Re: [CAD_CAM_EDM_DRO] Re: Threaded Rod WORKS!

I think that even the crudest of machines can be made to produce some
fairly accurate work. Perhaps not first crack but if you see that your
part turned out .005" to long then surely you would adjust the
dimensions to arrive at what you want for subsequent parts. (and keep on
adjusting to maintain the part spec IE as the cutter wears)

Bill D

cncdxf wrote:

>
> 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
>
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