Fanuc 21iT doesn't Zero out after home in Z

[Axxtion]

I purchased a used Fanuc 21iT on a Mori Seiki SL-3. It makes good parts and seems to run fine and hold tolerance.

The problem I'm having is that after power up, it doesn't zero out after homing Z. The X axis will zero out but the Z axis always pops up 11.8311. I have deleted all programs and offsets. I've tried to do the following that i found in a previous thread but i am confused about the homing methods it describes

1. Set 1815.5 (APC) = 0, 1815.4 (APZ) = 0, 1860=0, 1861=0 for the given axis
2. Power down
3. Power up
4. Set APC=1
5. Power down
6. Power up
7. Home the absolute axis. This can be accomplished with either manual referencing (if they have home switches), dogless (if they have the DLZ parameter enabled), double-bump torque method, or by MDI setting. Go with the method recommended by the machine tool builder. APZ should be 1 when completed. New values will automatically be loaded into par 1860 and 1861.

any ideas?

[dcoupar]

Check parameter #1240. I'll bet there's a value in there about 300000 (300mm). This is the coordinate value of the reference position. If you want Z to read 0 when you home it, set that to 0. You'll have to power off and back on.

This will drastically change the work shift and geometry offset values.

[stevo1]

Dave is correct to why your Z is reading that position. My question is what is the the problem with seeing this value once you reference the machine? The only time the positions matter is once you have activated your coordinate and tool offset. Then everything should read normal in your Absolute positioning.

Changing this parameter as Dave already stated changes the entire home position of the machine along with your tool offsets.

Stevo

[txcncman]

Machine Home Position and Machine Zero Position are usually not the same point.

[dcoupar]

My guess is that's what he's used to seeing. IIRC, the older Mori's I learned on all read 0 at Zero Return.

[Axxtion]

thanks for the response guys.

all the ref points and offsets where set at zero

i should have been more specific.

after powering up the machine and homing the machine, the control reads

relative x0.0000 z11.8311

absolute x0.0000 z11.8311

machine x0.0000 z0.0000

how do i get the relative and absolute registers to zero out on a cold start?

thanx again

[stevo1]

IIRC I don't think that you can. I believe that once reference is done the absolute will read the distance the machine is at from machine origin to 1st reference position. May I ask why you want it to read zero as the only time this position matters is once you active your workcoordinate and tool offsets in the program then everything should read normal. I don't have the manual with me here at home but I can double check to see if there is a parameter related to this tomorrow.

Stevo

[Axxtion]

my Z tool length offsets are in relation to the 11.8311 at the home position. If my part Z0. is 7.00 inches from the machine home, my Z offset reads 4.8311 rather than a -7.0000.

It seems that from a cold start and homing the machine, all registers should read zero?

thanx

[txcncman]

No. No. No. No. ALL registers will not read zero after a cold start and machine home procedure...UNLESS...the parameters of your machine have been set up that way.

I do not think I have ever seen a lathe yet that was set up this way. Mills, yes. Lathes, no.

I have seen Okuma lathes where the machine home position has like Z300.000. The machine was not even 300 inches long. Someone at some point set up the parameters that way. It did not effect the way the machine performed. It would cause a part zero to be located at 274.000 inches (From Machine Zero - someplace in space). When in operation, the CNC control would do all the math and when a tool was 1.000 positive from the part zero the "Absolute" position of the machine would read Z1.000. That was all the information I needed to see. Then I could allow the program to continue.

[Axxtion]

There is no problem making parts and i agree that it is more of a cosmetic/visual problem, but my old Fanuc 3t would zero out all the registers and i would like this 21i-t to do the same. maybe i'm an over the top anal retentive but hell, the x axis zero's out, why not the Z? :-)

[stevo1]

If you home out all the axis at first power up and then you program a G0X0Y0Z0 do any of the axis move?? I bet your X and Y stay put while your Z will move. You can also confirm this by looking at the values in parameter 1240 which is your 1st reference position. Your X and Y should read 0 while your Z will probably read 300510

Once your machine is referenced the absolute display will read the distance from reference position to machine home. That is why you are getting the difference in value. My guess is because the machine was setup to have Z0 at the chuck/table. I do this on most of my machines. Your tool offsets are probably reading all +values.

I do not believe that there is a parameter to change the absolute view once referenced because it will affect the view all the time. I will have a look in the manual and see.

You are not being anal with wanting everything to be the same. The problem is it all has to do with how your machine was setup. If it helps it sounds like the 21iT is setup how I normally setup my MT.

Stevo