Coordinate question for cam software

[WarrenW]

Hi,

When your looking at the work area in a cad/cam program, is the 0,0 coordinates always at the bottom left of most software? Thats the way the CNC is driven unless you have your axis setup different right?

Just curious because I'm working on my own program and right now the 0/0 coordinates for X/Y is at the top left.

Thanks,

Warren

[ger21]

Typically, yes. X+ is to the right, and Y+ is up. Usually.

[WarrenW]

Looks like I have to change my software around. I'm writing a 2D cam program for letters and numbers mainly. You enter the text, choose the font and size. You can adjust the precision also. the higher it is, the more points it creates to be smoother. It also recognizes inside island cuts for the letters so they are done first. It will output as a DXF file right now. But I'm going to work on creating the toolpath and gcode as well. I just have to think of a good name for it. I'm open to suggestions!

The GUI will look completely different - below is just a rough version for writing the main engine.

Warren

[HuFlungDung]

So long as you follow the axis direction convention as Ger21 stated it, the exact location of the profiles relative to the origin on the CAD screen should not matter, just so long as the user sets up the work offsets on the machine, so that the reference datum on the part corresponds to the lay of the profile position for CAM.

There are all sorts of reasons why some guys want to drag the profiles to a different quadrant, or maybe even center the profile on the origin, and do some cutting in all 4 quadrants.

I would not advise that you hard code in the position of the text profiles in your CAD.

Sorry if I've confused you, but I'm not quite certain what point you are driving at.

[ger21]

I meant to mention that, but forgot. What Hu is saying, is that 0,0 can be anywhere, is long as X+ is to the right, and Y+ is up. So all your coordinates can have negative values, if the user wanted it that way.

I'd give users the option to psotion the text when outputting the g-code. Let them reference the position from the center, or lower left corner, or any other options you might like to use.

[WarrenW]

Hmmmm, now I'll have to go back to the drawing board. I thought that the 0,0 point could be in any corner and the numbers would increase from there. So if the top right was set to 0,0, then the X/Y would increment as it moved out. I programmed it where you can choose any of the four corners as the 0,0 but the numbers don't go negative - everything becomes relative to that corner. Is that not needed then? If your standing at the base of the X axis of your machine, the X always increments to the right and the Y increments to the top right?

I was going to allow you to set a starting point anywhere but it was not going to be set to 0,0. But I guess thats what your saying. I should allow the user to click a point on their machine in the software to choose a starting point and that becomes 0,0?

Warren

[Geof]

CNC machines use standard Cartesian coordinates; upper right quadrant is X+, Y+; lower right quadrant is X+, Y-; lower left quadrant X-, Y-; upper left quadrant X-, Y+. Most, if not all, commercial machines have the home position, 0,0 in machine coordinates (G53), i.e.the Cartesian origin to the right and away from the operator. This means that in the machine coordinate system, G53, moves in both X and Y are negative; the machine cannot make a positive move in G53. Subsidiary coordinate systems may be specified using Work Coordinates. G54 to G59 are the standard ones but many machines can have more than six (not all systems use the same Gnn for Work Coordinates past G59). Depending on where the Work Coordinate systems are placed a program may have access to all the Cartesian quadrants. Placing the Work Coordinate at the limit of the machines travel on both axes gives you a subsidiary coordinate system in which any move on either axis has to be positive. Placing the Work Coordinate at the center of the machine travel on both axes gives you a symmetric Cartesian system and moves can use all combinations of + and -.

[HuFlungDung]

Warren

If you were going to allow only incremental positioning, then I can visualize your original method working. However, for absolute coordinates, just stick with the normal cartesian coordinate system layout.

Usually, even if using an incremental positioning subroutine, at the start, the machine is positioned somewhere with an absolute coordinate. At the end of a series of incremental movements, then another absolute coordinate is called to re-establish the accurate whereabouts of the work position on the machine.

Yes X+ is table right, Y+ is table away from you (towards the machine column).

[Geof]

Originally Posted by HuFlungDung If you were going to allow only incremental positioning, then I can visualize your original method working.....

Even in incremental text height will be represented by a negative number which is non-intuitive.

[ger21]

Originally Posted by Geof Most, if not all, commercial machines have the home position, 0,0 in machine coordinates (G53), i.e.the Cartesian origin to the right and away from the operator. This means that in the machine coordinate system, G53, moves in both X and Y are negative; the machine cannot make a positive move in G53.

Maybe for milling machines, but not necessarily for routers. G53 0,0 is where the home switches are, right?

[Geof]

Yes; I apologize, I keep forgetting. I did own a Biesse Rover 20 for a while as a joint project with a friend who is a cabinet maker. The differences between wood and metal machines drove me nuts so I sold it to him.

[WarrenW]

Okay, I understand now. This won't be a problem at all. In the setup it will ask for the table size which I'll set. Then it will ask for the material size and draw that as another area which will be inside the table area. And you can position it anywhere on the table you want. Then at anytime you can select where the 0,0 coordinate will be on the table. If you place it in the middle and some of the cutting areas are below and to the left, then the cutting will go into negative numbers.

Here is the latest screen shot of my software. I tried to make a nice interface for it. It does not show the border for the table or material yet. Its coming along though. I still have to add the X/Y coordinates on the bottom bar and also buttons to mirror X and/or Y if ever needed. I figure atleast 5 days and it may be ready for beta testing.

Warren