[Land-speed] 2 or 4 post lift?

[Ed Weldon]

Elon -- 
Very interesting question.  I couldn't use one of these things because my
shop ceiling is too low.
But before I'd buy one I'd run some basic structural calculations and look
for stresses over 10,000 psi (a very old rule of thumb for A-36 structural
steel and the like) assuming the loads I'd put on it.  Also I'd calculate
the Euler column thresholds on the posts.  For loads I'd figure actual
weights and allow 1.25 safety factor for mild shock loading.  I'd also
calculate the effect of the weight on the worst loaded post and multiply
that times 1.75 for the shock loading attendent to failure of a single
safety latch on top of the other loads.
And then there's the issue of earthquake loadings.  The Loma Prieta
earthquake caught my Dodge Dart station wagon up on jackstands and shoved it
4 feet to the side. (it survived unscathed)
I wouldn't dream of manufacturing and selling these things without a
licensed structural engineer's seal on the plans including his maximum load
ratings (unless maybe I was living out of the back of my pickup truck). And
good liability coverage too.....
Oh yeah, I've seen a good bit of imported square steel tube with defective
seam welds.  Something to examine for before buying.
My 2 cents worth.
Ed Weldon

----- Original Message ----- 
From: "Elon" <saltfever at comcast.net>
To: "land-speed submit" <land-speed at autox.team.net>
Sent: Monday, June 09, 2008 11:04 PM
Subject: [Land-speed] 2 or 4 post lift?


> Can folks give recommendations on different brands of garage/shop lifts. A
> couple of years ago I talked to two reps at a car show each representing a
> different brand. I can't remember the names but I was interested in the
> latching (locking) mechanism , the design safety factor, and the way they
> were certified or tested. It was discouraging. Neither rep new anything
> about safety factor, or what I was talking about. One brand was not
> certified by any organization and the other was certified by an
independent
> organization the company started! Talk about conflict of interest! That
> brand was proud of their testing and had examples of overload failures and
> some luke-warm information on the latch design. The other brand provided
> anecdotal data on the latch safety but no engineering analysis. Anyway,
that
> was a few years ago and I was hoping things had changed.
>
>
>
> If you have a lift could you indicate why you choose the style you have
and
> the brand name. Also, now that you have experience with it are there thing
> you wish you had considered before buying?  Thanks in advance,  -Elon
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