Starting Out Right - Mill Vs Lathe Coordinate System

[maker of things]

I think on a 3-in-1 everything will change when you pivot the z axis, depending I guess on whether your mill column is over the lathe spindle or off the back centered on the bed. If you are putting DROs on, possibly you could make a template that flips down and has the axis label according to the operation you are running. Or if your mill column is centered on the back of the bed, think of the machine as a mill with 4th axis, that would potentially be a simpler convention to learn.

 

[John Hasler]

The systems may be consistent, but on my 3-in-1, when switching from lathe to vertical mill, the z changes, doesn't it?

When looking out of the spindle you are looking in the -Z direction out at the XY plane. I believe this applies to anything with a spindle.

I assume (but don't know) that one of the spindles of a multispindle machine gets to be the principal spindle. I don't know how machinces like planers that have no spindle are handled: I'd put the XY plane in the plane of the table like a mill and make +Z away from the working surface.

 

[great white]

The systems may be consistent, but on my 3-in-1, when switching from lathe to vertical mill, the z changes, doesn't it?

Yes......and no.

The Z axis is always in line with the spindle.Lathe or mill:





So referenced to the machine, it doesn't change (Same idea as engine position on an aircraft or port/starboard on a vessel).

But it does from your perspective.

This is how it's always been explained to me by the guys in the machine shop so don't shoot the messenger if you disagree.

 

[John Hasler]

A better right hand rule: point your thumb in the +Z direction and your fingers curve from +X toward +Y. This also clairifies rotations as your fingers curve in the direction of positive rotation in the XY plane.

 

[planeflyer21]

Hi PocoJoe. Great question!

I'm not sure as to getting the DROs setup but here's what worked in shop CNC.

Most CNC machines come with a "machine zero". This seems to be the center of travel on all axes. In other words, as the operator faces the machine the table can travel an equal distance to the left (x-) or right (x+), an equal distance towards the operator (y-) or away from the operator (y+), and the mill spindle can travel towards the table (z-) or away from the table (z+).

The best quick definition for Z-axis I've heard is "the Z is movement of the tool". Works pretty well on mills or lathes.

I use the terminology "towards the operator" because, depending on the 3-in-1 machine you have the column may be to your left attached to the headstock or in front of you, attached to the lathe bed.

For me, when I still had my Smithy Granite, when doing milling I tried to set up the workpiece as close to being centered on "machine zero" as possible. This allowed me plenty of space to work with.

Glad to see you here in Tucson! There's a couple of us on here.

 

[PocoJoe]

Now I'm starting to appreciate the potential benefits of the igaging absolute scales, as it would make machine zero be highly reproducible. The less expensive aluminum scales arrived today, I need to see how they behave and if a repeatable origin can be set. And thanks to all for helping me get properly oriented!

 

[chevydyl]

When I stand in front of my cnc mill, X+ move the table to the left, which moves the tool to the right on the coordinate plane, Y+ moves the table towards the operator, tool goes up the coordinate plane. Z- is down through the part. Think of how the tool moves across your grid, like in algebra, nothing too it.
On the lathe Z- moves the tool towards the headstock, X- moves the tool away from the operator