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wrote:
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Personally, I hate trial and error. snip

Better not look at that video, Ed. Unless the guy tapping the fence
into a new position between measurements has calibrated knuckles, he's
certainly doing trial and error. ;-)

My approach was to do the five cuts, then measure the taper on the
strip with a digital caliper. I put an indicator with magnetic base on
the outboard end of the fence, then try an adjustment, say 10 or 20
thou. Then repeat the five cuts, and measure the new taper value. If
10 thou fence adjustment reduced taper by X thou, then adjust the fence
another (current taper/X) x 10 thou. One more test cut, and Bob's yer
uncle, it should be right on.

This morning I tried a modification to this. Instead of putting the
indicator at any position along the fence, I put it L inches away from
the fence pivot, where L is about the length of each side of the test
panel. With my 10 thou fence adjustment, I was basically finding a
calibration factor for the system with the indicator wherever it was
and the test panel whatever size it was. By keeping these dimesions
the same, the calibration factor is just 4 (the amount of the
squareness error is increased going around the four corners of the
panel).

I roughly squared the fence with a $6 combination square. The first
test on a ~24" panel gave 0.180" taper. I put the indicator 24" from
the pivot, adjusted the fence 0.045" ( = 0.180"/4) and the second test
gave me 0.005" taper over about 24". Although I've heard of a guy who
aligned his contractor saw to within 0.000050" of true, this squareness
is good enough for me. (I wonder what ever happened to him? ;-)

I expect some cosine error since the fence pivot point is offset from
the fence face, and my magnetic indicator base isn't terribly rigid,
but even if a third test cut was required it would be no biggie. I
didn't time it, but this probably took me ten minutes to square the
fence from scratch.

Now, if I had a TS-Aligner and an 18" precision square to square a
sliding table fence, for instance, rather than measuring, tapping,
measuring, tapping, etc., until I was happy, I'd try a little different
process:

1) Measure out-of-squareness. Call this X.
2) Move the TS-Aligner to the sliding table. Use one hand to hold it
against the fence at a position 18" from the fence pivot.
3) Use the other hand to tap the fence a distance -X and lock the fence
down.
4) Re-check out of squareness. It should be zero, or pretty close to
it.
5) Done.

And I don't like a shop cluttered with peices being saved for test cuts
or the cutoffs from test cuts.

There's no magic to a test panel -- it's just something of convenient
size that comes out of the offcut bin for a few minutes and goes right
back slightly smaller.

One could not do better
than to obtain the right setting without any test cuts.

Actually, the right setting with the least investment in time and money
is my definition of better. I don't have the square, so test cuts is
better for me. You do have one, so no test cuts is better for you.

A corollary is that if your customers have 18" precision squares, the
method in the video will help them, if your customers don't have such
squares, the video won't help them.

So, unless you're
astoundingly lucky and get the right setting on the very first try,
you're in it for at least ten test cuts with a panel which (as you
said) should be near the capacity of your sliding table (48" for me!).
I'd call lugging around a half sheet of panel stock on the sliding
table an ordeal which I would definitely be reluctant to perform. And
a half sheet of anyting is hardly a "scrap".

Sorry, I didn't express that well. I have the medium size Excalibur
table. With the fence at the front of the table there is about a 27"
cross cut capacity. I also have a bunch of 2' x 4' masonite offcuts
from some years ago that I use for 2' square test pieces. This size
also serves when the fence is at the back of the table, even though it
then has 48" crosscut capacity. Because error is multiplied by 4 each
time around, it turns you you don't need a big piece to get good
resolution. I haven't tried it, but 12" pieces would probably work
just fine, too.

Finally, at my age, there's no hope in resolving a scribed line to
within 0.010" by eye.

It sounds like you don't have a rotating stop for the zero position on
the fence. I'd strongly suggest looking into one. I set mine two
years ago, and after resquaring the fence this morning, the stop was
still dead on. This is with moving the fence between the front and
back of the table very frequenly over that time. If someone was
resquaring the fence from scratch each time it was moved, I could
certainly see why they'd avoid using the 5-cut method to square it.
With the rotating stop, set the fence against it and you're squared
without any measurement or adjustment.

The scribed line would then be a nice back-up to periodically check the
rotating stop hasn't moved.

Cheers,

Tim