Dull end mills, snapped drills: solid carbide we buy by the canful

A solid round tool is one piece of carbide from point to shank, the plain cylinder that goes into the holder. The flutes are the spiral grooves that cut and carry chips out. ITIA, the tungsten industry association, names fine-grained carbide as the material for round tools such as drills, threaders, reamers and routers.

Each one started as rod: ITIA says a carbide rod may be ground into a drill or an end mill, the final shape cut with diamond tools after sintering. Some are tiny. ITIA describes circuit board drills down to 150 microns across, turning at up to 300,000 rpm; a jar of them weighs little but is solid carbide all the same. Shops pick carbide for rapid hole drilling because it outlasts high-speed steel, a 2021 drilling study notes, and the result is a steady pile of dull tools.

Sources: ITIA, Cemented carbides (June 2010 newsletter excerpt); ITIA, recycling newsletter excerpt (May 2018); Materials (Basel) 2021, drilling Al6061-T651 (PMC8038506).

Round tools come out of the machine wet. OSHA groups metalworking fluids into straight oils and three water-mixed kinds, and university slides note that used fluids grow microbes, especially where water is present. Wear gloves to sort a wet can: OSHA says these fluids harm health through skin contact and mist, and IARC adds that coolant used to resharpen hard-metal tools builds up dissolved cobalt.

Through-coolant drills, with internal helical channels that carry coolant to the edge (University of Leeds paper), hold fluid inside, so stand them point down to drain. Then wipe and dry the tools before boxing them; USGS notes the zinc recycling process does not purify, so oil has to come off first.

Sources: OSHA, Metalworking fluids: health effects; King Saud University cutting fluid slides (2010 textbook); OSHA, Metalworking fluids; IARC Monographs Volume 86 (2006); Johns et al., WCCM XI 2014 (University of Leeds); USGS Open-File Report 01-349.

Not every carbide drill is solid. On a brazed-tip drill, a carbide tip is joined to a steel body with solder or brazing alloy, the fixing method university lecture notes describe for tips on a shank. Check masonry drills, which NTP lists among carbide's uses: a steel body with only a carbide tip is a tipped tool, not solid carbide.

ITIA says carbide brazed onto or cast into steel is the main reason those products recycle at a lower rate, and that brazed parts need the solder removed before processing. Leave the tips on; grinding them off makes the dust described above. Bag brazed drills with your other brazed tools and saw tips.

Sources: King Saud University metal cutting lecture (2010 textbook); NTP, Report on Carcinogens background document for hard metals (2010); ITIA, recycling newsletter excerpt (May 2018).