Printed from Kezuriba (kezuriba.net/en/troubles/drill-hole-undersize/)

Hole becomes undersized (drilling)

Drilling Drilling

Check first

Cutting heat at the cutting point is large (machining while thermally expanded)
Cutting speed is high
Insufficient coolant, or wear of the peripheral edge (indexable)

Try first

Use a through-coolant drill and increase the cutting fluid flow (raise the concentration for water-soluble fluid)
Reduce the cutting speed
Check the pilot hole by measuring it after machining, and select the drill diameter accordingly

?Likely causes

Cutting heat at the cutting point is large (machining while thermally expanded)One maker^[1][2]
Cutting speed is highOne maker^[1][2]
Insufficient coolant, or wear of the peripheral edge (indexable)One maker^[3]
Diameter became smaller from regrinding, or a carbide drill has little oversize allowanceOne maker^[4]

✓Fixes

Cutting conditions

Reduce the cutting speedOne maker^[1][2]

Setup

Check the pilot hole by measuring it after machining, and select the drill diameter accordinglyOne maker^[4][5]

Coolant

Use a through-coolant drill and increase the cutting fluid flow (raise the concentration for water-soluble fluid)Agreed by 2+ makers^[1][2][3]

↔Related problems

Hole becomes oversized (drilling)Hole bends or leans (poor straightness)Hole position shifts or hole is not round (rice-ball shape)Drill breaks Burrs at the hole exit (breakthrough)Chips clog (drilling)Drill chipping (periphery, chisel edge)Drill wears quickly (peripheral corner, margin, center)

📚Sources

Causes and fixes are summarized in our own words from cutting-tool makers’ troubleshooting guides and technical data. “Agreed by 2+ makers” means two or more makers say the same thing.

Mitsubishi Materials — Advanced Drilling: Trouble shooting mmc-carbide.com
Mitsubishi Materials — Hole making troubleshooting mmc-carbide.com
Sandvik Coromant — Drilling wear and troubleshooting sandvik.coromant.com
OSG — Why is tool life short when tapping stainless steel? faq.osg.co.jp
OSG — What should be kept in mind when tapping? faq.osg.co.jp