Need Help!- "absolute" position doesn't read correctly

[Joe.B]

Hello all!

It is nice to be here. I have been wanting to create a profile here for a while & have finally done so.

My question concerns a Fanuc 11M control (Mori Seiki MV-80).

What is your procedure for setting Z0 & setting the length offset (or, some call it the "height" offset) for your different tools?

Why do I ask?

I've never ran old mills like this before. We set Z0 to the center of the 4th axis. If I program a move to Z2.5, then I'd expect to see Z2.5000 in the ABSOLUTE position when the program is executed.

Unfortunately, this only works for the 1st tool that is set. If, for example, the 2nd tool is 1" shorter than the 1st tool (and I program this 2nd tool to come down to Z2.5), the absolute position will read Z1.5000

[txcncman]

On a Fanuc control, you should have 3 screens to show position. Machine. Absolute. Work.

Which screen are you looking at when you say it reads incorrectly?

Try viewing all at once. Press "POS" hardkey and "All" softkey.

[Joe.B]

Hello, txcncman.

The "ABSOLUTE" one is not correct.

What is your procedure for setting Z0 & setting the length offset (or, some call it the "height" offset) for your different tools?

[txcncman]

My setting method depends on company procedures and the job at hand. If it is a one or two tool job with only one work offset, I bring each tool down and set off the top of my stock material and make adjustments from there. If it has a lot of tools or will use multiple work offsets, I set all the tools off the table with a 1-2-3 block and then adjust the Z's for the work offsets. I work off the Machine numbers for setting.

I still do not understand why you think the Absolute position is incorrect. Is it reading incorrectly during program execution. During program execution, once the tool is called up (G43 H_) and begins moving toward the part, when it says positive 1.000, the tool tip should be 1.000 above your set Z zero point on the part.

[Joe.B]

Originally Posted by txcncman During program execution, once the tool is called up (G43 H_) and begins moving toward the part, when it says positive 1.000, the tool tip should be 1.000 above your set Z zero point on the part.

When the tool tip is 1.000 above the Z0 point... the absolute positon does NOT read 1.000.

The question is why.

[txcncman]

Well, you did not confirm or deny if this reading was during program execution.

Can you take a photo of the screen showing all the readouts with feed hold engaged and post it?

[Joe.B]

Originally Posted by Joe.B If I program a move to Z2.5, then I'd expect to see Z2.5000 in the ABSOLUTE position when the program is executed.

Yes, I did say "when the program is executed."

Now, if you can visualize the spindle comes down in Z... it is in single-block, so it stops once it executes this block of code: G44 Z2.875 H2;

Now these are all the numbers:

-16.861 = MACHINE POSITION
-19.213 = G54 POSITION (this is where the center of our chuck is)
2.875 = The actual distance of the tool above Z0.
0.000 = COMMON POSITION
-.476 = The tool's height offset (G44 is being used)
0.000 = The tool's wear offset
2.875 = what the program says
3.351 = ABSOLUTE POSITION

Note:

It is programmed to be 2.875 above Z0.
The tool is (in fact) 2.875 above Z0.
BUT ABSOLUTE READS 3.351.

Obviously, the control is taking the height offset & subtracting it.

i.e. 2.875 -- .476 = 3.351, which is the ABSOLUTE reading.
(If you subtract a negative, essentially you are doing addition.)

The problem is:

How do you get it to read Z2.875 in ABSOLUTE, instead of 3.351?
You can't take the height offset out... the tool would no longer be set right & would crash into the part.
You can't move the G54 or the COMMON... because that's where you want Z to be (relative to the chuck).
Putting something in the WEAR does you no good.
And you DO NOT want to "lie" in the program. You want Z2.875 (period).

So... now what can you do to this raggedy, old Fanuc 11M control?

[txcncman]

What happens when you use G43 to invoke Tool Length Offsetting? I have never ever operated a machine that used G44.

I am also surprised you have a Tool Length Offset of -0.476. You should have started with a Work Offset of 0.0000. On setting the tool length to the part, the table, whatever, I would expect it to be a much larger negative number. Tool Length Offset is the distance the Z axis must travel to the zero setting point. If you have 20.000 of Z travel from the table to the spindle face, and you load a tool that is 4.000 long, when you bring it down and touch the table you should have moved the Z axis -16.000. This number should be your Tool Length Offset. To find the Work Zero Offset, it would be the distance the Z axis need to travel from your tool setting point location to the desired Z zero point. If the center line of your rotary axis is 8.000 from the table, this would be the value for Z in your Work Zero Offset. I am thinking you have entered your numbers in the incorrect registers.

[Joe.B]

G44 & G43 has nothing to do with the problem.
If I had used G43 instead, the required offset would then be 0.476 instead of -0.476. That's all.

[txcncman]

My other suggestion for testing this situation is to leave the Work Zero Offset for Z at 0.000 and set the tip of the tool for the part zero by whatever means is conducive, such as putting a piece of 2.000 round stock on the rotary axis and touching the tool to the top, getting the Machine Z value, subtracting 1.000 for the radius of the stock and then putting that new value in for the Tool Length Offset. Execute the program and record the results.

[Joe.B]

Originally Posted by txcncman My other suggestion for testing this situation is to leave the Work Zero Offset for Z at 0.000 and set the tip of the tool for the part zero by whatever means is conducive, such as putting a piece of 2.000 round stock on the rotary axis and touching the tool to the top, getting the Machine Z value, subtracting 1.000 for the radius of the stock and then putting that new value in for the Tool Length Offset. Execute the program and record the results.

This makes the ABSOLUTE show a number that is really, really, different than the programmed number.

[Joe.B]

Originally Posted by Kenvin Is it reading incorrectly during program execution. During program execution, once the tool is called up (G43 H_) and begins moving toward the part, when it says positive 1.000, the tool tip should be 1.000 above your set Z zero point on the part.forest wall murals

It SHOULD say the programmed number... but it doesn't.
If the tool is programmed to be 1.000 up...
and the tool comes down to 1.000 up...

ABSOLUTE will not say 1.000 up.