Problem- Z zero setting on lathe

[pareicher]

Gentlemen,

I need your help. In the 25 years I have been programming lathes, I have always used the finish face of the part as Z zero. Single turret two axis, multi turret two axis, Multi spindle-multi turret, MillTurn,etc. If I am going to leave .03" for finish later, then the set up sheet and program reflect that so when the machinist is setting his tools, he moves the offset in the proper direction (although, they don't use g54, 55, etc. here). When the part is flipped, the new finish face becomes Z zero. If it is a fixture, it might be a reference on the fixture, but based at the finish face of the part.
We have a debate in house. The machinists want the programs to reflect excess stock at finish and use that as Z zero. Bad idea and not a standard method.
I am looking for your input to clarify what you use?

Thanks,

[pareicher]

Anybody out there?

[Eurisko]

We run castings, no barstock. Generally, the locating face of the jaw is set to Z zero.

There are exceptions. Some programs reflect extra stock for a second operation, and some don't. The operator doesn't have to set the Z. It is set at the beginning of the program. Machine Z is set at the chuck, and never changes. The program adds the jaw offset to machine Z to set the program Z.

Listen to your operators. A program only has to be written once.

The operators have to deal with it thousands of times.

[extanker59]

Boy, I really hate that idea of programming from the stock zero. That means that all the dimensions can't be glanced at and know that they will match the print (.500 deep c'bore on the print could now be .5325 in the program).
I see what Eurisko is saying about listening to your operators but I program, setup, and run my own parts and I would never program that way. Too easy to misunderstand a dimension, in my view.

[extanker59]

Rereading my initial response has me thinking. Maybe (really maybe) it might work if the operators had no control over the programs and stock. Then it might be quicker to set up (by a hair) and less prone to operator error?

[g-codeguy]

extanker, I am with you. I always program from the finish face. I have seen programs written with Z0 being the cut-off face. Never liked that. Have to say I've never encounter someone programming the raw material as being Z0. That has to be more of a pain for you than for an operator to make a skim cut to clean-up, and then taking a measurement so he knows how much more to take off. Awful easy for you to make a mistake in the program.

Sounds to me like they are just trying to give you a hard time. Or they are plain lazy. Or plain ignorant.

[Delw]

I been programming and running lathes since the mid 80's from 5c collet noses to 30" chucks and 80" face plates both castings and raw stock.
I always have z zero at the nose , I have tried it from the jaw faces, from the main zero point on the part(reference point were everything is called from) it messes everything up and people get confused when dont one set up one way and another the other way and tahts the last thing you want on a 10,000 casting.
however this is what I do.
I draw the part up in cad like on the org finished print then move the face of the part on the cad to z zero and everything were the dims are called from print it out with tol's. and give it to the operators or who ever is running it. they go by that Print not the org to get dims.
castings you do a little different, draw finished part add casting part in another layer etc etc then move the whole drawing to the front of the finished part of z zero.
this saves time and many many mathamatical mistakes, scrapped parts etc etc it takes 10-20 mins tops for a cad guy to make a quick print for that operation.
My opinion no one should run any part with out a operation sheet, all my parts that come in as completed prints and require operations get a set of in house operation sheets for every process no if's an's or butts about it even the simplest parts. that way anyone can run them. most companies we did work for provides them some didn't.

I am not saying that others that run off location faces are wrong as everyone has there own way of doing things and how they train there operators.

if you always in your head think that z+ is cutting air and z- is cutting material your crash rate and scrap rate will drop 99.999%
There are circumstances were a casting will have over the typical amount of set-off from the front face. I am assuming most guys rapid to Z.2 or Z.1 then move to cutting location, some castings I have had ,had up to 1" on the stock face to cut off so just make sure you put that in the Notes at the z zero point of your operation sheet in very big letters as it has gotten us in the past.

Delw