Using MetaCut Finish involves
nothing more then a very simple 3 step process. The simplicity of the
process hides the real complexity of making changes to your original
data without producing errors. Each of these steps will be discussed
1) Importing the data- The import facilities of MetaCut are quite
broad. You can import many different file types right "out of the box",
and more are being added on a regular basis. MetaCut's TOOL language
allows you to modify each of the import engines for special cases
of the file types. If you have a good knowledge of the TOOL language,
you can actually teach MetaCut to read a completely new file type. It is
even possible to instruct the import filter to manipulate the data as it
is imported. For instance, using the TOOL language, you could modify the
import filter to scale or even rotate the data as it was being imported.
"The polishing time on our molds has been
reduced by many hours."
Kintz Plastics, Inc., New York, USA
Used for: Aluminum molds
2) Optimizing the data- The optimization of the data takes three
primary forms. Reduction of direction change, adjusting feedrates, and
adjusting the accelerations and decelerations when necessary. The
following paragraphs will describe each of these in more detail.
The first of these is a reduction in direction change over a given area.
There are two methods available in MetaCut to reduce the amount and
severity of direction change within a path. One is to fit arcs, the
other is to fit curves to the point to point data. Either of these
methods will accomplish the goal of reducing the amount of direction
change over a given area.
So why do you care? Because by reducing the amount of direction change
over a given area, the machine is able to travel at higher feedrates
without slowing down for the thousands of small direction changes
produced in a point to point toolpath. This is true of an older machine
or even a brand new High speed milling machine with the latest high
speed control. In actual tests, MetaCut often reduces machining time by
as much as 50 to 60 percent! The reduction depends on many factors, but
if the part has any complex curves at all, there should be a significant
reduction in machining time.
The second optimization deals with adjusting the feedrates to prevent overtravel. After the early tests with arc fitting, it was determined
that even a very old control had more than ample time to process the
data after using Northwood Designs' algorithms. Machines that once
"shook" even at a moderate feedrates could now be run at rapid rates
without "shaking". This was wonderful with one small exception. Now the
machines could move so fast on finish passes that the laws of Physics
became a problem...
Inertia was the enemy. At very high feedrates you cannot change
direction rapidly. How fast you can change directions varies as a
product of the feedrate, the masses of the part and machine, and the
strength of the servo's on the machine. There are also other control
related factors. Once it was determined that we could move faster than
we could accurately machine, it was necessary to introduce additional
control to the toolpath. This control needed to vary with the rate of
change of curvature. Fortunately, we had a ready indicator of this rate
of change, the arcs we had used to fit the original data. Arcs have a
constant radius, if we could determine the correct feedrate for each of
the almost infinite possible arcs, then we could change the feed to
prevent the overtravel.
This was accomplished with the the Feedrate Table. The feedrate table
allows an infinite variety of feedrates to be generated and attached to
the correct arc. Each machine in your shop requires a different amount
of adjustment, and MetaCut allows you to produce the correct adjustment
for each of your machine tools. This will only take an hour or so for
each of your machine tools and will pay back this time every time you
make a part. The payback is in reduced machining time and in increased
Feedrate adjustments are not necessary on many high speed controls, the
feedrate tables are actually inside the control!
The third optimization is the exact stop and continuous mode adjustment.
The problem is that physics not only dictates how fast you can change
direction, it also makes it impossible to instantaneously change
direction. Where would you instantaneously change direction? Many
places, but for starters, every "step over" on your toolpath includes
two very sharp angles, often 90 degrees or more! This is certainly a
sharp change in direction. You can also have a "crease" right in the
middle of your path anytime you have an inside corner and the bit
diameter is greater then the radius of the corner.
So what should you do when you come to this situation? The only way to
cut this type of sudden direction change accurately is to come to a full
stop. Even if you are moving at a very slow feedrate, you WILL produce overtravel (error) in your cutting path. All controls must have two
cutting modes to be able to cut all shapes accurately, they may or may
not call them exact stop and continuous modes, but they must have them.
In essence, the exact stop mode decelerates and comes to a very brief
full stop before proceeding to the next entity in the path. The
continuous mode travels through the endpoints without stopping. You can
see the affects of this by machining a square toolpath that consists of
only four straight lines. Program the square at a high feedrate and run
it in exact stop mode (or the equivalent on your control). You will
produce a square with nice, sharp corners. Now run the same program,
only this time in continuous mode. You will see that the faster your
feedrates, the more you round the corners on the square. The only truly
correct way to machine a part, is to switch between these modes where
appropriate. MetaCut gives you this ability.
How did I manage to beat Physics in the past?...
You didn't. You machined much slower than necessary and probably in
continuous mode. This means that you programmed the entire part at a
slow enough feedrate that the errors that were produced were small
enough to be polished out. This is not very efficient but it was the
best you could do.
With MetaCut you are able to program with a completely different
philosophy. Instead of machining an entire part programmed for the
"worst case". You can look at your part and program for the "best case"
and just let MetaCut do all of the necessary feed adjustments and mode
switches. To be more specific. In the past you would look at a toolpath
and say to yourself something like.... " There is a steep wall in the
part where I will make a large overtravel if I travel faster than 15
inches a minute, so I'll program the part at 15 inches per minute." This
means you are also cutting the areas that could be accurately machined
at 300 inches per minute at 15 inches per minute.... not very efficient.
With MetaCut you will try and find the "best case" and you will instead
say something like " you know, I have a large flat area in the bottom of
this cavity, I could machine that at 300 inches per minute." Now you
would program the part at 300 inches per minute and then let MetaCut
look for all of the places that must be machined at a slower feed or
even where you should come to a full stop. In this second scenario, you
are always machining the part at the maximum feedrate your particular
machine is capable of without inducing overtravel errors. This is
obviously substantially faster and more accurate.
3) Exporting the data- MetaCut has just as much flexibility when
exporting data as it does when importing data. Each of the export
filters may be modified to suit particular problems on individual
controls or machines. The formatting capabilities of MetaCut are
exceptional. It is unlikely that you will find a human readable file
type that MetaCut cannot be modified to export with relative ease.
MetaCut can also save the original header and footer information or even
drill codes in a file if instructed to do so. If MetaCut does not
understand a particular series of codes when it imports a file, these
codes will still be in the appropriate position on the file when you