TABLE 25-34 Types and definitions of milling cutters (Cont.) Arrangement Type of teeth Application Size Appearance Double angle Teeth on two conical faces Vee slots 458,608,908 Rounding Concave quarter circle and flat face Corner radius on edge 1.5–20 mm radius Involute gear cutter Teeth on two involute curves Involute gears Large range ELEMENTS OF MACHINE TOOL DESIGN 25.45 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. ELEMENTS OF MACHINE TOOL DESIGN TABLE 25-34 Types and definitions of milling cutters (Cont.) Arrangement Type of teeth Application Size Appearance End mill Helical teeth at one end and circumferential Light work, slots, profiling, facing narrow surfaces 50 mm TANGED END TAPPED END Parallel Shank Tee slot Circumferential and both sides Tee slots in machine table For bolts up to 24 mm diameter Dovetail On conical surface and one end face Dovetail machine slides 38 mm diameter, 458 and 608 25.46 CHAPTER TWENTY-FIVE Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. ELEMENTS OF MACHINE TOOL DESIGN TABLE 25-34 Types and definitions of milling cutters (Cont.) Arrangement Type of teeth Application Size Appearance Skid end mill Circumferential and one end Larger work than end mill 40–160 mm diameter Cutter Arbor Cutting saw (slot) Circumferential teeth Cutting off or slitting. Screw slotting 60–400 mm diameter Thick Thin Clearance Concave- convex Curved teeth on periphery Radiusing 1.5–20 mm radius Concave Convex Thread milling cutter PARALLEL SHANK TAPER SHANK ELEMENTS OF MACHINE TOOL DESIGN 25.47 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. ELEMENTS OF MACHINE TOOL DESIGN TABLE 25-35 Suggested feed per tooth for milling various materials, mm Slotting and Form relieved Face mills Helical mills side mills End mills cutters Circular saws Materials to be milled HSS Carbide HSS Carbide HSS Carbide HSS Carbide HSS Carbide HSS Carbide Cast iron Soft (up to 160H B ) 0.40 0.50 0.32 0.40 0.22 0.30 0.20 0.25 0.12 0.15 0.10 0.12 Medium (160 to 220H B ) 0.32 0.40 0.25 0.32 0.18 0.25 0.18 0.20 0.10 0.12 0.08 0.10 Hard (220 to 320H B ) 0.28 0.30 0.20 0.25 0.15 0.18 0.15 0.15 0.08 0.10 0.08 0.08 Malleable iron a 0.30 0.35 0.25 0.28 0.18 0.20 0.15 0.18 0.10 0.10 0.08 0.10 Steel Soft a (up to 160H B ) 0.20 0.35 0.18 0.28 0.12 0.20 0.10 0.18 0.08 0.10 0.05 0.10 Medium (160 to 220H B ) 0.15 0.30 0.12 0.25 0.10 0.18 0.08 0.15 0.05 0.10 0.05 0.08 Hard a (220 to 360H B ) 0.10 0.25 0.08 0.20 0.08 0.15 0.05 0.12 0.05 0.08 0.03 0.08 Stainless a 0.20 0.30 0.15 0.25 0.12 0.18 0.10 0.15 0.05 0.08 0.05 0.08 Brass and Bronze Soft 0.55 0.50 0.45 0.40 0.32 0.30 0.28 0.25 0.18 0.15 0.12 0.12 Medium 0.35 0.30 0.28 0.25 0.20 0.18 0.18 0.15 0.10 0.10 0.08 0.08 Hard 0.22 0.25 0.18 0.20 0.15 0.15 0.12 0.12 0.08 0.08 0.05 0.08 Copper 0.30 0.30 0.25 0.22 0.18 0.18 0.15 0.16 0.10 0.10 