[Satchmopants]

I am hoping someone here can offer up some advise as I am at the end of my rope here.

I have a 1.25 in Boring bar hanging out 7.75 inches from the holder and I am boring aluminum tube to 3.9 dia x 7.65 deep in a part hanging out of the chuck 8 inches. I keep getting chatter and cannot seem to tune it out. I have been fighting with this for the last 3 days and have tried raising/lowering Feeds and Speeds. Altering the depth of cut. Repositioning the boring bar, Changing inserts ( have tried 3 different types). Every time I get the chatter reduced for one part it starts right up again with the next.

Any help Anyone could offer would be appreciated. Thanks in advance.

[HorridHenry]

Cause usually associated with chatter....

Tool not perfectly centered to the workpiece.
Unstable toolpost ie not solid.
Too much overhang of the workpiece in the chuck.
Worn bearings in the spindle ie lots of runout.

[Geof]

It is possible the chatter is originating in the tube not from the boring bar. Try wrapping something around the tube to act as a vibration damper. I have found stretching large O-rings over a tube can help. Aternatively cutting a split sleeve out of wood and clamping it on with hose clamps. Carefully and not too tight or the tube might deform. Also watch the speed because this will be out of balance.

[HorridHenry]

I have found stretching large O-rings over a tube can help. Aternatively cutting a split sleeve out of wood and clamping it on with hose clamps.

Then you have a problem on your Lathe if you need to do this,and really you should not need to do anything but centralise and clamp the workpiece.

Do a runout test with a DTI and see how much runout there is, if it flickers marginally then there's slight play in the bearings.if it flickers excessivly then the bearings need changing.

[Satchmopants]

Cause usually associated with chatter....

Tool not perfectly centered to the workpiece.
Unstable toolpost ie not solid.
Too much overhang of the workpiece in the chuck.
Worn bearings in the spindle ie lots of runout.

My money is on to much overhang. Have a 4.5 inch aluminum tube hanging out 8 inches.

Combine this with the boring bar hanging out 7+ inches and there I am.

Thanks for your input. If worst comes to worse I am going to choke up on the boring bar another inch and reprogram the part to approch bore from both sides.

[mcarvey]

I would second Geof's recommendation of exploring workpiece chatter, especially if your are turning to a relatively thin wall thickness (compared to the aspect ratio) 2 options to explore on this front- you can clamp something around it as Geoff suggested and/or you can try using the steady rest to reduce the length that is unsupported. If this solves the chatter issue then you know that the chatter is not associated with your boring bar/insert/speeds/feeds.
As HorridHenry suggested putting a DTI on the OD and/or ID is never a bad idea- it could be that the non chucked end of the workpiece has more run out than you thought, resulting in a very uneven chipload as it is cutting. If you shorten the stickoutof the boring bar to 2" or so (with your original workpiece) and the chatter goes away then the chatter is likely associated with boring bar length. If you chuck up a 2" long test workpiece, shorten the boring bar to 2" and the chatter doesn't go away, the bearings are the likely culprit.

Hope this helps,
-Matt

[Geof]

Then you have a problem on your Lathe if you need to do this,and really you should not need to do anything but centralise and clamp the workpiece.

Do a runout test with a DTI and see how much runout there is, if it flickers marginally then there's slight play in the bearings.if it flickers excessivly then the bearings need changing.

Don't be silly. Chatter has nothing to do with runout and has nothing to do with centralising the workpiece. Chatter is cause by deflection of the toolholder and or the workpiece under the cutting load. It is exacerbated when the conditions are such that one or more resonant frequency in the workpiec or toolhoder is excited.

[packrat]

This is blasphemy on this site, but, this is one of those places that a HSS tool is a better choice. The geometry and cutting edge is better for something of this nature, and aluminum doesn't need carbide.

[DMF_TomB]

1.25" dia stickout 7.75" from holder
.
try 2" stickout, after this proves to you it bores ok then get a bigger diameter boring bar.
.
stickout 1/4 of amount is 4x4x4=64x stiffer or less deflection
.
solid carbide boring bars are stiffer than steel but much more expensive.
.
boring bar diameter 2x bigger (2.5") is 2x2x2x2= 16x stiffer
.
these are basic Engineering principles. Laws of the Universe don't care if you don't have a bigger diameter boring bar. they are what they are.

[HorridHenry]

Don't be silly. Chatter has nothing to do with runout and has nothing to do with centralising the workpiece.

There are pages and pages out there that will disagree with you...this is just two out of the many.


http://www.practicalmachinist.com/vb...runout-215265/

Spindle Run Out Problem In HMT VMC 500 Machine, angular contact bearing fault.

Perhaps I had a better instructor than you?

[HorridHenry]

Why is that first link tied to this thread when it came from a site called cnczone.com?

Whats going on here?

The site I took the link from was....P r a c t i cal Ma c h inist....sorry had to seperate the letters as its coming back with CNCZone,,,weird

[Geof]

Your first link does not work for me.

Your second link refers to the spindle on a VMC not a boring bar on aluminum tube.

Try to find some relevant working links if you want, the fact remains that my post is correct.

[HorridHenry]

It was the first link that explained the chatter and runout on a lathe,however my post #11 will claify why this did not load.

[fizzissist]

Geof is correct.

Pay attention.

(hadn't thought of the split wood thing...good idea!)

There's a reason for the pile of rubber bands on the top of the lathe's headstock in my house.

There's also a reason I don't buy cheap boring bars or inserts. They chatter.

....and carbide is just fine for alum. In fact, it's wonderful. We're talking geometry and rigidity here, and loading (a function of feed).....

[underthetire]

Agree with Geoff. Run out simply gets cut out on a lathe. Mill is totally different. It's just a resonance problem from too much overhang in tubing. Ace bandages work well for this as well, but won't take coolant for long.

[Satchmopants]

Thanks for all the advice. Was finally able to tune it out through combo of cutting speeds and depth of cut. Funny enough lighter cut seeming to work better.