Re: CNC Part Setup

I'll sometimes use a similar procedure, especially for cutting uneven
or miss-shaped materials or when I want to fit a design to a block of
material with minimum waste.
Instead of writing down position coordinates, I just press a button
on a custom script within 3DS Max that calls Master5's ocx interface,
it reads the current position data and creates a reference point
straight in the drawing. I can then create a simple 3D model of the
material using these points if neccesary.
I can then scale and position the part and send the data back to
Master5 for cutting.
Works quite well,

Rab

>
> 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)