Newby Height gauge query
 

Using a surface plate, I've just checked my 12" high height gauge against
gauge blocks, with similar results for different gauge blocks.

What I've noticed is that the machined measurement surface of the height
gauge arm isn't parallel to the surface plate. (It's around 0.010" higher at
the tip as compared to its height at a position 1.5" closer to the column.)
The micrometer has (standard?) 0.0005" increments, so am I right in
expecting something better than this?
If the height gauge column is tilted with reference to the base, would I be
able to check for this by sighting against a precision engineer's square?
(Which I don't have, as yet.)
I can't see any signs of damage to the height gauge - it's an APE Microball
type, and was supplied in its fitted case.

Many thanks for any advice.

--
M Stewart
Milton Keynes, UK
http://www.megalith.freeserve.co.uk/oddimage.htm

Newby Height gauge query
 

Malcolm Stewart wrote:
Using a surface plate, I've just checked my 12" high height gauge against
gauge blocks, with similar results for different gauge blocks.

What I've noticed is that the machined measurement surface of the height
gauge arm isn't parallel to the surface plate. (It's around 0.010" higher at
the tip as compared to its height at a position 1.5" closer to the column.)
The micrometer has (standard?) 0.0005" increments, so am I right in
expecting something better than this?
If the height gauge column is tilted with reference to the base, would I be
able to check for this by sighting against a precision engineer's square?
(Which I don't have, as yet.)
I can't see any signs of damage to the height gauge - it's an APE Microball
type, and was supplied in its fitted case.
It doesn't take much to ding the base of the gauge, and make it sit
crooked. You may need to stone down a ding on the base, or rescrape
the base. You might be able to use a good square to check how vertical
the column is. I have a set of machinist squares, and was able to check
them when I hand scraped in a set of 3 precision squares. Well, those
machinist squares are not all that precise, apparently. I don't have
a reading on the error, but it looks like a substantial part of a
degree, ie. easily detected by backlighting the gap between the
ground square and the scraped one.

Jon

Newby Height gauge query
 

"Jon Elson" wrote in message
...

Jon
Thanks for your reply. Very early this morning, I tried laying the height
gauge column horizontally on the surface plate, and found it was bowed. The
bow was such that it might account for some of the tilt I'd found. Close to
the base, I found using my gauge blocks as squares (?) that the column
appeared to be square to its base. I'm hoping to purchase a couple of
squares later this morning. I assume that with two, I can check them
against each other. Will then have to decide how to straighten the column!

--
M Stewart
Milton Keynes, UK
http://www.megalith.freeserve.co.uk/oddimage.htm

Newby Height gauge query
 

Malcolm Stewart wrote:
"Jon Elson" wrote in message
...

Jon
Thanks for your reply. Very early this morning, I tried laying the height
gauge column horizontally on the surface plate, and found it was bowed. The
bow was such that it might account for some of the tilt I'd found. Close to
the base, I found using my gauge blocks as squares (?) that the column
appeared to be square to its base. I'm hoping to purchase a couple of
squares later this morning. I assume that with two, I can check them
against each other. Will then have to decide how to straighten the column!


You can't. The way metal bends, it stretches more easily than it
compresses, so that things get longer when they are bent. Straightening
them leaves them stretched, in most cases. It wouldn't be a big deal
except in a measuring instrument. It might be possible to get it
straight, although this can be real difficult. But, the accuracy has
almost certainly been badly affected, and I doubt you can fix that.

A sad case, for sure.

Jon

Newby Height gauge query
 

"Jon Elson" wrote in message
...
You can't. The way metal bends, it stretches more easily than it
compresses, so that things get longer when they are bent. Straightening
them leaves them stretched, in most cases. It wouldn't be a big deal
except in a measuring instrument. It might be possible to get it
straight, although this can be real difficult. But, the accuracy has
almost certainly been badly affected, and I doubt you can fix that.
A sad case, for sure.
Jon

Hi Jon,
All may not be lost. The height gauge is an APE Microball type in which the
coarse height is set, every 0.5", by clamping a shaped probe between the
gaps formed by a column of 0.5" steel balls contained in what looks like an
aluminium outer casing.
There's a photo of one, same size and very similar, here
http://www.gandmtools.co.uk/cat_leaf.php?id=1375
The coarse settings are on the other side of the column.
(Mine cost very much less than the one in the advert - which could explain
the problems; but I suspect the vendor sold in good faith.)

So, if I do manage to remove the bow, the length will be set by the steel
balls rather than the aluminium casing. I assume that the balls must be
under spring pressure as steel and aluminium expand at different rates.
Near the base, the column does appear to be at 90deg to the base checked
against a pair of engineer's precision squares.
At the moment, using shims I've managed to adjust the slope on the underside
of the gauging arm and it's now essentially parallel to my gauge blocks from
0 to 80mm, with ~ 0.25mm zero offset. Above that there's obvious tilt, and
it gets worse as I stack the gauge blocks. So lots to keep me occupied
after the holiday.
Thanks for your advice.
--
M Stewart
Milton Keynes, UK
http://www.megalith.freeserve.co.uk/oddimage.htm