HSS Ground Cobalt Jobber Drill Bit Set 1-10mm - 19 Pieces

 Specifications

Compatibility

Who Is This For?

The HSS Ground Cobalt Jobber Drill Bit Set 1-10mm is the correct specification for fabricators, precision engineers, maintenance teams, and skilled tradespeople who need the full range of half-millimetre metric diameters rather than a reduced site kit. The 0.5mm increments make it the standard choice for tapping operations, close-tolerance clearance work, and any application where selecting the exact correct diameter before drilling directly affects the quality of the finished result. It suits workshop benches, fabrication bays, and mobile maintenance vehicles equally well.

Typical Applications

• Tapping operations in steel and stainless steel requiring precise pilot holes to metric tap drill sizes across the M2 to M10 range

• Drilling clearance holes through steel plate, box section, and structural profiles to exact fixing diameters

• Stainless steel handrail, balustrade, and architectural metalwork fabrication requiring accurate, clean-entry holes across the full size range

• Industrial and plant maintenance drilling into machine frames, pump housings, motor mounts, and hardened mechanical components

• Automotive and HGV bodywork and chassis repair where close-tolerance hole sizes are required

• Sheet metal fabrication in aluminium, brass, copper, and mild steel where half-millimetre sizing prevents the over-size holes that a 1mm-increment set can produce

• Electrical and mechanical panel installation requiring precise knockout and clearance holes in steel and stainless enclosures

How to Use

1. Identify the correct diameter for the application. For tapping, refer to the appropriate metric tap drill size chart. For clearance holes, check the fixing manufacturer's recommended drill diameter.

2. Select the bit and fit it centrally into the drill chuck, tightening the jaws fully before starting.

3. Apply cutting lubricant to the tip before drilling into any ferrous material. On stainless steel, re-apply lubricant during the cut if the bit begins to heat noticeably.

4. Set drill speed to match the material and diameter. Larger diameters and harder materials require lower RPM. For stainless steel at 6mm, 600 to 800 RPM is a reasonable starting point. For mild steel at the same size, 1,500 to 2,000 RPM is appropriate.

5. Begin drilling with firm, consistent pressure. On stainless steel, do not allow the bit to dwell without cutting, as this work-hardens the material at the cutting face.

6. Clear swarf regularly on deeper holes. Packed flutes restrict chip evacuation and accelerate tip wear.

7. Ease pressure as the bit approaches break-through to protect the exit face of the workpiece and prevent the bit snatching as it clears the material.

Safety and Maintenance

Safety during use:

• Wear impact-rated safety glasses or a full face shield. Metal swarf generated during drilling is a direct eye hazard, particularly on smaller-diameter bits where chips exit at high velocity.

• Clamp or fixture all workpieces before drilling. Do not hold metal freehand against a rotating bit.

• Wear cut-resistant gloves when handling metal workpieces. Remove gloves before operating chuck or drill controls.

• Bits become very hot during use, especially at smaller diameters where heat builds quickly in the flute. Do not handle bits immediately after drilling.

• Do not force the bit or apply lateral pressure to smaller diameters. Bits below 3mm are susceptible to snapping under side load.

After use and maintenance:

• Wipe all bits clean of swarf and cutting lubricant before returning them to the metal case.

• Inspect tip geometry regularly. M35 cobalt bits can be resharpened using a dedicated HSS drill sharpener, recovering cutting performance close to the original grind.

• Return each bit to its correct numbered slot after use. Incorrect slotting risks tip-to-tip contact between adjacent sizes, which chips the cutting edges.

• Store the closed case away from moisture. Although the metal case is more resistant to site conditions than a plastic equivalent, sustained damp will affect the bit finish over time.

Frequently Asked Questions

Q: What is the difference between the 19-piece and 10-piece cobalt sets?

 The 19-piece set covers 1.0mm to 10.0mm in 0.5mm increments, giving access to every half-millimetre diameter in that range. The 10-piece set covers the same range in 1mm steps, which suits general site and installation work. The 19-piece is the correct choice when the job requires a specific tap drill size, a close-tolerance clearance diameter, or any application where the nearest 1mm size would produce an oversize or undersize hole.

