Where is Home XYZ000 Supposed to be located on a Mill?

Re: COORDINATE Systems and Onward Ho' Was: Where is Home XYZ000 Supposed to be located on a Mill?

Looks like I have been doing it backwards all this time, but I guess I'm not going to change now.:thinking: I might have to if I ever decide to start selling my controller software.

I don't know CNC but I don't see how you've got it backwards. "-X table moves right" equals "+X tool moves right". "-Y table moves toward column" equals "+Y tool moves toward column". "-Z tool moves down" equals "+Z tool moves up". It's a right-handed coordinate system with +Z up into the spindle and X along the length of the table. From my admittedly brief and incomplete research that is as near as it gets to an industry standard.
 
Re: COORDINATE Systems and Onward Ho' Was: Where is Home XYZ000 Supposed to be located on a Mill?

I don't know CNC but I don't see how you've got it backwards. "-X table moves right" equals "+X tool moves right". "-Y table moves toward column" equals "+Y tool moves toward column". "-Z tool moves down" equals "+Z tool moves up". It's a right-handed coordinate system with +Z up into the spindle and X along the length of the table. From my admittedly brief and incomplete research that is as near as it gets to an industry standard.

I guess you're right John, I was looking at the picture as the table movement rather than the tool. Glad you pointed that out.
 
Re: COORDINATE Systems and Onward Ho' Was: Where is Home XYZ000 Supposed to be located on a Mill?

I don't know CNC but I don't see how you've got it backwards. "-X table moves right" equals "+X tool moves right". "-Y table moves toward column" equals "+Y tool moves toward column". "-Z tool moves down" equals "+Z tool moves up". It's a right-handed coordinate system with +Z up into the spindle and X along the length of the table. From my admittedly brief and incomplete research that is as near as it gets to an industry standard.

This is correct. BTW: The conventions of X+, Y+, Z+ etc are indeed standard and not just so in CNC but in all milling. There is no standard convention for home positions though and Machine Home can be set anywhere you want it. There might be some brands of equipment that come preconfigured in a specific location -but it doesn't have to. And just to really make things crazy, I'm now getting ready to start doing some 4th dimension (rotary) cutting and things can get confusing. Some machines (like the Hurco I'm looking at) have built-in trunnion tables (5 dimensions) with finite ranges of motion. In those cases, the directions of movement have static definitions. My machine has a 4th axis that can be located in different places and I find myself triple-checking my strategies as I proceed.

Similar confusion takes place when folks learn to thread both LH and RH threads and furthermore, need to make ID and OD threads and/or do so with a conventional bit position or opposite-cut position. This can lead to confusion at first but, after a while, you'll find it comes second-nature.


Ray
 
Something to point out, the tool vs table movement issue is something that takes a bit of getting used to (took me a couple months to be honest). It especially tricky while jogging with the jog rate turned way up. Keep the jog speed low while you are learning, otherwise, it is very easy to go the wrong way, and snap a small cutter before you can stop or reverse direction.
 
One of the posts asks why the predominant convention is used (zero at the lower left corner of the part). I believe that this is because this is a drafting standard. The convention is to create a datum from which all other dimensions are measured. Most commonly this is the lower left corner of the part for a 2D drawing. So when putting the part on the mill, the convention was carried over. It doesn't have to be that way.

For most of us with milling vises with the back jaw fixed and the moveable jaw in front, this can be awkward, because you have to touch off the zero point every time you reinsert a new part. One way to avoid that is to index off the back, fixed jaw. But if you index off the back left edge, the dimensions are not to the drawing's datum. So you can make a case for indexing off the back right edge and reversing the sign of all X and y movement. Or maybe we should all go out and buy a new $600 milling vise with the fixed jaw in front...

Re the drafting convention, interesting bit of history: when I was in college, I signed up for a work-study program at the local bomb factory. Now I was an aspiring electrical engineer, but had to wait almost 3 months for the security clearance, sitting in an office outside the secured area (where all the interesting work was being done). For make work, they gave me a programmed instruction course on True Position Dimensioning. In TP dimensioning, all features are given a location and tolerance w.r.t. the datum. The text explained that this was to eliminate build-up of tolerances when features were dimension in a chain, like a series of holes. Cadcam has rendered much of this less important. Re getting the security clearance: the FBI finally interviewed me (a bearded kid from Berkeley ca. 1965) and asked me a lot of mindless questions, like "What magazines did your reference (my godfather) read when he was in college...(15 years before I was born!) This was back in the day of J Edgar Hoover and all of the FBI types had crew cuts and wore black suits with narrow black ties. It dragged on and on, no clearance, until by happenstance I was invited to a faculty party and introduced to the Dean of Engineering, who asked what I was studying. When he heard about my situation, he said he would contact the Atomic Energy Commission rep on campus...lo and behold, 2 days later my clearance was granted! I eventually did get to do EE work at the bomb factory, which was interesting and educational.

Craig
 
What convention is used for horizontal mills? Is +Z still into the spindle?
 
One thing to remember when setting up Mach 3The computer looks at the machine just opposite of how we see it. Picture it like your standing behind the Mill. It helps you to make a drawing of X +/-, Y +/- and Z +/-. Homing is nice to have but Once you get it set it's not really anything you need to mess with. Once you do get the axis homed you never need to touch it again.
There is a video on Youtube that explains how to set X, Y and Z to home. I seems complicated but it's not!
 
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