454 Modern Metalworking Copyright Goodheart-Willcox Co., Inc. • Use the correct size wrench on the arbor nut, Figure 26-28. Make sure at least four threads are engaged before tightening the nut. • Avoid tightening an arbor nut by striking the wrench with a hammer or mallet. This can crack the nut and damage the threads. • Do not force a cutter onto an arbor. Check to see what is creating the difficulty and correct the problem. • Use the proper procedure to remove an arbor or adapter from the milling machine. Removing an Arbor or Adapter from a Horizontal Mill 1. Loosen the draw-in bar nut a few turns. Do not remove it completely from the arbor. 2. Tap the draw-in bar head with a lead hammer to loosen the arbor in the spindle. 3. Hold the loosened arbor with one hand and unscrew the draw-in bar with the other. 4. Remove the arbor from the spindle. Clean and store it properly. 26.4.5 Cutting Fluids Cutting fluids serve many purposes. They carry away the heat generated during the machining operation, act as a lubricant to prevent chips from sticking or fusing to the cutter teeth, and flush away chips. Their lubricating quali- ties also affect the quality of the machined surface’s finish. 26.5 Cutting Speeds and Feeds The cutting speed and feed of the cutter determine the time required to complete a milling operation. In addition, the quality of the machined surface is almost completely governed by these factors. 26.5.1 Cutting Speed In milling operations, cutting speed refers to the dis- tance (measured in feet or meters) a point (tooth) on the circumference of the cutter moves in one minute. It is expressed in feet per minute (fpm) or meters per minute (mpm) and depends directly on the revolutions per minute (rpm) of the cutter. 26.5.2 Feed In milling operations, feed is the rate at which the work d moves into the cutter. It is given in feed per tooth per revo- lution (ftr). Proper feed selection is one of the most difficult tasks for the machinist. In view of the many variables (width of cut, depth of cut, machine condition, cutter sharpness, etc.) that affect milling operations, the feed should be as coarse as possible while still providing the desired finish. 26.5.3 Calculating Cutting Speeds and Feeds The usual procedure for determining the speed for a proj- ect is to start with a midrange figure and increase or reduce the speed until the most satisfactory setting is obtained. Suggested ranges are listed in Figure 26-29 (speeds) and Figure 26-30 (feeds). Refer to the rules and formulas in Figure 26-31 to calculate the cutting speed and feed. Goodheart-Willcox Publisher Figure 26-28. Loosen the arbor nut using the correct type and size of wrench. Wrench must fit snugly or arbor nut will be damaged Material High-speed steel cutter Carbide cutter Feet per minute Meters per minute* Feet per minute Meters per minute* Aluminum 550–1000 170–300 2200–4000 670–1200 Brass 250–650 75–200 1000–2600 300–800 Low carbon steel 100–325 30–100 400–1300 120–400 Free cutting steel 150–250 45–75 600–1000 180–300 Alloy steel 70–175 20–50 280–700 85–210 Cast iron 45–60 15–20 180–240 55–75 Reduce speeds for hard materials, abrasive materials, deep cuts, and high alloy materials. Increase speeds for soft materials, better finishes, light cuts, frail work, and setups. Start at midpoint on the range and increase or decrease speed until best results are obtained. *Figures rounded off. Goodheart-Willcox Publisher Figure 26-29. Recommended cutting speeds for milling. Speed is given in surface feet per minute (fpm) and in surface meters per minute (mpm).