Z=0 top of part or top of stock

[fjbart70]

Using mastercam X3.

Can't seem to find an example of how to set up porperly when there is extra stock on part.

Final part is 1" square, but I define the stock to be 1.5" so there is an extra .25" around part

Do you typically set the WCS and tool plane origin to the top of the part or the top of the stock? Or does the WCS need to be at top of stock and tool plane on the part?


What is the correct way?

[emonje]

It does not matter whether z0 is on the stock top or part top. I usually set mine on part but that's matter of choice.

If your stock is higher than top of final machined part, & you set z0 on part top, the amount will register in "Top of Stock" (instead of 0 it'll be 0.25 in your case). Just keep this in mind when inputting Clearance, Retract, Feed planes & Depth. And don't go rapid anywhere below 0.25+something.

[TXFred]

I set Z=0 to the top of the finished part. My first operation is to face the stock down to Z=0. After that, top of stock and top of part are the same thing. Any negative Z value is potentially cutting metal, and any positive Z value is above the metal.

Frederic

[fizzissist]

Originally Posted by fjbart70 What is the correct way?

There is no such thing as the "correct way" in machining. That's what makes us special, the ability to understand that there is only "appropriate for the particular job way". Every job is different, and that's what makes them all the same.

I'm unique. Just like everyone else.

I almost (Note: I said ALMOST) always use the highest in Z finished value for my Z0, because for one thing, it makes editing and reviewing easier, and my tool setting library and operations are set up around that approach. I know if I see a minus Z value, the tool better be working, if it's a plus Z, it'd better be going somewhere to work.

If you see a +Z, the tool is above the part, a -Z and the tool is into the part.

I also never program or position against stock, except for 1st op, because stock, by definition, is always different.

Generally, 1st tool is facing the top to establish a known Z, and that's my Z0,
and I'll use the tallest rough part's thickness to consider the first facing pass depth. That's the exception where my Z values will be + but I'm cutting.

[TXFred]

Originally Posted by fizzissist There is no such thing as the "correct way" in machining.

But there are an infinite number of incorrect ways. They can be identified by a loud bang, a blinking red light, or an audible alarm.

Frederic

P.S. I've found a couple.

[fizzissist]

Originally Posted by TXFred But there are an infinite number of incorrect ways. They can be identified by a loud bang, a blinking red light, or an audible alarm. Frederic P.S. I've found a couple.

...LOL!!

Sometimes followed with the skidding of a stuck tire on the ole' Kennedy on it's way to the parking lot....

[Superman]

There are many senarios of where to set the work origin

The choice should involve the simplest method of setting it, it should be a physical feature that can be the easiest to describe to another person that could end up repeating that same job. You need to fully cover any situations in setup to avoid an error.
A simple error may be how much stock is above the vice jaws verses the lowest cutting depth, this can be high-lighted when stock is thinner on a repeat job, allowing the cutter to "interfere" with the vice jaws

Initial operation, 1st op most common
1--> rear LH corner, rear jaw fixed, stop @ LH side
( model part located near datum corner, below top of stock )
pros...very easy to convey info and perform setup, Z+ values will be non cutting, excess stock is not even around the part if stock varies
cons...possible to have non-cleanup if stock varies & is too small

2--> XY datum = centre of stock, Z datum = top of stock
( model part located @ stock centre, below top of stock )
pros...easy to convey and perform info, Z+ values will be non cutting, excess stock is even around your part

3--> XY datum = centre of part, Z datum = top of part
( stock located around part centre, top of stock drawn above part )
pros...easy to convey info and perform info, Z+ values will be non cutting, excess stock is even around your part, instruction is the same as #2 and then to move it a set distance below top of stock

cons for all...danger of hitting holding fixture when batch stock thickness varies but only at initial setup

Subsequent ops
origin should be on a feature on the part that was done in a previous op, or on an item that can referenced back to a model feature. It needs to be a feature that dosen't move around too much, a hole is a better feature to locate than a part's corner
eg a clocking hole on a fixture plate, that has dowels in it to locate the part