Thursday, September 10, 2015

The shell, the spoon, and the nose bit


Woodworkers of long ago, had many shapes of boring bits. They needed a variety of shapes for different boring applications, end grain, across grain, flat bottom etc. In addition, without the benefit of “tailed assistant” to power your way through a piece of wood with brute force, the right bit for the right application was a matter of necessity.

Egyptians woodworkers using the bow drill
A more modern variation of the bow drill, the pump drill
Using a breast plate to apply pressure while using a bow drill.
Ever heard of a Parser bit? Another story for another day.

Boring bit technology evolved along with steel manufacturing advances and manufacturing capability.

The shell, spoon and nose bit were primitive bits by today standard, but although similar looking and often confused with each others, their small differences make them perform different boring jobs better.

As strange as it may seem, the idea of a revolving brace was a rather recent invention. For the longest time, boring was accomplished by a reciprocating motion, hence the bits were only cutting half the time. The modern Z shaped bit developed for the Yankee push drill solve that problem by offering two opposite cutting edges.

An early Yankee push drill.

A more modern MF Buck Rogers push drill

Vintage Yankee drill bits, shaped very much like shell bits.


It was only natural then that some of the first boring bits developed for the brace were patterned after that age old design.

My Sheffield plated brace. Someone previously replaced the iron screws 
by brass screws. They always came with iron screws, grrr.

The shell is derived from the pin-bit
The pin-bit is like a gouge sharpened both inside and outside. As sold they were sharpened only outside and obliquely, but it will be found that if sharpened inside just a little, and both the corners are removed (then it become a shell bit) so that the contact with the wood takes place in the center of the gouge-like end of the bit, its cutting is improved, while smoothing and polishing all over will allow the chips to escape more freely.
This condition is necessary in the working of every cutting tool. Clean, polished surfaces help the chips, shavings what have you, escape freely. 


Shell bits details; the one on the far left has its end broken, 
looking more like a gouge, the tip should be pointy.

The shell bit is only suitable for boring at right angles to the fibre of the wood, the sharp gouge-like edge cutting freely; in a hole of considerable depth the chips have a tendency to remain, choking the bit. It is however an excellent bit for boring right through. When the sharp edge of the shell bit is ground to a point, it form what is called a dowel bit, which is practically the same shape as a spoon bit but has a wider stem.

The spoon bit resembles the shell bit but is pointed to somewhat resembles a tea spoon, yet is more like the outline of a gothic arch, the metal being hollowed out to form a cutting edge. Unlike the modified gouge-like shell bit, its end is more like a small scoop. This bit bores easily, freely and well, will enter more exactly where the worker wishes, and is strong and cheap (sic).

Modern Spoon bit and taper reamer bit, the traditional chairmaker’s bits


The nose bit is of similar construction but. Its cutting edge, from which it derives its name, is a part of the steel bent nearly to a right angle, and sharpened so that it forms a sort of chisel. To avoid catching, the corners are rounded off. For boring across the grain it is not dependable, generally entering half its diameter away from where it was started. But for boring the end-way of the grain the nose bit is efficient and cheap (was anyway!) This bit must also be withdrawn now and then for the removal of chips, or it gets choked.

The nose bit

Next. In this evolution came the gimlet bits. Twist the end of a nose bit, about a half a turn, and you have a gimlet bit, also called a twist-nose bit, a half-twist or Norwegian bit, and also called a Swiss bit. Humm, those Norwegian and Swiss must have twisted lots of bits!? :-)


 This twist innovation helped clear out the bits, to prevent choking. This design would ultimately be perfected with the Russell Jennings bit and then modified with a solid core with the Irwin bit.

Russell-Jennings twist bit. Tighter twist makes it eject shavings easier and faster.
It also help drilling straighter than Irwin bits since the body twisted flutes are closer. 


Irwin bits, the twist goes around a center core making it more rigid
 than the Russell-Jennings twist bits.


The rest like they say, is history

Bob, the tool historian

3 comments:

  1. What about center bits? I've had my eye out for getting some of these but so far I've always been second.

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  2. Ah, you read my mind? That's the draft I'm working on right now for later.
    Hang in there :-)
    Bob

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