センタ穴ドリル計算機
JIS / DIN 333 / ANSI規格センタ穴ドリル。面取り径、切り込み深さ、適正回転数を計算。
Tool & Workpiece Parameters
ANSI B94.11M / 60°Recommended size for 0.75" stock: Size #3 (5/8" – 1")
ANSI Standard Center Drill Size Chart (#00 to #8)
Plain Type 60° Combined Drill & Countersink Dimensions & Lathe Workpiece Sizing
| Size | Pilot Dia (In / mm) | Body Dia (In / mm) | Pilot Len (In) | Rec. Workpiece OD | Steel RPM | Aluminum RPM |
|---|---|---|---|---|---|---|
| #00 | 0.025" (0.635mm) | 0.1250" (3.175mm) | 0.031" | 1/8" – 3/16" (3.0 – 5.0 mm) | 2,500 | 5,000 |
| #0 | 0.031" (0.794mm) | 0.1250" (3.175mm) | 0.038" | 3/16" – 1/4" (5.0 – 6.5 mm) | 2,200 | 4,500 |
| #1 | 0.047" (1.191mm) | 0.1250" (3.175mm) | 0.055" | 1/4" – 5/16" (6.5 – 8.0 mm) | 1,800 | 3,800 |
| #2 | 0.078" (1.981mm) | 0.1875" (4.763mm) | 0.090" | 3/8" – 1/2" (9.5 – 12.7 mm) | 1,400 | 3,000 |
| #3 | 0.109" (2.779mm) | 0.2500" (6.35mm) | 0.125" | 5/8" – 1" (15.0 – 25.4 mm) | 1,100 | 2,400 |
| #4 | 0.125" (3.175mm) | 0.3125" (7.938mm) | 0.145" | 1-1/4" – 2" (30.0 – 50.0 mm) | 900 | 2,000 |
| #5 | 0.188" (4.763mm) | 0.4375" (11.113mm) | 0.200" | 2-1/4" – 3" (55.0 – 75.0 mm) | 700 | 1,500 |
| #6 | 0.219" (5.556mm) | 0.5000" (12.7mm) | 0.235" | 3-1/2" – 4" (85.0 – 100.0 mm) | 550 | 1,200 |
| #7 | 0.250" (6.35mm) | 0.6250" (15.875mm) | 0.270" | 4-1/2" – 5" (110.0 – 125.0 mm) | 450 | 1,000 |
| #8 | 0.313" (7.938mm) | 0.7500" (19.05mm) | 0.330" | 5-1/2" – 6"+ (140.0+ mm) | 350 | 800 |
Why Center Drills Snap
The #1 mistake is setting machine RPM using the large body diameter instead of the delicate pilot tip. Running at body surface speed produces far too low an RPM on the pilot, resulting in excessive chip load per tooth that shears the pilot off flush inside your part. Always calculate RPM based on the pilot diameter!
Plain vs. Bell Type Center Drills
Plain Type (Type A): Standard 60° cone angle without protective bell. Best for general lathe turning between centers where the workpiece end won't be subjected to rough handling.
Bell Type (Type B / Type R): Features an additional outer flare (120° or radius) that creates a protective counter-edge around the 60° center, preventing burrs or drops from ruining the lathe center location.
Center Drill vs Spot Drill on CNC Mills
Never use a 60° center drill to spot for a standard 118° or 135° drill bit on a CNC mill. The drill web will hit the steep 60° walls first, causing drill wander and corner chipping. Use a 90° or 120° spot drill with an angle equal to or greater than your twist drill point.