Which Way Is Up?

[Nigel Graham 2Participant @nigelgraham2]

Whilst welcoming the general point of articles like Neil Raine’s, I was rather confused by his use of the “Z axis”

When I was at school and trying to learn A-level Maths, three-dimensional graphs went along a bit (x), across a bit (y), up a bit (z). I found the concept easy as I could relate it to Ordnance Survey maps I used for regular weekend walks in the countryside: East by NGR numbers, North by NGR numbers, and Up (hill altitudes – in feet at that time).

In later years vertical and horizontal milling-machines had Long[itudinal], Cross and Vertical travels.

I fitted a DRO to my mill: it calls the Long, Cross and Vertical travels, (x), (y) and (z), and I have noticed some writers use the co-ordinate letters generally. I use the words though, to avoid any confusion.

CAD: same Along, Across, Up (x), (y) and (z) convention: Z is vertical. If you rotate the view so the part’s Z axis becomes horizontal, that is with reference to that part so you still know its actual “top”. Or if you like, the axes are where they should be but you are “flying” around them.

 

Lathes and horizontal boring-machines: longitudinal and cross feeds still in the horizontal plane: (x, y). Add a vertical slide, as Mr. Raine suggests, or the borer’s rise-and-fall movement, surely its up-and-down travel is the vertical Z plane.

 

Or has someone somewhere deemed that just ‘cos it’s a lathe, the horizontal long travel is Z even though nowhere else?

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Similarly with any vertical drilling-machine on a fixed or magnetic base, bench, pillar or radial, the quill’s and head’s vertical movements are by (z).

Add a rotary-table to a milling-machine and you add a fourth, angular axis. Compound that by a second rotary-table or dividing-head on the first, adds a second angular axis so fifth axis altogether: as on some CNC machining-centres though they might be arranged in a different way. I don’t know what these two axes are called.

The plano-mill is a different beast, effectively a faceplate lathe standing on the back of its head, and the cross-slide working on a saddle that is now a cross-beam on two vertical columns. With its “long” feed now vertical, surely it works in the (Y, Z) planes as Y is still the horizontal, radial travel. These were (still are?) typically for turning and boring very large, heavy items more easily and safely set on a turntable than overhanging on the end of a horizontal shaft.

 

[Speedy Builder5Participant @speedybuilder5]

Simple- aeroplanes. X is along the fuselage

Y us along the wings

Z is up the tail fin

[David JuppParticipant @davidjupp51506]

The answer is ‘it depends’.  There is no single answer.

With machine tools the Z axis is conventionally aligned with the spindle.  So that gives different answer depending on the machine type.

With 3D CAD, there are 2 common conventions;

Option 1; the computer screen represents graph paper on your desk, X axis is from right to left across bottom of screen, Y axis is up the left hand side of the screen (so Z is out of the screen towards the operator).  The on screen view is like looking down from above.

Option 2; the screen represents viewing the scene from the side (looking out of a window at the world) – in this case Y is along bottom of screen and Z up the left hand side, with X out of the screen towards the operator.

All of these ways of arranging the axes are arbitrary – apart from the axes usually forming a ‘right handed set’ in how X,Y,Z are oriented relative to each other.

Confused?  Many people are.

[John HaineParticipant @johnhaine32865]

Mach 3 at least, and I think other CNC controllers, regard the lathe as being a milling machine resting on its left hand side.  So the cross slide becomes the X axis, the “bed slide” is Z, and if you had a vertical slide on the carriage it would be Y.

[John HaineParticipant @johnhaine32865]

Which is also why they call normal spindle rotation “clockwise” though from the operator’s perspective it’s clearly rotating anticlockwise! Got me very confused when I first did a CNC thread…

[BazParticipant @baz89810]

1. Nigel answering your question regarding rotary axes, a rotary axis aligned along the x axis, as you would put a dividing head etc on your manual machine is designated A, swivel the machines vertical head clockwise and anticlockwise and this is B axis

[Martin ConnellyParticipant @martinconnelly55370]

Pipe bending machines use YBC. B is rotation about the Y axis and C is rotation about the Z axis. So a piece of pipe makes a translational movement through the bend dies as a Y movement. The pipe then makes a rotation around this Y axis (plane of bend if needed), the B value, then the pipe is bent by the head making a rotation around the Z axis, the bend angle C

Martin C

 

[old martParticipant @oldmart]

Only being used to vertical spindle mills, I go for left-right=X, front-back=Y and knee and or quill=Z. As for lathes or horizontal mills, I have no idea.

[Nigel Graham 2Participant @nigelgraham2]

Thankyou Chaps!

Old Mart: a horizontal mill would be as for a vertical one. The axes refer to the table travel, not spindle orientation.

