Widening a hole by milling

Widening an existing hole can be performed either by circular ramping or circular milling.

Circular ramping

Circular milling

Circular ramping – 3 axes

• Constant ramping
• No entry or exits
• Cutter constantly engaged
• Ramping action – bottom cutting

First choice:

• Depth of hole is greater than the maximum a_p for tool
• Best hole concentricity and roundness
• In vibration sensitive applications

Circular milling – 2 axes

Circular milling is an alternate method to the traditional use of boring tools. Circular milling can be performed by moving most 90 degree cutters in a circular tool path.

• Constant Z
• Entering and exiting for each level
• Rolling entrance into cut should be programmed
• Hole tolerance with boring is not as good as with circular milling
• Step marks at each pass

First choice:

• Program tool path more than 360 degrees to avoid step marks
• Only one pass is required Cutter with high ap capabilityShallow hole
• Ramping capability poor or nonexistent – long edge without axial support

Calculating feed

Feed needs to be reduced due to:

• Increased ae relative to straight cutting, which reduces the chip thinning effect
• Peripheral feed is greater than the tool centre feed
• Calculate feed based upon D_vf.

Entrance into cut

Rolling into cut ensures thin chips on exit. Low engagement angle reduces vibrations and ensures high productivity.