Front	Rear

Open for Rigging

Technical Details

I acquired my Infernal Machine from Dwight Deal, 2007.

The Infernal Machine is 124 mm. tall, 84 mm. wide, and 44 mm. thick. It weighs about 300 g.

The shell is bent from 3.2 mm. aluminum sheet. The internal width is 13.0 mm. The shell has a pair of 6.6 mm. through holes for the cam axle located near the top of the shell, 41.2 and 50.4 mm. respectively from the inside of the shell groove. There is another 6.6 mm. through hole near the bottom of the shell. A homemade wing-bolt (made from a standard 1/4-20x1-1/4 bolt and a wing nut) passes through this hole and supports a small swivel used as a sling guide.

The cam is cut from 12.8 mm. aluminum plate. It has a smooth face and two 6.6 mm. pivot holes. From the hole nearest the face, the cam face increases in radius from 26 to 47 mm. over about 87°, giving an average equivalent spiral cam angle of about 23°. From the far hole, the increase is from 42 to 49 mm. over about 65°, giving an average equivalent spiral cam angle of about 8°. The cam axle is another homemade wing bolt, similar to the first.

Comments

The Infernal Machine is an important piece in the history of climbing cams that ultimately led to the Gibbs Ascender. The first significant step was when Robert Henshaw and David Morehouse developed the first widely-publicized type-1 lever cam ascender in 1965 (the "Iowa Cams"), and simultaneously introduce a very awkward ropewalker system. Dwight Deal soon modified the design, but used his "Infernal Machine" in a more traditional Jumar-type climbing system. The Infernal Machine that Dwight gave me differs from his published design (Baltimore Grotto News, VIII, 7, pp 168-173, reprinted in the 1965 Speleo Digest) by having only two choices for the cam pivot, not three. His initial design had a hole closer to the cam face (which would give it a very large cam angle), but Dwight found that the ascender would slip down the main line when using that hole. On the other hand, using the distant hole (with its very small cam angle) provided so much gripping force that the Infernal Machine would jam. Dwight’s 1965 experiments (on 9 mm. nylon) showed that the hole locations were quite critical: moving them as little as 1.5 mm. parallel to the cam face would change the performance noticeably. This would change the cam angle, and with a smooth cam, the cam angle is critical.

Incidentally, "SANDY R" stamped on this ascender is Sandy Renstrom, later Dwight’s wife.