Drill Bit Sizing Chart

Drill bits are used to remove material to create a hole. There are several considerations like the spiral (rate of twist or how it controls the rate of chip removal), the point angle (harder materials require a larger point angle where soft material require a sharp angle), the lip angle (the amount of support provided to the cutting edge)

and the functional length (how deep the hole can be drilled but also with length increases the chance for wandering or ending in an inaccurate location). Materials used to make the bits are low-carbon steel (inexpensive – do not hold edge well – only for wood), high carbon steel (much more resistant to heat build up – wood or metal),

high speed steel (even more heat resistant – metal, hardwood and other material at a higher cutting velocity), Cobalt steel (hold their hardness better at high heat – drills as above and even stainless steel), Tungsten carbide (extremely hard and can drill virtually any material)

and Polycrystalline diamond (more extreme than above used for automotive, aerospace and to drill abrasive aluminum alloys, carbon-fiber reinforced plastics, and other abrasive materials. Coatings include black oxide (inexpensive – heat resistance, lubricity and corrosion resistant),

Titanium nitride TiN (hard ceramic material for high speed twist bits extending cutting 2-3 times), Titanium aluminum nitride TiAlN (extending 5-more times), Titanium carbon nitride TiCN (another coating superior to TiN) and Diamond powder (for cutting tile, stone and other cementous materials).

Workpiece materialPoint angleHelix angleLip relief angle
Aluminum90 to 13532 to 4812 to 26
Brass90 to 1180 to 2012 to 26
Cast iron90 to 11824 to 327 to 20
Mild steel118 to 13524 to 327 to 24
Stainless steel118 to 13524 to 327 to 24
Plastics60 to 900 to 2012 to 26

Engineeringclicks, the number 1 mechanical design engineering portal has a really nice Drill size chart in inch and metric. Follow this link to check it out here.

Author: Doyle

I was born in Atlanta, moved to Alpharetta at 4, lived there for 53 years and moved to Decatur in 2016. I've worked at such places as Richway, North Fulton Medical Center, Management Science America (Computer Tech/Project Manager) and Stacy's Compounding Pharmacy (Pharmacy Tech).

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