During the milling process, and especially during corner engagement, tools undergo significant variations in cutting forces. One common and difficult situation is when a cutting tool experiences an “inside corner” condition. This is where the tool’s engagement angle significantly increases, potentially resulting in poor performance.
Machining this difficult area with the wrong approach may result in:
- Chatter – visible in “poor” corner finish
- Deflection – detected by unwanted “measured” wall taper
- Strange cutting sound – tool squawking or chirping in the corners
- Tool breakage/failure or chipping
Least Effective Approach (Figure 1)
Generating an inside part radius that matches the radius of the tool at a 90° direction range is not a desirable approach to machining a corner. In this approach, the tool experiences extra material to cut (dark gray), an increased engagement angle, and a direction change. As a result, issues including chatter, tool deflection/ breakage, and poor surface finish may occur.
Feed rate may need to be lessened depending on the “tool radius-to-part radius ratio.”
More Effective Approach (Figure 2)
Generating an inside part radius that matches the radius of the tool with a sweeping direction change is a more desirable approach. The smaller radial depths of cut (RDOC) in this example help to manage the angle of engagement, but at the final pass, the tool will still experience a very high engagement angle. Common results of this approach will be chatter, tool deflection/breakage and poor surface finish.
Feed rate may need to be reduced by 30-50% depending on the “tool radius-to-part radius ratio.”
Most Effective Approach (Figure 3)
Generating an inside part radius with a smaller tool and a sweeping action creates a much more desirable machining approach. The manageable RDOC and smaller tool diameter allow for management of the tool engagement angle, higher feed rates and better surface finishes. As the cutter reaches full radial depth, its engagement angle will increase, but the feed reduction should be much less than in the previous approaches.
Feed rate may need to be heightened depending on the “tool-to-part ratio.” Utilize tools that are smaller than the corner you are machining.