A boring bit is not a bit boring

Roger, Bob

This boring article presents a few of the many interesting variants (deviants may be a better word) in wood boring augers and twist bits. Robert Carlson and Thomas A. Stevens in the article “On the Origin of the Spiral Auger” (The Chronicle, 20, no. 4, December 1967) gave us an idea of why boring augers were so important. They noted that:

A standard house or barn frame required from 100 to 150 tree nails with the corresponding 1/2 to 1 inch holes; plus a like amount of 1 1/2- to 2-inch holes to start mortises. That was a lot of back-breaking work with a nose auger, but it becomes child’s play when compared to ship building. During the year 1800, eighty-two major vessels were launched from Connecticut River shipyards alone. Each of these vessels required the boring of thousands of holes from 3/4- to 1 3/4-inch in diameter, some of them through as much as twenty inches of solid oak.1

But one wonders, “Why so many designs?”Boring a hole in wood is an ancient task, and today may appear to be a trivial task. Most boring bits, at first glance, may look the same except for size. So why have there been so many patents for improvements to the basic boring bit? What were the patentees trying to improve upon?

The patent description written by Horace T. Love (patent no. 50,887, issued 7 November 1865) provides three very full pages of intimate detail on the technicalities of boring a hole. One piece of wood may be a very simple object, yet another piece may be entirely different and very complex, especially around a burl or knot. Wood may vary greatly in hardness, grain pattern, and grain direction. Below is a list, extracted from many patent descriptions, of some of the problems or improvements that patentees were trying to address in their inventions. Some patents address only one problem, while others address several. (Readers might want to first review the list of boring terms found on page 109.)

* Cut a hole with clean, smooth sides.

* Finish the hole without splintering the sides of the exit.

* Eject or remove chips with ease.

* For holes not bored all the way through, don’t leave a hole extending beyond the bottom of the floor cut.

* Don’t split the wood.

* Cut across grain, in-grain, and diagonally in a straight line-don’t wander or run.

* Cut end grain as easily as across grain.

* Bit is easy to turn, doesn’t bind, and doesn’t cause heat-producing friction.

* Cutting edges are easy to sharpen, without harming adjacent edges.

* Bit components are durable and strong.

* Bit is easy to reform or repair if it breaks.

* Bit is simple and inexpensive to manufacture.

* Requires less pressure to enter cut, bites readily, draws bit into wood.

* Cuts rapidly, with speed.

* Cuts both hard wood and soft wood equally well.

* Removes wood instead of compressing it.

* The cutting process is a slicing effect rather than a tearing effect.

* Bit is adjustable in diameter of hole cut.

* Can complete deep cuts without withdrawing bit to remove chips.

* Equal lengths of cutting edge cut equal amounts of wood, for even blade wear.

* The wood surrounding the hole is not disturbed (e.g. compressed or torn).

* Cuts hole of designated size accurately every time, with small tolerance.

* Capable of being manufactured to exacting tolerance, in a range of sizes.

* The bit is lightweight.

* The screw point resists clogging.

Some Design Variants

A review of a large sample (more than 25 percent) of the 269 United States patents for auger bits2 revealed that 67 percent addressed improvements to the cutting head, 33 percent to the twist, 20 percent to the lead screw, and 3 percent to the handle. (The numbers total more than 100 because several patents addressed more than one aspect.) All of the patents sampled except two were from before 1900. To illustrate the variety of designs covered by the patents, I have sketched what a few of them look like. Figures 1 and 2 illustrate end views of some of the patented cutting bits, and Figures 3 and 4 illustrate other views of some of the cutting heads, especially the spurs and vertical lips.

Screwy Lead Screws

Following are some photographs and descriptions of a few of the many interesting and uncommon variants to bit designs.

Triple screw threads

The June 1992 issue of The Chronicle includes an item by Charles Wright that discusses and shows a photograph of a triple-pod twist auger. Wright noted that he had never found another like it. The editor commented,

We recall a telephone discussion with Bob Carlson of auger research fame, more than twenty years ago, about a reference to a “triple twist auger” found in some nineteenth-century work. Neither of us had ever seen one and were not totally convinced there was such a thing. Not too long after this, Bob was away on an errand which allowed time for some tool prospecting. As frequently happened when he found something really interesting, he phoned us on his return. The interesting find was a three-twist auger. As we remember it, it was much like [this example.]3

At that point, only two such augers had been found (Wright’s and Bob Carlson’s). Figure 5 shows one of several from Jim Price’s collection.

Newton (patent no. X8349, issued 8 August 1834) invented the triple twist bit. His auger bit has three pods, three floor lips, and three screw threads. Each of the three horizontal, straight floor lips radiates from a thread at the base of the triple threaded screw at equal angles (120 degrees), and leads to one of the three pods. In his patent Newton claims the three pods and three floor lips as his, but specifically excludes the three screw threads. So the three-thread screw apparently was invented earlier, although I haven’t found any record of it.

Sanford (patent no. 36,534, issued 23 September 1862) includes a triple twist/triple lip/triple thread screw design in his patent for supplemental lips. Although the patent only claims the supplemental lips, he describes his bits as having single, double, or triple lips, each lip having a corresponding pod and screw thread.

Figure 6 shows the tip of an elegant gentleman’s gimlet with a single pod but with a three-thread screw. The three threads spiral to a single tiny three-sided point.

Pod extensions into the screw

Several patents apply to extending the pod into the screw. Percival’s patent (no. X9169, issued 14 October 1835) extended a straight pod to the screw point, allowing the screw to also cut. Gladwin (patent no. 248,854, issued 1 November 1881) took Percival’s idea and applied it to twist bits, with the spiral pod(s) extending into the lead screw some distance, even to the point. Figure 7 shows a portion of Gladwin’s patent drawing and some examples of Gladwin’s patent.

