Odd drill bit

Billh51

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image.jpeg image.jpeg last week while shopping at a local surplus center I ran across a drill bit I haven't seen before. The way the tip was ground is what got my attention . There were several of them in a small bin marked at 50 cents each so I bought a couple for the heck of it. They are 17/64" X 2-1/2" with kind of an inverted grind on the cutting edge.
I drilled about halfway through a piece of 1/2" aluminum to see how it cut and it leaves an almost flat bottomed hole, just a little nib in the center sticking up. Then I drilled a through hole and it was nice and clean when it came through. I did use some WD-40 as a lubricant.
Anybody seen these before or no what there purpose is ? There also was another bin with some stubby 17/64" 135* split points of which I bought several.
 
Not sure about the use for the inverted style drill, but 17/64" is a good clearance hole for 1/4" fasteners and is also usable for a tap drill for 5/16-18 threads, .004" looser than the "F" size drill normally called out for that thread. In hard, tough (or both) materials, a few thou more clearance can mean the difference between a broken tap fight and an easy tapping job that still supports the bolt threads well. The 135 degree point is also better for drilling the harder and tougher materials.
 
IMO, it's a router bit, not a drill bit. Notice there are no margins and the right hand spiral pulls the swarf up out of the cut.

Edit: On the other hand, a router bit with a 17/64 shank would be too strange.

The lack of margins and cutting through the OD first could be features intended to minimize lifting and tearing associated with drilling thin, relatively soft materials.
 
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I believe your drill bit is a "plunge router bit" and it will take a 1/4" collet to hold it. That one looks like carbide.
 
Size discounts router bit.

It could be for drilling clean holes in ikea type furniture parts where many pocket holes or counterbores.

Sure it is not metric?

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First thing I thought of was a spotweld cutter.

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Google "fishtail cutter". They are used to mill easily-melted thermoplastics, and also to mill flat-bottomed pockets.
 
It might work well with thin sheet metal, cutting on the perimeter but not grabbing.

If it's a straight 7/64 up onto the shank, you can rule out the router bit.
 
Wood bit. It won't splinter when it brakes through. Give it a try in plywood.
 
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