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Single
Rope (#818)I acquired this chest box from PMI in March, 2005.
My PMI, single rope is 75 mm. long, 197 mm. wide, 54 mm. high, and weighs 301 g. The back plate has 51 mm. tall vertical slots for attaching the box to a chest strap and 26 mm. wide horizontal slots for attaching shoulder straps.
The PMI box consists of a back plate, rupport post, roller axle, roller, and latching gate assembly. The construction made extensive use of CNC machining. The back plate is milled from 3.5 mm. aluminum plate, possibly 7075, and anodized. Although not obvious, the front face is milled to taper to the edges, where the plate is only 6 mm. thick. The back has two large irregular areas where superfluous metal was removed to a depth of 4.3 mm.. There are large (51.8 by 6.8 mm.) slots on each side for attaching one's main chest harness strap, and pairs of smaller (26.0 by 6.8 mm.) slots on the top and bottom for attaching the harness shoulder slings.
The post is milled from aluminum, anodized, and bolted to the back plate with three counter-sunk Allen screws, probably 1/4" (6.4 mm.). An extension on the side of the post provides lateral rigidity. It looks heavy, but the post is undercut on the othe side. There is a level area on the plate where the post attaches, so the overall plate taper does not affect the post's alignment.
The roller is 16.5 mm. wide and features a shallow U-shaped rope centering groove. The roller diameter is 28 mm. at the edges and 23.8 mm. in the center. I did not disassemble the roller to determine the type of bearing, but it feels like it is oilite and not a ball or roller bearing. The roller axle appears to be a 5/15" (8 mm.) round-head Allen cap screw with full-length thread secured against the post with a jam nut. I suspect that the post is threaded; otherwise the axle would probably wobble. The roller can wobble on the axle (very slightly - not signicficant at all) but the axle itself is rigidly attached to the post,
The
gate is 6.9 mm. thick, but milled from slightly thicker stock,
since there are two raised arcs on the roller side that bear against
the roller and separate the amin gate body from the roller by
about 0.7 mm.. Turning the gate does not turn the roller, so these
are not the main source of the roller drag. The gate latch is
a piece of 2.9 mm. spring wire bent into a zquared-off U shape.
When the gate rotates closed, the wire enters a large slot in
the back plate. The slot is tapered to flex the wire until it
can engage a small projection, where the wire snaps into place,
holding the gate shut. A cutout in the gate face provides access
for releasing the wire.
The PMI chest box is screened with "rock exotica"
(the manufacturer), "USA," "Patent pending,"
arrows indicating gate operation, the Reading
is Dangerous icon, "Always test gate to confirm it is
locked," and "Feb. 2005" on the caver's right.
It is screened with "Single CHEST ROLLER," "Do
not use a chest roller for promary life support," and the
PMI logo with "PMI" on the caver's left. A sticker on
the back reads, "WARNING" and "FOR DANGEROUS ACTIVITIES
RISK OF INJURY/DEATH CNNOT BE ELIMINATED. DO NOT USE UNLESS YOU
HAVE: READ ALL INSTRUCTIONS* RECEIVED SUITABLE TRAINING* CHECKED
GEAR BEFORE EACH USE* ACCEPTED TOTAL RESPONSIBILITY FOR YOUR SAFETY
AND GEAR SUITABILITY. ALWAYS USE A BACKUP - NEVER TRUST A LIFE
TO A SINGLE TOOL."
Tapering the front plate lightens the plate while retaining full strength - as any engineer knows, a center-loaded beam supported at both ends has most of its stress in the center, and should be thicker there. This is a nice feature that shows attention to detail. The milled areas in back lighten the plate considerably, as does the large undercut in the front post.
The gate assembly is particularly easy to operate with either hand. With the box right side up, I can open the gate with my right hand by using my thumb to depress the safety, or by using a finger of my left hand to do the same. I don't even need to grip the gate: thumb/finger pressure suffices to rotate it. The chest box can be turned upside-down for people who prefer using their other hand for manipulating the gate. The gate locks closed reliably with a distinct audible click.
The rollers turn with light resistance. I would prefer a free-running ball or roller bearing here along with a bushing design that allowed it to rotate more freely; however, the drag is small and probably not to be noticed.
The note, "Do not use a chest roller for primary life support" gets my nomination as one of the "DUH!" message of the year. Exactly how would a chest box support my weight, anyhow? No wonder… and by the way, in SRT, one customarily trusts ones life to a single rope.
This box is excellent. The only real complaint I have against
thsi bow is that I prefer double roller boxes - and that complaint
is addressed by the double roller version.
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Double
Rope (#819)I acquired this chest box from PMI in March, 2005.
My PMI, double rope is 75 mm. long, 197 mm. wide, 54 mm. high, and weighs 353 g. The back plate has 51 mm. tall vertical slots for attaching the box to a chest strap and 26 mm. wide horizontal slots for attaching shoulder straps.
The double rope version has a redesigned post that supports rollers on each side. One roller is centered on the plate, the other is offset to the climber's right. The back plate has three pairs of 7.2 mm. holes, giving additional chouces for attaching bungie pullies and other peripheral items, if one chooses.
The markings on my double are the same as on the single except for their location and that "Double CHEST ROLLER" replaces "Single CHEST ROLLER."
Offsetting the roller to one side makes some sense. A Mitchell climber would probably place the main line through the central roller and the long foot sling through the offset roller. People who climb with the long sling on the left foot might want to turn the box upside down. Except for the printing, it is symmetrical. On the other hand, some people might argue that a Mitchel climber has their weight on the long foot sling as often as on the main linem so the two rollers should be symmetrically placed about the center. Personally, I doubt that I could tell the difference.
This may be the finest double chest roller on the market at the time I write this. I saw no compelling reason to give up using my Alpine Box, although I did.
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