[ Don Teach and John Rhodes wrote to Julie about machining options
 [ using CNC (computer numerical control) machines.  -- Robbie

> Don Teach mentions CNC lathes as a means of duplicating some parts.
> Though it would likely not be practical for cast iron frames, CNC
> _milling_ would be an excellent choice for machining frames from
> brass or aluminum.

CNC is not a panacea.  I did not mention in the long message regarding
the castings that much of this project as possible is done with CNC.
This is what I called out in the ballpark cost of getting the parts
finished.

CNC is programming is what I do.  It is time consuming and has to be
debugged.  The main problem is that a job must be written for a given
tool.  There is no universal CADD/CAM, as Robbie and myself have found
trying to exchange engineering drawings.  Each shop has a "specialist"
who baby-sits the machines.

Has anyone priced a solid modeling program?  They run about the same
as having the patterns done the "old fashioned" way.

> At Hewlett-Packard, our model shop made extensive use of 3 to 5-axis
> 3D CNC mills, as well as wire EDM for producing short-run prototypes
> and test beds for printer development.  A commercial shop would
> probably charge $75/hour for run time on a 3D CNC mill.  The starting
> point for such machining is a suitable 3D-solids (computer) model of
> the component.  A finished part results, including holes sized to
> .001 inch.

I have no trouble making the computer models.  The problem is that any
shop I give them to will want their engineer to "fix" and "improve" it.
Because I am an "idiot" who does not "understand".

I was doing just this when I was told to go to the founder and pattern
maker.  Even the pattern maker said he could make the patterns in less
time than I could program and debug the *.dxf file.

Sure, when I was working for Apple Computers we had a Cray computer for
calculating the flow for injection molding the cases.  But this is a
hobby; $75 an hour is what the pattern maker charges for a weeks worth
of work.

> 3D CNC mill work could also be used to produce patterns for castings.
> It is trivial in most 3D design packages to stretch a (pattern) part
> to compensate for molding shrinkage.

My "Vellum" program  ($2500) can do this.

> Note that wire EDM is an alternative to hobbing for producing
> (straight-cut) spur gears.

I built one four years ago (sinker, not wire), and I have the
programming instructions for a friend's wire EDM machine.  It takes a
great amount of time to figure out the wire path and how to hold the
work.  If one is not careful it is easy to program a Moebius strip or
Klein bottle.  The machine does not know that these are impossible
shapes (unless made in sections).

"Punch a few buttons and let the machine do the work."  This is the
quote of the machinist who sold me my CNC for next to nothing.  It will
nicely mill something that is 3 x 8 x 12 inches.  By the time one gets
the clamps in place the work area is 2.5 x 2.5 x 5 inches.  The long
direction is how far the mill head can drop.  A 5-inch hole takes a
10-inch tool.

Whatever the outcome, I'll be using my CNC to finish where appropriate
the parts I have for my "Old Style Wurlitzer Long Roll Tracker frame."

I will have the programs to clean and finish the castings Mike Kitner
started.  So far it is much easier to chuck the parts into a friends
Sears Atlas and finish them by hand.

If CNC were so practical then why does it cost so much?  Have you
considered the setup costs?  There are administrative and maintenance
costs that companies like HP and Apple do not even see.

Julie Porter