You can forget a log fireplace in SoCal.
The South Coast Air Quality District outlawed open log fire burning
fire places years ago as an air pollution source problem.
of checking before and I do now. The Draw-A-Line and flip method will never
tell you how
far out of wack your square is
Pfui. Of course it will. The more the lines diverge, the more out of whack it is.
can measure the distance betwene the lines/knife marks with a caliper (good
That'll work. Feeler gauges will probably work better.
answer that question so why bother checking in the first place?
Of course you can easily answer that question. Decide what percentage error is
acceptable in your project, and you can easily calculate the permissible gap
marks. Suppose you want accuracy to one part in 1000 (99.9%). The gap between
pencil lines at a distance of 8" -- double the error in the square, remember --
must be no
more than 8 * 2/1000 = 0.016", which is easily measurable with feeler gauges, a
or a mike.
On Thursday, January 3, 2013 9:32:58 PM UTC-5, Doug Miller wrote:
"More out of wack" is not a quantity. I can only be used in relative terms.
'This' is more out of wack than 'this'.
Huh? Measure the distance between two lines with a feeler gauges?
So you decide before hand the accuracy you want to achieve and then choose the
appropriate square? Do you have different squares for different jobs? Are they
labeled as such?
A distance of 0.016" equates to an angle error of 0.5 degrees for your 8"
square. Would you calibrate anything with that "Square"? I wouldn't.
What is your limit of detection for measuring gaps between lines? I hope it's
less than 0.016", but I can understand if it's not.
Yes, and I was using it in relative terms. Where's the problem?
Sure, why not? You can easily see if the gauge overlaps the lines
or fits between them. BTW, the width of the pencil lines isn't
really relevant -- use a marking knife instead of a pencil.
I have a Starrett square that never leaves the wood shop. I also
have a Craftsman combination square, and a Stanley framing square,
that I use for carpentry projects. It never crossed my mind to use
the Starrett when I built a shed in the back yard a few years ago,
or when my son and I built a deck last summer -- that degree of
precision simply isn't needed, and there's no point in risking an
expensive precision tool on a construction site.
No it does not.
First of all, 0.016" is double the error, so the actual error is
0.008" over 8" or 0.001. The inverse tangent of 0.001 is 0.0573
degrees (rounded to 3 significant digits). If you want to be
really picky, the 8" distance is actually the hypotenuse of the
triangle, so we should use inverse sine instead, but the result is
the same to at least the seventh decimal place.
I wouldn't either -- *if* your number was right. It's not, though,
and I'm not sure why you seem to have a problem with using a
square that's accurate to one part in a thousand for woodworking.
I can estimate much finer gaps than that by eye. The thinnest
feeler gauge I own is 0.001"; anything less than that is too
fragile for wood shop use, and is pointless anyway. In practice, a
0.002" gauge is quite sufficient for woodworking.
On Thursday, January 3, 2013 10:28:59 PM UTC-5, Doug Miller wrote:
That's not how the math is done.
If your gap between the two lines (drawn from the same point) is 0.016" then
half the distance is 0.008" which is your "Opposite Side". Now I understand
the confusion here.
Your Opposite side is 0.008". The Adjacent side is 8".
distance is 0.008" which is your "Opposite Side". Now I understand the
And tangent = opposite / adjacent = 0.008 / 8 = 0.001.
(As I noted previously, the 8" is actually the hypotenuse, not the adjacent
side, but for
angles this small, it doesn't matter.)
Anyway... arctan (0.001) IS NOT 0.5 degrees. You're off by an order of magnitude.
If you *can't* tell the difference between a gap of sixteen thou and a gap of
six thou without
using precision equipment, then you need to visit an optometrist. Seriously.
accuracy required. And neither can you.
Don't tell me what I can and can't do.
You don't own feeler gauges, so you don't know how small a gap is visible, or
it can be estimated with a little practice.
No one mentioned using the top of their old Craftsman table saw to check
the accuracy of their squares. I frequently check my square by laying
the square on the table and checking the square using the edge and the
miter slot. or a corner of the table. However the slot is more
accessible since the saw has wings on the iron top to extend the work
For setup of saw and router table I use an aluminum triangle square. If
I drop it so what, while the edge maybe nicked it will not be knocked
out of square.
On 1/3/2013 6:30 PM, firstname.lastname@example.org wrote:
small gaps between the two pencil lines (especially with a thick pencil lead).
The most you might be able to detect is a 0.010" difference which equates to a
minimum detection of 0.036 degrees with an 8" square.
perfectly flat, otherwise you will not get an accurate calculation of your
square's angle error.
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