0.08 0.05 Monel 0.20 0.25 0.18 0.20 0.12 0.15 0.10 0.12 0.08 0.08 0.05 0.08 Aluminum a 0.55 0.50 0.45 0.40 0.32 0.30 0.28 0.25 0.18 0.15 0.12 0.12 a Coolant to be used. TABLE 25-36 Recommended cutting speeds for face and end milling with plain HSS and carbide milling cutters, m/min Depth of cut Roughing cut, 3 to 5mm Semi-finishing cut, 1.5 to 3 mm Finishing cut, below 1.5 mm Material to be milled HSS Carbide HSS Carbide HSS Carbide Cast iron Soft 25 68 30 80 36 105 Medium 15 50 25 68 30 80 Hard123816502068 Malleable Iron 25 68 30 80 36 105 Steel a : Soft 28 120 32 150 40 180 Medium 22 100 28 120 32 135 Hard 15 75 20 90 25 105 Stainless 18 50 22 68 28 80 Brass Average 30 75 45. 120 60 150 Soft yellow 60 120 90 180 120 240 Bronze 28 75 36 100 45 128 Copper 45 100 68 150 90 210 Monel 18 50 22 68 28 80 Aluminum a 75 240 105 300 150 450 a Coolant to be used Note: Cutting speeds for 12% cobalt HSS should be about 25% to 50% higher than those shown for plain HSS. Cutting speeds for cast alloy should be about 100% higher than those shown for plain HSS. Above speeds should be reduced when milling work that has hard spots or when milling castings that are sandy. 25.48 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. ELEMENTS OF MACHINE TOOL DESIGN TABLE 25-37 Feeds and speeds for hobbing Feed, mm/rev. of blank Hob Module Roughing (single Roughing speeds, Type of gear Material mm thread hob) (multithread hob) Finishing m/min High speed reduction and step up Steel 1.5–8 1–1.5 1–1.5 0.8–1.25 9–25 Instrument Steel 0.4–1.25 0.5–1.5 Up to 3 0.5–1.0 25–60 Non-ferrous 0.4–1.25 1.0–1.5 Up to 3 0.5–1.0 25–60 Aircraft Steel 2.0–4.0 1.0–1.5 Up to 3 0.8–1.25 15–45 Machine tool and printing press Steel, C.I. 2.0–6.0 2.0–3.2 Up to 2.5 1.0–1.5 15–30 Non-ferrous 2.0–6.0 2.0–3.2 Up to 2.5 1.0–1.5 25–450 Automotive, including trucks and tractors Steel 1.5–8.10 2.0–3.2 Up to 2.5 Up to 2.0 (3 starts) 1.25–2.0 15–45 High quality industrial Steel 10.0–25.0 2.0–2.5 1.25–2.0 12–30 Cast iron 2.5–8.0 1.25–3.2 General industrial Steel 10.0–25.0 2.0–2.5 1.50–2.5 12–30 Cast iron 2.5–8.0 1.25–3.2 Splines Steel 1.25–3.0 1.25–1.5 0.50–1.75 l8–45 TABLE 25-38 Selection of milling cutters Material Hardness One-piece construction High-speed steel Cutting portion 760 HV (62 HRC) Min Two-piece construction Shank portion Cutting portion High speed steel Parallel shank 245 HV (21 HRC) Min Body Carbon steel with tensile strength not less than 700MPa (190 HN) Tang of Morse taper shank 320 HV (32HRC) Min Note: The equivalent values within parentheses are approximate. Recommendations for selection of milling cutters: Tool Type N—For mild steel, soft cast iron and medium hard non-ferrous metals. Tool Type H—For specially hard and tough materials. Tool Type S—For soft and ductile materials. Material to be cut Tensile strength, MPa