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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.
You can buy good parts or you can buy cheap parts, but you can't buy good cheap parts.
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
[URL="http://www.pure-geometry.com/"]Pure Geometry LLC[/URL]
Vertical Lathe tool holders and more.
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.
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.Originally Posted by TXFred
Sometimes I will even use G91G28 X0.Y0. It just depends on what I am doing.
You can buy good parts or you can buy cheap parts, but you can't buy good cheap parts.
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
[URL="http://www.pure-geometry.com/"]Pure Geometry LLC[/URL]
Vertical Lathe tool holders and more.
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.
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...
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?
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"
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.
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.
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