ねじの下穴径の選び方
ねじの下穴径はねじの等級に関係するもので、２級程度のねじであれば穴加工の際の拡大量を見込んで以下の式で下穴径を求められます。
D＝ｄ－P
D：下穴径，ｄ：ねじの外径の基準寸法，P：ねじのピッチ
ドリルによる穴加工は、加工条件によって穴径がドリルの直径よりも大きくなります。
下記の表はこの式によって求めた下穴径の例を示したものです。
メートル細目ネジ 下穴表
| ネジサイズ | ドリル径 | |
|---|---|---|
| M1×0.20 | 0.80 | |
| M1.1×0.2 | 0.90 | |
| M1.2×0.2 | 1.0 | |
| M1.4×0.2 | 1.20 | |
| M1.6×0.2 | 1.40 | |
| M1.8×0.2 | 1.60 | |
| M2×0.25 | 1.75 | |
| M2.2×0.25 | 1.95 | |
| M2.5×0.35 | 2.15 | |
| M3×0.35 | 2.65 | |
| M3.5×0.35 | 3.15 | |
| M4×0.5 | 3.50 | |
| M4.5×0.5 | 4.0 | |
| M5×0.5 | 4.5 | |
| M5.5×0.5 | 5.0 | |
| M6×0.75 | 5.25 | |
| M7×0.75 | 6.25 | |
| M8×1 M8×0.75 | 7.0 7.25 | |
| M8×1 M8×0.75 | 7.0 7.25 | |
| M9×1 M9×0.75 | 8.0 8.25 | |
| M10×1.25 M10×1 M10×0.75 | 8.75 9 9.25 | |
| M11×1 M11×0.75 | 10.0 10.25 | |
| M12×1.5 M12×1.25 M12×1 | 10.50 10.75 11.0 | |
| M12×1.5 M12×1.25 M12×1 | 10.50 10.75 11.0 | |
| M14×1.5 M14×1.25 M14×1 | 12.5 12.75 13 | |
| M15×1.5 M15×1 | 13.5 14.0 | |
| M16×1.5 M16×1.0 | 14.5 15.0 | |
| M17×1.5 M17×1.0 | 15.5 16.0 | |
| M18×2 M18×1.5 M18×1 | 16.0 16.5 17.0 | |
| M20×2 M20×1.5 M20×1 | 18.0 18.5 19 | |
| M22×2 M22×1.5 M22×1 | 20 20.5 21 | |
| M24×2 M24×1.5 M24×1 | 22.0 22.5 23.0 | |
| M25×2 M25×1.5 M25×1 | 22.0 22.5 23.0 | |
| M26×1.5 | 24.5 | |
| M27×2 M27×1.5 M27×1 | 25.0 25.5 26.0 | |
| M28×2 M28×1.5 M28×1 | 26.0 26.5 27.0 | |
| (M30×3) M30×2 M30×1.5 M30×1 | 27.0 28.0 28.5 29.0 | |
| M32×2 M32×1.5 | 30.0 30.5 | |
| (M33×3) M33×2 M33×1.5 | 30.0 31.0 31.5 | |
| M35×1.5 | 33.5 | |
| M36×3 M36×2 M36×1.5 | 33.0 34.0 34.5 | |
| M38×1.5 | 36.5 | |
| M39×3 M39×2 M39×1.5 | 36.0 37.0 37.5 | |
| M40×3 M40×2 M40×1.5 | 37.0 38.0 38.5 | |
| M42×4 M42×3 M42×2 M42×1.5 | 38.0 39.0 40.0 40.5 | |
| M45×4 M45×3 M45×2 M45×1.5 | 41.0 42.0 43.0 43.5 | |
| M48×4 M48×3 M48×2 M48×1.5 | 44.0 45.0 46.0 46.5 | |
| M50×3 M50×2 M50×1.5 | 47.0 48.0 48.5 | |
| M52×4 M52×3 M52×2 M52×1.5 | 48.0 49.0 50.0 50.5 | |
| M55×4 M55×3 M55×2 M55×1.5 | 51.0 52.0 53.0 53.5 | |
| M56×4 M56×3 M56×2 M56×1.5 | 52.0 53.0 54.0 54.5 | |
| M58×4 M58×3 M58×2 M58×1.5 | 54.0 55.0 56.0 56.5 | |
| M60×4 M60×3 M60×2 M60×1.5 | 56.0 57.0 58.0 58.5 | |
| M62×4 M62×3 M62×2 M62×1.5 | 58.0 59.0 60.0 60.5 | |
| M64×4 M64×3 M64×2 M64×1.5 | 60.0 61.0 62.0 62.5 | |
| M65×4 M65×3 M65×2 M65×1.5 | 61.0 62.0 63.0 63.5 | |
| M68×4 M68×3 M68×2 M68×1.5 | 64.0 65.0 66.0 66.5 | |
