728VT REALLY weird chatter

55fairlane

55fairlane

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This started last night as I was drilling & reaming a 7/16 hole in a ¼ piece of 12L14 , the center drill chattered, then the body drill chattered, then the reamer. Let me say this, YES I understand proper speeds & feeds. I have seldom seen a center drill chatter.

Tonight, I wanted to finish the part I started last night, brand new ⅜ carbide finish mill, .030 deapth of cut, I get chatter, lots of it, kinda reminds me of when the slides on our big VMC go dry, so I pumped the oiler handle, and this happened, the mill dug into the work .005 to .007 .....WTF? I am so beyond baffled......up until this time I had not had any chatter.....I am stumped. By the by, the Z axis was locked, the quill was locked, the Y axis was locked. WTF? And yes one side appears to be deaper then the other side.

I hope @qualitymachinetools chimes in .....I'm wondering if I got another problem child

Anyways here is the picture ......anyone have any thoughts
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I'd start checking for something "loose", check the gibs, check the bolts holding the machine to whatever stand you have it on. When a machine's running characteristics change that suddenly I start looking for something that "let go" in some way.
 
kenjesse said:
I'd start checking for something "loose", check the gibs, check the bolts holding the machine to whatever stand you have it on. When a machine's running characteristics change that suddenly I start looking for something that "let go" in some way.
Click to expand...
Normally I would agree with checking the gibs ect, but this happened when I pumped the handle for the oiler (while the power feed was running)
Bolts holding the machine down, I will check those....the machine is on a factory cabinet with ¾ aluminum plate between the machine & the base. 1x1x2 "t" nuts for the bolts to go into & I use a torque wrench to tighten up the bolts. I put 250 pounds ish of lead & steel in the base to help dampen vibrations
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I am curious about the milling operation. In your picture, it appears that you were machining from right to left and attempting to remove .030 of material. Is that correct?
If so, the surface of the plate that you are milling needs to be just above the vise, with the absolute minimum stick-out.
If I am correct in my assumption about what type of milling operation you were doing, and you pumped the oiler while doing so, the only real explanation is that you "hydraulically" lifted the table slightly when pumping the oiler. When I owned my 833T, I found the gibs to be of marginal quality at best. Might want to reexamine the gib tightness and fit on the table.
 
I think what Neil said about hydraulically lifting the table sounds plausible, you could check that with a dial indicator attached to the spindle and measuring the table for lift. That doesn't account for the chatter prior to when you pumped the oiler. It does sounds like something has come loose.
 
Let me help everyone out here just a wee bit. I am professional machinist (tool maker) I might know how to machine something.
This incident happened as follows, POWER FEED ON, .030 deap cut, brand new ⅜ carbide end mill. I am feeding across the work, pumped the oiler, end mill looks to have "dug" into the work.

I like the hydraulic lift idea
 
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