# Milling Calculations 295

This class explains the common calculations necessary to plot the toolpaths for a basic milling program.

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## Class Details

Class Name:
Milling Calculations 295
Description:
This class explains the common calculations necessary to plot the toolpaths for a basic milling program.
Version:
1.0
Difficulty:
Intermediate
Number of Lessons:
17
Spanish
Related 2.0 Class:
Calculations for Programming the Mill 312

## Class Outline

• Objectives
• The Purpose of Toolpath Calculations
• Program Zero Location
• Face Milling Calculations
• The Face Milling Toolpath: Y-Axis
• The Face Milling Toolpath: X-Axis
• Pocket Milling Calculations
• The Pocket Toolpath
• Spot Drilling Calculations
• The Spot Drill Toolpath
• Drilling Calculations
• The Drilling Toolpath
• CRC on the Mill
• Full-Circle Milling Calculations
• The Full Circle Toolpath
• The Bolt Hole Pattern
• Summary

## Objectives

• Describe the basic elements of a toolpath.
• Identify the appropriate location for program zero on a part.
• Explain the general rules that govern face milling calculations.
• Calculate the Y-axis locations for a common face milling operation.
• Calculate the X-axis locations for a common face milling operation.
• Explain the general rules that govern pocket milling calculations.
• Calculate the initial coordinates to begin a boxing routine for a rectangular pocket.
• Explain the general rules that govern spot drilling calculations.
• Calculate the depth required to leave a chamfer with a spot drill.
• Explain the general rules that govern drilling calculations.
• Calculate the depth required to completely drill a hole.
• Explain a common method for removing ramping motions from a program’s toolpaths.
• Explain the general rules that govern full-circle milling.
• Calculate the starting locations for matching full radius and arc in motions.
• Calculate the coordinate location of a hole in a bolt-hole pattern.

## Glossary

Vocabulary Term Definition
approach A slight distance added to a toolpath at the beginning of a cut for safety reasons.
arc center method A method for programming circular tool movements that requires an I code and J code to indicate the location of the arc's center along the X- and Y-axes. The arc center method is best used for full-arc motions.
arc-in motion A partial-arc motion that leads into a larger arc motion. Arc in and arc out motions leave a smooth surface finish.
arc-out motion A partial-arc motion that exits from a larger arc motion. Arc in and arc out motions leave a smooth surface finish.
bolt-hole pattern A common specification on milled parts that requires a series of equally spaced holes around the circumference of a larger imaginary circle.
boxing routine A series of increasingly larger rectangular toolpaths used to machine a rectangular pocket.
CAD/CAM Computer-aided design/computer-aided manufacturing. CAD/CAM is the use of software to aid in the design and manufacturing of a part.
chamfer A small, angled surface added to an edge of a workpiece. A chamfer removes the sharp edge and helps eliminate burrs.
clearance Any useful space that is intentionally maintained between components.
contour feature A part feature that is non-linear, or curved.
coordinate system The numerical system that describes the location of an object by numerically expressing its distance from a fixed position along three linear axes. The coordinate system consists of the X-, Y-, and Z-axes.
cosine In a right triangle, the ratio of the length of the side adjacent to the angle divided by the hypotenuse.
cutter radius compensation An offset used on the machining center that accounts for variations in tool diameter. CRC is only necessary for tools that continuously cut along a horizontal plane.
deflection The unintended movement or repositioning of a component due to a mechanical force. Deflection of a cutting tool can cause poor surface finish and inaccurate dimensions.
end mill A thin, tall mill cutter with a flat bottom and cutting edges that wind up the sides. Both the bottom and side of the end mill provide cutting surfaces during milling operations.
face mill A flat mill cutter with multiple cutting teeth surrounding the tool. The bottom of the face mill is primarily the cutting surface during milling operations.
face milling A milling operation in which the surface of the workpiece is perpendicular to the spindle axis. Face milling primarily is used to mill the top surface of the part.
finishing pass A final cutting pass that produces the necessary surface finish and brings a feature to its proper size.
finishing stock The small amount of material that is intentionally left for a finishing pass.
hypotenuse In a right triangle, the side located opposite the right angle.
I code For circular interpolation, the program code that indicates the location of the arc's center along the X-axis. I and J codes are used for the arc center method.
J code For circular interpolation, the program code that indicates the location of the arc's center along the Y-axis. I and J codes are used for the arc center method.
length-to-diameter ratio A ratio describing the length of a cylindrical tool or workpiece compared to its diameter. Higher length-to-diameter ratios offer less rigidity.
milling cutter Any multi-point tool that is used to remove metal from the surface of a workpiece.
part program A series of instructions used by a CNC machine to perform the necessary sequence of operations to machine a specific workpiece.
pocket An interior recess that is cut into the surface of a workpiece. Pockets may be round or rectangular.
program zero The position that acts as the origin for the part program of a particular workpiece. This position is unique to each workpiece design, and it is selected by the part programmer.
R code For circular interpolation, the program code that indicates the length of the arc's radius. In certain canned cycles, an R code indicates the R level for tool return.
radius method A method for programming circular tool movements that requires an R code to indicate the size of the arc's radius. The radius method is best used for partial-arc motions.
ramping motion A linear motion of the tool that is required for a control to adjust for a particular tool offset.
sine In a right triangle, the ratio of the length of the side opposite the angle divided by the hypotenuse.
spot drill A short, sturdy drill used to start a hole and accurately locate it. Most spot drills have a 90° tip.
step-over The size of the cutter's diameter that is engaged in a cut. The step-over should be 75% to 80% of the cutter's diameter.
symmetrical part A part that can be divided by a line into two equal halves, with identical features that are equal distances from the dividing line. Both sides appear as mirror images of each other.
tangent In a right triangle, the ratio of the length of the side opposite the angle divided by the adjacent side.
toolpath The series of coordinate positions that determine the movement of a tool during a machining operation.
trigonometry The branch of mathematics that addresses the measurements and relationships of a triangle and its parts.
wear offset An offset used on a turning center and some machining centers that allows for the slight adjustment of tool tip location. Wear offsets account for part deflection, tool wear, etc.
X-axis On the mill, the linear axis representing coordinate positions along the longest distance parallel to the worktable.
Y-axis On the mill, the linear axis representing coordinate positions along the shortest distance parallel to the worktable.
Z-axis On the mill, the linear axis representing coordinate positions perpendicular to the worktable. The Z-axis is always parallel to the spindle.