I think I just learned something.

I am trying to bore a 5 inch diameter hole in 6 inch diameter
aluminum bar stock about 5 inches deep.

I was getting tool chatter.  At first I thought I needed a stiffer
boring bar. My boring bar is about .75 inch in diameter.

I discovered if you speed up the carriage feed the chatter goes away
more or less.

Some of you guys on here are expert machinist.

Have you heard of this before ?

Paul Lamar

Paul, The spindle speed formula    RPM= Surface Feet per Minute x 4/
tool Diameter SFM for aluminum is 400 & R is .002/.009 And the feed
rate formula     Feed (rate per minute)= RPM x T (number of teeth) x
R (chip load)

Ray Hellstrom

Thanks Ray,

Interesting.

Paul Lamar


Paul,
Are you using a carbide cutting tool? If so, a large nose radius can cause chatter.
Also, I didn't mention that the depth of cut, which should be the adjusted with the speed to produce a continuous chip which forms due to plastic deformation of the crystal structure in the unmachined work surface and the shear occurs along the shear plane. As the cutting tool compresses the metal immediately ahead of the cutting tool, the deformation of the crystal structure elongates, the material above the cutting edge is forced along the chip tool interface and away from the tool.

Ray Hellstrom


No it is a sharp point.

BTW do any of you guys know where I can get a six inch diameter steady rest?


Paul Lamar

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