Drill bit question

I bought a bunch of drill bits at yard sales recently. Some only have flutes about a third of the way up the shaft, then clear shaft. They're as long as normal bits, so they haven't been resharpened until becoming that short. Can someone explain these to me?

Steve

I have seen something similar used in places that work primarily with thin material and sheetmetal type stuff. The work piece is never very thick so you don't need full length flutes, but still have enough length on the bit to reach places that a stubby bit would not. I suppose it makes them more rigid and perhaps less expensive. There is a generic name for them that is escaping me right now.

Sounds like what I know as aircraft drills. Though I've never poked holes in airplanes, I assume they're intended for drilling thin materials in awkward spots where the extra stiffness of the unfluted shank is desirable.

Yup. Some of the short flute drills are used with sheetmetal work. I used them for many years. The short flute on them was nice because when you came to the end of the flute you kept going to clean the little bit of metal left in an otherwise round hole. For riveting this was essential to get the rivet to go into the hole. I used to buy them from a guy that had a boothe in the Ft. lauderdale Thunderbird flea market who sold tooling, drills and a bunch of other related stuff. The spotting drills have a different angle than the other drills. the spotting drills are usually 90 degrees.

John

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I have some medical drills that are like this; long shaft and short flute length.

They're called "Kaufmann" drills. I don't know how I know that.

They are for sheet metal work.

Nick

It means it will fit in a 3/8" chuck - AKA reduced shank.

"Steve B" fired this volley in news:jslnat$c19$2 @speranza.aioe.org:

It's a style of drill with a reduced shank so it will fit common power drills and presses. Generally, sizes up to 1-1/8" have 1/2" shanks, with flats on the larger sizes to prevent slipping.

Lloyd

"Lloyd E. Sponenburgh" fired this volley in news:XnsA081E3E3EDA25lloydspmindspringcom@216.168.3.70:

should have said, "1/2" to 1-1/8"

I've seen smaller Silver & Deming bits than 1/2", but they'd only be of use if you had a 1/4" or 3/8" limit on your chuck.

LLoyd

It means that it has a 1/2 inch shank.

The 1/2" shank fits the largest MT2 (or B&S7) collet and permits a hobby milling machine with limited Z axis travel drill large holes, in steps. They slip more easily in the chuck or collet than a full-sized shank. The ones with three lobes don't slip, instead they knock you around when they grab and remind you to buy a bigger, slower drill.

A Jacobs 36 chuck that will take a 3/4" drill shank is over 3" long and restricts the height of the work piece on a small mill or lathe.

jsw

That means that it has a reduced shank. I guess that they were the first to commercially provide such drill bits, and now they are often sold in sets under that name as a generic instead of a brand name.

Enjoy, DoN.