Re: Direction follower ?

This is basically a geometry problem; what you need to do, is keep the
cutter tangent to the curve defined by the cutting path.

If the pivot of the cutter is exactly above the cutter i.e. the cutter
is not offset (unlike a ball caster), you can approximate the tangent
of the curve as the line between two points of the curve, infinitely
close together, on each side of the cutting point. That tangent is the
direction the cutter should take, for each point along the curve.

If the pivot point is offset from the actual cutting point, you follow
the same process described above, and in addition simply move the
cutter position along the tangent found, by the appropriate offset
amount.

Having an offset cutter would allow you to not need an additonal axis
(the cutter angle) to control, as the movement of the cutter would
define the angle needed.

Is this of any help ? Let me know if this is not clear. I am bad at
explaining things...

You will have to write extra code, but depending on the representation
of your initial toolpath, it could be done in a simple perl script
that takes your toolpath as input and massages it in the correct
toolpath.

For any geometric problem of this type, I highly recomment to use and
experiment with IRIT ( http://www.cs.technion.ac.il/~irit/
(Open-source, all platforms)) a 3D modeller mainly oriented toward
geometric operations. It can help you visualize the problem, and
compute the solution. IRIT may be overkill since it is research/math
oriented, and the learning curve is steep, but you can do amazing
things with it.

I am currently working on methods to automate toolpath creation from a
given volume with IRIT. Yes, I know software exists to do that, but it
is not open-source, and I like to do it since I can :-)

bruno

--- In CAD_CAM_EDM_DRO@y..., "mayfieldtm" <mayfiet@i...> wrote:
> Dave:
>
> I can almost picture the cutter on a swivel like a ball castor on a
> chair.
> You would have to figure out how to compensate the tool path,
because
> the cutting position is offset from the tool holder position.
>
> Then also, If your cutting stain glass, the parts need not be super
> accurate and the cutter/holder offset can be very small and track
> good enough.
>
> The only alternative I see is to mount the cutting wheel directly
> under a rotatable tool holder and rotate the tool holder in the
> direction your moving.
>
> However you do it, you may find yourself writing your own controler
> code.
>
> Tom M.
>
>
>
>
> --- In CAD_CAM_EDM_DRO@y..., "turbulatordude" <davemucha@j...>
wrote:
> > Hi Brian,
> >
> > Thanks,
> >
> > I too know that you cannot cut rectangles without lifting the
> cutter.
> >
> > But, my intention is to cut patterns. curves and such.
> > So, just as you could curve your cutter when you cut by hand, the
> > cutter should rotate to always be aligned to the direction of cut.
> >
> > Dave
> >
> >
> >
> >
> >
> > --- In CAD_CAM_EDM_DRO@y..., "Brian" <ka1bbg@w...> wrote:
> > > Hi, well my years of cutting glass tell me if you spin the
wheel
> > with
> > > pressure on it you probably will break the glass or make a star
> > crack. to
> > > make square edges you must lift,orientate,start the new cut
> before
> > the old
> > > cut line to make a clean break reliably. good luck brian f.
> > > ----- Original Message -----
> > > From: "turbulatordude" <davemucha@j...>
> > > To: <CAD_CAM_EDM_DRO@y...>
> > > Sent: Wednesday, July 17, 2002 9:56 PM
> > > Subject: [CAD_CAM_EDM_DRO] Direction follower ?
> > >
> > >
> > > > Hi all,
> > > >
> > > > I am still toying with cutting glass and found that a weighted
> > > > standard glass cutter will cut glass easily enough.
> > > >
> > > > the problem is turning the cutter so it is always facing the
> > > > direction of cut. This is similar to knife cutting vynal,
but
> it
> > > > appears to me that the action would have to be pretty
accurate
> in
> > > > angling in the direction of cut so as to score the glass
> cleanly.
> > > >
> > > > Any ideas on how best to do this ?
> > > >
> > > > Dave
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > Addresses:
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> > > > FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
> > > >
> > > > OFF Topic POSTS: General Machining
> > > > If you wish to post on unlimited OT subjects goto:
> > > aol://5863:126/rec.crafts.metalworking or go thru Google.com to
> > reach it if
> > > you have trouble.
> > > > http://www.metalworking.com/news_servers.html
> > > >
> > > > http://groups.yahoo.com/group/jobshophomeshop I consider
this
> > as 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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