Re: How to go from 2.5 D to real 3 D ??

Rab & Fred,

I agree the end result is what counts. Getting to that end result
can sometimes be tremendousely easier with a machine that will do
circular interpolation in three axis.

Yes, it can be done in CAM with very large unmanageable files that
have to be drip-fed to most current mainline type controllers having
limited memory.

Going back to my earlier simple example. Machine a hemi-spherical
pocket, say, 4" diameter by 2" deep. For convience use a 1" diameter
ball end mill. You guys program it with short line segments, I'll
program it using arcs.

To use the short segments you'll have to fire up your CAM program
draw the part and process the Gcode. Load it into the controller,
most likely drip-feed it. How many lines of code do you think it'll
take, a couple thousand, maybe? What if it turns out the segment
length is unacceptible and leaves too faceted an appearance on the
part? We all know from experience that can happen, sometimes you
can't make a judgement on segment length until you run a trial. Back
to the computer, try again. Time is money.....

I can program that part standing in front of the machine. My program
would have something like ten lines of code including the usual
setup/housekeeping/tool business. Basically my program would cut the
arc, return the tool to starting position, rotate and repeat until
the complete 360 degree pocket is cut. What if I don't like the
surface appearance? Change one repeat parameter and I'm off and
running.

Granted, this is a simple example, but it's real world. I've made
dozen$ and dozen$ of quick and dirty molds this way. Mostly those
weren't hemi-spherical, they did have an outer profile made up of
arcs.

My point here is, it's very worthwhile paying a few bucks more and
getting a controller that has the 3 axis circular interpolation
capability. It may not give you the ability to do things you
couldn't do otherwise, it might let you do them easier and in less
time, though.

Along these same lines I suggest always paying more and going for a
more full featured control, get as many features in the control as
you can. Whatever you can do to lessen your dependence on CAM, the
further ahead time and money-wise you'll be.

thanks,

Doug

--- In CAD_CAM_EDM_DRO@y..., rab@r... wrote:

(snip)


> I quite agree Fred, the end result is what counts, I've used a
Roland
> engraver for complex 3D modelling tasks, although it was advertised
> as being only 2.5D.
>
> Given that arcs are ultimately broken down into small linear
> movements and given the increasing power and capacity of todays
> computers and controllers, does anyone see the day that arcs offer
> little or no real benefit ? Or do they offer another benefit that I
> don't understand ?
>

(snip)