Re: [CAD_CAM_EDM_DRO] EMC and DROs

> Just my opinion, but if you've got the cross slide driven with a stepper
> and ball screw, why not do the carriage as well? Adding a stepper to it
> should be easier then adding it to the cross slide! THEN, you can
> design your curve or template, generate the Gcode and cut the part.
> Much easier then to try cutting EMC down to one axis, and trying to be
> the other axis yourself! ;>)

In an ideal world you would be correct, however there is the
substantial cost of the motor, drive, and screw able to move the
heavier carriage. Also the time to machine the mounting brackets, and
fact that the carriage may not move smoothly if driven from behind the
bed, where an add-on screw would have to go. All of this when I need
to produce one precisely curved part now, and only desire to make more
at some uncertain point in the future.

I really do want 2-axis CNC eventually, but I've either got to go
through the whole ball screw expense and difficulty again (the cross
slide only took me 2 years to get around to finishing, and it's still
not concentric), or modify the leadscrew so I can drive it - and then
live with its backlash and any cyclic error I introduce in the
pulley mounting.

In comparison, using the power feed and reacting to the position of
the carriage as read with a linear encoder that may not be accurate,
but at least does not suffer from cyclic error, which as far more
serious for me as it results in a wavy surface. May not be the most
efficient machine, but it may be the simplest route to making my
current part.

Or, anybody care to quote on turning 35 lbs of cast iron chips off a
12.5" spinning mandrel? I've got the do-it-yourself attitude pretty
deep, but at then end of the day my real goal is to build musical
instruments, not machine tools.

Chris Stratton

-------------------------------------------------
Christopher C. Stratton
Engineer, Instrument Maker, and Horn Player
ccs@... 617 628 1062
http://web.mit.edu/~stratton/www/brassbuild.html