Sutton 7.9mm Blue Bullet Stub Drill Bit - Metric - HSS
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The Sutton D186 Blue Bullet Stub is a stub drill in HSS with a blue steam-oxide finish. It has 30° right-hand helix flutes (R30), a 118° Form C self-centring point (over 3 mm), and is made to DIN 1897.
Rigid twist drill; self-centring point geometry; for use in automatic lathes and hand drilling machines.
This is the metric range: 121 sizes from 1 to 13 mm, with flute lengths of 6 to 51 mm and overall lengths of 26 to 102 mm. Pack quantities by size: 1 mm to 7.5 mm: pack of 10; 7.6 mm and over: pack of 5.
Where this product is used
- Rigid, short-reach drilling in ferrous materials, including automatic lathes and hand drilling machines.
- Machine drilling on a drill press, mill or lathe and, where the drill's catalogue entry allows it, hand-held drilling.
- Materials rated Optimal for this drill: non-alloy steel, about 0.15 %C, annealed; non-alloy steel, about 0.45 %C, annealed; non-alloy steel, about 0.45 %C, quenched and tempered (250 HB); non-alloy steel, about 0.75 %C (annealed and quenched and tempered); and low-alloy steel (under 5% alloying elements), annealed.
- Also rated Effective: low-alloy steel, quenched and tempered (275 to 350 HB) (some grades); high-alloy and tool steel (some grades); austenitic stainless steel; duplex stainless steel; grey cast iron; nodular cast iron; malleable cast iron; wrought aluminium and magnesium alloys; thermosetting and fibre-reinforced plastics; and chilled cast iron.
- Hole depths to 3 × Ø. Step feeding or pecking is required beyond 3 × Ø.
Finish
Blue (steam oxide). The blue steam-oxide finish is for ferrous metals: it helps prevent chip build-up on the cutting edges (especially in carbon steels), the oxide layer protects the surface and it carries lubricant well.
Cutting speeds and feeds
Cutting speeds (Vc) and feed numbers for this drill are from the Sutton Application Guide. The table lists the material groups covered, with the speed and the rpm and feed it works out to at Ø6 mm and Ø10 mm. Speed (rpm) = Vc × 1000 ÷ (π × Ø). Treat these as starting values and adjust for the machine, set-up and coolant.
| Material (VDI 3323 group) | Rating | Vc (m/min) | Feed no. | Ø6 mm: rpm / feed | Ø10 mm: rpm / feed |
|---|---|---|---|---|---|
| Non-alloy steel, about 0.15 %C, annealed | Optimal | 25 | 5 | 1,330 rpm / 0.125 mm/rev | 795 rpm / 0.19 mm/rev |
| Non-alloy steel, about 0.45 %C, annealed | Optimal | 20 | 5 | 1,060 rpm / 0.125 mm/rev | 635 rpm / 0.19 mm/rev |
| Non-alloy steel, about 0.45 %C, quenched and tempered | Optimal | 15 | 4 | 795 rpm / 0.1 mm/rev | 475 rpm / 0.16 mm/rev |
| Non-alloy steel, about 0.75 %C, annealed | Optimal | 15 | 4 | 795 rpm / 0.1 mm/rev | 475 rpm / 0.16 mm/rev |
| Low-alloy steel (under 5% alloying), annealed | Optimal | 15 | 4 | 795 rpm / 0.1 mm/rev | 475 rpm / 0.16 mm/rev |
| Low-alloy steel, quenched and tempered (275 HB) | Optimal | 15 | 4 | 795 rpm / 0.1 mm/rev | 475 rpm / 0.16 mm/rev |
| High-alloy and tool steel, annealed | Optimal | 10 | 4 | 530 rpm / 0.1 mm/rev | 320 rpm / 0.16 mm/rev |
| Austenitic stainless steel | Effective | 10 | 4 | 530 rpm / 0.1 mm/rev | 320 rpm / 0.16 mm/rev |
| Duplex stainless steel | Effective | 8 | 4 | 425 rpm / 0.1 mm/rev | 255 rpm / 0.16 mm/rev |
| Grey cast iron, ferritic / pearlitic | Effective | 25 | 6 | 1,330 rpm / 0.16 mm/rev | 795 rpm / 0.24 mm/rev |
| Grey cast iron, pearlitic | Effective | 20 | 5 | 1,060 rpm / 0.125 mm/rev | 635 rpm / 0.19 mm/rev |
| Nodular cast iron, ferritic | Effective | 20 | 6 | 1,060 rpm / 0.16 mm/rev | 635 rpm / 0.24 mm/rev |
| Malleable cast iron, ferritic | Effective | 20 | 6 | 1,060 rpm / 0.16 mm/rev | 635 rpm / 0.24 mm/rev |
| Wrought aluminium and magnesium, non heat treatable | Effective | 40 | 6 | 2,120 rpm / 0.16 mm/rev | 1,270 rpm / 0.24 mm/rev |
| Wrought aluminium and magnesium, heat treatable | Effective | 40 | 6 | 2,120 rpm / 0.16 mm/rev | 1,270 rpm / 0.24 mm/rev |
| Thermosetting and fibre-reinforced plastics | Effective | 30 | 4 | 1,590 rpm / 0.1 mm/rev | 955 rpm / 0.16 mm/rev |
| Chilled cast iron | Effective | 20 | 5 | 1,060 rpm / 0.125 mm/rev | 635 rpm / 0.19 mm/rev |
Feed rates (mm/rev) for the feed numbers above:
| Ø (mm) | Feed no. 4 (mm/rev) | Feed no. 5 (mm/rev) | Feed no. 6 (mm/rev) |
|---|---|---|---|
| 2 | 0.04 | 0.05 | 0.06 |
| 3 | 0.055 | 0.07 | 0.09 |
| 4 | 0.075 | 0.09 | 0.12 |
| 5 | 0.09 | 0.11 | 0.14 |
| 6 | 0.1 | 0.12 | 0.16 |
| 8 | 0.13 | 0.16 | 0.2 |
| 10 | 0.16 | 0.19 | 0.24 |
| 12 | 0.18 | 0.23 | 0.28 |
| 16 | 0.23 | 0.29 | 0.36 |
| 20 | 0.28 | 0.34 | 0.42 |
| 25 | 0.33 | 0.41 | 0.5 |
| 32 | 0.41 | 0.5 | 0.6 |
| 38 | 0.46 | 0.56 | 0.68 |
| 45 | 0.52 | 0.64 | 0.76 |
| 52 | 0.58 | 0.7 | 0.84 |
| 63 | 0.67 | 0.8 | 0.96 |
Drilling notes
- Step feeding or pecking is required for holes deeper than 3 × Ø.
