surface gauge - why flat base?

> not moved in a straight line. I worked at a place that had a height
> gauge with three flat feet about 3/4" diameter. It was a pain to use
> because of this vibration when roatating the gauge. You had to be real
> careful and move it slowly.

Did "flat bottomed" gauges show the same behaviour (assumiung
you had some) ?

BugBear

Posted by Robert Swinney on July 2, 2008, 12:22 pm

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bugbear, waxing trollish, sez: "Did "flat bottomed" gauges show the same
behaviour (assumiung you
had some) ?

Fuggegitabbit already! Go back and visualize the arc the "vertical" member
would swing in if the 3
points weren't all equal.

Bob Swinney

etpm@whidbey.com wrote:

> On a granite surface plate trying to rotate a surface gauge or height
> gauge is likely to cause chatter.

More so than a cast iron plate? How curious (and interesting)

> The gauge will tend to skitter when

BugBear

** Posted from http://www.teranews.com **

Posted by Maxwell Lol on July 5, 2008, 8:09 am

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> Fuggegitabbit already! Go back and visualize the arc the "vertical" member

would swing in if the 3

> points weren't all equal.

Think of it this way:

A three footed gauge will generate error if ANY of the feet are
imperfect.

A flat-bottomed gauge has more that three points. It has
hundreds. If one of those has an error, it will not affect the
gauge.

Posted by on July 2, 2008, 2:34 pm

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On Wed, 02 Jul 2008 16:37:38 +0100, bugbear

>etpm@whidbey.com wrote:

>> On a granite surface plate trying to rotate a surface gauge or height
>> gauge is likely to cause chatter.

>
>More so than a cast iron plate? How curious (and interesting)
>

> > The gauge will tend to skitter when
>> not moved in a straight line. I worked at a place that had a height
>> gauge with three flat feet about 3/4" diameter. It was a pain to use
>> because of this vibration when roatating the gauge. You had to be real
>> careful and move it slowly.

>
>Did "flat bottomed" gauges show the same behaviour (assumiung
>you had some) ?
>
> BugBear

I don't know about cast iron plates. We did also have a round based
height gauge with the vertical beam mounted close to one edge and it
chattered the worst. Rectangular based height gauges did not have this
behaviour.
Eric

Posted by Dave Baker on July 2, 2008, 1:28 pm

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> Given that a surface gauge (and indeed height gauges)
> need to sit securely on a surface plate,
> why don't they have a tripod support
> (which sits secure regardless),
> instead of having a flat base, which
> is only stable if it's carefully made truly flat?
>
> Surely a 3-point base gives equivalent functionality
> in perpetuity at a lower build difficulty.

1) If both surfaces are flat then depressions or damage to either doesn't
matter. A tripod would follow such depressions.

2) For a surface gauge perpendicularity doesn't really matter but for a
height gauge it does. How do you know if a tripod is set up perpendicular?
The answer is you don't.

3) Wear. Three points of contact would wear much faster than a flat base.
--
Dave Baker

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