Re: Poor CNC Machine Finish

Bryant,
Try machining a 'right angle triangle' shape, do you get the same
surface finish on all three sides? If you do then it is more likely
to be a machining rather than a machine problem, look at speeds feeds
and workholding. If its a knee type machine, ensure the knee is
locked when machining.
If you get a good finish on the parallel edges, but not on the
(interpolated) diagonal edge, then it is most likely a machine fault.
Check for loose drive belts, lube pump failure, loose/overtight gibs.
Examine the parallel machined edges carefully, you can sometimes see
if an axis is oscillating (hunting), if you suspect this, try
swopping the X & Y motors over, does the problem move? If yes, then
you most likely have a motor/tacho or servo problem. If the problem
doesn't move, then you are probably looking at a mechanical problem.

Some machine manufacturers have a 'euclid test piece' that they
machine, it is a useful diagnostic shape, which can tell you a lot
about the condition of a machine. Perhaps someone on this list has an
example?

HTH

Dave Pearson

--- In CAD_CAM_EDM_DRO@y..., "bryantmorgan" <bryantmorgan@y...> wrote:
> I don't know if this is the correct forum but thought i would give
it
> a shot. I am new to the forum and am the owner of a republic lagun
> machining center that I purchased at an Auction it is a 96 with
about
> 8k hours on it. I set the machine up myself leveled it using a
> starret 12 inch precision level, put an indicator in spindle and
ran
> across table to check for levelness and adjusted the lag on the
axis
> motors all by the manual. After doing all this i still get a poor
> surface finish which looks like chatter and i know for a fact the
> machine is capable of better because i have a few machined parts
that
> where with the machine when i got it. With all this in mind i have
> determined it must have to do with my setup of the machine and am
> wondering what else i could try and or what I am neglecting to do.
>
> thanks alot,
>
> bryant