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 briefly below.

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.

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 accuracy.

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 export it.

Arc and line approximations

MetaCut Finish will automatically produce a highly accurate approximation to an ordered set of points (and lines) such as commonly found in toolpaths. Separate tolerances are provided for lines and arcs. These tolerances may be viewed as the maximum deviation from the original points in the file. In addition to maintaining a tolerance to the original points, a maximum deviation from the original lines is also maintained.

Arcs may be fit in one of three methods: 1) relative to the standard orthogonal planes (XY,XZ,YZ). 2) relative to any rotation of the standard orthogonal plane. 3) to completely arbitrary planes (3D arcs). Almost all controls will machine arcs using the first method, some controls will allow method number 2, and a few controls are able to machined true 3D arcs. (*note- a 3D arc is not a helix).

MetaCut Finish  will always fit the most appropriate entity. If any set of data falls within tolerance for both a line and an arc, MetaCut Finish  will only produce the entity with the closest fit. MetaCut Finish  also has user defined limits for largest and smallest arc radius as well as the smallest distance between arc endpoints and smallest arc length. All settings may be saved to a named parameter set which may be loaded at any time while in MetaCut Finish.

NURBS approximations

The NURBS curve fitting available as an option for MetaCut Finish produces both small and accurate files for use with controls which support true NURBS machining. The benefits of this technology include very smooth finishes similar to the arc fitting, but with absolutely no dependence on planes as there is on most controls with arcs. In addition the control will prevent overtravel of the machine tool when using NURBS machining. The NURBS machining also produces good results with true 3D toolpaths such as "flowline" type toolpaths.

NURBS machining is the next step forward in complex mold machining.

Automatic feedrate modification

MetaCut Finish is able to continuously vary the feedrates while your part is machining. This feedrate adjustment is easily adjusted by the user for optimal feeds on different machine tools. Feedrate adjustments are used to prevent following error while simultaneously decreasing your machining times. By changing the feedrates of individual arcs MetaCut Finish will machine large arcs at high feedrates while slowing down for small radius arcs.

Exact stop / Continuous switching

With the greatly increased feedrates available when machining using MetaCut Finish, sudden changes in tool direction can produce overtravel. MetaCut Finish will set your machine to exact stop mode (come to a stop at the endpoint) whenever the change in direction exceeds a user defined angle. When the toolpath becomes smooth again your machine will be set back to continuous mode (keep moving through the endpoints). This feature combined with the "automatic feedrate modification" feature will help to maintain accuracy while still allowing your machine to travel at the highest possible feedrates for any given situation.

Import / Export and the TOOL language

Northwood Designs, Inc. has developed a complete language similar in syntax to the C language but with specialized abilities which are particularly useful for the manipulations of the types of files commonly found in the CAD/CAM industry. This language is available to the end user and may also be used to make custom programs.

Import and export of files is handled in two ways within MetaCut Finish. Many common formats are "hard coded" to allow for quick I/O. With the first release, MetaCut Finish will support ASCII, DXF, G&M codes, and Mastercam NCI as hard coded formats. These will not be complete import/export filters but will instead support the types of entities which will be commonly used in MetaCut Finish. These include lines, arcs, and NURBS curves. We expect support for additional entity types to be added as necessary. The second type of import/export is the "custom" engine. These filters use the TOOL language and are completely customizable. This gives the product the ability to import file formats that are not included with the base package. You can also modify existing filters.

Batch Language

There is a full featured batch language which allows the user to run the product from a batch file over a network. The batch language allows for the loading of multiple files which may be optimized using different parameters, then exported with different export filters. All unattended. This is useful for running multiple conversions of large files overnight or for running across a network.

General Features

• Unlimited undo (limited only by your disk space).
• You may save an unlimited number of default settings for different machine tools or uses.
• The primary toolset is greatly simplified and combined into a dragable toolbox, the most commonly used features are always close at hand.

Things to keep in mind when considering MetaCut Finish

• MetaCut Finish was not designed to fit arcs to your old toolpaths. The best results are obtained with new files made with the process in mind. You can use MetaCut Finish with old files but the results may not be as optimal.
• Best results are obtained with higher precision files, this usually means 6+ numbers after the decimal point in the original file. MetaCut Finish can format and truncate all data on export.
• Your original file should be run to small chordal deviations for best results. MetaCut Finish will actually return a smaller file from a highly defined large original file than it will from a coarsely defined small original original file.