Chatter in the x axis but not in Y ...???

Hi Gang..

I was cutting a square about 4" on a side 6061-T6 aluminum. 5/8 three flute, in my KMB-1. Depth of cut .060 ~ I finally raised the rpm and it settled down. Just wondering what the cause is. I need some bearings in the head; but I don't know if the precision spindle bearings are the problem.. The mild noise may be from other bearings.

Any ideas appreciated.

Best regards,


Reply to
Stan Dornfeld
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"Stan Dornfeld" wrote in news:oxQCg.10647$

Climb or conventional?

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I doubt that it's anything spindle related, since spindle related chatter would probably affect both axes equally. We just had a similar thing (bad finish in Y, but fine in X), happen in one of our Fadals. We have a service (Ex-Fadal techs), come out periodically to do maintenance on the machines. I believe it was a gibbs adjustment issue in our case.

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======================== This *MAY* not be a cnc/spindle bearing problem at all. All mechanical systems have resonance points, and modes, that is frequencies and directions. As you change jobs and fixtures your resonance frequencies and modes will change.

The manufacturers go to great lengths to eliminate resonances in the normal operating ranges, but with time and wear...

Try bolting a heavy piece of steel to a corner of your table to see if what (if anything) changes. If you have lighter and heavier tool holders to fit the end mill try changing these.

If the chatter frequency / mode-axis changes, you may have another problem.

Cheap and easy to check before starting to replace parts [one after another]

I like BottleBob's suggestion to check the gib adjustments. How hard are these to get to / adjust on your machine? Any special tools required? When was the last time these were adjusted?

Unka George (George McDuffee)

...and at the end of the fight is a tombstone white with the name of the late deceased, and the epitaph drear: ?A Fool lies here, who tried to hustle the East.?

Rudyard Kipling The Naulahka, ch. 5, heading (1892).

Reply to
F. George McDuffee

Unka George:

Uh oh, did I misspell gib? I must have confused it with my Gibbs CAM system. LOL

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Stan, Dittos on the gibb adjustment. I had a similar problem on a bridgeport not long ago. Lousy finish in one axis. It took a little playing around with the adjustment to get the finish back to normal. I took a test cut after each adjusment to see what it looked like and was amased at the variety of finishes you can get when the gibb is off adjustment. Everything from herring bone to diamond. Good luck Duffy

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F. George McDuffee wrote in news:

Me too. But I would also check backlash since it's in X and the machine is basically a CNC knee mill (unless I'm mixing up the machine with something else).

If the rpm was raised without changing the feed rate, then the cutting forces were effectively lowered. Since that seemed to help, I'm thinking something has gotten loose.

Reply to
D Murphy

Or a thrust bearing needs replacing.

Reply to
John R. Carroll

Stan, This wouldn't be the same axis that you re-did the ballscrew nut on?

Best, Steve

Reply to

All good suggestions- checking the machine tools state of adjustment. Is this chatter consistent with other jobs or just this one. Is the fixturing possibly holding the piece less rigidly in the X-axis direction than the Y? Less than perfect workholding has made some perfectly good machining cuts sound like hell. I like to feel around to troubleshoot if possible. See if the vibration is coming through the spindle or through the part.


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Dang! BIG Surprise. *smile

ALL the good answers.

Tone.. I was climb milling.

B'Bob.. I respect your reply.. I did had the "X" axis apart and the table off the machine. This was the ballscrew repair axis. The screw sounds Sooo good. Maybe I need to snug up the gib a bit more.

Thank you.

Duh.. Would "X" axis chatter be rattling the "Y" axis? Or....> ~ ~

It seems reasonable that only one axis chatter would not indicate spindle difficulties.

Duffy.. Very good information. I will keep it on the tip of my mind while making adjustments. *Grin

McDuffee.. Your response gives something to consider, for sure. ty..

D Murphy.. Didn't think backlash.. I placed new "marbles" in the ballscrew and replaced the thrust bearings (Duplex pair) "Can you stand it?" a 750 pound preload. *Sheesh! I calculated the helix angle of the .812 - 32 threaded bearing nut; and figured the ft/lbs torque needed then pulled about

150% of that. The extra was for overcoming friction... etc. I do need to check for backlash though. Good thought. *S

John R. Carroll.. Please read D Murphy Thanks! For the reply.

Steve... Yeah... *Smile

Dale... Thought about the vise... It was a short job. Done. Next time I'll add two more bolts the vise to see the effect.

I appreciate all for your times and considerate comments.

Best regards,


Reply to
Stan Dornfeld

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