Brinell hardness, H B Tool type a Carbon steel Up to 500 N or (S) Above 500 up to 800 N Above 800 up to 1000 N or (H) Above 1000 up to 1300 H Steel casting H Gray cast iron Up to 180 N Over 180 H Malleability cast iron N Copper alloy Soft Sor(N) Brittle Nor(H) Zinc alloy Sor(N) Aluminum alloy Soft S Medium/Hard Nor(S) Aluminum alloy, age hardened Low cutting speed N High cutting speed S Magnesium alloy Sor(N) Unlaminated Nor(S) a Tool types within parentheses are non-preferred. Courtesy: IS 1830, 1971 25.49 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. ELEMENTS OF MACHINE TOOL DESIGN TABLE 25-39 Dimensions for interchangeability of milling cutters and arbors with tenon drive A z A r a a 1 dφ dφ s×45 s×45 b 1 r 1 b All dimensions in millimeters Arbor Cutter d a abr a 1 b 1 r 1 h6/H7 h11 H11 Max H11 H13 Max sz b 5 3 2.0 0.3 3.3 2.5 0.6 0.3 0.075 8 5 3.5 0.4 5.4 4.0 0.6 0.4 þ 0.1 0.100 10 6 4.0 0.5 6.4 4.5 0.8 0.5 0.100 13 8 4.5 0.5 8.4 5.0 1.0 0.5 0.100 16 8 5.0 0.6 8.4 5.6 1.0 0.6 0.100 19 10 5.6 0.6 10.4 6.3 1.2 0.6 0.100 22 10 5.6 0.6 10.4 6.3 1.2 0.6 þ0.2 0.100 27 12 6.3 0.8 12.4 8.0 1.6 0.8 0.100 32 14 7.0 0.8 14.4 7.0 1.2 0.8 0.100 40 18 9.0 1.0 16.4 9.0 2.0 1.0 0.100 50 16 8.0 1.0 18.4 10.0 2.0 1.0 þ0.3 0.100 60 20 10.0 1.0 20.5 11.2 2.0 1.0 0.125 a The tolerance on d is not applicable to gear hobs. b z ¼ maximum permissible deviation between the axial plane of the tenon and the axis of arbor of diameter d. Courtesy: IS 6285-1971 25.50 CHAPTER TWENTY-FIVE Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. ELEMENTS OF MACHINE TOOL DESIGN TABLE 25-40 Dimensions for interchangeability of milling cutters and milling arbors with key drive dφ C C C 1 C 1 a r KEYWAY IN CUTTER KEYWAY IN ARBOR KEY SECTION a a b s×45 r 1 All dimensions in millimeters Key Keyway d a a Tolerance Tolerance Tolerance Tolerance Tolerance h6/H7 h9 b b S on Sa c C on CC 1 on C 1 r on rr 1 on r 1 822 26.7 8.9 10 3 3 0.16 þ0.09 3 8.2 11.5 0.4 0–0.1 13 3 3 0 3 11.2 0 14.6 þ0.1 0 0.16 0 16 4 4 4 13.2 0–0.1 17.7 0 0.6 –0.2 –0.08 19 5 5 5 15.6 21.1 22 6 6 0.25 0þ0.15 6 17.6 24.1 1.0 27 7 7 7 22.0 29.8 0 0.25 0 32 8 7 8 27.0 34.8 1.2 –0.3 –0.09 40 10 8 9 10 34.5 43.5 50 12 8 12 44.5 53.5 þ0.2 1.6 60 14 9 0.40 þ0.20 14 54.0 0–0.2 64.2 0 0–0.5 0.40 0–0.15 70 16 10 0 16 63.5 75.0 2.0 80 18 11 18 73.0 85.5 100 25 14 0.60 25 91.0 107.0 2.5 0.60 0–0.20 –0.20 a The tolerance on diameter d is not applicable to gear hobs. IS: 6285, 1971. b Tolerance on thickness b of key: square, h9; rectangular, h11. c Tolerance on keyway width a: light drive fit, N9. For keyway in arbor: running fit, H9; light drive fit, N9. For keyway in cutter: C11 ELEMENTS OF MACHINE TOOL DESIGN 25.51 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. ELEMENTS OF MACHINE TOOL DESIGN TABLE 25-41 American National Standard