Re: xyz
Posted by
Jon Elson
on 1999-11-07 23:36:40 UTC
"Arne Chr.Jorgensen" wrote:
movement front/back is Y, and the knee up/down is Z. On machines with
a quill, the quill can be Z, although if you tilt the head, it throws off the
supposedly orthogonal nature of the axis system.
A, B and C would be rotational axes parallel to X, Y and Z, respectively.
U, V and W are auxilliary linear axes parallel to the X, Y and Z, respectively.
If you had both a quill and knee under NC control, the knee could be W, as
parallel to the main Z axis.
On real multi-axis machines, the A and B axes may be rotary movements of
the head with the spindle in it.
On a horizontal mill, I think the standards are the same, but the spindle is
parallel to Y, instead of Z.
As for polarity, the normal cartesian system is used to represent directions
on the PART, not the motion of the machine. So, if +X is to the right, then
the table of the machine must move left, so the tool is moving right relative
to the part. In the same manner, +Y is the table moving to the front, and +Z
is the knee moving down, or the spindle moving up.
move right, away from the chuck. +X would have the cross-slide
move away from the spindle axis, making a larger radius cut.
so the CNC control can know the physical limit positions, and report an error
before starting a move rather than hitting the limit switch during the move.
These coordinate systems are referenced from a 'home' position switch.
Machine error compensation tables also need the absolute coordinates to
apply corrections for encoder or leadscrew errors.
The relative coordinate system is usually referenced to the part being made.
machine such that the tool was just touching the surface of a part you wanted to
call Z=0.0, you could do an MDI command such as G92 Z0.0 to make the
relative coordinate for Z go to zero at this position.
so that all coordinates are positive, but you don't need to do so. For instance,
I have a bunch of parts that have a center hole that is the best reference point.
So, I make the CNC programs call that X=0,Y=0. I indicate to center the
spindle over the hole, and set X and Y to 0. Some coordinates will then be
+, some -. So, you CAN use all 4 quadrants, but you don't have to.
Jon
> From: "Arne Chr.Jorgensen" <instel@...>Normally, on vertical knee mills, the long table travel is X, the shorter table
>
> Hi,
>
> I have a simple question ( I hope ) and because may Netscape ( or
> onelist ) change space and tab, I use
> "." as seperator. ( wow - these drawings look like s...:)
>
> 1: ( a mill )
>
> .................V
> ----------------
> \__________________\
>
movement front/back is Y, and the knee up/down is Z. On machines with
a quill, the quill can be Z, although if you tilt the head, it throws off the
supposedly orthogonal nature of the axis system.
A, B and C would be rotational axes parallel to X, Y and Z, respectively.
U, V and W are auxilliary linear axes parallel to the X, Y and Z, respectively.
If you had both a quill and knee under NC control, the knee could be W, as
parallel to the main Z axis.
On real multi-axis machines, the A and B axes may be rotary movements of
the head with the spindle in it.
On a horizontal mill, I think the standards are the same, but the spindle is
parallel to Y, instead of Z.
As for polarity, the normal cartesian system is used to represent directions
on the PART, not the motion of the machine. So, if +X is to the right, then
the table of the machine must move left, so the tool is moving right relative
to the part. In the same manner, +Y is the table moving to the front, and +Z
is the knee moving down, or the spindle moving up.
>On a simple lathe, there are only 2 axes. +Z would have the carriage
> 2: ( a lathe )
>
> -+
> ...| --------------<______
> -+
> ....... \ .....\
> ----\___\ ------------
>
> What is the axis for (1) and (2) ?
move right, away from the chuck. +X would have the cross-slide
move away from the spindle axis, making a larger radius cut.
> Where is zero ?Anywhere you define it.
> Do you have an absolute, and a relative zero ?Some machines have absolute coordinate systems, which are generally used
so the CNC control can know the physical limit positions, and report an error
before starting a move rather than hitting the limit switch during the move.
These coordinate systems are referenced from a 'home' position switch.
Machine error compensation tables also need the absolute coordinates to
apply corrections for encoder or leadscrew errors.
The relative coordinate system is usually referenced to the part being made.
> What do you do in G-codes ?Umm, anyhing you want. In reference to the above, if you were to move the
machine such that the tool was just touching the surface of a part you wanted to
call Z=0.0, you could do an MDI command such as G92 Z0.0 to make the
relative coordinate for Z go to zero at this position.
> The thing is that I am just doing a little experiment, and I needIn milling and turning, you can often set some corner of the part as (0,0)
> to know how the thing really moves.
> I need to know if I have to use all 4 quadrants in the xy plane,
> and what is + and - direction.
so that all coordinates are positive, but you don't need to do so. For instance,
I have a bunch of parts that have a center hole that is the best reference point.
So, I make the CNC programs call that X=0,Y=0. I indicate to center the
spindle over the hole, and set X and Y to 0. Some coordinates will then be
+, some -. So, you CAN use all 4 quadrants, but you don't have to.
Jon