Re: Updated review: SuperBar by MasterGage, Inc.

On Sep 19, 2:39 pm, j...@xxxxxxxxxxxxxxx (John Cochran) wrote:
If you were off as little as 2 degrees in the other direction, the
error angle would be close enough to 32 degrees to account for your
reading. And frankly, 2 degrees is pretty darn close considering that you
most likely only have about an inch or two distance.

Yep. It's not an elaborate setup (mag base, 2,3,4 block, calibrated
eyeball, etc.). The result is close enough to say that it verifies
your formula.

I came up with my formula by looking at the geometry of the situation.
Just looking at a right triangle, what you're attempting to measure
is the change in length of side B. However, what you're actually measuring
is the change in length of hypotenuse C. For a tilt angle of 0 degrees,
you run into the happy situation of both lengths being the same. However,
for any other tilt angle, the hypotenuse will always increase in length
faster than the side.

Good analysis. It's what I was thinking too. For the most part, this
is the sort of situation that you read about but never actually
experience. Most people don't deliberately tilt the dial indicator
off axis with the object being measured. In all my years I've never
had the occasion to do it. There's always some way to resolve the
issue so that the readings represent the actual geometry.

Now I agree that you always want to have a tilt angle as close to zero as
possible. Not only does it give you a better absolute reading on the error,
but I suspect that many dial gauges don't like having lateral loads on
their spindles and in fact may have a fair amount of "wiggle" in their
spindles when a lateral load is applied to them which would tend to make
determining the exact tilt angle rather hard to calculate, predict, or
measure.

Yep, you're absolutely right. Using the Offset Bar on the TS-Aligner
products solves the reading problem but it does not avoid the lateral
forces on the plunger. Some indicators have more "wiggle" than others
but for the most part this isn't an issue. There is also increased
friction in the movement which reduces sensitivity, but with
sufficient pre-load this isn't an issue either.

Some might think that this setup magnifies the reading, making it
easier to eliminate small alignment error. Well, not only is the
error magnified, but any instability is too. And, blade alignment
isn't the only procedure which benefits from having the stylus close
to the table surface. Using a square or angle blocks to set the miter
gauge benefits greatly as well.

In order of overall perference, I would have to say that using a blade
replacement plate is the least desireable solution to the problem.
You are far better off doing the alignment over the shorter distance,
tilting the indicator, or (my favorite) using an Offset Bar. Marking
a spot on the blade and rotating the blade so that all your
measurements are with the stylus tip on that spot will always be more
accurate, much more convenient (no need to swap out the blade), and
much less expensive (just get a $0.49 sharpie).

Ed Bennett
ejb@xxxxxxxxxxxxxx

http://www.ts-aligner.com
Home of the TS-Aligner

.

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