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Classic eccentrics:  Andy Warhol, Howard Hughes, Queen Victoria, Albert Einstein, Oscar Wilde, and angle adjustments on ultralight manual wheelchairs.

Indeed, eccentric adjustments on ultralight manual wheelchairs can prove just a difficult to make sense of as a true eccentric's personality.  However, while few principles govern people who are eccentric, adjustments that are eccentric are entirely based in absolute engineering, easy to understand once the concept is clear.

To understand eccentrics, first consider how mounting points function in relation to angle adjustment.  Two fixed mounting holes won't allow any angle adjustment of caster barrels or back canes.  Slotted mounting points do allow angle adjustments, where the top mounting point can be located in a different fore-aft position than the bottom, creating angle.  Slots, however, work on friction, where impacts can knock slotted mounts out of alignment - and, this is where eccentrics (in washer or bolt-head form), become a meaningful securement solution.

An eccentric is a hexagonal piece, with one offset hole, that fits into a channel on an angle-adjustable component, most commonly, a caster barrel.

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When in place, the hole in the eccentric aligns with the mounting slot.  However, because the eccentric fits into the retaining channel, it locks the bolt in a fixed position, eliminating movement in the slot when secured.  Now, because the eccentric's hole (or, shaft, if it's an eccentric bolt), is offset, rotating the eccentric's position in the channel allows the eccentric to be set in eight positions along the slot, commonly allowing the component to adjust in angle from 82- to 98-degrees, as with caster barrels.

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In relation to caster barrels, angle adjustment is critical, as caster barrels must be set at 90-degrees to the ground, regardless of frame angel, for proper performance.  To adjust caster barrel eccentrics:

1. Loosen the top and bottom eccentric hardware nuts on the caster barrels, so that the eccentrics can rotate outside of the channel.

2. Pivot the caster barrel, so that it aligns at 90-degrees with the ground, straight up and down.  

3. To ensure absolute accuracy to 90-degrees, use a hand level, angle-finder, square, or large hardcover book to square the barrel with the ground (which should be level within reason).

4. While maintaining the desired barrel position, rotate the eccentrics until they naturally fit into the channel.  There is a little play in the system, so slight movements of the barrel are sometimes needed to achieve proper fit of the eccentrics.

5. Reconfirm the angle, and tighten the hardware.

6. Apply the exact same eccentric position to the other barrel.  

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Angle-adjustable back canes usually only feature a single eccentric on each side, where the hardware is loosened, the canes positioned, then the eccentrics fit into place and tightened.

One can never fully explain eccentrics like Queen Victoria, who insisted on setting a place at dinner for her husband for 20 years after his death, or Andy Warhol, who had a snap surgically implanted in his head so his toupee wouldn't fall off.  However, when it comes to eccentric hardware on manual wheelchairs, the mysteries quickly become fully explained, making adjustments practical, reliable, and precise.

Published 2/06, Copyright 2006, WheelchairJunkie.com