When You Don't Make the Cut You May Have to Live with the Chatter

We had a number of technical support questions this past week about unsatisfactory finishes in the bore. As we talked with the customers and potential customers we asked, “What is the depth of your cut?” and “ What is the nose radius on your carbide insert?”

The reasons for asking these questions is one of the most common mistakes made when cutting a precision finish bore is not leaving enough material in the bore so the boring tool can work properly. 

When the depth of cut is less than the radius on the insert 

(or boring tool) the cutting pressure builds up and tries to push the insert out of the cut. You can see from the arrows on the diagram that all of the cutting force is away from the cut and there is no cutting pressure trying to stabilize the tool in the cut.  

On the second diagram the depth of cut is greater than the insert which gives some stabilizing pressure from the end of the insert so the tool does not want to skip out of the cut.

A general rule of thumb is to have a depth of cut .005/.010” more than the radius of the cutting tool. This will give you a stabilizing force to help eliminate chatter from your bore.

There are many other factors that can affect the finish of a bored hole such as the rigidity of the fixturing, the depth to diameter ratio of the bore to the boring tool shank and spindle rigidity. We will try to give you common sense tips for these factors as we add to our blog.

If you have any questions regarding precision finish boring or modular boring please leave us a comment or send us an e-mail. We enjoy working with our customers to improve their manufacturing processes.