# Thread: X, Y & Z...Is it only me????

1. Member
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## X, Y & Z...Is it only me????

Hi all,

I know this is a simple question, but I can't get a handle on it!

Given the spindle is the Z axis by definition. Z is vertical on the mill, and horizontal on the lathe.

The X and Y axis are in the same 2-dimensional plane, which is perpendicular the the Z axis.

X and Y axes are displaced 90 degrees from one another.

When standing in front of a mill, the convention seems to be that the X axis is table travel left and right, and the Y axis is movement in and out, with respect to the column.

Why is this?

With the lathe, is the X the cross travel, and the Y up and down?

Why is this, if this is the case.

There must be some rule...for defining which is the X and which is the Y, but I sure can't see it or find it anywhere!

Anybody???

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3. Senior Member
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As was presented in the link that Aboard_Epsilon posted... it actually makes perfect sense!

The Z-axis is closer/farther from the machine tool spindle. If you stand a lathe up and rotate it so that it looks a bit like a vertical head milling machine, then all the coordinates remain the same. Z axis is up and down and the x-axis is left and right.

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I think he was asking how do you select X vs Y, not why is the carriage Z on a lathe.

X = longest travel axis that moves perpendicular to the spindle
Y = second longest travel axis that moves perpendicular to the spindle

So on a vertical mill, left/right = longer travel than fore/aft, so left/right = X.
On a lathe, crossfeed = longer travel than tool height so cross = X.

Compound feed would be something completely different, because it can rotate & translate.

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## Starters

This is for "starters" - I will post more later that should clarify things some-what:

..................................................

Common Codes
G-codes are also called preparatory codes, and are any word in a CNC program that begins with the letter 'G'. Generally it is a code telling the machine tool what type of action to perform, such as:

rapid move
controlled feed move in a straight line or arc
series of controlled feed moves that would result in a hole being bored, a workpiece cut (routed) to a specific dimension, or a decorative profile shape added to the edge of a workpiece.
change a pallet
set tool information such as offset.
There are other codes; the type codes can be thought of like registers in a computer

X absolute position
Y absolute position
Z absolute position
A position (rotary around X)
B position (rotary around Y)
C position (rotary around Z)
U Relative axis parallel to X
V Relative axis parallel to Y
W Relative axis parallel to Z

.................................................. ........

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## This may help?

Hi All, This is copied from EIA-267-B

Have fun.
Bob G

7. gnm109 Guest
It's still confusing, especially after reading the nice chart. LOL

I've wondered about something but I just solved my own confusion. Bear with me...........

Most two axis DRO's are available for either mill or lathe. The black box is the same, differing only in programming that can be performed by the owner for either use. The mounts are of course different for each application.

My Mitutoyo 2-axis has a Model KA black box. The manual covers both applications, mill and lathe. I bought it for a mill and the face plate says X and Y.

I always wondered why it had a printed plastic sheet with extra X, Y, and Z stickers for the face plate. Obviously that's to reassign the axes for a lathe after having done the reprogramming.

Nice.
Last edited by gnm109; 10-01-2009 at 10:33 PM.

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main thing to be careful of is that you keep track whether the DRO is reading in radius or diameter mode (even on the mill).

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Hi all,

Thanks for the replies so far.

Bob G provided an interesting explanation. But it seems to add to the confusion in my mind. I know conventions are what they area and can accept them...

Now if we take a conventional mill, with the spindle axis vertical, then when viewing it while standing in front, then the z axis is the spindle axis, the x axis is left to right, with the right direction positive, and the y axis is front to back, with the Y axis positive in the direction of the column (or negative towards the operator). All fine and good.

BUT...

It appears if this machine were tilted on its back, then the z axis would remain the same, but then the x axis would now point to the right, when viewed from behind the spindle.

This is exactly opposite from what it was when the machine was standing up as it was originally.

So the confusion continues.

The example that Bob G provided says that the Z axis is positive in the direction that increases the distance between the work piece and the cutting tool. Well in the lathe, the distance between the cutting tool and the work is set by the cross travel or compound or combination of both. NOT by the headstock...which we want to call Z even though it is not holding a tool like it would be in a mill.

So...are there two independent standards for X, Y, and Z, dependent on whether the tool is rotating, or the work is rotating?

I know this should be simple. Is it, and am I just anal retentive or something similar?

Thanks for helping me understand...

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So lets confuse it a little more.....

I guess you could refer to the carriage as M if the spindle traveled, but the spindle does not travel, so the carriage is predominant, so it becomes Z.

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