Doesn't work for me with a pub table, all that happens is I get the
"what's he up to now?" look from the landlord. So back to the tried
and tested folded beer mat that the bloody cleaners throw away each
Any continuous-surface-floor (no jumps, steps, holes) would be ok,
if the ends of the legs are coplanar. Most likely one of the pub
table legs is shorter than the others, by about the thickness of a
folded beer mat.
My curious mind got to wondering when I first got involved with this
whole silly musing about four legged stools and wavy floors.
Looks like it was over 12 years ago, and this link provides a grandios
explanation of why what I said really does work:
Happy Independance Day to all.
Jeff (Who can't recall any other US holidays referred to by their dates
instead of their given names. He doesn't think that the shipment of
mayonaise on the Titantic <Cinco de Mayo> is a US holiday yet.)
Very cool. I like your logic much better than mine. :)
Even without the constraint of the rotation, it's (now) easy to see that if
you keep three legs on a wavy floor and move it around randomly, you will
always be able to find a spot where the the forth leg would hit the floor
making all 4 touch at that point. The rotation idea is simple proof that
there there must always be at least one location where that was true
(assuming the chair legs were correctly aligned on a plane).
On 03 Jul 2008 20:19:38 GMT, firstname.lastname@example.org (Curt Welch) wrote:
There is of course a "flaw" in this proof (pun intended)...it assumes
that the available floor space is big enough for all 4 legs of a stool
to be on it at the same time. You'd have a hard time proving it in my
I'm not questioning wether a (truly)flat base works,
or can be made to work.
I was trying to explore
whether an alternative design, with lower production
costs, can also be made to work
I would guess that making a block with a single flat side is in fact far
easier and cheaper to mass produce than any type of tripod. The cheapest
way to make a tripod with precision flat feet might even be to make a block
with a flat side and them remove the extra material to turn it into a
Making a tripod with pointed feet so that you don't have to deal with the
flatness issue ends up with something that will damage your surface plate
so that's not much of an option. Making hard rounded feet on the tripod is
again, only harder than just making a block with a flat surface and also
risks damage or excess wear to the surface plate. So though it might seem
like an interesting approach, I think the answer is that in practice, there
is no type of tripod that makes more sense than a block with a flat side
for use with a surface plate.
BTW, my new surface plate just showed up today and I just spent the last
hour making a flat piece of aluminum for the fun of it.
I use my height gauge to scribe my workpiece.
Most of the time this means sliding the height gauge on
the surface plate. Much less damage to the surface plate
using a full periphery contact surface than if that pressure
were concentrated on three points, yes?
Well ... a 3-point base has less surface area, so it is more
likely to wear out of spec more quickly for a given amount of use.
Remember that it is important that the height gauge's beam be truly
vertical. I guess that you *could* fit the base with a high precision
bullseye level and make two of the three contact points adjustable so
you could set it truly horizontal (and the beam truly vertical) before
each use. But, of course, this requires the surface plate to be truly
level before you start. :-)
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The height-gage base is flat, and covers some area, considerably more than
three small "feet", (think *pounds-per-square-inch* of contact area, here)
so it can be moved around on the surface plate and still remain true, plumb,
lever - whatever - CONSISTENT. To minimize wear (which translates to
*inaccuracy* ). Dimensional stability at temperature-change is better on a
flat base, too.
Good granite surface plates can easily be lapped to .00001, if the operator
is savvy, and the big metrology companies have some people who travel around
and do just that - by hand! Small dings in the surface will not affect the
result of a good height gage with a big base, whereas a three-legged thing
could easily be rendered utterly useless if one leg got into a small ding..
That is another reason that granite plates are preferred for inspection-lab
and calibration-lab purposes.
Iron, no matter how good a job of scraping is done - and I have seen a
number of really good ones - get dinged and they raise a spot. Maybe good
enough for work-cell spot-checking, but not the most durable nor precise.
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