Q: What does M35 cobalt HSS mean and why does it matter for hard metal drilling?

 M35 is a steel grade specification in which 5% cobalt is alloyed into the high speed steel matrix. This raises the material's red hardness, the temperature at which the steel begins to lose its strength and cutting edge. Standard HSS (M2 grade) softens at lower temperatures and loses its cutting geometry quickly when drilling stainless steel or hard alloys. M35 cobalt maintains its edge under the sustained heat that hard metal drilling generates, producing cleaner holes and lasting considerably longer between resharpenings.

Q: What does DIN 338 mean and why is it a useful specification to look for?

 DIN 338 is a German industrial standard adopted widely across the UK and Europe that specifies the dimensions, geometry, and tolerances of jobber-length twist drill bits. It defines shank diameter, flute length, overall length, point angle, and helix angle to precise values. For a buyer, DIN 338 compliance means every bit in the set will seat and run true in a standard chuck, sizes are consistent and interchangeable with jigs and guides that reference the same standard, and the geometry is repeatable across the full 19-piece range rather than varying between sizes.

Q: Can I use this set for tapping operations in steel and stainless steel?

 Yes, the 0.5mm increments in the 19-piece set make it directly suitable for selecting tap drill sizes across the M2 to M10 metric range. For example, an M4 tap requires a 3.3mm pilot hole and an M6 tap requires a 5.0mm pilot. Both are present in this set, where a 10-piece set with 1mm increments would leave a buyer short of the correct diameter for several common thread sizes.

Q: Are these bits suitable for use in a pillar drill or drill press?

Yes. The straight shank and DIN 338 geometry means this set is compatible with pillar drills, bench drill presses, and magnetic base drills using standard chucks, in addition to handheld cordless and corded drills. For fixed-machine drilling, the precision ground construction of these bits is an advantage: tighter dimensional tolerances produce rounder, more accurate holes than rolled alternatives, which matters more in a fixed-machine application than in freehand site drilling.

Q: How do I avoid work hardening stainless steel when drilling?

 Work hardening occurs when the drill bit rubs against the stainless steel surface without cutting, generating heat that increases the surface hardness at the drilling zone. To avoid it: apply cutting lubricant before starting, set a lower RPM than you would use for mild steel, maintain consistent forward pressure throughout the cut, and never allow the bit to dwell or spin in the hole without advancing. If the bit begins to feel as though it is skating rather than cutting, extract it, allow both the bit and workpiece to cool, re-apply lubricant, and restart with increased pressure.

Q: Can these bits be resharpened?

 Yes. M35 cobalt bits can be resharpened on a dedicated drill bit sharpener configured for HSS. The cobalt content makes the steel slightly harder and more resistant to the sharpening wheel than standard HSS, so use a sharpener rated for cobalt or HSS-Co grade steel. Avoid overheating the tip during sharpening, as excessive heat will draw the temper from the cobalt steel and reduce its hardness. A correctly resharpened bit recovers close to its original geometry and cutting performance.

Q: Why is the metal carry case important?

Cutting edges on ground cobalt bits are harder than standard HSS but also more susceptible to chipping when tips contact each other during storage. The metal carry case with individual labelled slots keeps every bit separated and protected, preventing the edge damage that occurs when bits are stored loose in a toolbox or rattled together in transit. The metal construction also withstands the conditions of a site van or workshop rack far better than a plastic case.

Q: Why should I buy the HSS Ground Cobalt Jobber Drill Bit Set 1-10mm from CMT Group?

 CMT Group has supplied UK construction and industrial sites since 2010, with a fleet of over 100 FORS Silver-accredited vehicles covering 90% of the country. Orders placed online by 7pm are dispatched for next working day delivery, with a VIP dedicated vehicle service available for time-critical requirements. Trade buyers access agreed contract pricing, full order visibility, and integrated invoicing through the EDGE procurement portal, which connects directly to existing purchasing systems and eliminates manual data entry for teams managing spend across multiple projects.