Reply by runswithscissors

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Posted on What twist drill bits to buy?

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2892 posts in 2225 days

#1 posted 04-08-2015 06:09 AM

I prefer cobalt bits for metal, as they can stand the heat generated. In fact, they are the only bit for drilling stainless steel (there are ways to do it with ordinary HSS, but won’t go into that here).

But cobalt bits can be somewhat brittle. I’ve even snapped off bits up to 5/16” or more, usually when the bit hangs up. This can happen easily even in aluminum.

For enlarging holes in thin metal (16 gauge or thinner) the step drills work great, better than a twist drill, as they don’t make a wonky shaped hole. Harbor Freight’s seem to work fine, and are a lot cheaper than others I’ve seen. They work best in mild steel. Tool steel is a little too hard for them. Their’s are Tin coated, though I’m not convinced that Tin coating really does much for an ordinary twist drill.

I took a chance on a set of HF cobalt bits, as they were very reasonable in price. They seem to hold up as well as the much more expensive ones I normally buy individually at my local hardware store. I can’t help you with a “best brand” recommendation, but probably someone else on here can.

For intermediate size holes (say 1/4” to 1/2”) I prefer brad point drills to forstners, as the forstners don’t clear the chips very well in the smaller sizes.

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