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The CMI Shorti came out with the CMI 5000 handled ascender. I obtained mine from Speleoshoppe in 1979. The pair consists of a left-handed and a right-handed ascender; although the parts are designed symmetrically so that with proper tools an ascender can be disassembled and reassembled to the opposite handedness. Each ascender is is 116 mm. high, 76 mm. wide, 25 mm. thick, and weighs 175 grams. The shell is milled from a custom aluminum extrusion and is extremely strong. The shell body is 6.5 mm. thick and gray anodized. The U shaped rope groove is 14.2 mm. in diameter. The cam mounting groove is rectangular. Two cam pivot holes are provided; one for the left and one for the right-handed configuration. The unused hole allows using the optional safety kit discussed below. The attachment holes are rounded 28.6x28.6 mm. right triangular cutouts in the shell, with the resultant attachment lying outside the cam attachment point.
The cam is a skeletonized steel casting with a (2)(5.4)^4(3.4)^2(3.2)^2 conical tooth count. The teeth are fairly dull compared to those of other toothed ascenders. The cam radius, measured from the pivot, increases from 35 to 48 mm. over an angle of 48 degrees. The cam pivot is a solid 6.4 mm. pin held by an external retaining ring. The pivot is centered 49 mm. from the inside of the rope groove. The cam safety is an elbow shaped lever mounted on a roll pin in the cam. A single spring serves as cam spring and safety spring. Normally this spring holds the safety where it protrudes from both the top and bottom of the cam. The bottom protrusion interferes with the shell's cam channel and prevents opening the cam. When the top of the lever is pushed towards the cam teeth, the lower protrusion rotates into a recess in the cam, thus allowing the cam to open.
The only markings are "Cmi" in raised letters on the cam.
The shell on this ascender is very strong, but a competitor pointed out that the CMI cam was weaker than some of the competition's. Personally I feel the CMI cam strength is more than adequate for my purposes. The ascender can be opened with one hand, but the safety is awkward, particularly when used in the "wrong" hand. The location of the attachment points leads to substantial ascender canting each time it is loaded; this results in some efficiency loss while climbing. The ability to convert from left-handed to right-handed configurations is a nice feature, but I recommend that it not be done in the field since the small retaining ring tends to become airborne if the proper tools are not available.
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I acquired my CMI Shorti II from Charles Knowles in 2007, but it dates from about 1980, since it came out between the Shorti and shorti III, which I acquired in 1979 and 1981, respectively.
The CMI Shorti II is 116 mm tall, 76 mm wide, and 28 mm thick. Mine weighs 168 g. The extrusion is the same as the one used on the SHorti, but it is milled differently so that the attachment openings are closer to the rope. The Shorti II has a new cam esign as well. The cam is a skeletonized steel casting with a (2)(5.4)^4(3.4)^2(3.2)^2 conical tooth count on the left-hand ascender and (3)(5.4)^4(3.4)^2(3.2)^2 on the right-hand one. Both cams have a reinforcing rod not seen on the Shorti. The spring channel in the cam has been enlarged to accommodate a stronger cam spring. The safety pivot diameter was increased. The Shorti II cam is also plated, while the Shorti cam was unfinished.
The only markings are "Cmi" in raised letters on the cam, and a sticker which on each of mine is too faded to read. I suspect it read "Shorti II" and "Cmi."
Apparently it did not take CMI long to realize that the shape of the Shorti frame was a blunder. In effect, the Shorti II frame looks like a mirror image of the Shorti. This relocates the attachment points to where they can reduce ascender canting to a minimum. A lesser change angles the top and bottom of the rope channel. The rope runs over a right angled corner in the Shorti, but the Shorti II changes these to obtuse angles. The cam is probably stronger, but I don't notice a difference in how it functions. Overall, the Shorti II is certainly better than the Shorti - moving the attachment points is the key improvement.