 

Happy New Year!

[David SeniorParticipant @davidsenior29320]

Just to clarify, on a modern CNC lathe the main bed direction is Z, so the main carriage moves along the Z axis (as David Jupp says, the Z axis aligns with the main spindle). What we would refer to as the cross slide is moving along the X axis, and if we had a vertical slide mounted on the cross slide, travel along that would be on the Y axis. The physical orientation (left, right, up etc) is largely irrelevant because the machines can be oriented differently (cross slides tend to be at the back and angled upwards)

With all the talk about the younger generation joining (or not) the ME community, I think it is important that we try and keep the terminology aligned with what is currently being used in industry, to avoid confusion.

I was watching a youtube video yesterday about setting up tool stores on a DRO. The gentleman doing the video was using the wrong nomenclature for his axes. When someone pointed this out in the comments, his attitude was that this was how he liked it so he was sticking with it. Endless confusion!

Dave

[Michael GilliganParticipant @michaelgilligan61133]

I’ve had this tucked-away for reference

Today is probably the time to share it

It doesn’t answer Nigel’s opening question … because the answer to that is

“it’s a matter of choice”

… but it does properly define the relationship of the six axes:

MichaelG.

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[NealebParticipant @nealeb]

Michael’s little picture also illustrates another common convention – when you see the little XYZ axis diagram on a CAD screen, they generally seem to be colour-coded so that RGB maps to XYZ. Useful to remember when the letters are too small to read!

Setting up a DRO for the first time can confuse – it’s the business of table moving left versus tool moving right. Get it wrong on a manual mill in your own workshop and you can probably live with it. Get it wrong setting up a CNC mill and you will be out of step with every CAD/CAM package on the planet!

[Michael Gilligan]

On Michael Gilligan Said:

…  doesn’t answer Nigel’s opening question … because the answer to that is

“it’s a matter of choice”

… but it does properly define the relationship of the six axes:

MichaelG.

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Michael’s diagram is my starting point; same as SpeedyBuilder’s definition, except Speedy’s version is simplified and easier to remember, hurrah!

For historic reasons X, Y and Z are messy.  Wise engineers should approach axes with caution because there are several alternatives, and the other guy might be using a different system, or maybe he’s confused.  On this forum, discussing lathes, mills, and cross-tables, I prefer front/back, right-left, and up-down to axis names.   Less ambiguous in the workshop I feel, though unhelpful in CAD or when forced to do coordinate maths.    Then I switch to Speedy-Michael!

Z is tricky.   I was taught “Y to the sky” at school (2D O-Level), which is downright confusing later, because Z is up-down in 3D geometry.   Worse, in the real world, there is no up!  The earth’s surface appears flat to us but isn’t, and, as blobs of flesh sat on it, it feels clear what down is.  Not so, the earth is a large spherical mass,  and we are pulled towards the centre.  That means ‘up’ varies with where we are on the planet, hence jokes about Australians being “upside down”.  Beyond that, planet earth isn’t the centre of the solar system, our Sun isn’t the centre of our Galaxy, and our Galaxy isn’t the centre of the Universe.  Everything spins on it’s own axis.  There isn’t a single frame of reference.  There is no ‘up’.

On earth up/down being a bit different for everybody rarely matters, thank goodness.  But it can’t be ignored entirely because there are many engineering problems where it bites.  For example, levelling the long lathes used to turn ship propeller shafts.  No need to account for the curvature of the earth on a lathe bed only a few metres long, but curvature error grows with bed length, becomes serious, and eventually has to be engineered out.

Dave

 

 

[Michael GilliganParticipant @michaelgilligan61133]

Which way is Up ?

https://youtu.be/0ZoSYsNADtY?feature=shared

MichaelG.

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[noel shelleyParticipant @noelshelley55608]

Gentlemen please ! It’s the first of the New Year, lets just have simple sums or sit in the corner and recite your times tables ? HAPPY and hopefully HEALTHY New Year to you ALL. Noel.

[Nick HughesParticipant @nickhughes97026]

Another couple of diagrams for you:-

 

 

[ChrisLHParticipant @chrislh]

I’m not only confused about which way is up, I can do it with left & right and away & towards. After several sticky moments not being sure which way to go I marked up my machine so that I could check twice and cut once. In my case not helped by my Y travel being opposite to that on most machines.

This is the first time I have attempted posting photos on the new forum and it’s a case of being easy when you know how. But because I didn’t know how it’s taken me all afternoon to do it; surely something more that just “click the photo ikon” in the “how to” section could be risked. Just pointing out the presence of the little draggable squares in the corner of the image could have saved me hours of frustration.

[Author]

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