Milling a 16 finish on a 60 DEG internal chamfer

[jemop430]

Hello all!

I am working to put a 16 finish on an internal chamfer.

It is a chamfer inside another hole where the diameter goes from .516 to .208 and the chamfer is on the .208 diameter.

Currently I have tried a normal circular chamfer toolpath which left chatter. I then tried (using a 3/8 4-flute chamfer mill carbide/uncoated) to do a peck drill path to rough out the chamfer (it's somewhere between a .050 and .100 chamfer) then a G82 drill cycle with a 3 second dwell and was getting chatter. I have tried really slow feeds and speeds (.4 IPM with 300 RPM), a moderate feed and speed (1.5 IPM and 2400 RPM) and a slow feed and fast speed (.4 IPM and 7000 RPM). I have tried various depths of cut from .001 to .010 for the finish. Nothing has worked.

I am cutting 3-16 Stainless on a Doosan Daewoo 3016 Vertical Mill.

My next thought was to try some improvisational Burnishing.
Seeing as burnishing tools are very expensive and I haven't seen any with a 60 DEG taper I need some creative solutions.

I am planning on trying to use a 60 DEG chamfer tool and spinning it backwards (M2) at a very slow feed and speed (.2 IPM 100RPM .001 DOC) to try and burnish the chamfer.

Has anyone else tried this? Am I crazy? Any other ideas on getting a 16 finish?

Thank you!

Luke
CNC Mill Programmer/Operator

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[jemop430]

Here is a hastily painted picture of the chamfer

[jemop430]

In case anyone stumbles upon this and needs a solution here's what we did:

We rounded the cutting edges on a 60 deg chamfer mill and then using an M4 we spun it counterclockwise at a spindle speed of 200 RPM and udes it to burnish the last .002 of the chamfer. It worked out pretty great!