http://its.fvtc.edu/MachShop1/drillpress/cutspeeds.htm

Table 3   Recommended Cutting Speeds for Drilling with High-Speed Steel DrillsFor reamers, use 1/2 to 2/3 the speed given in this table.

Material Hardness,Bhn

Cutting Speed, fpm

Material Hardness, Bhn

Cutting Speed, fpm

Plain Carbon SteelsAISI–1019, 1020, 1030, 1040, 1050, 1060, 1070, 1080, 1090

Alloy SteelsAISI-1320, 2317, 2515,3120, 3316, 4012, 4020,4120, 4128, 4320, 4620,4720, 4820, 5020, 5120,6120, 6325, 6415, 8620,8720, 9315

Alloy SteelsAISI-1330, 1340, 2330,2340, 3130, 3140, 3150,4030, 4063, 4130, 4140,4150, 4340, 4640, 5130,5140, 5160, 52100, 6150,6180, 6240, 6290, 6340,6380, 8640, 8660, 8740,9260, 9445, 9840, 9850

Stainless SteelsStandard GradesAusteniticAnnealedCold-DrawnFerriticMartensiticAnnealed

Quenched & Tempered

Free Machining Grades

120–150150–170170–190190–220220–280280–350350–425

125–175175–225225–275275–325325–375375–425

175–225225–275275–325325–375375–425

135–185225–275135–185

135–175175–225275–325375–425

80–12070–9060–8050–7040–5030–4015–30

60–8050–7045–6035–5530–4015–30

50–7040–6030–5025–4015–30

40–5030–4050–60

55–7050–6030–4015–30

Stainless Steels (Cont.)Cold-DrawnFerriticMartensiticAnnealedCold-DrawnQuenched & Tempered

Tool SteelsWater HardeningCold WorkShock ResistingMold

High-Speed Steel

Gray Cast-Iron

Malleable IronFerriticPearlitic

Aluminum AlloysCast-Nonheat TreatedCast-Heat TreatedWrought-Cold DrawnWrought-Heat Treated

225–275135–185

135–185185–240275–325375–425

150–250200–250175–225100–150150–200200–250250-275

110–140150–190190–220220–260260–320

110–160160–200200–240240–280

60–90100–120

100–13090–12050–6030–40

70–8020–4040–5060–7050–6030–4015–30

90–14080–10060–8050–7030–40

120–14090–11060–9050–60

200–300150–250150–300140–300

150–300

AusteniticAnnealed 135–185 80–100

Brass & Bronze (Ordinary)

Bronze (High Strength)

30–100

The spindle speed must be set so that the tool will be operating at the correct cutting speed. To set the proper spindle speed, we need to calculate the proper revolution per minute or RPM setting. We stated earlier that cutting speed or surface speed would change with the size of the tool. So to keep the surface speed the same for each size tool, we must use a formula, which includes the size of the tool, to calculate the proper RPM to maintain the proper surface footage.

Calculating RPM for Drilling Top

The RPM setting for drilling depends on the cutting speed of the material and the size of the drill bit. The RPM setting will change with the size of the bit. As the drill bit gets smaller, the RPM must increase to maintain the recommended surface footage. Take the case of the wheel. Think of the drill bit as a wheel and the cutting speed as a distance. A larger wheel (drill bit) will need to turn less revolutions to cover the same distance in the same amount of time than a smaller wheel (drill bit). Therefore, to maintain the recommended cutting speed, larger drills must be run at slower speeds than smaller drills.

The drill press must be set so that the drill bit will be operating at the proper surface speed. Spindle speed settings on the drill press are done in RPMs. To calculate the proper RPM for the tool, we must use the following formula:

Cutting speed (CS) X 4Diameter of cutter (D)

This simplified version of the RPM formula is the most common formula used in machine shops. This RPM formula can be used for other machining operations as well.

Let's put this formula to work in calculating the RPM for the drilling example below. Use the recommended cutting speed charts in Table 3.

A 0.50 drill is being used to drill a piece of 1018 steel with a brinnel hardness of 200. Calculate the RPM setting to perform this drilling operation.

Cutting Speed = 70 (fpm)Diameter of Cutter = 0.500

Although you have calculated the RPM, remember that this is only a recommendation. Some judgment must be made in selecting the actual RPM setting to use. There are always outside factors that must go into deciding on the proper speed and feed to use. Ask yourself these questions before deciding on an RPM setting. How sturdy is my setup? Go slower for setups, which lack a great deal of rigidity. Am I using coolant? You may be able to use a faster speed if you are using flood coolant. How deep am I drilling? If you’re drilling a deep hole, there is no place for the heat to go. You may have to slow the RPM down for deep whole drilling.

