SPEEDS AND FEEDS FOR MILLING Machinery's Handbook, 31st Edition
1110
Work
Work
Feed
ar
ar
Feed
D
Cutter
Cutter D
e
Fig. 3. Fig. 4. In this example, the cutting conditions match the standard conditions specified in the speed table for radial depth of cut to cutter diameter (3 in⁄4 in), and depth of cut (0.01 in), but the desired feed of 0.006 in/tooth does not match either of the feeds given in the speed table (0.004 or 0.008). Therefore, the cutting speed must be adjusted for this feed. As with turning, the feed factor F f is determined by calculating the ratio of the desired feed f to maximum feed f opt from the speed table, and from the ratio V avg / V opt of the two speeds given in the speed table. The feed factor is found at the intersection of the feed ratio row and the speed ratio column in Table 15d. The speed is then obtained using the following equation:
Optimum speed Average speed
V V
f
Optimum feed Chosen feed
. . 0008 0006 075 . =
. 2320 4755 20 .
opt avg
= =
=
=
f
opt
. 125 143 1.3 2320 134 10 10 3109 . . . . # # # + = ^ h = ⁄ 2
F
d = F 1.0
1.0
V F
=
=
ar
f
, fpm and ⁄ 4 Example 2, End Milling: What cutting speed should be used for cutting a full slot (i.e., a slot cut from the solid, in one pass, that is the same width as the cutter) in 5140 steel with hardness of 300 BHN using a 1-inch diameter coated carbide (insert) 0 ° lead angle end mill, a feed of 0.003 in/tooth, and a 0.2-inch axial depth of cut? . 3 82 3109 2970 rpm # = = The speed and feed data for end milling 5140 steel, Brinell Hardness Number = 275– 325, with a coated carbide tool are given in Table 11 as 15 ∕ 80 and 8 ∕ 240 for optimum and average sets, respectively. The speed adjustment factors for feed and depth of cut for full slot (end milling) are obtained from Table 15b. The calculations are the same as in the previous examples: f / f opt = 3 ∕ 15 = 0.2 and V avg / V opt = 240 ∕ 80 = 3.0, therefore, F f = 6.86 and F d = 1.0. The cutting speed for a 45-minute tool life is V = 80 3 6.86 3 1.0 = 548.8, approximately 550 ft/min. Example 3, End Milling: What cutting speed should be used in Example 2 if the radial depth of cut ar is 0.02 inch and axial depth of cut is 1 inch? In end milling, when the radial depth of cut is less than the cutter diameter (as in Fig. 4 ), first obtain the feed factor F f from Table 15c, then the axial depth of cut and lead angle factor F d from Table 15b The radial depth of cut to cutter diameter ratio ar / D is used in Table 15c to determine the maximum and minimum feeds that guard against tool failure at high feeds and against premature tool wear caused by the tool rubbing against the work at very low feeds. The feed used should be selected so that it falls within the minimum to maximum feed range, and then the feed factor F f can be determined from the feed factors at minimum and maximum feeds, F f 1 and F f 2 as explained below.
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online