| M70×6 M70×4 M70×3 M70×2 M70×1.5 | 64.0 66.0 67.0 68.0 68.5 | |
| M72×6 M72×4 M72×3 M72×2 M72×1.5 | 66.0 68.0 69.0 70.0 70.5 | |
| M75×4 M75×3 M75×2 M75×1.5 | 71.0 72.0 73.0 73.5 | |
| M76×6 M76×4 M76×3 M76×2 M76×1.5 | 70.0 72.0 73.0 74.0 74.5 | |
| M78×2 | 76.0 | |
| M80×6 M80×4 M80×3 M80×2 M80×1.5 | 74.0 76.0 77.0 78.0 78.5 | |
| M82×2 | 80 | |
| M85×6 M85×4 M85×3 M85×2 | 79.0 81.0 82.0 83.0 | |
| M90×6 M90×4 M90×3 M90×2 | 84.0 86.0 87.0 88.0 | |
| M95×6 M95×4 M95×3 M95×2 | 89.0 91.0 92.0 93.0 | |
| M100×6 M100×4 M100×3 M100×2 | 94.0 96.0 97.0 98.0 | |
| M115×6 M115×4 M115×3 M115×2 | 109.0 111.0 112.0 113.0 | |
| M120×6 M120×4 M120×3 M120×2 | 114.0 116.0 117.0 118.0 | |
| M125×6 M125×4 M125×3 M125×2 | 119.0 121.0 122.0 123.0 | |
| M130×6 M130×4 M130×3 M130×2 | 124.0 126.0 127.0 128.0 | |
| M135×6 M135×4 M135×3 M135×2 | 129.0 131.0 132.0 133.0 | |
| M140×6 M140×4 M140×3 M140×2 | 134.0 136.0 137.0 138.0 | |
| M145×6 M145×4 M145×3 M145×2 | 139.0 141.0 142.0 143.0 | |
| M150×6 M150×4 M150×3 M150×2 | 144.0 146.0 147.0 148.0 | |
| M155×6 M155×4 M155×3 | 148.0 151.0 152.0 | |
| M160×6 M160×4 M160×3 | 154.0 156.0 157.0 | |
| M165×6 M165×4 M165×3 | 159.0 161.0 162.0 | |
| M170×6 M170×4 M170×3 | 164.0 166.0 167.0 | |
| M175×6 M175×4 M175×3 | 169.0 171.0 172.0 | |
| M180×6 M180×4 M180×3 | 174.0 176.0 177.0 | |
| M185×6 M185×4 M185×3 | 179.0 181.0 182.0 | |
| M190×6 M190×4 M190×3 | 184.0 186.0 187.0 | |
| M195×6 M195×4 M195×3 | 189.0 191.0 192.0 | |
| M200×6 M200×4 M200×3 | 194.0 196.0 197.0 | |
| M205×6 M205×4 M205×3 | 199.0 201.0 202.0 | |
| M210×6 M210×4 M210×3 | 204.0 206.0 207.0 | |
| M215×6 M215×4 M215×3 | 209.0 211.0 212.0 | |
| M220×6 M220×4 M220×3 | 214.0 216.0 217.0 | |
| M225×6 M225×4 M225×3 | 219.0 221.0 222.0 | |
| M230×6 M230×4 M230×3 | 224.0 226.0 227.0 | |
| M235×6 M235×4 M235×3 | 229.0 231.0 232.0 | |
| M240×6 M240×4 M240×3 | 234.0 236.0 237.0 | |
| M245×6 M245×4 M245×3 | 239.0 241.0 242.0 | |
| M250×6 M250×4 M250×3 | 244.0 246.0 247.0 | |
| M255×6 M255×4 | 249.0 251.0 | |
| M260×6 M260×4 | 254.0 256.0 | |
| M265×6 M265×4 | 259.0 261.0 | |
| M270×6 M270×4 | 264.0 266.0 | |
| M275×6 M275×4 | 269.0 271.0 | |
| M280×6 M280×4 | 274.0 276.0 | |
| M285×6 M285×4 | 279.0 281.0 | |
| M290×6 M290×4 | 284.0 286.0 | |
| M295×6 M295×4 | 289.0 291.0 | |
| M300×6 M300×4 | 294.0 296.0 |
