Re: Parts cutout technique?

Brian,

Two methods are commonly used:

Tabs. On the final pass of a part which is being cut from a sheet or
block of material, raise the z axis slightly for a short distance (at
two or more opposing points around the part), before plunging again
to full depth for the rest of the outline. The thickness, number,
length, and location of these tabs will be determined by the part; so
I cannot tell you exactly what to do. But often the tab can be "weak"
enough that normal deburring operations will easily remove it...

Sequential fixturing/clamping. Here you cut the part in two (or more)
related machining operations. Lets imagine a rectangle for an
example. Clamps are placed on the two long edges, near the opposing
corners. Then everything which can be "reached" without hitting the
clamps is cut. Then additional clamps are added, and the old clamps
removed. To allow for this manual intervention (tho' with air clamps
this can be automatically done); a program stop is used in a single
toolpath; or two separate toolpaths can be used. In our example, we
would add clamps in the area already cut; and remove the clamps we
started with. Now restart the machining cycle, or run the 2nd
toolpath.

Think about where to "break" the toolpaths... In our example, it
would be better to break at the corners, than in the "middle" of the
long or short sodes, where the "two-pass" machining might show. More
complicated parts will have other opportunities for logical toolpath
division.

The secondary toolpath cuts the remaining features. A variation of
this (or an expansion on the idea, really) is to use the first part
of the program to create datum surfaces/features; which are then used
for locating the part prior to the second operation. This is a
powerful, efficient way to create parts. A futher expansion is to set
up so that these operations result in a movement of the part(s) from
position to position on the machine, using as many parts as the
machine size will accomodate. In this way, you are adding raw stock
AND removing finished parts each time the machining cycle is
interrupted...

Oftentimes, the use of sequential ops can remove the need for tabs,
and still allow a cut around the entire part periphery. For ex: In
the first pass we drill/bore a few holes. two of these are used to
establish location, and a bolt through two or more others holds the
part for the "rest" of the cutting. Sometimes these "fixturing"
holes/features are NEEDED in the final part, other times they are
only there for fixturing.

Hope this helps,

Ballendo

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "bdrmachine
<bdrmachine@h...>" <bdrmachine@h...> wrote:

> Sure clamping will work, but it would have to be done during the
> machining cycle. Is there a more automated method?
>
> Thanks
> Brian
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude
> <davemucha@j...>" <davemucha@j...> wrote:
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "bdrmachine
> > <bdrmachine@h...>" <bdrmachine@h...> wrote:
> > > I'm finally making chips with my cnc mill, but not much more.
> > > I have a 2.5 inch connecting rod that I'm cutting out of the
> middle
> > > of a .375 T6061 AL plate. The rod gets marred up / damaged
> during
> > > the final cut. Are there any suggestions / techniques to
> prevent
> > > this?
> > >
> > > Thanks
> > > Brian
> >
> > the part is probably getting tossed as it breaks free. just put

a

> > clamp or two on it to hold it steady.
> >
> > on some larger parts, one needs to add clamps after the cutter
> passes
> > and remove clamps before impact. obviously, slower feeds lets

one

> > work at a less hectic pace.
> >
> > Dave