Here’s one method of finishing a fillet using an 80-degree insert.
Just because a pocket calls for a fillet with a tight radius doesn’t mean the entire thing should be rough-machined with a tool having that radius. As cutting tool manufacturer Greenleaf explains, radii like these typically are small. Therefore, a tool having such a radius is generally weak and must be indexed or changed numerous times if the plan is to use it to complete the entire operation. However, there are a number of effective methods available to finish fillet radii after performing roughing operations using a different, more appropriate tool. The company highlights four of them here.