Re: [CAD_CAM_EDM_DRO] CNC Part Setup

Hi Rob:
This is certainly the most unusual setup method I've ever heard about!!
I can see the rationale for your approach, but I can't say I'd personally
adopt it too fast.
It must make checking the code almost impossible, so I assume you're relying
100% on your CAM setup to give you what you need.
Have you never had any surprises with your code generation?
I have, and I find it awfully nice to be able to go to the line that's
generated the little brown stain in my trousers and find out why.
I also find I can generate straighter straights if I"m travelling parallel
to an axis rather than generating interpolated moves for everything.

But hey; if it works for you..... :-)

Cheers

Marcus

----- Original Message -----
From: "Rob Anderson" <randerson@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Thursday, March 07, 2002 7:47 AM
Subject: [CAD_CAM_EDM_DRO] CNC Part Setup


> Gentlemen, here is a post I just placed at the shopmaster web site. I
think
> it fits in here and hope it helps. My response was in regards to a new
guy
> wondering about different ways to set up a part in a CNC.
>
> Greetings,
> Your head is swimming and you are wondering how to set up parts. This is
> just the beginning! I taught CNC machining and injection mold
manufacturing
> for five years at a university and I have had the good fortune to work
with
> awsome toolmakers from all over the world. What I've found is that there
> are a lot of ways to set up a part for milling. Some always set up (zero)
> on the lower left corner so all numbers are positive. Others indicate in
on
> the middle of the part. Some on the middle, closest edge to you.
>
> Here's what I do on critical things and why. I throw my part on the vise
> crooked. Intentionally it is mounted so it looks like I walked by, tossed
> it down, and bolted or clamped it to the table where it landed. I then
> verify the top is flat (parallel) table. From there I use a wiggler (A
> spinning shaft with a spring) and touch off on two locations on each of
the
> four vertical edges (assuming a square or rectangular part). Each time I
> touch off I write these numbers down using the machine absolute coordinate
> system. When finished "wiggling off" I have 8 points which I plot in
> CAD/CAM, as mentioned using the absolute coordinate system from the mill.
> In CAD I make a square using these 8 points by connecting each set of
> points. Of course you have to extend the lines once connected. Once I
have
> an outline of the raw part in CAD, I take the PART model in cad and move
> and rotate it to make it match the outline of the box I just drew (DON'T
> MOVE THE REFERENCE BOX!!!). Typically I keep the part model and the
> reference square-(frozen) on two different layers to make manipulation
> easier.
>
> I then generate my G-Code using a cam package. Cool thing is the numbers
in
> the CAD/CAM model
> match the absolute numbers on the mill. No worry about loosing your G54
> (home) position.
>
> This method is by far the most time intensive method for setting up. But
in
> the five years I used it, I didn't screw up any parts because of being
> located in the wrong position or from being .002" or so off in the wrong
> direction. Reason being by indicating on all four sides you are halving
(at
> a minimum) the error from only wiggling on two edges. Plus if you make a
> typo keying in your numbers it shows up in CAD as the reference square you
> draw comes out goofy looking.
>
> Authors note: I didn't say there were no screw ups in five years, only
that
> I was not indicated or homed wrong. There was still plenty of scrap, this
> was just one less worry. :-)
>
> The advantages to this system are big. Less mistakes and no "influence"
> from you with regards to
> "thinking" the part is "close enough". By this I mean when you indicate a
> part in as parallel with an x or y axis, at some point you say ok that
small
> amount of error is acceptable. The way I mentioned circumvents this.
>
> Disadvantages: Slower, more work, and you can not use the handles on the
> mill in manual mode to make a slot in the x or y axis as your part is
> sitting crooked (unless you want a slot running at an angle across your
part
> :-)
>
> I didn't always use the above described method, only when I needed it to
be
> right and really accurate the first time. - which is frequently the case
> with injection molds (or home made gun parts :-)
>
> Hope that helps
> Rob Anderson
> Mechanical Engineer Tritronics
> (And really curious guy in general)