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Axis orientation (or, where is zero?)

Question on axis numbering

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Roy Garden03/04/2019 21:48:01
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21 forum posts
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20190403_191605.jpg

So, in an attempt to make life ever more difficult to avoid filing . .
Fitted the gubbins above to the mill to enable curve machining . . sort of . .

But, what I've now figured out is that I don't actually know what "normal reference" is for a DRO.

If I have the table back as far as it comes to me, and hard left(as I'm looking at it), is that 0x, 0y ?
So winding away from me and right the x and y increment?
Should Z be zero at the top and increment on the way down?

Before I start to play with the curve functions I want to be at least working with "standard" references. If I start with some halfarsed variation on axis increments I'll confuse my timid little napper even more.

What is the right way to have the numbers going?

(And yes, I'm tickled with the instal and yes, I have cocked up the Z axis reader, but it works . . and I may even get round to fixing it, maybe)

cheers
Roy


Clive Foster03/04/2019 22:19:33
1885 forum posts
59 photos

If your DRO system has the ability to remember multiple zero positions it doesn't really matter when you are going to be the only person using the machine. Just make sure you know how its set.

I view the table movements as being Cartesian co-ordinates with zero in the centre of travel, X going negative as the table moves to the right and Y going negative as it moves towards me. Other folk do it differently. You will have to experiment to get the hang of curve cutting. If your system is anything like the one on my Sino SDS2M system you will find it effective but needing considerable patience. Think CNC experience by manual moves. I did one job and decided life was too short! Admittedly a fairly ambitious job.

My Z axis is on the knee of my Bridgeport. I find it convenient to have Z negative corresponding to downwards movement of the knee i.e number goes up as the distance from cutter to work increases. I pay little attention to where zero Z actually is resetting whenever needed. I usually touch off the work with the end of the cutter, set to zero and move as needed until the correct depth of cut has been reached. Other folk prefer to set zero to the finish depth of cut which has advantages in that you always know where the end of cut is.

I frequently set temporary zero positions in X and Y axes depending on works best for the job. Invariably set to set to zero when using the 1/2 function to find the middle of a workpiece or part there-off.

I always work in absolute co-ordinates. Working relative can save some messing around with zeros but I don't like the potential for getting lost.

One fixed zero memory. No 1 is centre of X & Y travels. Always select that one and move back to zero-zero before shutting down. Most modern DRO systems will retain position memory after shut down but its unwise to rely on that. Disaster potential is high if it does go wrong and you don't notice before starting work.

Clive

Andrew Johnston03/04/2019 22:21:03
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4930 forum posts
560 photos

By convention on a CNC mill X positive is to the right, Y positive is away from the operator and Z positive is upwards. That's how my CNC mill is configured. The DRO on my manual mill is different. It's just how I set it up years ago and I see no need to change. I've only got X&Y on the manual mill, never felt the need for Z.

The zero can be wherever you like. That's an advantage of the DRO you can set zero to somewhere convenient for each job. That may be a corner on the work, or the corner of the fixed vice jaw, or the centre of a round workpiece. The important thing to note is that zero relates to the work not a set position on the machine.

Andrew

blowlamp03/04/2019 22:27:06
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1204 forum posts
82 photos

Z: spindle moving away from table is the plus (+) direction.

X: spindle moving over to the right of the table is the plus direction - table travels to the left.

Y: spindle moving over to the back of the table (or top when viewed from above) is the plus direction - table travels to the front/down.

These need to be correct for the various DRO functions to work predictably. smiley

 

Zero can be wherever you want it.

Edited By blowlamp on 03/04/2019 22:29:20

Edited By blowlamp on 03/04/2019 22:33:48

SillyOldDuffer03/04/2019 22:34:18
4836 forum posts
1017 photos

Not sure how your gubbins works Roy, but usually with a DRO you set zero relative to reference edges on the work. Starting with an new lump of metal, the first step is usually to mill a couple of clean edges from which the DRO can be zeroed on a corner. If it's necessary to move the work on the table, the mill can be re-zeroed back onto that corner. If a corner isn't convenient, another fixed feature like the centre of a hole can be used.

When working to a 2d drawing, it's easier to reference from the same points as the dimensions on the drawing. A good drawing will be dimensioned consistently to make this straightforward by choosing good reference points, such that the number of times it's necessary to re-zero or puzzle out positions is minimised. In an imperfect world, it's OK to shift zeros to a new start point provided it's always done from a known feature.

Dave

Roy Garden03/04/2019 22:45:35
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21 forum posts
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Many thanks,
It would appear I have X and Y standard and have Z reversed.
I'll change that.

Like RC, it doesn't matter how you do it, 'till you try to copy someone else, then you find out the differences and have to work around them, for me, being a biff, best if the differences are small.

Michael Gilligan03/04/2019 23:20:59
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14236 forum posts
621 photos
Posted by blowlamp on 03/04/2019 22:27:06:

Z: spindle moving away from table is the plus (+) direction.

X: spindle moving over to the right of the table is the plus direction - table travels to the left.

Y: spindle moving over to the back of the table (or top when viewed from above) is the plus direction - table travels to the front/down.

.

^^^ Easy to visualise as a graph, laid in front of you on the machine table

MichaelG.

JasonB04/04/2019 06:59:20
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Moderator
16521 forum posts
1755 photos
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Easy way to do it is look at the old handwheel dials. When they move in a positive direction your DRO should also move in a positive direction for X and Y.

John Haine04/04/2019 08:28:43
2691 forum posts
138 photos

? On my VMB the handwheel dials are identical so the "positive" turning direction takes the table in opposite directions depending which one you turn!

vintage engineer04/04/2019 09:04:54
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194 forum posts
1 photos

On production work, you may need to put zero on the edge of a set up. You should have a +/- button on the DRO so you can change direction at will.

Emgee04/04/2019 10:17:03
1265 forum posts
210 photos

A lot of the work I do on the mill is small pieces held in the vice, I set the X zero to the LH side of the fixed jaw and the Y zero to the face of the back jaw.
I use a length stop which is set as the LH side of the fixed jaw so part set-up is simple.

Z zero set to suit each part but normally Z zero is 1mm clear of the job, all tools used for the job are referenced to the No.1 tool in the program so after a toolchange the tool will be 1mm clear of the job to allow fast traverse to the working position.

Emgee

Neil Wyatt04/04/2019 10:40:26
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Posted by John Haine on 04/04/2019 08:28:43:

? On my VMB the handwheel dials are identical so the "positive" turning direction takes the table in opposite directions depending which one you turn!

Go by the right hand handwheel, except when there are two full moons in the month of the wind is in the North-East.

I suspect choosing the handwheel you use most would be the best option.

Neil

Edited By Neil Wyatt on 04/04/2019 10:41:02

Tim Stevens04/04/2019 16:05:23
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1098 forum posts

It can help to use as zero a marked point on the job in hand, for all three axes. Then if anything goes wonky, or you are in doubt, you can re-set the position or check it to make sure. A tiny centre-pop mark which will stay visible but won't mar the final product is all you need.

I think.

Cheers, Tim

Michael Gilligan04/04/2019 21:35:05
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14236 forum posts
621 photos
Posted by Tim Stevens on 04/04/2019 16:05:23:

It can help to use as zero a marked point on the job in hand, for all three axes. [ ... ]

.

Hence the 'Ickey Ball' : **LINK**

http://www.wdsltd.co.uk/product/3018/tooling-ball-reference-pin-ickey-balls-with-collar-wds-3505/

MichaelG.

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