What is the "proper" zero origin

tommylight wrote:

Just putting this out there:
LinuxCNC can do homing in many ways, have 0 wherever is suitable, and sent axis wherever you want at the end of the homing procedure.
Some examples, besides the "normal" home switches at machine minimum and 0 at machine minimum,
-home switches at maximum travel and 0 at minimum
-home switches at maximum travel and 0 at minimum while end of homing sends the machine to maximum travel
-home switches at minimum and 0 at minimum while end of homing at maximum travel, used this a lot before PlasmaC as it would home and move the gantry away for easy loading of metal sheets on the table.
-home switches at max or min and 0 wherever is needed/required, just set the ini for positive and negative travel, and again ending up wherever needed.
 

Like I prefaced at the beginning of the thread, I'm aware of how to set it all up. I think that we established that "0" is kind of an arbitrary thing but there should be a "standard" way of doing things. I've been using LinuxCNC on a mill for like 6 years and I can't even answer where the "standard" for "0" is on a mill

So I think we established that generally XY 0 on a mill is the table run to the left and toward operator. Every movement in machine coordinates is negative.

So the question is if there's a standard for a gantry machine, is it still that the head XY 0 is forward and to the left  facing the front of the machine? Since the head moves and not the table, all XY is positive of 0.

From there we all know you can just do whatever you really want as long as + and - directions are right. There should always be a concensus that there is a "standard" way of doing things

rodw wrote:

My theory is the front of the machine should be defined from where the operator stands. The x axis should run across your chest with the positive direction running left to right. The Y axis should run away from the operator with the positive direction running front to back.

So if you get the directions right, its time to pick a point for the origin of the absolute machine coordinates. The most obvious point is front left so that all dimensions are positive. That's how I set my mill up.

 
 

What you're describing is backwards. If your table is front left your tool is pointing at the rear right corner of your table. If that is zero then all of your movements are negative. Directions never change, but they are always based on the tool, not the table. If you stood on your table with it zeroed at the front left and stared at the spindle while you moved the table to the right (you can only move it right) then your spindle will appear to travel left which is negative. Zeroing a mill table at the front left is the same as zeroing a gantry at the rear right.

blazini36 wrote:

Referencing to the front left is what you described a factory mill as doing, the difference here is that all travel after reference on the mill is negative of 0, and in this case with a gantry head all travel after referencing to that same corner is positive of 0. Is that correct?

Yep.

I think the common thread among commercial machines I've used is that the tool is away from the table front left at the home/reference point.

As you've pointed out, this means the mill table is at the front left, and the gantry head is at the back right.  Relative to the workspace, both machines have the tools at the back right.

Once the machine is at that position, it's a toss-up as to what the machine location is set to - either zero or max travel.

Just set that part to whatever makes the most sense to you.  Me - I like machine zero to be tool at front left of table/workspace so G53 locations are all positive.

blazini36 wrote:

rodw wrote:

Zeroing a mill table at the front left is the same as zeroing a gantry at the rear right.

No not at all. Here is my gantry with X0,Y0 marked with a yellow cross
 

Why would 0,0 on a milling table be in any different position?
Here is a cartesian plane I referred to
 

Both my milling table and my plasma table fall in the top right hand side quadrant where all dimensions the tool moves from 0,0 are positive.
What chance have we got if we can't understand each other

However in relation to the gantry, if the operating position was on a side (which it  will be if you had a 90 metre long gantry like ones I have seen), the origin could well be in a different corner. That's why I say it needs to be in relation to where the operator runs the machine from.

Why would 0,0 on a milling table be in any different position?

Because like I said 0,0 is referring to the XY coordinates of the tool not the table. It is never referring to the table ever. However on a standard mill you do not move the tool in X and Y, You move the table.

So on your router you move the head to the front left corner and your tool is at it's negative most X and Y so now call that 0,0. Stick a square piece of stock on center of the bed, which corner of the stock is your tool pointing at? Every move your tool makes from that point is positive of zero

Now go to a milling machine. Move the table to the front left call that X,Y 0,0. Stick that same square piece of stock on the center of the table, which corner is the tool pointing at? With your mill's table to the left front corner are you telling me that you can move anything in the positive direction on X or Y? I hope not because you can't.

Moving the table left on a mill is the same as moving the head right on a router because in both cases the tool is moving to the right of the working surface

 

Thats the thing. I always refer to the movement of the tool in relation to the table for any machine, not the table movement on a milling machine.

rodw wrote:

Thats the thing. I always refer to the movement of the tool in relation to the table for any machine, not the table movement on a milling machine.
 

Lol what? Now why couldn't you just say "oops you were right....brainfart". I once argued with PCW for 2 pages and had to say "hey I'm a dumbass" after I realized I was wrong.

Everytime I said what I said I was pretty clear about "moving the table", if you read what I wrote you knew exactly what I meant.

Thats the thing with communication. Its very easy to get it wrong and people get upset over it. I was taught that it was the responsibility of the sender to make sure the message is received as intended.

Perception is reality for a person even of its wrong. So what I perceived is not what you wrote.

I'm not saying either of us were wrong, its just that we were both misunderstood! 

I'm just messing with ya but look....

.......If your table is front left your tool is pointing at the rear right corner of your table. 

Directions never change, but they are always based on the tool, not the table.

Zeroing a mill table at the front left is the same as zeroing a gantry at the rear right.

That's from the 2nd post in this page. That's pretty clear if you ask me. If you argue against that as you did than you obviously oppose it. I didn't misundersand you, I understood that you were arguing against those statements right there.

I don't get pissed on forums, but every argument has 1 of 3 outcomes. 1) I prove you wrong and you say "oops", 2) you prove me wrong and I say "oops", or 3) somebody realizes they were wrong and says "well that's what I meant". The first 2 don't bother me either way, I'm not a fan of the 3rd.