staggered teeth, T-slot milling cutters with Brown and Sharpe taper and Weldon shanks (ANSI/ASME B94, 19, 1986) With B. and S. With Weldon taper a shank Cutter Face Neck Bolt diam., width, diam., Length Taper Length Diam., size DWNLNo. LS 1 4 9 16 16 64 17 64 ——2 19 32 1 2 5 16 21 32 17 64 21 64 ——2 11 16 1 2 3 8 26 32 21 64 13 32 ——3 1 4 3 4 1 13 32 25 64 17 32 573 7 16 1 5 8 1 1 4 31 32 21 32 6 1 4 73 15 16 1 3 4 1 15 32 5 8 25 32 6 7 8 94 7 16 — 11 27 32 53 64 1 1 32 7 1 4 94 13 16 1 1 4 All dimensions are inches. All cutters are high-speed steel and only right-hand cutters are standard. a For dimensions of Brown and Sharpe taper shanks. See information given in standard Handbook. Tolerances: On D, þ0.000, À0.010 inch; on W, þ0.000, À0.005 inch; on N, þ0.000, À0.005 inch, on L, Æ 1 16 inch; on S, À0.0001 to À0.0005 inch. TABLE 25-42 American National Standard 60-degree single-angle milling cutters with Weldon shanks (ANSI/ASME B94, 19, 1985) L D S w 60 Diam., DS W L Diam., DS W L 3 4 3 8 5 16 2 1 16 1 7 8 7 8 13 16 3 1 4 1 3 8 5 8 9 16 2 7 8 2 1 4 11 1 16 3 3 4 All dimensions are in inches. All cutters are high-speed steel. Right-hand cutters are standard. Tolerances: On D, 0.015 inch; on S, À0.0001 to À0.0005 inch; on W, 0.015 inch; and on L, Æ 1 16 inch. 25.52 CHAPTER TWENTY-FIVE Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. ELEMENTS OF MACHINE TOOL DESIGN TABLE 25-43 American National Standard multiple flute, helical series end mills with Brown and Sharpe taper shanks a (ANSI/ ASME B94, 19, 1985) L w D Diam., DW L Taper No. Diam., DW L Taper No. ––––11 5 8 5 5 8 7 ––––1 1 4 27 1 4 9 1 2 15 16 4 15 16 71 1 2 2 1 4 7 1 2 9 3 4 1 1 4 5 1 4 722 3 4 89 All dimensions are in inches. All cutters are high-speed steel. Right-hand cutters with right hand helix are standard. Helix angle is not less than 10 degrees. No. 5 taper is standard without tang: Nos. 7 and 9 are standard with tang only. Tolerances: On D, þ0.005 inch; on W, Æ 1 32 inch; and L, Æ 1 16 inch. a For dimensions of B. and S. taper shanks, see information given in standard handbook. ELEMENTS OF MACHINE TOOL DESIGN 25.53 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. ELEMENTS OF MACHINE TOOL DESIGN TABLE 25-44 American National Standard form relieved, concave, convex, and corner-rounding arbor-type cutters a (ANSI/ASME B94, 19, 1985) w w H H H D Concave Convex Corner - Rounding D C C w R D Diameter C or radius R Diameter of hole H Cutter Width W Nom. Max. Min. diam. D b Æ:010 c Nom. Max. Min. Concave cutters c 1 8 0.1270 0.1240 2 1 4 1 4 1 1.00075 1.00000 1 4 0.2520 0.2490 2 1 2 7 16 1 1.00075 1.00000 3 8 0.3770 0.3740 2 3 4 5 8 1 1.00075 1.00000 1 2 0.5040 0.4980 3 13 16 1 1.00075 1.00000 3 4 0.7540 0.7480 3 3 4 1 13 16 1 1 4 1.251 1.250 1 0.0040 0.9980 4 1 4 1 9 16 1 1 4 1.251 1.250 Convex cutters d 1 