The greatest indicator of proper and improper cutting speed is the color of the chip. When using a high-speed steel drill bit, the chips should never be turning brown or blue. Straw-colored chips indicate that you are on the maximum edge of the cutting speed for your cutting conditions. When using carbide, chip colors can range from amber to blue, but never black. A dark purple color will indicate that you are on the maximum edge of your

cutting conditions. Carbide cutting tools are covered in much greater detail in another section of your learning materials.

Let’s try some more examples.

A 1.00-inch, high-speed steel (HSS) drill is being used on a piece of 1045 steel with a brinnel hardness of 300. Calculate the RPM setting to perform this cutting operation.

Cutting Speed = 50 (fpm)Diameter of Cutter = 1.00

A 3/4-inch (HSS) drill is used on a piece of (leaded) 11L17 steel with a brinnel hardness of 100. Calculate the RPM setting to perform this drilling operation.

Cutting Speed = 130 (fpm)Diameter of Cutter = 0.75

Calculating RPM for Reaming

The drill press RPM setting for reaming depends on the cutting speed of the material and the size of the ream. The RPM setting will change with the size of the ream. As the ream gets smaller, the RPM must increase to maintain the recommended surface footage. Although you will find specific cutting speeds for reaming, a simple rule of half the speed will work for most reaming operations. Using half the spindle speed you calculated for the drilling operation is a commonly accepted method for determining the reaming speed in most machine shops.

Let’s try an example.

A high speed steel "G" drill is being used prior to reaming a 3/8 hole on a piece of 1095 steel with a brinnel hardness of 300. Calculate the RPM setting to perform the drilling and reaming operations.

Cutting Speed = 40 (fpm)Diameter of Cutter = 0.3701 (G drill)

Half the speed for reaming would be = 432 / 2 = 216 RPM for reaming.

Calculating RPM for Countersinking and Counterboring Top

The drill press RPM setting for countersinking and counterboring also depends on the cutting speed of the material and the size of the tool. The RPM setting will change with the size of the tool. As the cutting tool gets smaller, the RPM must increase to maintain the recommended surface footage. Although you will find specific cutting speeds for countersinking and counterboring, a simple rule of 1/3 the speed of a drill of the same size will work for most countersinking and counterboring operations. The RPM for a counterbore would be fairly simple to calculate using the 1/3 method, but calculating the RPM for a countersink brings about a different set of circumstances. The countersink is tapered (Figure 4).

Figure 4

As you can see from the figure, the RPM setting would be slower for a countersink being cut at diameter "B" rather than for a countersink being cut at diameter "A".

  

The part prints will usually state the finished diameter of the countersink (Figure 5).  Use this as the diameter for calculating the spindle speed setting. Otherwise, use an approximate size and watch your chip color carefully.

Figure 5

Let’s try an example.

Let’s calculate the RPM for the countersink in Figure 5. The material is 1045 steel with a brinnel hardness (bhn) of 200.

Cutting Speed = 75(fpm)Diameter of Cutter = 0.38 for a 0.38 drill

One-third the speed for countersinking would be = 789/ 3 = 263 RPM.

Center Drill RPM Calculations 

A center drill or combination drill and countersink (Figure 6) is used for spotting holes in workpieces or for making center holes for turning work. Center drills, as you can see from the illustration, are short and sturdy and will not bend or flex under pressure. When calculating the proper RPM for using a center drill, use the diameter of the pilot for your calculations. Center drills will break if they are run too slowly. Using the smaller diameter of the center drill will assure that the RPM setting is sufficient. If you find that the drill chatters as you reach the proper depth, slightly decrease the RPM setting.

Figure 6

Let’s try an example.

Lets calculate the RPM for the center drilling 1018 steel with brinnel hardness (bhn) of 100. A #4 center drill with a pilot drill diameter of 1/8 inch will be used.

Cutting Speed = 100(fpm)Diameter of Cutter = 0.125

RPM Calculation for Threading Top

(Power Tapping)-Selecting the best RPM for power tapping can be very complicated. There are many variables that must be taken into consideration when selecting the best spindle speed for machine tapping. Among the variables are:

A. Material to be tapped. Cutting speeds need to decrease with the hardness of the material.

B. Length of the hole. The deeper the hole the slower the RPM

C. Size of the chamfer on the tap. Taps with long chamfer tapping short holes can be run faster. However, taps with long chamfers tapping long holes must be run slower.

D. Pitch of the thread. Coarse taps need to be run slower than fine taps.E. Percentage of full thread. The higher the percentage of full threads the slower the

RPMF. Type and amount of cutting fluid. The greater the amount of cutting fluid getting

to the tap the faster the RPMG. Surface treatment of the tap. A tap that has been nitride or oxide coated can be run

much faster than a tap, with no coating.H. Type of tap. Spiral-fluted and spiral-pointed taps can operate at higher cutting

speeds than can straight-fluted taps.

