In article ,
"Swingman" writes:
"Jeffrey Thunder" wrote in message

You don't understand. Yes, the resulting angle when you join
the pieces is indeed 90 degrees. But the joint won't look right.

Au contraire ... it is you who apparently "don't understand". This is
woodworking, where the absoutes of mathematical theory are often of little,
or no, consequence, because of the tolerances involved.

Who mentioned anything about "absoutes [sic] of mathematical theory"?
All I said is that if the complementary angles aren't very close to
45, the resulting joint will look bad.

While I will grant you that the "length' of cut becomes an issue the _wider_
the stock, you are apparently assuming that most miter joints cut this way
are done in wide stock and the angular error is great enough. From practical
experience, that is NOT the case in typical woodworking projects.

At what point is the "angular error" great enough
to be a problem? The original contention (if you read the post)
was that it didn't matter if the cut was 45 degrees, as long
as the angles were complementary. I say it does matter.

If you take two one inch wide (say) sticks (or do as I
suggested before and use paper), cut one at 40 degrees, say, and
the other at 50 degrees, the resulting joint will look crappy.

Once again, the difference in angle in a properly built sled is so small as
to make joint length mismatch a none issue in the width of the stock likely
to be used in the typical woodworking project that requires miter joints.

By "properly built," you mean the angle is fairly close to 45 degrees.

Now, the 'proof is in the pudding', so to speak. I am telling you that I use
such a miter sled on the table saw and that the resultant joints "look" NO
differently than when cut on my SCMS, and more importantly, ultimately fit
better around the four corners. I routinely use the sled to make picture
frames, and to frame glass table tops, with NO ill effects on appearance
whatsoever.

So tell us, what complementary angles does your sled cut in order
to make such nice joints?

Now, lest you think I am the only one ... one of the most asked about table
saw miter sleds is the one used by David J. Marks on Wood Works, which is
designed using this very principle.

Theory is fine, but practical application, particularly when using the
tolerances involved in woodworking, is far less likely to stifel creative
solutions in cutting tight joints.

IOW, if you haven't used such a miter sled on a table saw, you need to
loosen up and give it a try before embarking on a theoretical campaign to
discount its usefulness for cutting miters in typical woodworking projects.

I have and do use sleds on a table saw.
What Barry suggested is incorrect: that the angles
don't matter as long as they're complementary.


--
Jeff Thunder
Dept. of Mathematical Sciences
Northern Illinois Univ.
jthunder at math dot niu dot edu