Scrap carbide end mills, drills and reamers

Shape will not tell you: ITIA’s 2008 figures put about 95% of high-speed steel (HSS) into machining tools such as drills, taps and milling cutters.

Weight in the hand

It is the simplest check at home. Two commercial carbide grades measured 15.17 and 14.91 g/cm³ in a 2023 university study; NIST lists iron, the base of every steel, at 7.874. Next to an HSS tool of the same size, the carbide one is plainly heavier: nearly double, going by iron.

Markings and finish

Read the shank. HSS, HSS-E, HSCo or M42 etched there means high-speed steel. A drill sold as cobalt is high-speed steel too; USGS counts the high-speed steels used for cutting tools among the cobalt-bearing steels. Gold TiN, a coating ITIA lists for carbide, is just as common on steel drills, so a coating color proves nothing.

Tipped tools

On a carbide-tipped drill, reamer or masonry bit, a short carbide tip is brazed into a steel body. Look near the cutting end for a joint and a thin line of braze. Larger burs are commonly built the same way, with a carbide head on a steel shank. We buy those too; keep them in their own bag and see brazed carbide and saw tips.

Magnet and spark

USGS lists a magnet and the “analysis of the spark pattern generated when the alloy is ground on an abrasive wheel” among the ways scrap sorters tell alloys apart. Steel answers a magnet, and cobalt, the usual carbide binder, is ferromagnetic as well, so a pull on its own does not separate them (more in is carbide magnetic).

Leave the bench grinder off. The National Toxicology Program lists cobalt-tungsten carbide powders and hard metals as reasonably anticipated to be a human carcinogen, and a grinding wheel is what turns a tool into that powder. Whole tools are another matter: ITIA expects normal use of finished carbide articles to produce little or no exposure. Send a photo instead of sparks.

Sources: ITIA: Tungsten in steel; OSTI: WC-Co grade densities (2023); NIST: element densities, table 1; USGS Circular 1196-M (2004); ITIA: Cemented carbides, a success story; OSHA: Cobalt dust; ITIA: Health and environment; NTP Report on Carcinogens: cobalt-tungsten carbide.

USGS notes that the zinc process for carbide scrap cleans nothing up along the way, which is why the scrap has to be sorted with care and pretreated to strip oil, solder and coatings. Leave coatings and solder to the recycler. Sorting and draining start at your bench.

• Solid carbide goes in one bag, carbide-tipped tools and brazed burs in a second, HSS and cobalt drills in a third. We buy high-speed steel scrap as well.
• Pull tools out of collets, shrink-fit holders and chucks.
• Let coolant drain off, wipe away cutting oil, and bag the tools dry.
• Flutes slice thin plastic. Double up heavy bags, or set a small box or coffee can inside the shipping carton.
• Write on each bag what it holds.

Carbide is dense, so a small box gets heavy before it looks full. USPS requires dense items such as tools and machine parts weighing 20 to 45 pounds to travel in a box of at least 200-pound test board (or an equivalent wood, metal or plastic container), and no USPS mailpiece may weigh more than 70 pounds. Split a big lot over several boxes, brace the contents and tape every seam; see ship your scrap and the sorting guide.

Sources: USGS Open-File Report 01-349; USPS Domestic Mail Manual 601; USPS Domestic Mail Manual 201.