The RPM formula for tapping is no different from the other formula we have been using, but the consideration mentioned for tapping must be made before we actually do any power tapping. Until you know how the tap will operate under your conditions, start with 1/3 to 1/2 the calculated RPM and gradually increase the RPM to the capacity of the conditions. A table of recommended cutting speeds for threading is included in Table 7.

Table 7   Cutting Speeds for Machine Tapping

Material Cutting Speed, fpm

Material Cutting Speed, fpm

Low Carbon SteelsUp to .25% C

Medium Carbon Steels.30 to .60% CAnnealedHeat Treated(220 to 280 Bhn)

Tool Steels, High Carbonand High-Speed Steel

Stainless Steels

Gray Cast-Iron

Malleable IronFerriticPearlitic

Zinc Die Castings

40 to 80

30 to 60

20 to 50

20 to 40

5 to 35

40 to 100

80 to 12040 to  80

60 to 150

Aluminum

Brass

Manganese Bronze

Phosphor Bronze

Naval Brass

Monel Metal

Tobin Bronze

PlasticsThermoplasticsThermosetting

Hard Rubber

Bakelite

50 to 200

50 to 200

30 to 60

30 to 60

80 to 100

20 to 40

80 to 100

50 to 10050 to 100

50 to 100

50 to 100

Let’s try an example.

Let’s calculate the RPM for tapping a 1/2-13 UNC hole. The material is 1018 steel with a brinnel hardness (bhn) of 100.

Cutting Speed = 50 fpmDiameter of Cutter = 0.50 for a 1/2 tap

http://its.fvtc.edu/MachShop3/speedCalc/SpeedRPM.htm

Cutting Speeds & RPM CalculationsSpeed/Feeds Home

Milling machines are used to perform a wide variety of machining operations. There are those operations that are strictly milling operations, but we also use milling machines to perform other operations such as drilling, reaming, tapping, and boring. The rules and principles of cutting speeds and R.P.M. calculations that apply to these "other" operations being performed on milling machines are still used in the same manner. An example of this would be reaming. Reaming is done at half the speed and twice the feed as drilling. This rule still applies on the milling machine as it does on the drill press or the lathe.

Cutting Speed for Milling- Cutting speed is the speed at the outside edge of the milling cutter as it is rotating. This is also known as surface speed. Surface speed, surface footage, and surface area are all directly related. Two wheels can illustrate a nice example of this. Take two wheels, one wheel which is three feet in diameter and the other wheel which is one foot in diameter, roll each wheel one complete turn (Figure 1).

Figure 1

Which wheel traveled farther? The larger wheel traveled farther because it has a larger circumference and has more surface area. Cutting speeds work on the same principle. If two cutters of different sizes are turning at the same revolutions per minute (RPM), the larger cutter has a greater surface speed. Surface speed is measured in surface feet per minute (SFPM). All cutting tools work on the surface footage principal. 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 (Figure 2).

Steel

IronAluminum

Lead

Increasing Cutting SpeedFigure 2

The hardness of the cutting tool material has a great deal to with the recommended cutting speed. The harder the cutting tool material, the faster the cutting speed (figure 3). The softer the cutting tool material the slower the recommended cutting speed.

Carbon SteelHigh Speed Steel

Carbide

Increasing Cutting SpeedFigure 3

The depth of cut and the feed rate will also affect the cutting speed, but not to as great as an extent as the work hardness. These three factors; cutting speed, feedrate and depth of cut are known as cutting conditions. Cutting conditions are determined by the machinability rating. Machinability is the comparing of materials on their ability to be machined. From machinability ratings we can derive recommended cutting speeds. Recommended cutting speeds are given in charts. These charts can be found in your Machinery’s Handbook, textbook or a chart given to you by your tool salesperson. In Table 4 you will find a typical recommended cutting speed chart.

Milling-Machine Operations

Table 4. Recommended Cutting Speed for Milling in Feet per Minute (fpm)

Work MaterialHardness,Bhn

Cutting Speed, fpm

High-Speed Steel Carbide

Plain Carbon Steel, AISI1010 to AISI 1030

to 150

150 to 200

110100 to 140

10080 to 120

600400 to 900

450300 to 700

The milling machine speed must be set so that the milling cutter will be operating at the correct cutting speed. To set the proper speed we need to calculate the proper revolution per minute or RPM setting. We stated earlier that cutting speed or surface speed would change with the size of the cutter. So to keep the surface speed the same for each size cutter we must use a formula that includes the size of the cutter to calculate the proper RPM to maintain the proper surface footage.

