g54 issue

hi

i am having problems with homing the z axis (g-54) on my machine.
i have somehow managed to change a parameter that resets my z axis to "-.5010" i tried many things to get it to stay at zero, with no success.
i will rehome everything to zero, but after i select rehome z and confirm that i wish to change the setting as it is already homed, it stays to that negative value.
i tried different files, and even no files while resetting and i get the same result.
HELP!!!

Are you confusing the idea of "homing" and "touching off" an axis (aka setting the G54 coordinates)?

It sounds like you touched off the Z G54 coordinate system such that the machine Z0 position (home position) equals -.5010. Rehoming the Z axis will not change the G54 coordinate offset. There are a few ways you can return the G54 offset to 0. One way is to use the touch off button (Axis Gui) and set Z=0 (when the machine is at the home position.) Another way is to use the MDI command G10 L2 P1 Z0 (doesn't matter where Z is located), this will directly set the G54 Z offset to 0.

Another possibility is that you could have a G92 offset in effect. Clear that by issuing the MDI command G92.1.

well, that was painless! thank you!
could i impose on your generosity of knowledge sharing one more time?
1) how did i create that mess?
2) could you explain the offset/touch off buttons and how to correctly use them?

jacques

i suppose one of the nice things about getting old is the patience factor also grows....
so, now the problem is that when i use the step mode to proceed with the design, as soon as the spindle powers up and reaches it's speed, the next step is that it will plunge into the board right to the end of the shank! but i do not see any values other than zero after i home the 3 axis.
is there a way of making sure that all of the settings are reset to zero? perhaps in my fumbling around yesterday, i changed the default zero values in assorted places....

jacques

First I have a question. Do you have home (or limit) switches on the machine so that you can have repeatable homing positions?

Having a consistent repeatable home position makes using the work coordinate systems (G54-G59.3) much more useful.

When you home the axis, you are setting the "Machine Coordinates". This is the base positions everything is measured from. So if your machine origin is X0 Y0 Z0 and that position is Z at the top of it's travel, X all the way to the right and Y all the way forward. That is great but it doesn't help you much when running any real parts programs.

Ok you have a program you need to run. It mills a part held in a jig, or some sort of fixture on your table. Your G-code file is setup such that the top front right corner of the part needs to be located at X0 Y0 Z2.0. You set up the part in the fixture and low and behold the top front right corner of the piece is not at that position, it is somewhere in the center of your table and several inches down from the top of the Z travel. Here is where the work coordinates and touching off come into play. You just jog the machine so the point of the tool is at the top right front corner of the piece then touch off the G54 coordinates to X=0, Y=0, and Z=2 (or use MDI command G10 L20 P1 X0 Y0 Z2). Now you can run your file.

It gets even better, say you have 3 identical fixtures in a row on your machine. You can set up G54 for one, G55 for the next and G56 for the 3rd, then run all three parts using the same G-code, and just change the work coordinate system.

It is very nice for repetitious work, when parts can be changed out in a fixture and always located in the same spot.

nope, no limit switches. should i get some or is it just "a toy"?

... You just jog the machine so the point of the tool is at the top right front corner of the piece then touch off the G54 coordinates to X=0, Y=0, and Z=2 (or use MDI command G10 L20 P1 X0 Y0 Z2). Now you can run your file...

1) i assume that "top right" is arbitrary-- that the xy point can also be "bottom left" ?
2) what is the difference between using the "home axis" button, the "touch off" button, and the "tool touch off" button? which of these 3 are you referring to to touch off the g54 coordinates?
3) i understand (i think) that in the mdi string x0 sets x=0, y0 sets y=0, but z2 sets z to what? don't i also want z=0?
4) so when i set the xyz parameters in the cam software, that is the xyz of the table, not the xyz of the material blank?

excuse my dumb questions. i just want to understand rather than doing something blindly....

jacques

p.s. you explain things in a way that is so easy to understand....

jacques

1) Yes completely arbitrary, Use what ever is convenient for the part you are machining and the code you are using.
2) On a basic hobby router with no home or limit switches there may not be much difference. but on more complex machines it can be vital that the home position is always in exactly the same position. (for example on a machine with an automatic tool changer) Also having a repeatable home position allows you to take advantage of the soft limits, and tool offsets (if your machine can do tool changes with repeatable tool lengths).
3) Say the G-code you are running is configured that Z0 is the bottom of the 2 inch thick piece. It can be a lot simpler to touch off to the top of the piece than the bottom. You touch off to the top and set the value to 2. When you touch off you can set that position value to what ever you need it to be, again it is completely arbitrary.
4) What ever works for you and your system of how you get things done.

as per usual, your answers are precise and to the point. thnx again.

jacques

p.s. i suspect i will have other questions for you in the future....

jacques

jlroch wrote:

nope, no limit switches. should i get some or is it just "a toy"?

Home and Limit switches certainly are not toys. They can very important. They are especially important on large powerful machines capable of damaging themselves if limits are exceeded.

On a small light hobby router (a toy) where the machine can slam into a hard limit stop without breaking anything, limit switches probably are not very important, but home switches can still be useful.

well, my "toy" is not a toy, it's a shop machine, so i will get limit switches installed (machine was custom made, so it wasn't something i thought of getting).
thnx again.

jacques