Re: [CAD_CAM_EDM_DRO] newbie question

Steve Ross wrote:

> Hi All
> I am trying to learn all about cnc. One question that keeps puzzling me is
> when you use Cam software you need to tell the program what kind of cutter
> you will be using for it to generate the G code. When you operate the mill
> operating program it also asks what type of cutter you are using. My
> question is why the redundency. If the G code is based on the cutter why is
> the machine software asking for the cutter information too.

The only place this come up is where the CNC control is asked to correct
for the length, or especially the diameter, of the tool. This is used in shops
where reground tools of odd diameter (such as .497") are used. Since the
CAD/CAM program doesn't know the precise diameter of the tool, it provides
the part outline, NOT the cutter path, and the CNC control computes the proper
cutter path based on the part and the tool's precise diameter.

There is a similar scheme for tool length compensation, but it really is just a
fixed offset for the Z axis, where the diameter compensation is a complete
recomputing of the tool path.

The diameter compensation can also be fudged to compensate for tool deflection
causing the part to come out slightly off size. I have used it to make the machine
take roughing passes and then a finishing pass, using the same program.
By changing the tool table's field for tool diameter and the re-running the same
program, you can control how close to finished size the cutter goes.

Jon