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Mazak Powerturn 2000. Z home danger?

Solidus

Aluminum
Joined
Jul 20, 2004
Location
Melb Australia
This is a large (28", 2m BC), older (fanuc 6T) lathe which, due to its long bed, has a movable Z home stop clamping to the front way. It was supplied with a scale running just under the way, now missing, which allowed approximate repositioning of the home stop via a pointer. The scale was removed by a previous owner.

After reading the thread about the possibility of encoders' rev counters reading incorrectly if homed in the proximity of the reading heads, I got worried and informed the boss that presumably the missing scale registered the safe zones as well as aiding positioning. He countered that since the manual made no mention of the subject, our machine might use a different encoding system. I countered that the older Mazak manuals are more like a fill in the blanks game.


He is prepared to listen on the subject, but leaves me to do the legwork :rolleyes:

Anyways, after a little research, I don't see any possibility other than I (and my boss) am leaving myself open to a pretty nasty crash at some time due to this problem. My last job was turning 300lb gear blank forgings at up to 300 rpm :eek:

Can anyone give me somthing definative on this one?

Cheers all, Vincent

[ 02-05-2006, 07:18 AM: Message edited by: Solidus ]
 
ON LONG BED LATHES I CHANGE THE PERAMETER SO YOU NEVER HAVE TO ZERO RETURN Z. SLANT BEDS THAT CAN TRAVEL PAST THE TAILSTOCK ARE THE EXCEPTION. WHEN USING THE TAILSTOCK IT SURE MAKES LIFE EASIER. AS FAR AS A SAFE ZONE I HAVE NEVER SEEN THAT AS A PROBLEM. MOST PARTS ARE IN THE 500 TO
7000 LB RANGE.
 
Tex, that's an interesting bit of advice. I'll look through the parameter manual for that one. Seems that not too much would change in the running of the machine. I guess at start up you would simply rezero at the job face rather than hit the home position?

As for anyone else who may be able to help, don't be shy, I'd like to get to the bottom of this one!

BTW-The following thread was what allerted me to this problem

THREAD

summed up by this post by machtool

Pete.

I’d concur with you on setting the reference switch at a half pitch away from the reference null on the encoder. We were always taught to do that. Get the machine to reference off the encoder, then looking at your diagnostics for the ref switch, MPG the axis away from the switch until it breaks, then MPG back slowely in the approach direction until the switch just makes, and note the axis position. Then adjust the switch dog until its half a pitch away from the true zero encoder position. You can do that with a multimeter if it’s on a machine with out diagnostics.

The theory being that if you put the switching position 180 degrees away from the reference pulse, you have the most available tolerance for error. So the axis has plenty of time to decel and find the reference marker.

I see that occasionally, when it’s been set up too close to the ref marker. The switch can get gummed up with coolant or swarf, and react a bit slower, and the axis home will jump 6 – 8 -10mm Regards Phil.
I'm still curious as to the answer to the initial question so I"ll rephrase .

Since on my machine the Z limit switches are triggered by the movable Z home, I have no way of ensuring the micro switch and masterpulse are not triggering too close together.

Am I correct in this?

What part is played by the scale (missing on this machine) in solving this problem? A new scale is $1000 US so we will only buy, or have one made if it will solve a problem.(Tex may have already solved it
)

Thanks Vincent
 
I guess at start up you would simply rezero at the job face rather than hit the home position?
YES.
ORIGIN W AT FACE WITH FACING TOOL.
MOVE Z AWAY FROM FACE G50 AMOUNT FROM FACING TOOL.
ORIGIN W. THIS IS YOUR HOME.

Am I correct in this?
YES.
THAT MAZAK SET UP WAS AN AFTER THOUGHT. THAT TYPE BED WAS WHAT THEY WERE MAKING FOR THEIR MANUAL MACHINES AT THE TIME THEY GOT INTO CNC'S.


"DON'T NEED NO STINKING SCALES!" :D
 
Tex. This might sound like a stupid question but hey, I've only been G coding for a year (and that's been by the seat of my pants :D ). Will G28 still work without the Z home? Save me wasting ten minutes at work tomorrow. Yes or no will do


I like the old girl. My skinning cuts on those forgings ran up to 1/2" at times at around 20 thou feed and she didn't complain. Tho I should start looking in to torque ratings at some stage. The power meter never topped 40% so I assumed the 40 HP was adequate. She'll cut within a thou all day long if you mind the offsets while she warms up.

Cheers Vincent
 








 
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