Re: Newbie: G Code Programming Question

Hi George,

I believe Dolphin draws the offsets needed for toolpaths on command!

The origin you want to be a convenient point on the part (stock). a
rectangular part, or in fact any part where edges are readily available,
it is usually referenced from a pair of edges.

So I pick up the left edge, and the front edge with my edge finder
(LL). If the part has no convenient edges (circular part), then the
center of the circle can be used. You can find the center of a hole (or
a rod) with an edge finder as well.

There are no hard and fast rules! Use whatever edges are convenient!
It's a good idea, however, to pick edges or reference points that won't
be machined off!

OK, let's suppose we have a rectangular piece of stock ( a 1/4" plate)
that we want to finish to size. We'll use the existing LL corner the
origin. First align the left edge square to the X axis. We'll select a
point, say .020", in from the LL corner (in from Y as well), to allow us
to take a finishing cut on the left and front edges. The CAD program
will run the cutter along the tool path, which is offset "outside" the
intended part. The "inside edge" of the cutter thus follows the edge we
want to cut (along X = 0 and Y = 0, then along X = 1 and Y = 1).

The CAD/CAM program does this for us very nicely! If we write the code
by hand, we would have to constantly add or subtract 1/2 the tool
diameter, to get it to follow the tool path. Lay out the square on the
CAD program, LL at 0,0 (origin). first draw a LARGER box outside the
desired square, by 1/2 the tool diameter. Then as you'll notice in the
white paper, we "round" the corners. This becomes our tool path.
Visualize moving a circle around this path. See how it swings around
the corners. The "inside" egde of this circle (cutter) will follow the
desired square.

See my "CNC for hobbyists" paper in the list's files section.


http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/CNC%20for%20Hobbyists.pdf

Under the Drawing heading, there is an example of cutting a square.

To summarize, draw the part outline, draw a tool path, then "program"
the tool path!

Have fun!

HTH

Alan KM6VV
Amateur CNC Machinist


gglines1 wrote:

>
> Alan,
>
> Thanks, I do use the lower left corner because that matches how I
> usually measure locations on parts from drawings.
>
> Do you use the origin point at the center of the spindle or the edge
> of the cutter when writing G-code?
>
> I purchased Dolphin Partmaster/CAD but haven't looked at it much so
> I don't know if it has cutter compensation. I'm trying to learn to
> program directly in G-code first as a base, then I thought I would
> tackle the huge CAD learning curve.
>
> Thanks,
>
> George
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, Alan Marconett KM6VV
> <KM6VV@a...> wrote:
> > Hi George,
> >
> > For normal coordinate location (for us hobbyists), the LL corner
> is a
> > good choice. This is quite often the way the part is drawn.
> > Occasionally, as for cylinder end covers, the center works out
> good.
> > I'd start out at the LL corner. If necessary, the other corners
> can be
> > used as well. If I use my vice aligned with the Y axis, I like to
> touch
> > off on the fixed jaw, which is aligned with the X axis, and in the
> > rear. Just don't forget which axis the drawing is made to. Bad
> things
> > happen if the coordinate "frames" don't match!
> >
> > For tool radius compensation, first draw the part outline, then an
> > "offset" around the part is drawn. Programs like Vector CAD/CAM or
> > similar make this easy. Perhaps your CAD software has this. The
> offset
> > should be 1/2 the dia of the tool.
> >
> > HTH
> >
> > Alan KM6VV
> >
> >
> > gglines1 wrote:
> > >
> > > I'm just starting to CNC program in G-codes. I'm uing MillMaster
> > > Pro for Windows by Microkinetics on a mill/drill.
> > >
> > > My software doesn't have tool radius compensation and I'm looking
> > > for advice on how to approach programming toolpaths. I hope I
> can
> > > explain this clearly. I'm finding calculating the cutter
> waypoints
> > > tough.
> > >
> > > Should I CENTER the spindle on the workpiece origin (0,0) or the
> > > EDGE of the end mill on the workpiece origin 0,0? For example,
> let's
> > > say I have a 1" x 1" (I'll ignore Z) workpiece with a 3/4" end
> > > mill. If I set the center of the spindle (using absolute mode)
> on
> > > 0,0 (front left corner of workpiece), then I have to reposition
> the
> > > spindle by -.375 in both X and Y or half the distance of the
> cutter
> > > to get to the edge of the workpiece. The second way I could do
> it
> > > is to move the cutter to X-.375 Y-3.75 and then initalize that
> point
> > > as the origin (0,0).
> > >
> > > Any suggestions on which way to approach this?
> > >
> > > Many thanks,
> > >
> > > George
> > >
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> http://groups.yahoo.com/group/jobshophomeshop I consider this to be a sister site to the CCED group, as many of the same members are there, for OT subjects, that are not allowed on the CCED list.
>
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