Problems with Haas spindle bearings?

[barryhc]

Hello:

I'm having some chatter problems recently with a Haas VF-6. I have checked just about anything you could think of, and all conditions seem to be good. I suspect the spindle bearings may be just a "tiny bit" less preloaded than when new, and "recently". We are cutting titanium, and we are very good at it.

There is no spindle noise, and no other indication of trouble. Four different cutters however for a twice monthly job are exhibiting increased difficulty with chatter.

Does anyone have any experience of this type, and is there any alternative to completely replacing the spindle?

Thanks, and have a great day, > Barry

[big_mak]

Has your titanium always been coming from the same place?

I know some places have gotten a Russian variant instead of the american one, and it was much harder to machine.

I've seen this with aluminum plate too when the Supplier switched from Kaiser/Alcoa Plate to a Russian Suppliers. Kaiser and Alcoa Would Clean up @ nominal size usually, and the Russian one wouldn't, and it plugged cutters like there was no tomorrow!

[bigbaz]

Can you get the use of a pullstud dynometer to test the strength of the pullstud mechanism as the belleville washers can lose some of their strength over time leading to poor surface finish, the slicing action of helical fluted milling cutters tends to pull the tool forwards causing chattering.

[big_mak]

That is a good point BB. I can see this being a factor especially if you've cut a lot of titanium on that machine.

[barryhc]

Thanks Big Mak.
That is a relevant concern, and I have been through it with russian aluminum in the past. Very terrible gummy stress relieving stuff. In this case the material is supplied by the customer who is very picky about their material.

Also, I would have noticed differences in spindle load, chip formation, and surface finish in finish cuts, none of which is the case.

bigbaz:

Looking at the draw stud force makes a lot of sense. I don't have the equipment. I'm checking with our local distributor about what spindle condition checks can be made.

The condition of the spindle taper is also some concern. We generally use the machine rather "lightly", although when it was new be did some work that caused some "spindle fretting". About 6 months ago we also did some work that showed spindle fretting, for about one day. We won't run that again.

The condition is not severe, but we can still see impessions on tool tapers over a period of time, even when these tools run at very light loads. This simply shows that the condition occured in the past, and could contribute to problems with tools taking slightly heavier cuts.

By the way, the tool and cut causing the most trouble right now is only consuming 34% spindle load, while showing 32% cutting "air".

I'm curious whether services are available to recondition the spindle taper while "in the machine"?

Thanks > Barry

[extanker59]

Really? 32% spindle load while cutting air? Mine is at 0% cutting air. Sounds like bearings to me, unless I misunderstand you.

[big_mak]

There are guys who can do it for you.

I think Frank Mari has done it with a few customers.

I saw a video somewhere with a boring bar mounted in a chuck with the spindle running and programmed to follow the spindle taper.

We did it @ work with a tool post grinder mounted to the table.

[barryhc]

Extanker:

Yes 32 % spindle load cutting "air". It has been this way since the machine was new, it has nothing to do with spindle bearings. The Mori Seiki reports 0 spindle load until cutting load occurs. This is just a function of relativity in computer logic.

No big deal, the result is that cutting metal differs by 2 % relative to cutting air.

Thanks BigMak:

I have considered doing the same since 25 yrs. ago, on other machines, and never came up with the dire need, or "the guts".

A taper guage combined with bluing, or any other test of accurate taper would make it possible, or at least reasonable.

Tell me more.


Thanks > Barry

[big_mak]

That pretty much how we did it, but no taper gage. we gat a brand new quality? holder and used that for the gage with blue and went at it.

On the Haas I don't think anything from the draw bar should get in the way. we did this on an old Cincinati profiler where we had to remove the draw bar before we started(It was the spring loaded threaded end type, don't know if you've seen those).

With the tool post grinder it worked pretty well.

I'll see if I can dig up the vid from Mari.

[Edster]

If your thinking of doing it yourself, I would at least give spindle grinding service a call and get a quote. They ground a spindle taper for one of my machines and did an excelent job. They have a special setup for grinding the taper so your not using the machine for the motion of the grinder.

[HuFlungDung]

Barry,
Do you get any heat in the spindle at all, supposing you run without coolant circulation through the head? If it seems to run cool at all speeds, then that would be an indication of a lack of preload. My own VF3 had this condition and I rebuilt the spindle. Upon disassembly, I could see evidence that the inner preloading collar was not tight against the upper most spindle bearing (in the lower pair) as they both had signs of spin marks.

I do stuff with my VF3 that causes fretting frequently, but I don't give it a second thought. The material lost is negligible, if anything, it makes the toolholders fit the spindle better The fret zones give you the real story on the spindle to tool taper contact. By comparison, using bluing is like spreading peanut butter on it to see if it fits I'd use felt marker before I'd trust what bluing told me. But maybe that's just me

[Edster]

I do stuff with my VF3 that causes fretting frequently, but I don't give it a second thought. The material lost is negligible, if anything, it makes the toolholders fit the spindle better The fret zones give you the real story on the spindle to tool taper contact. By comparison, using bluing is like spreading peanut butter on it to see if it fits I'd use felt marker before I'd trust what bluing told me. But maybe that's just me

That's like saying valve float or detonation in an engine is nothing to worry about. I had fretting going on on my fadal vmc15. I called sgs and they ground my spindle. It went from around 30% contact area to around 95% contact area. I also installed new drawbar belvilles. The spindle works much better no more fretting.

I've got a gauge that measures pull force on the pullstud too. Cheap insurance if you ask me.