4 0.2520 0.2480 2 1 2 1 4 1 1.00075 1.00000 3 8 0.3770 0.3730 2 3 4 3 8 1 1.00075 1.00000 1 2 0.5020 0.4980 3 1 2 1 1.00075 1.00000 3 4 0.7520 0.7480 3 3 4 3 4 1 1 4 1.251 1.250 1 1.0020 0.9980 4 1 4 11 1 4 1.215 1.250 Corner-rounding cutters e 1 8 0.1260 0.1240 2 1 2 1 4 1 1.00075 1.00000 1 4 0.2520 0.2490 3 13 32 1 1.00075 1.00000 1 2 0.5020 0.4990 4 1 4 3 4 1 1 4 1.251 1.250 All dimensions in inches. All cutters are high-speed steel and are form relieved. Right-hand corner rounding cutters are standard, but left-hand cutter for 1 4 inch size is also standard. a For key and keyway dimensions for these cutters, see standard handbook. b Tolerances on cutter diameters are þ 1 16 , À 1 16 inch for all sizes. c Tolerance does not apply to convex cutters. d Size of cutter is designated by specifying diameter C of circular form. e Size of cutter is designated by specifying radius R of circular form. Source: Courtesy: ANSI/ASME B94, 19, 1985, Erik Oberg Editor Etd., Extracted from Machinery’s Handbook, 25th edition, Industrial Press, N.Y., 1996. 25.54 CHAPTER TWENTY-FIVE Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. ELEMENTS OF MACHINE TOOL DESIGN [...]... 25-52 For draw clearance Refer to Table 25-53 For design of speed-change gear box for machine tools, kinematic schemes of machine tools, layout diagrams or structural diagram for gear drives, version of kinematic structures in machine tools, etc Refer to subsection ‘‘Designing spur and helical gears for machine tools’’ from pp 23-109 to 23-138 of Machine Design Data Handbook, McGraw-Hill Publishing Company,... which affects the blank diameter when d=r lies between 15 and 20 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website ð25 -159 Þ ELEMENTS OF MACHINE TOOL DESIGN ELEMENTS OF MACHINE TOOL DESIGN Particular 25.67 Formula D¼ pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi d... drawing TABLE 25-62 Mean values for m (standard coefficients) Material First draw % Redraws % Particulars Aluminum, soft Aluminum, deep drawing quality Brass Copper Steel Steel, deep drawing quality Steel, stainless Zinc Tin 40 40–50 20–25 20–30 45 40 35–40 40–45 35–40 50 35–45 20–25 15 20 15 20 15 20 15 20 15 20 10 15 Blanking and piercing (full-edge) tough (soft) sheet brittle (hard) sheet Making V- and... 0.07 0.08 0.09 0.1 1000 800 630 500 400 315 250 200 160 125 100 80 63 50 40 31.5 25 20 16 12.5 10 8 6.3 5 4 8 3 6 5 Total ram stroke H, mm B2 C 2 6 1 26 1 1 1000 800 630 500 400 315 250 200 160 125 100 80 63 53 40 31.5 25 20 16 12.5 0.8.83 0 0.5 4 0 15 0 25 0 0.2 76 0 15 0 1 0 Total ram stroke H, mm ELEMENTS OF MACHINE TOOL DESIGN 8 6.3 5 λ = 1:10 0.925 0.412 0. 