Note: As a general rule, the minimum depth of cut should be 1.5 to 2 times the tool nose radius. The maximum feed rate should be approximately one half the tool nose radius for rough turning using carbide inserts.
For milling, the maximum depth of cut is equal to the flute length or the insert height and the maximum width of cut is the cutter diameter. However, these measures are not practical in most cases. A more widely used practice is to set the maximum depth of cut to 2/3 of the flute length and the maximum width of cut to 2/3 of the diameter, as well. These basic conditions should be followed for the remainder of this workbook. Drilling calculations should be based on High Speed Steel (HSS) values for Turning and HSS End Mill values for Milling.
Chart 1-5 Feeds and Speeds for Milling
| HSS End Mill | Carbide End Mill | Carbide Inserted Face Mill | |
| Carbon Steel Feed in/tooth | 25–140.001–.004 | 210–1000.006–.012 | 90–685.020–.039 |
| Alloy Steel Feed in/tooth | 5–85.001–.004 | 40–450.006–.012 | 39–475.020–.039 |
| Stainless Steel Feed in/tooth | 20–80.001–.003 | 200–700.006–.012 | 210–385.020–.039 |
| Aluminum Feed in/tooth | 165–850.002–.006 | 600–2000.008–.015 | 755–1720.020–.039 |
Refer to the following formula to calculate revolutions per minute (r/min).
where
CS = Cutting Speed from the charts above or the Machinery’s Handbook
π = 3.1417
D = Diameter of the workpiece or the cutter
Refer to the charts above or the Machinery’s Handbook for the feed in inches per tooth (in/tooth) for chip load recommendations. Also review the formula below to calculate the feed aspect of the metal-cutting operation.
F = R × N × f
where
F = Feed rate in inches per minute (in/min)
R = r/min calculated from the preceding formula
N = the number of cutting edges
f = the chip load, per tooth, recommended from the charts above or the Machinery’s Handbook
1. On a CNC lathe, a facing cut is needed to establish the part-zero surface. The alloy steel bar stock is 2.5 inches in diameter and has 1/32 inch of excess material to be removed from each side. A carbide-inserted tool with a 1/32 inch nose radius will be used for this operation. Because the diameter changes as the tool travels toward the centerline, what should the r/min be? What should the SFPM be? What should the depth of cut be?
2. When finish turning an aluminum bar that is 2.3125 inches in diameter with a carbide-inserted turning tool that has a 1/64 inch tool nose radius, what is the r/min and feed rate required if the depth of cut is 1/64 inch per side?
3. An internal threading operation is required on a CNC lathe to make a 1-8 UNC thread in a carbon steel part. The cutting tool material is High Speed Steel. What should the r/min be for this operation?
4. Calculate the appropriate speeds and feeds for each of the required tools in the lathe process planning project above and enter your answers on your CNC Setup sheet in the comments section.
5. Calculate the appropriate speeds and feeds for each of the required tools in the mill process planning project above and enter your answers on your CNC Setup sheet in the comments section.
6. In this example, the material is stainless steel. A .5625 inch diameter hole is to be drilled through a plate that is 1.25 inch thick. Calculate the r/min and feed rate best suited for this operation. Use the HSS end mill values from the chart.
7. A carbon steel plate 4.0 inches square requires a 2.0 inch diameter hole to be machined through the center. A pre-drilling operation uses a 1.25 inch diameter HSS drill and a finishing operation uses a .875 diameter 4-fluted HSS end mill to circle mill out the remainder of material. What is the r/min and feed rate for the drill? What is the r/min and feed rate for the end mill?
8. A 5-tooth 3.0 inch diameter carbide face mill is used to machine an alloy steel bar that is 2.0 inches wide and 6.0 inches long. There are two depth passes of .080 inch each required to bring the part to size. What is the r/min and feed rate for this cut?
9. A 4.0 inch flat aluminum bar requires a profile to be cut on both ends. A 2-fluted HSS end mill 7/16 inch in diameter has been selected for the job. The part thickness is 1/2 inch and the amount of axial metal removal is 1/2 inch. What are the appropriate r/min and feed rate?
10. Use the formula and data given above to calculate the feed and speed required for each tool in the programming exercises that follow. List your results in the comments section of the CNC Setup Sheet.
Coordinate Systems
1. Use Figure 1-3 to identify the absolute coordinates for each axis and for each point of the profile of the turned part, based on diametrical considerations.
2. Use Figure 1-3 to identify the incremental coordinates for each axis and for each point of the profile of the turned part, based on radial considerations.
Figure 1-3 Identify Absolute and Incremental Coordinates
3. Use Figure 1-4 to identify the absolute coordinates for each axis and for each point of the profile of the milled part. Start at part zero and proceed clockwise.
4. Use Figure 1-4 to identify the incremental coordinates for each axis and for each point of the profile of the milled part.
Figure 1-4 Identify Absolute and Incremental Coordinates
5. List the absolute coordinate values for X, Y, and Z for each of the 15 points as indicated in Figure 1-5). The part is 3.0 inches long, 2.0 inches wide and has a height of 2.25 inches. The slot is cut through the centerline of the width and is .50 wide and .375 deep.
Figure
