I'm trying to drill a hole for a wedding knife cake set I made. I'm able to drill through the metal ring and epoxy handle without any issues. But I can't drill through the knife tang and server tang (I guess my heat treat went extremely well!).

A Reddit for Machinists of all varieties. From Old School conventional guys, to CNC Programmers, to the up and coming next generation.

Almost all of these bits are dull black or gold-ish colored and don't have much else in the way distinguishing them (that I know to look for). They just look like generic drill bits (not forstner, paddle, etc).

I researched and it appears cobalt bits are designed for harder materials, like hardened steel, while HSS bits are for softer materials.

There are also copper coloured metal drill bits that are more suitable for metals, then there are darker metal drill bits that you use for walls.

Image

It does matter - wood drill bits won't work on metal (destroying the bit in the process, unless used on thin and soft metals) and metal drill bits will increase splintering and tear-out when used on wood (but this depends also on the wood type and the diameter of the bit, and for smaller diameters there is little difference between wood and metal drills bits).

As for how to tell them apart - wood drill bits have two distinguishing features: a spar (also brad) and a lip. The spar helps in keeping the bit centered when starting the hole and prevents wandering of the bit on the surface of the wood. The lip acts like a chisel, slicing through the wood fibers in the circumference of the drilled hole, improving the quality of the finish. This is most important for through holes, where the lips helps reduce "blow-out" of the wood when exiting the wood on the other side. Wood bits are typical black and silvery in color, but other colors exist.

Image

Metal drill bits, on the other hand, have just an angle at the tip. They often are fully black (plain HSS), golden (often titanium oxide finish) or coppery (often cobalt steel) in color:

Stack Exchange network consists of 183 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Image

I was using a drill press and the bits just kept spinning and barely made a dent. I switched to a new cobalt bit and that barely did anything. Then I switched to a HSS Dewalt drill bit and drilled using a hand drill in a scrap piece of steel to see if it would work.... which it did. Went through extremely easy.