Re: [CAD_CAM_EDM_DRO]A question of size managenent.

I'll just be quick. This is the start of one of the first arc moves (after a long line)

Unit MM
Rapid X 0.000 Y 79.525 Z 60.000 ToolComp Off Tool# 2
Feed 800.0
Line X 0.000 Y 79.525 Z 35.625
Line Y 78.0500 Z 35.8970
Line X 245.3910 Y 78.0630 Z 35.8860
Line X 246.9320 Y 78.0410 Z 35.8920
Line X 248.4550 Y 77.9960
Line X 249.9760 Y 77.9220
Line X 251.4950 Y 77.8180
Line X 253.0130 Y 77.6850
Line X 254.5270 Y 77.5220
Line X 256.0380 Y 77.3290
Line X 257.5440 Y 77.1070
Line X 259.0460 Y 76.8560
Line X 260.5430 Y 76.5760
Line X 262.0350 Y 76.2660
Line X 263.5190 Y 75.9270
Line X 264.9970 Y 75.5590
Line X 266.4680 Y 75.1630

This is the first pass and is on about about a 153.75 mm radius (hard to be exact because the tool path is a quarter inch above the
part)

Sorry got to cut short..

Bill



Marcus & Eva wrote:

> Hi Bill:
> I think I am misunderstanding something here.
> As far as I know, LINES versus ARCS are completely different entities in a
> CAD system.
> They are handled differently mathematically.
> There is no such thing as "line segments of arcs" (correct me, anyone , if
> I'm wrong here!)
> When the CAM portion of a CAD-CAM system recognizes an entity that is an
> arc, it will apply a G02 or G03 move to it, even if it is a bunch of little
> tiny arcs strung together.
> Arcs, by definition , must lie completely on a single plane.
> Splines and Surfaces cannot be handled by most controllers directly.
> So, the CAM system throws out a series of short lines that approximate the
> surface or spline.
> You can tell the CAM system how far the lines are allowed to deviate from
> the contour of the surface or spline.
> Any curved contour that does not completely lie on a single plane is a
> spline, even if it looks circular when viewed from "above".
> I'm not sure, without a picture, what you were trying to cut.
> If you got your toolpath from a surface though, it will be composed of short
> linear moves EVEN IF THE SURFACE WAS ORIGINALLY CONSTRUCTED FROM A PAIR OF
> ARCS!!
> The CAM system does not know or care (I'm anthropomorphizing here) what the
> original constructor was, and does not recognize the sequential line
> segments as approximating an ARC.
> Instead, it recognizes them as approximating a SURFACE.
> It no longer cares about the start or end point of the arc, or its origin.
> The only way I know, to get back to the arcs that you wanted, is to
> reconstruct them on the surface, and you need to construct an arc for every
> level that you want the tool to follow.
> You then create your toolpaths to follow the ARCS rather than the SURFACE.
>
> I agree, it would be nice if a means existed to take line segments that
> approximate an essentially circular surface or spline and convert them into
> arcs; Mastercam can do this, but only to a very limited extent.
> The problem is recognizing when the deviation from circularity represents
> the approximation, and when it represents the beginning of a direction
> change in the spline or surface.
> The CAM system will never know for sure just where the start and end points
> of the arc really are, and exactly what the radius is. This is true even if
> you constructed the surface or spline from arcs originally.
>
> So, to get back to the nub of the issue:
> If you want G02 and G03 (arc commands) output, you MUST be following arcs
> when you set up your toolpaths.
> If you follow surfaces or splines, even when they were made from arcs... you
> will always get G01 (linear) moves.
>
> Cheers
>
> Marcus
> -----Original Message-----
> From: BillDarby <ddarby@...>
> To: CAD_CAM_EDM_DRO@egroups.com <CAD_CAM_EDM_DRO@egroups.com>
> Date: Wednesday, November 29, 2000 9:58 PM
> Subject: Re: [CAD_CAM_EDM_DRO]A question of size managenent.
>
> >Hi Again Marcus
> >
> >Well,,,, I suspect that every owner of these Cad programs is faced with
> this size problem and if their CNC will not handle an arc
> >command they are simple forced to live with it. However my controller is
> conversational and does utilize the arc command and
> >would benefit from having a short conversion program that would convert
> line segments of arcs into arc commands. I don't imagine I
> >am alone with this problem. I would expect that thousands of guys are
> living with it as we speak.
> >
> >Bill Darby
> >
> >
>
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