HSS Drill Bits.

What are HSS Drill Bits?

HSS drill bits, also known as high speed steel twist drills, are part of Accu's machining and threading tools range and are the standard drills for metal when a hole needs to be clean, round and on size. Each twist drill bit has a plain cylindrical shank the same diameter as the hole it cuts, two helical flutes spiralling up the body and a conical point with two cutting lips, finished either in black oxide or in the gold of a titanium nitride coating. High speed steel keeps its hardness when friction heats the cutting edge, so the bit carries on cutting cleanly through steel, stainless steel and cast iron long after a carbon steel drill would have blunted.

Accu's twist drill bits are metric throughout, made by YG-1 with every diameter held to an h8 tolerance, and the jobber drills are built to DIN 338, the German standard for straight shank jobber length drills. That makes these HSS drill bits for metal the everyday choice for general engineering, maintenance departments, fabrication shops and prototyping benches, where one set of HSS drills has to cope with whatever material arrives next.

How HSS Drill Bits Work

The shank is clamped in a three-jaw chuck or collet and the drill is fed axially into the workpiece while it rotates. The two cutting lips shear material from the bottom of the hole and the flutes carry the chips up and out while letting cutting fluid reach the point. A 118-degree point suits general work in softer steels and non-ferrous metals, while the flatter 135-degree point spreads the load across harder materials. Split point geometry grinds away the dead chisel edge at the centre, so the drill starts on its mark without walking and needs less feed force to cut.

Picture a maintenance engineer fitting a geared motor to a mild steel mounting plate on a packaging line conveyor. The motor bolts down with four M8 cap head screws into threaded holes, so each hole is drilled with a 6.8 mm jobber drill bit and then tapped. A split point drill starts exactly on the marked centre, which keeps all four holes in line with the motor's bolt pattern. Drill oversize and the thread loses engagement and can strip under vibration. Drill undersize and the tap binds and can snap in the hole.

Materials HSS Drill Bits Are Made From

Every drill in Accu's range is made from engineering-grade tool steel, chosen for its hardness at cutting temperatures and its toughness under the flex and shock loads of hand and machine drilling:

• Steel - HSS: Holds a hard cutting edge at the temperatures generated in metal drilling and is tough enough to tolerate the flex of hand-held and pillar drill work without chipping. Used for the D1105, D1GP125 and D1GP165 series.
• Steel - HSS-E: High speed steel alloyed with cobalt, at 5% in the DLGP195 series and 8% in D4105 and D4107, for greater hot hardness and wear resistance in stainless steel, titanium and other hard-wearing materials.

Two finishes are available across the range:

• Black Oxide: A conversion finish that reduces friction, helps the flutes hold cutting fluid and gives light corrosion protection in storage.
• TiN Coated: A gold titanium nitride coating harder than the steel beneath it, which cuts friction and heat at the cutting edge for longer tool life than uncoated HSS.

Sizes & Types of HSS Drill Bits Available

Accu's range of HSS drill bits covers a wide spread of metric diameters, almost entirely in jobber length, across six YG-1 series:

• Diameter (D): 0.3 mm to 20 mm.
• Shank Diameter (d): 0.3 mm to 20 mm.
• Flute Length (I): 3 mm to 140 mm.
• Total Length (L): 19 mm to 205 mm.
• Point Angle: 118 degrees and 135 degrees.
• Geometry: Standard and Split Point.
• Helix Angle: 20 to 33 degrees.
• Finish: Black Oxide and TiN Coated.
• Stub/Jobber/Long/Extra Long?: Jobber (5xD) and Stub (3xD).
• Tolerance: h8.
• Series: D1105, D1GP125, D1GP165, DLGP195, D4105 and D4107.

The size steps are not the same across the range. From 1.1 mm to 13 mm a TiN coated drill is available at every 0.1 mm increment: D1GP125 covers 1.1 to 1.9 mm, and the split point D1GP165 covers 2 to 13 mm, which takes in every common metric coarse tapping size from M3 (2.5 mm) to M14 (12 mm). The black oxide D1105 series runs from 0.3 to 1 mm in 0.1 mm steps, then in whole millimetres from 2 to 20 mm. Anything above 13 mm is therefore black oxide with a standard 118 degree point only.

Cobalt is held in three individual sizes rather than as a full range: a 1 mm DLGP195 jobber at 5% cobalt, plus a 6.75 mm D4105 split point jobber and a 7.75 mm D4107 stub drill, both at 8% cobalt. These three are the only bits in the range with a 135 degree point, and the D4107 is the only stub length. Flute and overall length follow from diameter under DIN 338 rather than being chosen separately. Every shank matches its cutting diameter, and none of the range has through-coolant channels.

Once the hole is drilled, Accu's Machine Taps and Hand Taps cut the thread. For quick M3 to M10 threads in thinner material, where a separate drill and tap is more than the job needs, Accu's Wera Combination Drill & Tap Bits are an alternative that drills, taps and deburrs in one pass from a ¼" hexagon shank.

FAQ

Q: What does HSS mean on a drill bit?

A: HSS stands for high speed steel, a tool steel alloyed with elements such as tungsten, molybdenum, chromium and vanadium. Its defining property is that it stays hard at the high temperatures created at the cutting edge, so an HSS drill bit can run at higher speeds and cut harder metals than a plain carbon steel bit, which softens and blunts once it gets hot.

Q: What is the difference between SDS and HSS drill bits?

A: They describe different things. SDS is a shank and chuck system for rotary hammer drills, and SDS bits usually carry a carbide tip designed to hammer and chip their way through concrete, brick and stone. HSS describes the material of a bit that cuts by rotation alone; it has a plain round shank held in a standard chuck and is made for metal, plastics and wood. An HSS drill bit should never be used with hammer action. Equally, a masonry bit won’t cut steel cleanly.

Q: Which is better, HSS or cobalt drill bits?

A: It depends on the material being drilled. Cobalt drill bits, often labelled HSS-E or HSS-Co, are themselves high speed steel with 5% to 8% cobalt added, which raises heat resistance and helps the cutting edge survive in stainless steel, titanium and hardened alloys, but they usually cost more and are slightly more brittle. For mild steel, aluminium, cast iron and general workshop drilling, standard HSS bits, especially TiN coated ones, are the practical choice; cobalt earns its place when the job generates heat that would wear a standard bit quickly.

Q: What is a jobber drill bit?

A: A jobber drill bit is a standard length twist drill, long enough to drill through most general workpieces while staying short enough to remain rigid and hold its position. In metric sizes jobber drills are made to DIN 338, which sets the flute and overall length for each diameter. They sit between the shorter, stiffer stub drill and the long series drills made for deep holes. Jobber drills are used in pillar drills, hand drills, milling machines and lathes for everyday drilling in metal.

Q: Can HSS drill bits be used on stainless steel?

A: Yes, provided the technique suits the material. Austenitic grades such as A2 (304) and A4 (316) work harden if the drill rubs instead of cutting, so run at a low speed with firm, steady feed, keep the drill cutting without pausing in the hole and use cutting fluid to control heat. HSS drill bits for stainless steel last longer with a TiN coating or added cobalt, and a split point helps the drill bite straight away rather than skating across the surface.

Bespoke HSS Drill Bits Manufacture.

High precision, bespoke manufacture of HSS Drill Bits to customer specification. State of the art facilities specialising in both small batch prototyping and large scale manufacture.