Calculating RPM- The RPM setting depends on the cutting speed and the size of the cutter. The RPM setting will change with the size of the cutter. As the milling cutter gets smaller the RPM must increase to maintain the recommended surface footage. Again, take the case of the wheel. Think of the cutter as a wheel and the cutting speed as a distance. A larger wheel (cutter) will need to turn fewer revolutions per minute to cover the same distance in the same amount of time than a smaller wheel (cutter). Therefore, to maintain the recommended cutting speed, larger cutters must be run at slower speeds than smaller cutters.

The milling machine must be set so that the milling cutter will be operating at the proper surface speed. Spindle speed settings on the milling machine are done in RPMs. To calculate the proper RPM for the tool we must use the following formula:

Cutting speed (CS) X 4Diameter of cutter (D)

This simplified version of the RPM formula is the most common formula used in machine shops. This RPM formula can be used for other machining operation as well.

Lets put this formula to work in calculating the RPM for the machining example below. Use the recommended cutting speed charts in Table 5.

Milling-Machine OperationsTable 5. Recommended Cutting Speed for Milling in Feet per Minute (fpm)

Work MaterialHardness,Bhn

Cutting Speed, fpm

High-Speed Steel Carbide

Plain Carbon Steel, AISI1010 to AISI 1030

to 150

150 to 200

110100 to 140

10080 to 120

600400 to 900

450300 to 700

AISI B1111, AISI B1112, AISI B1113, Steel

140 to 180

140

110 to 200

650

400 to 1200

Plain Carbon Steel, AISI 1040 to 1095

120 to 180

180 to 220

220 to 300

19580 to 120

8570 to 110

6030 to 80

600400 to 800

350300 to 500

200100 to 300

All Alloy Steels Having .3% or Less Carbon Content:AISI 1320, AISI 3120, AISI 4130, AISI 4020, AISI 5020, AISI 4118, AISI 9310, etc.

180 to 220

220 to 300

300 to 400

8065 to 100

6030 to 80

4030 to 50

350300 to 600

300200 to 350

125100 to 150

All Alloy Steels Having More Than .3% Carbon Content:AISI 1340, AISI 2340, AISI 4140, AISI 4150, AISI 4340, AISI 5140, AISI 5150,AISI 52100, AISI 8660, AISI 9260, etc.

180 to 220

220 to 300

300 to 400

8060 to 100

5530 to 80

3020 to 50

325275 to 450

250180 to 300

10080 to 130

A milling cut is to be taken with a 0.500 inch high speed steel (HSS) endmill on a piece of 1018 steel with a brinnel hardness of 200. Calculate the RPM setting to perform this cut.

Cutting Speed = 90 (fpm)Diameter of Cutter = 0.500

Since the available spindle speed settings are generally not infinitely variable, the machine cannot be set precisely to the calculated RPM setting. Some judgment must be made in selecting the speed to use. Try to get to the speed which is nearest to the calculated RPM, but if you can’t consider these conditions. Are you roughing or finishing? If you are roughing, go slower. If you are finishing go faster. What is your depth of cut? If it is a deep cut, go to the slower RPM setting. Is the setup very rigid? Go slower for setups that lack a great deal of rigidity. Are you using coolant? You may be able to go to the faster of the two settings if you are using coolant. The greatest indicator of cutting speed is the color of the chip. When using a high-speed steel cutter the chips should never be turning brown or blue. Straw colored chips indicate that you are on the maximum edge of the cutting speed for your cutting conditions. When using Carbide, chip colors can range from amber to blue, but never black. A dark purple color will indicate that you are on the maximum edge of your cutting conditions. Carbide cutting tools are covered in much greater detail in other section of your learning materials.

Let’s try some more examples.

A milling cut is to be taken with a 6.00 inch (HSS) side milling cutter on a piece of 1045 steel with a brinnel hardness of 300. Calculate the RPM setting to perform this cut.

Cutting Speed = 55 (fpm)Diameter of Cutter = 6.00

A 1-inch (HSS) drill is used on a piece of 1010 steel with a brinnel hardness of 100. Calculate the RPM setting to perform this drilling operation.

Cutting Speed = 140 (fpm)Diameter of Cutter = 1.00

A milling cut is to be taken with a 3.00 inch carbide face milling cutter using coated inserts on a piece of 4140 alloy steel with a brinnel hardness of 200. Calculate the RPM setting to perform this cut.

Cutting Speed = 400 (avg. fpm)Diameter of Cutter = 3.00

http://www.sperdvac.org/cutting_speeds_and_feeds/cutting_speeds_and_feeds.htm

Jati KukuhPrakosa A.D.RB110508131007