[acrodave]

I have a Comet VMC I acquired last July, and have been working on it off, and on since..... I now have it running consistently, but have found an annoying trait, which I am sure is something I am doing.....

Every time I change tools, the thing will run the Z axis to about 3 in below the part zero position, before coming back up to the normal z-up depth, after which it runs fine until I do another tool change ..... disconcerting to say the least!!

As long as I position the XY such that there is room for this "excursion", before doing a tool change, it runs fine ......

Idea's as to what I'm doing wrong??? I'm new to the Mits control, as all of my other machines are Haas.

Dave

[HuFlungDung]

Perhaps this is a result of a cancellation of the tool length offset? Haas is pretty convenient in this regard, as it has a couple of different systems to reckon the tool length offset.

I am not sure what kind of tool change macro the Mits uses, but you might try adding in a return to Z home before you call for the next tool. This should lift the tool well up and out of the way so that if it does a curtsy, it won't hit anything.

Another possibility to check for, would be a parameter setting which affects whether the tool length offset executes as an immediate discrete machine motion, or whether it combines with the next movement of the axis. I know Mits lathe has a parameter to this effect, don't know about mill.

[Caprirs]

I suspect there is a line in your tool change macro which references a G30 Z Pp. This may have been done as a position check or something. You can take a quick look to see if there is something odd set in the parameters. Run the tool change macro and see if the Z-to-China move is being called by a G30 Z P. If so, you'll need to change a parameter.

To access the machine parameters, from the DIAG/IN-OUT screen, press the soft key for PLC-I/F. In the bottom fields, enter 1001 in DEVICE, leave DATA blank, and put M into MODE then press the INPUT key. Then TOOL/PARAM screen and use the soft key for ZP RTN. Press the NEXT key twice to view the Z axis. Look at the right column for parameters 13-16 (#1_rfp-#4_rfp).

Typically, #1 and #2 are used for the high and low tool change positions on carousel/umbrella style ATCs and #3 and #4 are zero. If your machine has a swing arm ATC, I would guess only one of the four reference point returns is used.

[HuFlungDung]

Could also be something as simple as forgetting to use a G91 with your G28
G91 G28 Z0
behaves differently than
G28 Z0

[acrodave]

Thanks everyone, I will try these possible solutions, and let you know if any of them fill the bill......

CNC machines ...... the ultimate in a love/hate relationship!!!! ;<)))))

Dave

[onthebumper]

Look in your control paramters. Turn on M Point Neglect. This will solve your problem.

[acrodave]

Well........ I've tried all of the below, to no avail ..... it still does it.

Parameters 13-16 (#1_rfp-#4_rfp) are all zero, it that makes any difference.

I have noted one thing, which is, undoubtedly, significant...... any time I do a tool change, it changes the tool, then moves to the XY position I ask it to do for a clear area, and then goes down in Z to below the workpiece ..... there the spindle starts, and then it raises to the Zup position, and continues on normally...... What I have discovered is that the Z goes down to the exact position where the tool was set. I use an indicator mounted vertically in a stand, and set all of the tools to that height ..... the part Z zero is then referenced from that indicator.

As it happens, the parts I'm running now have the part Z zero at, about 2 inches above the indicator position, so the tool plunges that amount below the part zero before coming UP to the Zup position.

It's clear that this means something, but I still haven't been able to figure out WHAT. I am sure that if I set the tools to zero at the table level, it would plunge to that position ......

When I ran parts which had the part zero, below the tool set point, this problem did not arise, but it would have if the part zero was less than the zup amount below the tool set point.

I tried eliminating the G28 before the tool change ..... no difference ....... same for adding a G91 before the G28.

I suppose I could raise the tool set position up a foot, and the problem would go away, but It would sure be easier to figure out why this is happening.....

I'm still mystified .......

Any other idea's????

Dave

[HuFlungDung]

I think what you are witnessing is the execution of the tool length offset. I'm running a Meldas 50L, and I know there is a setting for it which has to do with the execution of the tool length offset, either as a seperate motion (like yours is) or combine the tool length offset with the next motion command.

You might search through your manual and see if you can find a similar setting.

If there was no option to permit combining the length offset with the next move, I would take the precaution of always setting the tools to a guage that is higher than the top of the workpiece. It decreases the pucker factor if the length offsets are never so long as to bring the tool down to G5x Z0 even by accident.

[Caprirs]

How about adding a G49 code just before executing the tool change? G49 should cancel tool length offset comp.

Can you post up your tool change macro for us?

[acrodave]

I tried the G49 ...... no difference.....

How do I get to the Tool Change Macro??

Dave

[Caprirs]

To access the ATC macro, the Edit Lock C parameter must be turned off.

- Go to DIAGN-IN/OUT screen and press the soft key for PLC-I/F.
- At the bottom of the screen in the first three fields, enter 1001 in the DEVICE field, leave DATA empty, and M in MODE and press input.
- Go to TOOL/PARAM, and press the soft key for BASE.
- Use the NEXT key to get to page 5/10.
- Change #7 edit lock c to 0.
- Go to MDI/EDIT and press the soft key EDIT, then FILE. Look up the ATC macro file number and open it with the editor or output it to your PC. If you make any change to the ATC macro, be sure you have a back up copy.
- Edit Lock C will revert back to it's "protect" setting when you power the control off and on again.

[HuFlungDung]

What does setup parameter #1099 and #1100 look like on that control? Name and value?

[acrodave]

Hmmmnnn ....... I guess I will have to "fess up" again ......

I cannot find any parameter that would approach that number....

The only ones approaching that number are the ballscrew compensation parameters, and all of those are set at zero.

Fact is that in "setup" I can only find 20 parameters....

I've spent a lot of time with the manuals, and in front of the machine, and cannot find these parameters.....

Dave

[chippy1]

The M520AM does not have #1099 or 1100 parameters. That would be on an M50 or newer control.

You talked about finding the ATC Macro. You should be able to see a program in your file page that is labeled as 9000 or greater. This program Macro is locked by edit lock C as was indicated by Caprirs. Follow his instructions to unlock. Once in the machine parameters you should see a menu for Macros. You may have to tap the menu button once more to change to the second page to see it. Menu 6 Page 1 of 2 (6-1/2). You can locate the Macro program file name on that page.

Below, one of the suggestion was to turn on M-Point Neglect in the Control Parameters. Did you ever do this? You may have to power down the CNC to make this parameter take effect.

Regards,

Chippy

[acrodave]

I tried the M point neglect parameter both ways, and it made no difference.

The only thing which has made any difference is, effectively, setting the tools about a foot off of the table (using my toolsetter, which is about 2 in high, and then adding 10 inches), and then setting the work z accordingly.. That eliminates the dip below the part zero.

This leads me to suspect that it is connected to when the tool offsets are applied, as has been suggested ....... but I cannot find any parameters which seem to address this ....

I'd sure like to thank everyone for all of the helpful suggestions ...... I'm sure we will figure this out ....... if we live long enough!!!

Dave