View Full Version : Is the cente/cutting edge of a boring bar always half the bar diameter?

12-21-2008, 02:02 PM

I'm planning on making some boring bar holders to fit the 4 position turret tool post on my lathe.

That leads me to my question. All the boring bars I've used in the past were made by me, and I always had the cutting edge of the bar/HSS tool bit set at 1/2 the bar's diameter. Are commercial boring bars done the same way? If they aren't, I'll have to leave room to shim the boring bar holder in the turret tool post.

I'd rather not have to use shims, would be nice if I could just place the boring bar holder in the tool post and go.


12-21-2008, 02:17 PM
It is better to have the cutting edge on the center line.

12-21-2008, 02:19 PM
You can bore out a holder perfect dead center...and your bar can still be off...any round bar will rotate.
So you have to rotate it to center.
Then of course there's HSS bits in other boring bars..center height can be affected just by how you sharpen the bit. But...you still need the bar at proper center height

12-21-2008, 03:13 PM
If I understand your question ...

On commercial insert-style boring bars, the distance from the center of the bar to the tip of the insert is usually greater than half the bar diameter. This dimension is referred to in catalogs (Kennametal, etc.) as the "F" dimension. The minimum bore diameter for such a bar would theoretically be twice the "F" dimension, but in reality is somewhat smaller when used on a lathe.

12-21-2008, 05:31 PM
Not all commercial bars have the cutter on center line. Some of the 2" bars we use if you set the "bar" on center line the cutter is below centerline. They got lots of meat hanging under neath them too. I always wondered why cause it is hard to use them in 2" holes and someone always grinds part of that meat off to clearance them instead of using a smaller bar til the big one fits!