- When drilling a cast or black (not machined) surface, reduce the drilling speed by 20%.
- For optimal positional accuracy and hole size, spot the hole first with a Sutton spotting drill (D175).
- For hole depths greater than 7 × Ø, pre-drill a pilot hole first for accurate hole position and to stop the drill wandering. The pilot can be drilled with a short, rigid drill, about 3 × Ø deep, at reduced feed.
Deep holes: reduce speed and feed as hole depth increases.
| Hole depth | Reduce speed by | Reduce feed by |
|---|---|---|
| 3 x diameter | 10% | 10% |
| 4 x diameter | 30% | 10% |
| 5 x diameter | 30% | 20% |
| 6 to 8 x diameter | 35 to 40% | 20% |
Accuracy
Sutton drills are ground to an h8 diameter tolerance (the diameter may be at nominal or smaller, never larger) with a small back taper behind the point.
| Drill diameter (mm) | h8 tolerance (minus only) | Back taper per 10 mm flute length |
|---|---|---|
| 0.2 to 3 | 14 µm | 0 to 0.008 mm |
| 3 to 6 | 18 µm | 0.002 to 0.008 mm |
| 6 to 10 | 22 µm | 0.002 to 0.009 mm |
| 10 to 18 | 27 µm | 0.003 to 0.011 mm |
| 18 to 30 | 33 µm | 0.004 to 0.015 mm |
| 30 to 50 | 39 µm | 0.004 to 0.015 mm |
Troubleshooting
- Drill breaks. Dull point: sharpen; Drill has front taper due to wearing: sharpen; Insufficient lip clearance on point: grind correctly; Lip clearance too great: regrind to correct clearance angle.
- Outer corner breaks down. Flutes clogged with chips: remove drill from hole and clear the flutes; Cutting speed too high: reduce speed; Dry cutting, no lubricant at cutting edges: apply cutting fluid.
- Cutting edges chip. Lip clearance too great: regrind to correct clearance angle; Feed too heavy: reduce feed.
- Hole rough. Dull point: sharpen; Feed too heavy: reduce feed; Dry cutting, no lubricant at cutting edges: apply cutting fluid; Fixture/clamping not rigid: secure job firmly.
- Hole oversize. Unequal angle or uneven length of cutting edges: regrind to same lip lengths and angles; Spindle run-out / loose spindle: check machine.
Key specifications
| Specification | Detail |
|---|---|
| Catalogue code | D186 |
| Range name | Blue Bullet Stub |
| Type | Stub series |
| Material | High Speed Steel (HSS) |
| Finish | Blue (steam oxide) |
| Flute geometry | 30° right-hand helix (R30) |
| Point | 118° Form C self-centring point (over 3 mm) |
| Standard | DIN 1897 |
| Diameter tolerance | h8 |
| Designation | Ferrous Materials |
| Drilling depth | up to 3 × Ø |
| Sizes in this range | 121 sizes, 1-13mm |
Related drilling products
Compare other Sutton drills: D101 Silver Bullet jobber and D113 long series. Sets are in the Metric Jobber Drill Sets and the Imperial Jobber Drill Sets. Need help choosing? Our guide to choosing the right drill bit and drill bit selection guide cover drill types and materials, and the speeds and feeds chart and cutting tool troubleshooting guide cover speeds and common problems.
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Sutton D186 Blue Bullet Stub Drill Bit - DIN1897 - HSS: 7.9
SKU: A0006548 | Model: D1860790
This is the 7.9mm diameter option of the Sutton D186 Blue Bullet Stub Drill Bit - DIN1897 - HSS. Key details for this option: flute length 37mm, overall length 79mm.
