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Products : MetaCut Finish : How it works

 

MetaCut Finish & Pro

How it works


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.


 


"The polishing time on our molds has been reduced by many hours."

George Lawton
(CNC Programmer)
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 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.

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