Simple G-code commands...

[WilliamD]

I'm nearing completion of my CNC router, and am going to use it mostly for woodworking. I'm going to use a joystick with it and do most of my joinery that way, but some things would take too long to program in AutoCad, go to CAM and then G-Code. So are there simple functions for "move X+ .25," or move any axis a given number of inches from any given point? Or does everything have to reference tool bit diameter and all those other parameters. I'm reading the .pdf that's recommended here, and I'm sure it will just take time. But all I really want are the simple functions to make simple straight moves. Any help would be grealy appreciated!

[ger21]

Most controllers have an MDI, or manual data input mode. Go there, and type G91 to get into incremental mode, then, to move x .25, typ G1 X.25

[Geof]

Manual entry of G-code allows for very simple commands. Your "move X+.25" made as a rapid motion is simply G91 G00 X.25; G91 is the command for an incremental move which simply tells the machine to move the specified distance from its current position, G00 is the command for a rapid move.
If this is a cutting motion a feed command is also needed and the commands become G91 G01 X.25 F10.; G01 is the command for a feed motion and F10. commands a rate of 10.0 inches per minute (ipm).

You will have seen the command G90 which is the one for an absolute move. This is a move to the specified point with reference to another point called the origin or work coordinate. For G90 moves you need to know the location of your origin, which I will not go into at this time. The important thing is that the move is not from where you are to a position .25" away in a positive direction, but from where you are to a location X.25 from the origin.

With a G91 move you always know how far and in what direction your machine will move; with a G90 move you know where it will stop so you need to know what your start position is to know how far and in what direction it moves.

Typically on a commercial CNC machine you would put the machine in MDI mode (Manual Data Input) and would enter these commands directly from the keyboard and the machine would perform the movement provided there was enough travel available before it reached the limit of its travel.

You do have to include other commands to start the spindle running but you can manually set the height of the tool and write entire programs without telling the machine what your tool diameter. BUT you have to take the diameter into account in the distances that you tell the machine to move. For instance if you want to machine around the edges of a 10" square using a 1/2" diameter cutter you need to have the machine do a 10.5" square. It is possible but it is tedious until you are familiar enough with doing this to do it almost automatically.

The fact is that if you are just doing straight line moves and simple circles it is fairly simple to prepare a G code program by hand and it is a good idea to develop this ability because in the future if you start doing more complicated stuff and have to use CAD/CAM you will use some of this knowledge in telling your CAD/CAm program where to start and end toolpaths.

[ger21]

What version of AutoCAD are you using?

[WilliamD]

Thanks guys! That makes some sense. I was also going to make some simple things in cad and do the gcode for them, and then try to decipher it, but it's still a little complex. I think those G90 and G91 functions will be the ticket. Ger, I'm using AutoCad 2006. I'm also using Mach 2/3, does that have an MDI mode? It seems to have everything else, so I would imagine so.

[ger21]

I wrote a macro to convert your drawing in AutoCAD into G-code. Here's the thread. http://www.cnczone.com/forums/showthread.php?t=8226
Newest version here: http://home.comcast.net/~cncwoodwork.../AC2GCv039.zip

Be sure to read the .pdf It works great with Mach3. If you need help with it let me know.

Yes, Mach3 has an MDI mode. Just choose MDI from the screen buttons on top.