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The CMI Shorti III came out with the CMI 5003 handled ascender. I obtained mine from Pathfinder Sports in 1981. At first glance it appears very similar to the CMI Shorti, but there are several significant differences. The pair consists of a left-handed and a right-handed ascender; although the parts are designed symmetrically so that with proper tools an ascender can be disassembled and reassembled to the opposite handedness. Each ascender is is 120 mm. high, 79 mm. wide, 28 mm. thick, and weighs 194 grams. The shell is milled from a revised custom aluminum extrusion and painted black. The shell body is 6.5 mm. thick, and the rope channel is reinforced to 8.3 mm. thick. The rope groove is larger (17 mm. in diameter) and semicircular. The cam mounting groove is rectangular. Two cam pivot holes are provided; one for the left and one for the right-handed configuration. The unused hole allows using the optional safety kit discussed below. The attachment holes are rounded 28.6x28.6 mm. right triangular cutouts in the shell, but the cutouts are reversed from the Shorti so the resultant attachment point lies close to the main rope.
The cam is a plated skeletonized steel casting, with an internal brace not found on the Shorti. The teeth are conical with a (1)(2.3)^2(4.3)(2.3)^5(2) tooth count. The teeth axes are parallel to the upper surface of the cam, and decrease in size towards sides of the cam. The teeth are fairly dull compared to those of other toothed ascenders, and the lower teeth had their points ground flat during manufacture, probably unintentionally. The cam radius, measured from the pivot, increases from 36 to 50 mm. over an angle of 48 degrees. The cam pivot is a solid 6.4 mm. pin held by an external retaining ring. The pivot is centered 47 mm. from the inside of the rope groove. The cam safety is similar to the Shorti's, and functions in the same manner. The safety is molded plastic, and the enlarged actuating lever lies along the top of the cam rather than sticking up from the cam. The roll pin is larger than in the Shorti. A single spring serves as cam spring and safety spring.
The ascender is moderately well made, although the cam teeth were carelessly damaged by the manufacturer. Orienting the cam teeth axes parallel to the top of the ascender cam is an improvement. This design gives the teeth a slight downwards alignment with respect to the climbing rope. This increases their grip, reduces tooth friction while raising the ascender, and provides a small self cleaning action at the same time.
The ascender can be opened with one hand, but the safety is is even more awkward than on the Shorti. I suspect that the new design was developed to reduce the risk of accidentally opening the ascender, but I don't find this to be a problem. In any case, the correct way to prevent accidental opening is to install the optional safety kit. CMI should have rounded the insides of the triangular attachment holes.
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The CMI Shorti III came out with the CMI 5004 handled ascender.
The cam differs from the cam on the Shorti III. The teeth are no longer downsloping, and the tooth pattern is different. The safety has a notch in it that serves no function, and the plastic appears to be harder than on the Shorti III.
The only discernible difference between the frame of this ascender and the Shorti III is in the rope channel design. The Shorti IV rope channel extends farther towards the cam pivot and has a small lip inside.
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CMI manufactured an "Optional Safety Kit" for the CMI Shorti ascender. The kit adds 11 grams to each ascender, and increases the width to 37 mm. I purchased on from Pathfinder Sports ca. 1980 and installed it on one of my Shorti ascenders. Later I modified one of my Shorti IIIs with another. The kit consists of two new cam pivot pins, each with a check pin attached by 1.7 mm. stainless steel cable. A simple 6-step set of instructions describes how to replace the original cam pivot and replace it with the one from the kit. Once installed, the check pin can be inserted through the unused pivot hole in the ascender shell from back to front. The pin will then prevent the cam from opening. A finger loop in the cable provides a means of gripping the pin firmly for removal.
The safety pin substantially reduces the chance of the cam opening accidentally. It does not interfere with the normal safety, so both must be overridden for the cam to open. On the other hand, the optional safety kit adds extra steps to common procedures such as passing knots or rebelays, so I do not use it.
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©2008, Gary D. Storrick