Chicago-Latrobe
Chicago-Latrobe 47720 135 Degree Cobalt Jobber Drill Bit
A 135-degree split-point cobalt jobber drill bit sized at .3125 inch for heavy-duty drilling
- TypeDrill Bits
- MaterialHAWA
- 135° split point starts drilling on contact without walking
- Cobalt steel resists heat and wear in hard metals
- 5/16 in jobber length suits standard drilling tasks
- Straw bronze finish reduces friction during operation
- Non-coolant design simplifies use in portable tools
135° Cobalt Jobber Drill Bit
The Chicago-Latrobe 47720 is a heavy-duty jobber length drill bit made from cobalt steel for drilling hard materials. Its 135 degree split point reduces walking and starts holes cleanly without a centre punch. The straw bronze finish identifies the cobalt alloy and resists wear. It suits maintenance, fabrication and automotive workshops that need reliable fractional inch tooling.
Heat resistance and cutting behaviour
Cobalt steel retains hardness at the elevated temperatures generated when drilling stainless steel, titanium and high-strength alloys. The 135 degree point geometry distributes cutting forces across two edges, lowering thrust requirement and reducing heat buildup in the workpiece. No coolant holes are present, so external lubrication or peck drilling manages chip evacuation and temperature in deep holes.
Replaces general-purpose high-speed steel bits
This bit upgrades from standard HSS jobbers when drilling work-hardening or abrasive metals that dull conventional edges quickly. The cobalt substrate extends edge life in materials that cause rapid flank wear on HSS. The jump is worth it for shops that regularly drill 5/16 inch holes in difficult alloys and need fewer bit changes per shift.
Highlights
- 135° split point starts drilling on contact without walking
- Cobalt steel resists heat and wear in hard metals
- 5/16 in jobber length suits standard drilling tasks
- Straw bronze finish reduces friction during operation
- Non-coolant design simplifies use in portable tools
Specifications
| Brand | CHICAGO-LATROBE |
|---|---|
| Type | Drill Bits |
| Material | HAWA |
Questions about this item
How do I install the 135-degree split-point cobalt bit in my drill chuck, and what step is often missed?
Open the chuck fully, insert the 5/16 inch shank straight, and tighten securely; the step people miss is checking that the split point sits perfectly centred before drilling.
What maintenance or replacement will the 47720 cobalt jobber bit need over time?
The cobalt alloy holds an edge longer than standard steel, but the 135-degree split point will eventually dull and require resharpening or bit replacement.
At what point does the 135-degree split-point design hit its limit during sustained drilling?
Heat buildup in the cobalt material becomes the first limit during continuous use, especially without coolant through holes, reducing cutting efficiency.
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