An impossible bit?

[John Schreiber]

It's hard to see in the pictures, but this bit twists in the normal direction for most of it's length, but near the bottom, it twists backwards, then back to normal again.
125535
It's from a set of low priced brad point bits that I've had for a couple of years. I've probably never used this particular bit before. I checked the other ones in the set and none have the same problem.

How are drill bits made? How could this happen?

[David Christopher]

John, thats pretty cool, Ive never seen anything like that

[Jamie Buxton]

Photoshop.

[Scott Hildenbrand]

Huh... Question is, how does it drill? Chuck it up and try it on a 2x4 down into the x4 or something.. Couldn't see it being made to be like that if all the others are not.

[David DeCristoforo]

That's an ack basswards bit... very rare....

[jim hedgpeth]

Cool!! I'd keep it somewhere as a conversation piece.

Jim

[Russ Kay]

Reminds me a little of some of those combination spiral router bits, where the "entry" part of the bit is upcut, designed to help clear chips efficiently by pulling them out, and the other end is downcut, designed to leave a clean edge at the finished face. Just a thought.

[Rich Engelhardt]

Hello,
I had a similar set!

I can't recall where I bought them. but I do remember they were super cheap.
The first time I used one of the bits, it started out ok, then just quit drilling. I figured it was because the point had immediately dulled.
I looked at the bit and noticed the "twist" was going the wrong way.
No problem, i just flipped the drill to reverse.
Same thing. Drill a little and stop.
I checked the bit again, and noticed the twist was now going the other way!

LOL!
You get what you pay for.

[mike holden]

John,
drill bits are made by grinding out the flutes using a narrow grinding wheel set on an angle to the drill shaft.

As a quality person, I have had to root cause a number of "the tooling cant make that" errors. Almost always it is operator error. In this case, I would imagine that first, the tooling is hand cranked, geared to maintain geometry, but fed by a hand crank. Then the operator got halfway, noticed he was going the wrong direction, and rechucked the drill blank and finished it. Further guess, since the part was not simply tossed in the recycle bin, it was piece work, i.e. the worker got paid by the number of pieces produced.

Quite the conversation piece.
Mike

[Mitchell Andrus]

It's hard to see in the pictures, but this bit twists in the normal direction for most of it's length, but near the bottom, it twists backwards, then back to normal again.


How are drill bits made? How could this happen?

I made one like this.

When over heated, (and it's a cheaply made bit) it'll twist as you use it and set with a reverse twist. I've got a picture of it on paper somewhere (pre-digital).
.

[Lee Schierer]

Brill bits are milled on a CNC type machine. The only way this could happen would be if the CNC hesitated in its rotation or if the metal rod was slipping in the chuck. Must be poor quality control if it wasn't caught in the processing.

[Phil Thien]

They have compression bits for routers, where the flutes reverse in the middle. Perhaps the machine that made that bit was accidentally set to create compression flutes?

[Chuck Saunders]

I would vote slipping chuck or drive during manufacture

[george wilson]

I also have a set of Chinese brad point bits that includes one just like that one!

[Rick Gooden]

I purchased a cheap set a couple of years ago that had the same thing. I believe they came from HF.