|
Chris;
If the tripod jackstands did indeed have three points your argument
might make some sense but most have a flat steel plate welded to the bottom so
in reality they have a flat triagular one point bottom, like the
ones that my neighbor loaned me. I, on principle, don't like most of
the jackstands sold anyhow, three or four sided, they just don't look as
trustworthy as a solid block of wood. About the only jackstands that I have
liked were home made ones with a built in screw jack to cinch them up tight and
a nice wide spread at the bottom, one set actually had a three point
base. Either ramps, a hoist, or a pit would be my first choice.
Best Regards
Arran Foster
1954 Imperial Newport
Needing A Left Side Taillight Bezel and other trim parts.
----- Original Message -----
Sent: Wednesday, March 19, 2003 8:44
PM
Subject: Re: IML: Three-legged
jackstands
It would seem the operative issues here are the "legspan" of a
stand and the sturdiness with which it is built.
While many tripod
stands are indeed garbage, tripods are by the laws of geometry (not physics,
actually) more stable, because three points define a plane whereas four points
can form an irregular surface. In other words, all three legs of a
three-legged table or tripod or whatever always touch the ground when you set
it down. It's why three-legged tables never wobble but four-legged ones can.
And it's why photographers use tripods rather than, um,
quadripods?
There have been three-wheeled cars in history, and
while even tricycles can tip over, so can 4-wheeled cars and SUVs or 4-legged
jackstands. Static (stationary) objects are affected by different laws of
physics than moving objects, especially vehicles with steering and suspension.
And perhaps cows and dogs and such have four legs so they can remain standing
if they lift (or lose) one leg... the animal kingdom does not rigidly adhere
to the laws of physics when it comes to the design department.
(As an
aside, you can also remove one rear wheel from a Citroen DS and drive it
around on three tires... Don't corner too fast because the tires are not
symmetrically positioned under the car's center of gravity, but I've witnessed
it being done and not just in a straight line!)
The real reason I bring
this up is so people don't think just any four-legged jackstand is better than
any three-legged stand. As Arran said, the spread of the legspan (especially
in relation to their height) and sturdiness of their construction make a huge
difference. Sturdiness, stability, and sensible placement on a hard and level
surface (and under a suitable part of the car) are key. Placing a few steel
wheels under the car so it can only drop so far if it falls might also be a
good safety net (provided you're thinner than the wheels).
And always
wear your cell phone where you can reach it in case you need to (and still
can) call for help...
I wish you all years of safe hobbying, my
friends... and I extend my belated condolences to Greg and Russell for the
tragic loss of their friend (as well as my thanks for their willingness to
share their pain for the good of others).
Chris in LA
A. Foster
(monkeypuzzle1@xxxxxxx) wrote:
I disagree with one statement in this
posting. Tripod jack, or axle stands, are cheap garbage, do not use them.
Anytime that I have seen stands fall over, or tip, it was always the
three legged kind. Four legged ones always have a wider, more stable stance
then three legged ones, it just plain physics. Its the same reason that you
don't see three wheeled cars or three legged cows. I was loaned a pair or the
tripod type and I threw them in the trunk and decided not to use them, they
were just too tippy especially when they were
extended.
|
Back to the Home of the Forward Look Network