Re: [CAD_CAM_EDM_DRO] CNC Part Setup

Hello Rob,
make it complicated but well done.
It reminds me to a project I had in my mind until last year (when
Siemens gave me a quote for 32K$ only CNC control and servos / for a
machine I quoted total budget 30K$)
My idea was a portable bedway grinding machine you bolt tight around a
machine to work over. Indicate position, geometry and orientation in the
xyz room on the not worn spots. And forget about the indicating
procedure.
Bolt or mill some reference points on the machine to rebuild and you
might even take of your bedway grinder and come a few month later to
make the rest.
Good observation.
Sven Peter

Rob Anderson wrote:

>
> 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)
>
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