boring at a slow RPM

d1camero · Aug 27, 2006

With my custom upright, I am boring the main bearing hole (see pic) in 6061. Unfortunately I can only spin the upright at about 700RPM, any higher and there is too much vibration. Any suggestions on how I can prevent chatter with my carbide boring bits?

thanks
d1

d1camero · Aug 27, 2006

CatHead · Aug 27, 2006

generally you cure chatter by reducing speed and increasing feed...

How much of a cut are you taking with that little bar?

possibly not rigid eneough for the cut you are taking and its springing, causing the chatter

Id use a larger boring bar for the size hole you are boring

mister honey · Aug 27, 2006

1. Is the bore out of round? That would be my first concern from the out of balance condition.

2. Use a larger diameter boring bar or a square shank lathe tool with appropriate boring clearance under the insert.

3. Use a HSS tool with a high positive top rake (15°-25° and small nose radius (.015 inch or so)

Mike

d1camero · Aug 27, 2006

Thanks guys. The out of balance is caused by the shape of the upright being quite a bit heavier at one end.

I will get my hands on a stiff boring are and use HSS.

Don

jkilroy · Aug 27, 2006

Using the largest bar you have got, that will fit, is my general rule.

bluchip · Aug 27, 2006

Topic: boring at a slow RPM

I thought you meant the forum!

LD · Aug 27, 2006

This is one of those cases you should chuck up in a 4 jaw and put some heavy shims under the jaws opposite the heavier side to balance the load.

Also agree,that's a wimpy bar you got there.

richardny · Aug 27, 2006

while aluminum can be cut at any speed, 700 rpm looks way to high for this application

i would go 350 rpm

speed is gained by doing it correctly, not by going fast, the eternal fallacy

nobody else can do it faster, either, is the rule

collet closer handle usually starts rattling at 650 rpm, I take my cue from that (anythiong oput of balance may be critical at 650 rpm)

Cuda · Aug 27, 2006

You got more guts than I do if your spinning that mess at 700 RPM in a 3 jaw!!!, but you need a bigger bar and even at a slower RPM you can get a good finish in alu. if you use a cutting oil, or even WD40 works pretty good too.

richardny · Aug 27, 2006

I once had a 14" dia. cylindrical aluminum job being held in aluminum soft jaws running at 1200 rpm and one of the 3/8 bolts holding the softjaws to the underlying steel jaws broke.

This caused the softjaw to hit the ways of the machine and the chuck with the part still in it broke off the spindle, all while I was cutting. (No, I wasn't the guy who set up the job, and I avoid using very old screws.)

The chuck could have been airborne and gone anywhere, but it fell down right next to the lathe as if it had been laying on the bed and rolled of it sideways. All the energy was absorbed by the shop floor.

I was surprised as hell, and there was very little breaking-off noise accompanying the incident. Take a look how thin the walls of a lathe spindle are. It tore of clean like you would tear a piece of paper. No effort required whatsoever.

It pays not to stand sideways from the turning chuck, further to the end of the lathe.

TheMetalDoctor · Aug 28, 2006

A streak of coolant or oil up the front of your shirt is a good indicator that you are standing in the wrong place!

TMD

Peter S · Aug 28, 2006

Wow, home workshops can be dangerous places. 700 rpm is not slow :eek:

d1, No doubt you have got the message, that is too fast for a set-up like that. No need to spin it fast at all with a decent boring bar.

A decent boring bar in my opinion would be a quality brand with replacable positive triangular carbide tip, but you can also silver solder (or grub screw) HSS onto the end of a mild steel bar and sharpen that up.

Carl Darnell · Aug 28, 2006

Aluminum likes about 10deg or more of back rake and a very small round nose and high speed. Can you drill and tap the part and add counterweight to it?

Jamie · Aug 28, 2006

D1;
Hi, thought you were going with either the face
plate, or at least the 4 jaw chuck?
I would have to agree with both Mike & Richard,
about reducing the rpms to 350, specialy with
that setup, and increasing the back rake.
From the picture it looks like you have one of
those QCTP from KBC tools, if you do, you have
a 1" Boring Bar Holder with the set, if memory
serves me correctly. Use that instead of what
you are using, more rigid.
Jamie

mojojerry · Jul 6, 2008

The one time you got a chance to show everyone what a great big stiff one you had and you had to pull out that skinny little thing.

ha ha .

I just thought you could use a smile.

Good luck mojo

Metalcutter · Jul 6, 2008

After you try everything else... You might try this:

If a boring bar is on dead center and chatter starts, the boring bar flexes downward and into a deeper cut. This enhances the tendency to chatter. (You might draw a picture to see it.)

If you move the boring bar above center about a degree, then when chatter tries to start, the bar still flexes downward, but into a shallower cut. This can lessen the tendency to chatter.

Regards,

Stan-

SND · Jul 6, 2008

did someone say 2006?

boring at a slow RPM

Aluminum

Aluminum

Hot Rolled

Stainless

Aluminum

Diamond

Stainless

Aluminum

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Hot Rolled

Hot Rolled

Titanium

Diamond

Titanium

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Plastic

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