Re: EMC coordinate systems, etc.

>Message: 9
> Date: Fri, 20 Oct 2000 14:42:39 -0600
> From: John Murphy <john@...>
>Subject: ENC coordinate systems

>When I draw/generate my NC files (probably camexpert under linux with
>some hand editing to better support Z axis movements), How do I set my
>origin? I'm guessing I should match up 0,0 (x,y) in my drawing with
>a matching 0,0 position for the mill. Any suggestions here
>for linux based solutions would be great, I don't have windows).
>

As far as I know there are no low cost CAM solutions in Linux(under $500). It could happen any time. At least one Vector-cam user is running it under Linux with Win4Lin.

Setting coordinates is usually a very flexible thing. When I first started out in CNC machining, I would struggle with a machine for a few programs, then settle down to whatever I could get to work. In the intervening years, it has gotten much easier to understand, and I have learned a few tricks that help a LOT.

1) Whatever you draw in your cad system, That's what you get. This is very important, as it means that whether the part moves or the machine slides move, you produce what is drawn. Placing the origin at the back-left-top of the part means that if you want to place a hole 2 inches to the right and 2 inched toward the front is 2 inches +(plus) in X, and 2 inches -(minus) in Y. Any place that you move your origin from that position is still going to get the same result from the same +/- commands. The Z axis is always Zero at the top of travel, any move below that is a minus direction. If your coordinate system is not layed out this way, you will have to struggle with mirror images in your drawing, and that is a pain in the posterior.

2) If you are using a mill vise. It is very practical to set your Y axis zero on the fixed jaw, if the jaw movement is parallel to the Y axis. Why? "This means that I have to program all my Y values as minus!" That's right, who cares, the cad system takes care of it for you. It becomes important when you change to the next part & have to set your coordinate axes again. One is ALWAYS done for you!

3) Development of cutter compensation programs for CNC is primarily useful for holding tight tolerances. The benefits of using "as drawn" lines vs offset ones are not too good if you have a decent Cad program that will make accurate offsets, but struggles to make overlapping teardrops. Check to see if your program can cut a dovetail contour(draw an offset curve) that has an opening smaller than your cutter. If not junk it & buy a system that won't gouge your work. In Vector the development of approach & depart contours is almost automatic, and it truly becomes a choice of "how you want to do it", not a decision of "how can I figure a way to machine this part". The approach & departs to turn on and off cutter comp, as well as the generation of the code can be done without any need to do any editing of the program.

4) The use of 3D (Z axis control) is extremely important. One of the most common mistakes that people make in CNC programs is forgetting to retract the tool before jumping to the next contour. Crunch. Your CAM system should let you see the Z movement & you should be able to rapid down to a clearance plane & feed in to the work for pocketing and other 2 1/2 axis work.

5) Use of G-code. There are several controller programs around that don't use G-code. Certain people have said that it is obsolete technology, that they can do it better without using G-code, and on and on. However, if people will take the time to understand what G-code can do, they will realize that it is not a question of technology, but a question of control. The G-code standards, even as loosely as they are interpreted by software manufacturers, provide complete control of the tool under nearly all conditions. That's all you need. Even if you never see or understand G-code, the output from your cam system will be reproducible and if you move to another Cam system, the machine will still be usable.


Vector Cad only is still $100 through the end of the month
The StlWork competition had no entries in September. What? nobody wants free software?


Best Regards, Fred Smith- IMService
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