.001mm.
>
>
> Thank you John for taking time to respond.
>
> The mill in question is an Nantong factory built CNC workbench mill
> (about 800 lbs. with electrical control box). The mill is

virtually

> new, however the owner has replaced the stepper motors and ball
> screws and populated the control box (which was empty) with
> components that are generally available (and that he sells).
> Commercially distributed versions of similar mills from Nantong
> reputedly achieve positioning and repeatability in the neighborhood
> of 0.0001". As I said earlier, he is estimating only 0.001 on his
> machine.
>
> It appears to me that his modifications were not too successful.
>
> Any thoughts or guidance?
>
>
> Regards to all,
> Another John