Re: Threaded Rod WORKS!

Chris,
What if the person has a 6" X 6" cutting area and the
threaded rod is off by .005 or more over that distance. The
machine will still be a learning tool and it can turn out great
parts for RC cars and planes. Have you ever measured a handmade
part. Looks great-works great but don't mic it out. I have
been following lots of peoples progress. I see them selling
their stuff off on Ebay after getting frustrated. To learn CNC you
need a machine. After getting your feet wet you can then buy
some expensive leadscrews. My guess is that at that point you
will build a second machine using what you learned or buy one!

Bob

--- In CAD_CAM_EDM_DRO@y..., ccs@m... wrote:
>
> > Select only a good piece of threaded rod. Leave the rusted
ones
> > at the store. If you use threaded rod on your machine, don't be
shy
> > tell them how it works! Accuracy, everybody talks about accuracy.
What
> > is everybody using their machine for. I never see any project
being
> > descussed here anymore.
>
> Bob,
>
> I can see that threaded rod may be a good way to start out in some
> situations. In fact I probably wish I had prototyped my bearing
> mounts by machining the ends of allthread, rather than the ballscrew
> (which wasn't that expensive by itself, but can't easily be replaced
> as the outfit had a $200 minimum order)
>
> And many hobby machines may not need much accuracy, however there is
> one aspect that I will call 'incremental precision' which they do
> need. The primary reason I am building cnc machines is to make
> calculated curves for musical instrument tooling. I did some of
this
> manually with a crude digital readout, not realizing that the
readout
> had a very small (maybe .002") amount of cyclic error due to the
> unwise way I connected the encoder to the screw. This showed up in
my
> finished part as a very noticeable ripple superimposed on the
contour
> - it even transfered from the bell mandrel I had machined through
into
> the first few trumpet bells, until I carefully filed it out.
>
> So, absolute accuracy may not be important for many applications,
but
> cyclic error can really ruin your day if you are machining curves or
> even diagonal paths. Of course, cyclic error over a short distance
> may be as likely to result from poor screw mounting as from errors
in
> the screw itself.
>
> Chris Stratton
>
>
> -------------------------------------------------
> Christopher C. Stratton
> Engineer, Instrument Maker, and Horn Player
> ccs@m... 617 628 1062
> http://web.mit.edu/~stratton/www/brassbuild.html