Re: [CAD_CAM_EDM_DRO] Re: Finding Z zero for CNC

Randy,

That's a good thing being I'm a machinist, reality is that many of us don't
use this. Paper for a quick setting, electronic edge finder for accuracy,
but at a few $K for a good electronic unit makes them out of the reach of
most.

Now lots of production shops used very accurate presetters for their
tooling. For our Star there is an optical microscope presetter to ensure
tool alignment. The lathes have tool touch probes. Most of our concern is
knowing how each tool is set up in relationship to the others.

If you know where your tools are and you have a little extra stock the
material location only has to be within a few thou. It's second operations
that require the high accuracy of the alignment. This is why many shops have
moved to more complex machinery that allows more of the operations to be
done on the one machine. We have an 8 axis screw machine, a 5 1/2 axis Mac
turn and soon a 5 axis trunnion machining center. Then you can machine 5
surfaces in one set up it becomes much easier to ensure accuracy. We also
use machinable vise jaws to hold parts in alignment.

One of the things I teach my apprentices is how to figure out what are the
most important features and how to set up so that you can keep all those in
alignment with each other. This is where geometric tolerancing has come in
as an excellent communication between the engineer and the machinist
providing the engineer knows what they are doing. You can slap on enough
tolerances that close the loop to the point there is zero tolerance for
error. I always say absolute finite dimensions equal infinite cost. I hate
lazy engineers that don't adjust their cad defaults to relate to tolerances.
I have one customer that has everything to the 6th decimal place, meanwhile
they just want a drilled hole.

If your on a budget, like most of us home machinists, test cuts on a scrap
piece will help with setting the tool offset. Consider placing a piece of
scrap to the side of your table that you can make a pass on to check your
tool setting. Your x and y should be the same from tool to tool.

Greg Nuspel
Prototype Machinist
Cheema Tool and Manufacturing
Calgary, Alberta

> Greg
> This is how most machinists do it, providing you don't need super close
> tolerances.
>
> Randy Abernathy