515 0.58 0.69 0.825 0.875 0.975 0.63 0.463... of Use as given at the website Die ELEMENTS OF MACHINE TOOL DESIGN 25.63 ELEMENTS OF MACHINE TOOL DESIGN Particular Guide pin busing Guide pins Formula Punch Punch holder Punch Tensile Workpiece Stripper Die block Compressive Tensile Die holder Die Bolster plote FIGURE 25-31 Common components of a simple die Courtesy: F W Wilson, Fundamentals of Tool Design, American Society of Tool and Manufacturing... tan À 0:0218 t 2 ð25 -150 Þ when ri ¼ 2t t ri þ 2 2 Initial length of strip of metal (Fig 25-35) Li ¼ T À t À 2ri þ K þ Bending allowance for right angle bend to take into account reduction of length K and T (Fig 25-35) b ¼ ri þ t À t r þ 4 i 2 ð25 -151 Þ ð25 -152 aÞ b ¼ 1:037t ð25 -152 bÞ when ri ¼ 2t The bending force Fb ¼ Wt u ð25 -153 Þ Planishing force Fp ¼ WKsy ð25 -154 Þ where K and W are... ELEMENTS OF MACHINE TOOL DESIGN 25.79 0 40 5 31 50 2 0 lo 20 60 1 125 00 1 0 8 3 6 ve 50 0 4 5 31 25 C m 315 355 40 45 50 56 56 A1 D1 n- 1 0.1 0.08 0.063 E2 0.05 0.04 0.035 0.025 Z 0.02 0.016 0.0125 0.01 0.008 0.0063 ∑ α α… 28 mi 0.2 2 6 1 5 1.2 1 8 0 63 0 5 0 25 n, F2 20 21 1000 800 600 500 400 315 250 200 160 125 100 80 63 50 D2 40 31.5 25 20 16 12.5 10 E1 0.125 4 15 3 .5 2 18 II 0.16 6.3 5 15 13 A2... ELEMENTS OF MACHINE TOOL DESIGN ELEMENTS OF MACHINE TOOL DESIGN Particular 25.61 Formula SHAPING (Fig 25-27) The force of cutting can be found by empirical formula Fz Fz ¼ Ft ¼ 9:807Cp kd x sy SI ð25-135aÞ where Fz in N Fz ¼ Ft ¼ Cp kd x sy Customary Metric Units ð25-135bÞ where x, y, k and Cp have the same values as in lathe tools; Fz in kgf Equation (25-135) can be also used for the case of planing machine. .. the website ELEMENTS OF MACHINE TOOL DESIGN 25.74 CHAPTER TWENTY-FIVE Particular Formula FORMING PROCESS: Note: The Symbols, Equations and Examples given in the book entitled ‘‘Mechanical Presses*’’ by Professor Dr Ing Heinrich Makelt and translated by R Hard¨ bottle, are followed and used in Symbols, Equations and Examples with reference to Figs 25-41 to 25-49 in this Machine Design Data Handbook The... (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website ELEMENTS OF MACHINE TOOL DESIGN ELEMENTS OF MACHINE TOOL DESIGN Particular 25.75 Formula For determination of blank-holder force for deep drawing Refer to Fig 25-45 For chart for extrusion molding and impact extrusion: a, extrusion molding . 0 .15 0.10 0.10 0.08 0.08 Hard 0.22 0.25 0.18 0.20 0 .15 0 .15 0.12 0.12 0.08 0.08 0.05 0.08 Copper 0.30 0.30 0.25 0.22 0.18 0.18 0 .15 0.16 0.10 0.10 0.08 0.05 Monel 0.20 0.25 0.18 0.20 0.12 0 .15. 0.20 0.08 0 .15 0.05 0.12 0.05 0.08 0.03 0.08 Stainless a 0.20 0.30 0 .15 0.25 0.12 0.18 0.10 0 .15 0.05 0.08 0.05 0.08 Brass and Bronze Soft 0.55 0.50 0.45 0.40 0.32 0.30 0.28 0.25 0.18 0 .15 0.12 0.12 Medium. 0.20 0.25 0.12 0 .15 0.10 0.12 Medium (160 to 220H B ) 0.32 0.40 0.25 0.32 0.18 0.25 0.18 0.20 0.10 0.12 0.08 0.10 Hard (220 to 320H B ) 0.28 0.30 0.20 0.25 0 .15 0.18 0 .15 0 .15 0.08 0.10 0.08