On 03/20/2015 09:47 AM, Marius Liebenberg wrote:
A question for the the avid machinists among us (not me that much). I have my mill setup to have the x axis travel along the table (long axis) and the Y axis is the short travel. My homing sequence brings the table all the way left and forward to put the tool at the right hand back corner.If that is the right way of doing it, is the travel negative for both axis from home or is it done another way?
The homing feature sets the zero location for G53 which is the machine space. Setting the limit values in the .ini or configuration file relative to this machine zero tells the software where the motion limits are. The machine will travel to this limit and stop instead of hitting a firm limit such as a limit switch, or a hard limit which is metal to metal contact. The firm limit causes an error which requires some effort to clear. Hitting a hard limit can cause damage, overload or e-stop. The soft limits also allow the software to warn you if a g-code program or move will try to go beyond a limit. Generally, the machine zero and limits don't need to be really accurate, unless you want to reuse fixtures or if something like a tool changer needs an accurate machine position.
On my Shizuoka mill, I jog each axis to match up two zero marks (tape actually), which gets me close, then I fine jog to zero the hand wheel dials and set home. This gets me to the machine zero within the accuracy of the machine. If I have a vise that I zeroed with a user workspace such as G54, I can reuse that workspace with reasonable confidence.
On the Tormach mill that I'm using, the homing is set up to use home switches. I press the home button for each axis and the machine automatically scans for the home switch and sets zero within the accuracy of the home switch. I have a probe on this machine, so it is convenient to probe for the workspace zero each time I need to, so reusing workspace zeros is not needed nor desirable. The machine zero only needs to be accurate enough for limits. Attached is an example of the machine zero at the top left corner, where the tool is, the machine limit space in blue dashed lines, and the workspace zero where the axis pointers are. In machine space, all Y and Z moves are to negative position values.
Many people don't set up machine home or limit positions and set the workspace zero for each part. The machine zero is wherever the axis positions happen to be when the machine is powered up. This runs the risk of hitting firm or hard limits,and doesn't use software to be smart with handling limits and zeros.
-- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/
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