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 added chip load stabilizes the cutter and gets it on a different
frequency.
Larry Childs

Thanks Larry.

 Nice to know.

Paul Lamar

Paul,

There is no substitute for rigid tooling, particularly when boring holes -
The unavoidable tool deflection causes the tool to "dig in" and sets up a
vibration due to the geometry of the hole - As the tool digs in it deflects
more which causes additional digging in - This progresses until the load due
to deflection becomes greater than the resistance to making a chip - When
the chip occurs the load is released somewhat causing the "chatter"

This doesn't occur when turning the outside unless the tool is set above the
centerline of the work - One trick on internal boring with relatively
non-rigid tooling is to raise the tool slightly above the centerline so that
deflection doesn't cause the tool to dig in - Also tools should be dead
sharp and have a sharp point and the cutting face relatively square to the
direction of feed - Flood coolant helps along with light cuts -

That's my experience - Your mileage may vary - Others may disagree -
(political waffling)

Roland Friestad

Thanks. I was considering making a stiffer boring bar. I had some one inch square
cold rolled that fit in the tool holder.

I found this  1.25 by 14 inches long at Shars for 54 bucks.

Paul Lamar

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