3 Unit 2: Speeds, Feeds, and Tapping
Objective
After completing this unit, you should be able to:
- Identify and select vertical milling machine setups and operations for a variety of machining tasks.
- Select a proper cutting speed for different types of materials.
- Calculate cutting speeds and feeds for end milling operations.
- Explain how to correctly set up for power feed tapping.
Cutting Speed
Cutting speed is defined as the speed at the outside edge of the tool as it is cutting. This is also known as surface speed. Surface speed, surface footage, and surface area are all directly related. If two tools of different sizes are turning at the same revolutions per minute (RPM), the larger tool has a greater surface speed. Surface speed is measured in surface feet per minute (SFM). All cutting tools work on the surface footage principle. Cutting speeds depend primarily on the kind of material you are cutting and the kind of cutting tool you are using. The hardness of the work material has a great deal to do with the recommended cutting speed. The harder the work material, the slower the cutting speed. The softer the work material, the faster the recommended cutting speed (See Figure 1).
Steel Iron Aluminum Lead
Figure 1: Increasing Cutting Speed Based on work material hardness
The hardness of the cutting tool material will also have a great deal to do with the recommended cutting speed. The harder the drill, the faster the cutting speed. The softer the drill, the slower the recommended cutting speed (See Figure 2).
Carbon Steel High Speed Steel Carbide
Figure 2: Increasing Cutting Speed Based on Cutting tool hardness
Table 1: Cutting Speeds for Material Types
| Type of Material | Cutting Speed (SFM) |
|---|---|
| Low Carbon Steel | 40-140 |
| Medium Carbon Steel | 70-120 |
| High Carbon Steel | 65-100 |
| Free-machining Steel | 100-150 |
| Stainless Steel, C1 302, 304 | 60 |
| Stainless Steel, C1 310, 316 | 70 |
| Stainless Steel, C1 410 | 100 |
| Stainless Steel, C1 416 | 140 |
| Stainless Steel, C1 17-4, pH | 50 |
| Alloy Steel, SAE 4130, 4140 | 70 |
| Alloy Steel, SAE 4030 | 90 |
| Tool Steel | 40-70 |
| Cast Iron–Regular | 80-120 |
| Cast Iron–Hard | 5-30 |
| Gray Cast Iron | 50-80 |
| Aluminum Alloys | 300-400 |
| Nickel Alloy, Monel 400 | 40-60 |
| Nickel Alloy, Monel K500 | 30-60 |
| Nickel Alloy, Inconel | 5-10 |
| Cobalt Base Alloys | 5-10 |
| Titanium Alloy | 20-60 |
| Unalloyed Titanium | 35-55 |
| Copper | 100-500 |
| Bronze–Regular | 90-150 |
| Bronze–Hard | 30-70 |
| Zirconium | 70-90 |
| Brass and Aluminum | 200-350 |
| Silicon Free Non-Metallics | 100-300 |
| Silicon Containing Non-Metallics | 30-70 |
Spindle Speed
Once the SFM for a given material and tool is determined, the spindle can be calculated since this value is dependent on cutting speed and tool diameter.
RPM = (CS x 4) / D
Where:
- RPM = Revolutions per minute.
- CS = Cutter speed in SFM.
- D = Tool Diameter in inches.
Milling Feed
The feed (milling machine feed) can