Re: [CAD_CAM_EDM_DRO] CNC Positioning

On Tuesday 13 April 2004 02:32 pm, Leslie M. Watts wrote:

> The router control will have a known point of reference
> thet is created by a homing procedure. Many ways are used
> to do this...detect a switch closure or particular encoder
> encoder pulse, lightly drive into a stop, etc.
>
> In my router 0,0,0 is the center of travel of all axes.
> This is defined in the machine control.

What, in your CAM software?

> Now there are G-codes hand programmed or generated by CAM
> software that define the motions. This is read by the control
> to create the motion. There are g-codes for offsetting as well.
>
> I try to keep things very simple and straightforward to avoid
> crashes and unintended cuts. I will explain the steps to engrave
> and cut out a single carved plaque:
>
> The shapes and carving are are created on a CAM system in the office.
> This creates a file which is copied on to the machine controller hard disk.
> All single (custom) parts have their center defined as x=0 and y=0.
> The surface to be cut is made Z=0 with cuts into the wood a negative
> number. Again this is all done by the CAM program before the file
> goes out to the machine.

Now you seem to be saying up there that your zero reference point is the
center of movement for all axes, and here you're saying that it's the center
of the part and the surface of it, for z=0. Which is it? Or are you saying
that you need to center the part when you clamp it?

> Now on the machine the plaque blank is placed with it's center roughly
> at the default x=0 y=0 of the machine and clamped.

Roughly...

> The blanks vary in thickness from job to job so now the MACHINE CONTROL
> is used to set the point where z=0 (the plaque surface). This is done
> by manually jogging the tool down quite close to the surface. The remaining
> small gap is measured (I use a small spark plug gap gage) and the control
> is put in to MANUAL DATA ENTRY mode. This simply allows one to execute
> typed in G-gode commands without running a g-code program. I then type in:
>
> G92Zn
>
> where n is the gap I measured with the gage. Now the control will
> consider the work surface as z=0.
>
> The cam program is then run. Tool changes for carving and cutting out
> are in the program as well as things like pauses to flip the work
> to do two sides. Locating pins or other devices are helpful with
> two sided work.

I can see where locating pins would be useful for lots of stuff... But that
would require some accurate drilling, I guess.