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Twist Drills
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Speeds
The speed of a drill is usually measured in terms of the rate at which the
outside or periphery of the tool moves in relation to the work being drilled.
The common term for this is "Surface Feet Per Minute", abbreviated to
sfm. The relation of sfm and Revolutions Per Minute, or rpm, is indicated by
the following formulas:
sfm = .26 x rpm x Drill Diameter in Inches
rpm = 3.8 x sfm / Drill Diameter in Inches
In general, when operating a drill at a speed anywhere within its range for the
particular material involved, reductions in speed result in more holes before
regrinding is necessary. On every job there is a problem of choosing a speed
which will permit the most economical rate of production which is also
determined by drill costs, pieces produced in a given time and down-time for
tool changing. The most economical speed for operating a drill will depend on
many variables, some of which are:
1. Composition and hardness of material
2. Depth of hole
3. Efficiency of cutting fluid
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4. Type and condition of drilling machine
5. Quality of holes desired
6. Difficulty of set-up
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Speeds shown in the table below include a range in feet-per-minute. On most
jobs, it is usually better to start with a slower speed and build up to the
maximum after trials indicate the job can run faster.
| Material |
Speed in feet per minute (fpm) |
| Aluminum and its Alloys |
200 - 300 |
| Brass and Bronze (ordinary) |
150 - 300 |
| Bronze (High Tensile) |
70 - 150 |
| Die Castings (Zinc Base) |
300 - 400 |
- High Temperature Alloys (Solution Treated)
- Cobalt Base: HS25, S816, V36
- Iron Base: INCO 800, A286, N155
- Nickel Base: INCONEL 700, U500, Rene41
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-
- 10 - 20
- 10 - 20
- 7 - 15
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- Iron Cast (soft)
- Cast (medium hard)
- Hard Chilled
- Malleable
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- 75 - 125
- 50 - 100
- 10 - 20
- 80 - 90
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| Magnesium and its Alloys |
250 - 400 |
| Monel Metal or High-Nickel Steel |
30 - 50 |
| Plastics or Similar Materials (Bakelite) |
100 - 300 |
- Steel-Mild - .2 to .3 carbon
- Steel - .4 to .5 carbon
- Tool - 1.2 carbon
- Forgings
- Alloy-300 to 400 Brinell
- High Tensile (Heat Treated)
- 35 to 40 Rockwell C
- 40 to 45 Rockwell C
- 45 to 50 Rockwell C
- 50 to 55 Rockwell C
- Maraging (Heat Treated)
- (Annealed)
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- 80 - 110
- 70 - 80
- 50 - 60
- 40 - 50
- 20 - 30
- -
- 30 - 40
- 25 - 35
- 15 - 25
- 7 - 15
- 7 - 20
- 40 - 55
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- Stainless Steel
- Free Machining Group: 303, 303SE, 430F, 416F, 42OF
- Chromium-Nickel Group (Non-Hardenable):
- (300 Series) (1) (400 Series) (2)
- Straight Chromium Group (Heat Treated): (400 Series) (3)
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- -
- 30 - 100
- -
- 20 - 60
- 10 - 30
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- Titanium Alloys,
- Commercially Pure
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- -
- 50 - 60
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| 5AI-2Sn, 8AI-1 Mo-1 V (Annealed) |
30 - 40 |
| 2 Fe-2Cr-Mo (Annealed) |
30 - 40 |
| 6AI-4V, 4AI-4Mn, 7AI-4Mo (Annealed)
| 25 - 35 |
| 6AI-4V, 4AI-4Mn, 7AI-4Mo (Solution Treated & Aged)
| 15 - 20 |
| 2Fe-2Cr-2Mo (Solution Treated & Aged) |
15 - 20 |
| Wood |
300 - 400 |
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(1)Austenitic (2) Ferritic (3) Martensitic
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