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Solid Carbide & Coolant-Through Drills

Solid carbide drills cut faster and hold size better than high-speed steel, but they need a rigid machine and a low-runout holder. Coolant-through designs push coolant out the tip for deeper holes and better chip removal.

Ref CT-0014DIN 6535DIN 6537

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

A solid carbide drill is ground from a single piece of tungsten carbide. It is stiffer and more heat resistant than a high-speed steel drill, so it can run at much higher speed and feed on a CNC machine. Most carry a coating such as TiAlN or AlTiN. Coolant-through (also called through-coolant or internal coolant) drills have one or two small channels running the length of the drill to holes at the cutting tip. Coolant pressure from the spindle or holder flushes chips up the flutes and cools the edges, which matters most in deep holes.

How to identify

Carbide is heavier than steel and has a dull gray look under the coating. The shank is usually marked with the diameter, a part number and the length class. Coolant-through drills show two small holes on the point face and a hole in the shank end. Shank shape follows DIN 6535 on most metric drills.

DIN shank and length forms

Mark	Meaning	Notes
HA	Plain round shank	For collet, hydraulic and shrink-fit holders
HB	Shank with drive flat (Weldon style)	For side-lock holders
HE	Shank with inclined whistle notch	For whistle notch holders
DIN 6537 K	Short series, about 3 x D flute length	Stiffest; best hole position
DIN 6537 L	Long series, about 5 x D flute length	Deeper holes; less stiff

Drills for 8 x D and deeper are made to maker standards. They often need a pilot hole first.

Key points

Carbide does not tolerate runout or vibration. Use a holder with low runout, such as hydraulic, shrink-fit or a precision collet. Check runout at the tip.
Coolant-through drills need enough coolant pressure and flow to reach the tip. The required range is in the drill maker's data.
Use the drill maker's speed and feed tables. Carbide speeds are well above high-speed steel speeds. See cutting speed basics.
Deep-hole drills often need a short pilot hole and a slow entry at reduced speed before full speed.
Regrinding is possible, but coatings and point geometry must be restored by a qualified service.

Common mistakes

Running carbide in a worn drill press or handheld drill. The tip chips.
Using a side-lock holder on an HA shank.
Starting a long drill without a pilot hole.
Running a coolant-through drill with flood coolant only on deep holes.
Pecking too often with carbide, which can chip the edges. Follow the maker's cycle.

Governing standards: DIN 6535 (cylindrical shanks for carbide tools); DIN 6537 (carbide drills, short and long series). Drill maker's cutting data.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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