[Steve Seebold]

I set a job up last night and aftet I ran about 4 parts I started losing the G54 position on the Y axis. Every part was about .010 off center and the more parts I ran, the worse it got. After about 8 parts, it was about .030 off.

After a thorough cleaning, I discovered the Y axiz stop had a significant build up of chips.

The cure was to run the X axis to its 18 inch limit and the Y axis to about minus 6 inches. That exposed the limis switch stops and I was able to give them a good cleaning.

I think a solution to this problem is to be careful where you blow chips, and if you start having a problem, STOP and clean the switches.

[TXFred]

Do you re-home the machine after every part? Why?

I home my machine when I start it, or when I have to hit the E-stop button, but that's about it.

I'm not criticizing. I'm always interested in how others do things. It's the best way to learn.

Frederic

[crawley]

what txfred said. not sure how the limit switches would affect positioning? I've never homed or ref'd my machine except for the day I got it. Maybe there is an advantage I don't know about, I'm pretty novice.

[Steve Seebold]

Do you re-home the machine after every part? Why?

I home my machine when I start it, or when I have to hit the E-stop button, but that's about it.

I'm not criticizing. I'm always interested in how others do things. It's the best way to learn.

Frederic

I use G91G28Y0. after every part, but when the switch or the stop cam has chips built up on it, then it will trip the home switch before the table actually gets to the home position.

Sometimes I will even use G91G28 X0.Y0. It just depends on what I am doing.

[TXFred]

I use G91G28Y0. after every part, but when the switch or the stop cam has chips built up on it, then it will trip the home switch before the table actually gets to the home position.

Sometimes I will even use G91G28 X0.Y0. It just depends on what I am doing.

See, I learned something too! I knew that G28 went home, but I didn't know that it could alter the home position.

At the end of my programs, I use:
M998
G59 P20
G00 X0 Y0

This lets me move the mill to a predefined point at the end of the program, for easier access to the table. It's a trick I learned from running a fully enclosed Haas. It paid to put the relevant parts of the table in front of the doors at the end of each cycle. And since the location is defined by a work offset, the operator could tweak the location without altering any g-code.

Frederic

[kevinro]

I set a job up last night and aftet I ran about 4 parts I started losing the G54 position on the Y axis. Every part was about .010 off center and the more parts I ran, the worse it got. After about 8 parts, it was about .030 off.

After a thorough cleaning, I discovered the Y axiz stop had a significant build up of chips.

The cure was to run the X axis to its 18 inch limit and the Y axis to about minus 6 inches. That exposed the limis switch stops and I was able to give them a good cleaning.

I think a solution to this problem is to be careful where you blow chips, and if you start having a problem, STOP and clean the switches.

Hmmm.... Not being a GCODE expert, G28 returns to the reference point? Does it reset the coordinates as well?

Knowing how limit switches work internally, I sure wouldn't want to rely on them for setting a precision position. They are spring loaded and subject to temperature changes which will affect the contacts.

[FuddMcDee]

I personally use G28 only on the Z axis, and G53 to end the program.
most programs end as such
G91 G28 G0 Z0 M5
G90 G49 G53 X-6. Y-0.5 M9

Kills the coolant and spindle and brings the table to a comfortable unloading position.

I'm with TXF, only after a start up or E-stop, though i can see how homing after each cycle could be benificial...

[crawley]

So I ran 72 parts today, 12 parts per cycle, 6 cycles total, 1.3 hours a cycle, about 8 hours total. I ended up losing less than .003 in any axis after running for 8 hours, and part to part that become meaningless. Like I said I've never homed or ref'd in thousands of hours of machine time, but I have no machining experience before I bought the tormach a few years ago and just kind of started milling stuff everyday and learning by myself. I'm sure there is a good reason but it isn't presenting itself to me- why would you ever home your machine?

[FuddMcDee]

Well, for our old busted machines (all 3 pre 86, with minimal maint since), homing the machines, at least on the z axis, serves as a way to mitigate any difference we get from cycle to cycle. I tried running a program that simply returned the Z axis to the same spot every time, and hole depths jumped all over. One could assume that you shouldnt have this problem on properly maintained machinery, but i like the idea of the machine refrencing a physical stop, as opposed to something it "remembers"

[crawley]

makes sense, thanks! I figure I kind of have the golden machine, I bought it from Tormach as a Demo, their first series II demo machine, and it has worked flawlessly since the day it arrived. It seems to hardly ever lose steps, many mornings, even after I hit the e-stop to shut it down the night before (and obviously the z axis brake takes over), it will lose less than .001 in z and less than .0005 in x and y. I figured they had this thing dialed in and it hasn't disappointed.

[FuddMcDee]

makes sense, thanks! I figure I kind of have the golden machine, I bought it from Tormach as a Demo, their first series II demo machine, and it has worked flawlessly since the day it arrived. It seems to hardly ever lose steps, many mornings, even after I hit the e-stop to shut it down the night before (and obviously the z axis brake takes over), it will lose less than .001 in z and less than .0005 in x and y. I figured they had this thing dialed in and it hasn't disappointed.

I gotta get one of those!
I'm surprised that it allows you to run without homing after an e-stop, maybe its just my self-learned programming, but i get an alarm if i try to run a cycle without the machine having "learned" home positions again.

[compunerdy]

I have used mine for over a year as well and have never once homed it besides the first say when I setup the machine.

[Gerry Sweetland]

Sorry, dumb question from someone who has only owned a CNC machine for a year but is "homing" the machine the same as "ref all" in the Mach3 screen?

I always ref the machine after I power it up and before I load the first g code program for the day. I then proceed to set my XYZ zeros for the program (vice corner, etc.) If I am going to run another g code file I don't necessarily ref all again as long as I haven't hit E-stop previously, I just set zeros again for the new part (most of the time just the Z as I almost always use vice corner as X and Y zero.)

But once I shut down the machine and controller for the night and start up the next day I always ref all before loading a program g code file.

Gerry

[philbur]

Correct execution of M998 requires the machine to be referenced. See section 7.9.2 of the user manual.

Phil

[TXFred]

Sorry, dumb question from someone who has only owned a CNC machine for a year but is "homing" the machine the same as "ref all" in the Mach3 screen?

Yup. Same thing. It's recommended to do it any time that the steppers may have lost position. So home after powering up, after hitting the Emergency Stop, or after halting a program in Mach by hitting the ESC key. All of these events have the potential to make the machine lose position.

Frederic

[compunerdy]

If you are going to turn on the machine and then zero everything to your part is there still some reason to ref all?

[Steve Seebold]

If you would like the machine to have any idea where it is, you should always reference all axis' before you run a part.

If you just bygosh and bygolly (ya know, plus or minus a hammer handle) work, then why bother.

[compunerdy]

I said if you zero all the axis to your part/program. How does this equal the machine not knowing where it is?

[AiR_GuNNeR]

If you are going to turn on the machine and then zero everything to your part is there still some reason to ref all?

If you lost steps, then it would be simply a matter of re-referencing and your part zero would be re-established. If you don't reference at all, then you would need to re-establish your part zero.
The other concern is some posts will output g code that sets the tool change position for manual tool changes based on machine zero. If you don't reference the machine on startup, who knows where that will take the spindle.

[compunerdy]

That makes sense. I was trying to understand the reasoning behind using Ref all/home instead of just zeroing the machine to the part/program since it seems a lot of people will talk as if it is a sin to not use it. I guess if you never use it and do not have problems then what difference does it make.