Cutting Tool Selection Guide
Solid Carbide Drill Selection Guide: Diameter, Length (3D/5D), Point Angle and Material Groups
Choose the right solid carbide drill: diameter and 3D/5D length, 140° point angle, P/M/K material groups for steel, stainless and cast iron — plus what to send for a matched quotation.
Solid Carbide Drill Selection Guide: Diameter, Length (3D/5D), Point Angle and Material Groups
Most drilling problems blamed on “tool quality” — oversize holes, wandering, short life, broken drills — actually start with selection: the wrong length series, a point angle unsuited to the material, or a drill designed for steel being run in stainless. This guide walks through the decisions in the right order, written for machining users and for the distributors and importers who supply them.
1. Start With the Workpiece Material (P, M, K)
Cutting tools are grouped by ISO workpiece materials, and drills are no exception. P group (steels, including alloy and carbon steels) is the most forgiving. M group (stainless steels) work-hardens and holds heat in the cut, so it needs sharp, polished flutes and reliable chip evacuation. K group (cast irons) produces short, abrasive chips that wear the drill corners. Matching the drill series to the group is the first decision: at CutStars, GXD drills are aimed at P and K materials, and GSD drills at M-group stainless steels.
2. Diameter and Length: When 3D Is Enough and When You Need 5D
Standard solid carbide drills cover diameters from D3.0 to D20.0, most commonly in 3D and 5D length series (the number is the usable flute length as a multiple of diameter). Choose 3D for shallow holes and rigid setups — a shorter drill deflects less and runs more stably. Choose 5D when hole depth demands it, and pay extra attention to chip evacuation and coolant delivery as depth increases: packed chips, not the carbide itself, are what snap most deep-hole drills.
3. Point Angle and Flute Design
A 140° point is the common choice for solid carbide drills in steel and stainless: it centers well, keeps thrust forces manageable and supports accurate hole position. A self-centering point geometry reduces wandering at entry, which matters most on the first millimetres — a drill that starts off-centre rarely recovers. Flute design matters just as much: a J-type flute with a reinforced core combines strong chip evacuation with the rigidity to run at higher feed rates, instead of trading one for the other.
4. Coolant: External vs Internal
For shallow holes in steel with good chip evacuation, external coolant is usually sufficient. For 5D depths, stainless steels, or any hole where chips struggle to escape, internal (through-tool) coolant delivers coolant and chip flushing exactly where the heat is generated, and is the safer choice for tool life and hole quality.
5. What Correct Selection Looks Like in Practice
In a production test on 55 steel automotive wheel hubs (Mazak machining centre, BT40), a correctly matched GXD solid carbide drill finished 1,100 parts per drill — 68.75 m of total drilling length — versus 1,000 parts with the previous tool, while the higher stable cutting speed (71 vs 56 m/min) raised machining efficiency by 28% and cut cost per part. Similar selection gains appear in other materials: gear steel parts rose from 440 to 480 parts per drill, and holes in a stainless steel distributor head from 380 to 460 per drill. The pattern is consistent: most of the gain comes from matching the drill to the material and hole, not from exotic grades. See our wheel hub drilling case for the full test results.
6. What to Send Your Supplier for a Matched Recommendation
A supplier can only match a drill if it knows the job. Send: hole diameter and tolerance, hole depth (or required ×D), workpiece material and hardness, machine and holder type, coolant type (external or internal), the tool you currently use and the life it achieves, and the problem you want solved — life, speed, hole quality or breakage. With that information, a recommendation can be made in one round instead of three.
CutStars supplies solid carbide drills from D3.0 to D20.0 in 3D and 5D for P, M and K materials, with standard sizes in stock and custom sizes on request. Send your hole and material details to info@cutstars.com or WhatsApp +86-151 1148 8179 for a matched recommendation and quotation.