Newish vf3 can't hold location of .001, HFO says it's twisted. does that make sense?

I am wondering if someone can shed some light on an issue I seem to be having with one of our fairly new Haas VF3ss (1 year old)
We have 2 identical VF3ss machines, purchased about 6 months apart, and I have noticed some inconsistencies with the repeatability of the “older machine” as compared to the repeatability of the newer one.

The issue has shown itself during machining of a small part requiring features held within .001 concentricity to a previously ground bearing journal. On the “newer machine” this has not been an issue at all, I can hold .0003 fairly easily by sweeping in the journal and adjusting my offset accordingly. Typically The offset will stay consistent and I will continue to maintain my tolerance with little issue.

However this current run of parts was to be run in the “older machine” using the same fixture, I could not get the machine to hold the location tolerance at all. I went through my whole setup and ran a few tests to eliminate my fixturing as the issue.
To prove that the issue was independent of any of my setup, I indicated the journal within .0002, set my work offset to that indication, and set the z offset to cut above the part 1.0 inches. After running the program which did not cut the part at all, and moving the machine back to the initial work zero, the offset had drifted by .0009
I eventually gave up fussing with the machine and moved the fixture to the new machine and without changing anything in my program, or setup I ran the next part within .0003 with no issue

Is .0009 inch considered within the machines expected repeatability?

I spoke with my HFO this morning and a tech instructed me to place an indicator on the table and touch the spindle, while pulling along the x and y axis.. there was no dead spot or backlash, which lead him to believe the machine has twisted.

Other than sweeping the table, is there anything I can do to make sure that is the issue before I have them come out to re-level it?

Obviously .0009" is not acceptable, but what are you "Sweeping" it with? Do you have a level to check the machine with?

Normal repeatability is around .0002".

Mike

Sweeping it with a .0001 incriment dial test indicator in the spindle, with about a 10 inch circle (best I can do with the indicator holder I have right now)

I do not have a level that I trust other than some woodworking levels my co-worker has.

A quick check for twist that is a bit crude but can give an indication is to try how much torque is needed to turn the levelling screws. I think the VF3 has six and if they need about the same torque to move them in pairs across the machine then they are all carrying an equivalent load and it may not be level but it is supported more or less evenly. If there is a difference across the machine I would suspect it could be twisted and you need to go through the entire levelling procedure which I think is in the manual.

Note that the torque will differ between pairs. The pair of screws at the back under the column are carrying more weight than the front pair and the middle pair sometimes don't carry very much at all, which can mean the machine is sagging. Conversely sometimes people crank the middle ones to much and the machine hogs (that is hog meaning the reverse of sag not hog as in rip metal off).

Just get the Haas tech in there to re-check the machine for level. sometimes the machines do settle and move. and the woodworking levels won't work. At the same time have them do a ball bar test on it.

If it were an issue of wear in a ball screw of something like that, then moving the fixture to a seldom used location will show a difference.

Mike

I'd consider picking up a Precision level.
199Z Master Precision Level
It is pretty much the cost of having a tech come out and level "A Machine" for you...
If machine is way out...expect the machine to move abit after the tech leaves...it takes time for the casting to move.
It would be nice to verify it is still right on.

Building and floors shift, machines shift...it is not a once and your done forever.

Have another machine? is it level?

What do you do when you need to move machine over to make room for a new one?

How do you level your lathes now?

Even if you didn't go for the Master Level...a good machinist level is better then a carpentry level.

If you have a few machine you definitely want to pick up a good precision level. You should sweep the table and see what you see. A few months to half a year ago we were running a job on a VF-4 that is about 8 years old, where we sweep a bore and then machine an OD. Part was coming out .010 concentricity to the bore. And the problem did end being that for whatever reason the machine was no longer level. But you could see quite a bit of movement on the indicator sweep and it matched up with what we saw with the level. I had never had that problem before and was surprised how much of a difference leveling it made.

Make sure the level is good, and then redo your test.

Does the machine cut round holes? If not, the thrust bearings may need adjusting or what happened to our machine is some one adjusted the gibs trying to get cutter chatter out of their parts making the machine way to tight causing the machine to cut a four leaf clover.

Joe

You can get a very good level for less then $200.00

Athack

I used to run an 40x60 VMC that was "well used." We had a job that involved drilling/boring/reaming dowel pin holes in a casting. To get consistent parts we had to approach each hole in the same direction each time as we worked around the hole pattern. If you just rapided directly from one to the next they would vary +/-.0010 on location.