Unusual double threads

While many screw threads are double, especially on double twist bits, there are a couple of unusual double threads. Shailer (patent no. 323,454, issued 4 August 1885) wanted to have a perfectly symmetrical point for straight cutting with a single thread screw for strength, so he added a second thread at the very tip of the screw. In addition, for double twist bits with double floor lips, he added a second thread at the very base of the screw so that each floor lip extends into a thread. The second thread quickly joins the first so that the major portion of the screw remains single threaded. You will need to look carefully to find this one, if it was ever produced. See Figure 8 for his patent drawing.

Caldwell (patent no. .504,018, issued 29 August 18.93) has each floor lip continue as a spiral thread to the end of the screw, producing a double-threaded screw with each thread terminating beyond the apex of the cone in a sharp radial cutting edge, thus forming a double pointed screw. Figure 9 shows Caldwell’s patent drawing and an example of his patent on a small gimlet having only one pod.

Herrmann-Moller (patent no. 2,114,668, issued 19 April 1938) has a double-pointed screw with a single pod bit, but his points arc at different horizontal distances from the bit axis. He also allows for more than two points, each at different radial distances from the axis. See Figure 10 for his patent drawing.

Other unusual lead screws.

Gerard (patent no. 400,659, issued 2 April 1889) has a screw with a single steep pitch thread that is asymmetric in cross-section. It is tapered in on its under side (toward the point) and flat on top. Pictured in Figure 11 are his patent drawing and an example of an asymmetric thread that is the opposite of his patent. This screw has double screw threads whose top surface (toward the handle) slopes outward and a bottom surface that is perpendicular to the axis. The floor lips, although an extension of the threads, radiate in a straight horizontal direction from the screw axis instead of the thread base, and have long vertical lips at their ends. The floor lips are beveled on their backsides.

Hallenscheid (patent no. 703,576, issued 1 July 1902) has a design I would like to see in action, but it may have never been produced. His lead screw is offset from the bit axis so that the bit cuts a hole wider than the bit diameter. In Figure 2, the sketch labeled S14 is an end view of his bit.

Twisted Twists

Pictured in Figure 12 (two views) is a very confused twist that I bet you haven’t seen very often. It was made this way and was not caused by twisting too hard. This is a tapered double pod twist where each pod reverses direction twice. The pods start up the shaft in the normal right-handed style for a quarter turn, then reverse into a left-handed direction for a quarter turn, and then reverse again. The bit (actually a gimlet) has a single thread screw with the pod extending into the thread as in Gladwin’s patent.

Mannes put a boring bit on a saw, or vice versa. His patent (patent no. 2,652,075, issued 15 September 1953), beginning at the tip and moving toward the handle, starts as a single twist that then becomes a double twist for most of its length. On the double twist, each of the two web faces on each twist has two parallel rows of pyramidal teeth. These teeth allow the twist to be used as a rasp or saw once the hole has been bored, able to cut in any direction. The handle is unspecified, but the example shown in Figure 13 has a screwdriver style handle and was manufactured in Germany. The twist goes from tip to handle and is 14 inches long.

Now that you are up to speed on all this boring stuff, don’t overlook the bit bucket at the next antique shop.

Related “Boring” Information

Following is a summary of the related boring articles that have appeared in the almost seventy years of The Chronicle, as well as a book about boring stuff that ought to be on your bookshelf

The January and March 1935 issues of The Chronicle (vol. 1, nos. 9 and 10) contain a two-part article by L. L. Thwing titled “Drills and Drilling Methods.” It relates the ancient history of drills and drilling.

Robert H. Carlson and Thomas A. Stevens wrote an excellent article titled “On the Origin of the Spiral Auger” (The Chronicle 20, no.4, December 1967). That issue and the December 1968 issue (The Chronicle 21, no.4) also contain a listing of augers and auger bit makers, compiled by Carlson and Stevens.

Carlson published an article titled “Typical Process of Making a Double Twist Auger” (The Chronicle, 21, no. 1, 1969) in which he provides a blow-by-blow description of the manufacturing process.

James Price published two articles (The Chronicle, 44, no. 2, June 1991 and 46, no. 1, March 1993) detailing the history of the solid-center auger bit and conclusively documenting that George Shetter was its original inventor.

Eugene Klingler wrote a three-part article (The Chronicle, 45, nos. 1, 2, and 3, 1992) on “Tools for the Brace.” He presented a broad overview of bit history and discussed many types of boring tools for the brace, including several types of bits.

In 1992, James Price published a book focused entirely on bitstock tools and their patents. Titled A Sourcebook of United States Patents for Bitstock Tools and the Machines That Made Them, Jim called it the first approximation. It lists 162 United States patents for auger bits. Then, in August 2002, Jim produced a CD containing over six thousand patent images of boring tools that included 269 patents for auger bits.


1. Robert H. Carlson and Thomas A. Stevens, “On the Origin of the Spiral Auger,” The Chronicle 20, no. 4 (1967): 49-53.

2. Jim Price, A Sourcebook of United States Patents for Bitstock Tools and the Machines that Made Them, (CD, August 2002).

3. Charles Wright, “An Unusual Twist,” The Chronicle 45, no. 2 (1992): 58.


This article comes to you from the twisted mind of Bob Roger, a member of E.A.I.A., P.A.T.I.N.A., and the Canadian Corkscrew Collectors Club. His articles on self-boring barrel spigots and hand-held green corn shredders have appeared in recent issues of The Chronicle.

Copyright Early American Industries Association Sep 2003

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