Limiting Chatter

[Dtuck]

Short summary:
Material P-20
Finish requirement 16 RMS
Depth 1.5"
Inner diameter 1.0"
Angle of cut 3 degrees
Need to radius for the flat inner area.
Question:
Are there really better small boring bars out there to limit chatter?

 

[mrainey]

I'm skeptical about holding a consistent 16 finish with a boring bar, even under the best of conditions.


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[Tmoose]

Short and fat is where it's at.
What is the diameter of the bar you're using?
I'd be shooting for one at least .75 inch diameter with no more than 1.6 inch overhang.

What is the wall thickness of the part? Depth of cut?

varying the speed during the cut can sometimes work wonders. Some experimental machine tools use the output of a vibration sensor to actively control speed.

What is the hole diameter tolerance? Maybe a spade drill or boring bar with pads would do the trick.

 

[Dtuck]

The tolerance is +/-0.0003" on the machined surface and the flat inside the steel needs to be machined on the same finish pass. The 0.75" boring bar doesn't fit and allow for the cut across the inside flat. Shape is like this.
__
/ \
_/ \_

 

[MikeHalloran]

Wild hair idea, half baked:

Cylindrical sleeve nearly as big as hole to be cut, with eccentric bore, close fit in holder.

Boring bar close fit in sleeve's eccentric bore.

Cross feed at bottom of hole by rotating sleeve in holder and boring bar in sleeve at the same time, moving the cutting edge radially inward. Maybe you can do it with just levers, maybe you need gears.

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The other choice is cutting the bore and radius with the outer corner of a wide tool in the end of a fat boring bar. I.e. the end cutting edge extends across half the bore.


Either way, getting the center cut relies a lot on luck.


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Speaking of which, maybe you could just use a fat center cutting endmill as a boring tool.




Mike Halloran
Pembroke Pines, FL, USA

 

[mrainey]

Find a way to grind it.


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