Hertel 66693490 Screw Machine Drill Bit Letter L Tin Hss

Product Description

The HERTEL 66693490 is a screw machine length drill bit sized to Letter L (0.290 inches) with a 135-degree split point and a titanium nitride (TiN) coating over a high-speed steel body. Screw machine length bits are shorter than jobber-length bits, which reduces deflection and improves rigidity when drilling in a drill press, CNC machining center, or turret lathe. The split point geometry enables self-centering entry without a center punch and reduces the thrust force required to start a hole. The TiN coating extends surface hardness and tool life compared to uncoated HSS. This bit is appropriate for machinists, tool and die workers, and production drilling applications in metal fabrication shops.

This drill bit is suited for production and precision drilling in mild steel, aluminum, copper, brass, and similar ferrous and non-ferrous metals. Its screw machine length profile makes it a practical choice for short-reach setups in CNC lathes, drill presses, and machining fixtures where a jobber-length bit would introduce excess runout. The straight-cylindrical shank accepts standard three-jaw drill chucks. The heavy-duty grade rating indicates it is intended for demanding, repetitive drilling cycles rather than occasional light-duty use.

Key Features

• Letter L size: 0.290 inches diameter for close-tolerance drilling
• 135-degree split point self-centers on entry and reduces required thrust force
• TiN coating increases surface hardness and extends tool life over uncoated HSS
• Screw machine (stub) length reduces deflection and improves rigidity in short-reach setups
• Web-thinned parallel web construction reduces cutting resistance through the chisel edge
• Right-hand spiral flute evacuates chips efficiently during through-hole and blind-hole drilling
• Heavy-duty grade rated for high-cycle production drilling environments

Compatibility

Designed as a direct-fit replacement for Letter L screw machine length drill bits in any standard three-jaw drill chuck or collet system accepting a 0.290-inch straight-cylindrical shank.

Installation Notes

This bit should be installed and removed with the machine fully powered down and the spindle at a complete stop. Secure the straight shank firmly in a calibrated chuck to minimize runout before beginning a drilling cycle. Use cutting fluid or coolant appropriate for the workpiece material to manage heat buildup, particularly during high-cycle production runs. Inspect the cutting edges and TiN coating for wear or chipping before each use and replace the bit when point geometry is no longer within tolerance.