Can someone tell me how to make accurate 45 % cuts that actually fit
together nicely? I was building an deck and have some herringbone and
mitered joints that were an devil to do , using number 2 grade spruce. I
love making sawdust.
Again, what are you using to make the cuts? Blade choice is important,
too, of course.
If the material is construction-grade lumber that isn't fully dry, it'll
almost certainly shrink when it dries and any 45 will open up anyway
I don't understand. You want to make an accurate 45 deg cut, but they don't
match because of the poor grade of wood? If the cut is accurate it will fit
no matter the grade of wood.
You need either a good miter box, a good miter saw or an accurate square.
What are you doing now? The only professional trick is to have both cuts
Not really. On a table saw, use two miter guides set to 45, one on
each side of the blade. Make one cut on one side, then make the mating
cut from the other side. Even if you don't have exactly 45, the two
cuts will be complementary and join perfectly.
Same thing on a radial saw, except the blade is set to 90 and you
build a jig that holds the work piece at 45 on either side.
Incorrect. The two surfaces may meet but the resulting angle of the
two boards will not be 90 degrees unless the cut is exactly 45
degrees. The OP implied he needs the resulting angle to be 90
If the outer edge of the V-shaped guide is 90, then it will be 90 even
if the miter isn't exactly 45. (e.g. 45 1/2 and 44 1/2.)
Both the interior and exterior edges may not line up (picture a 30/60
Agreed. It's a deck, not piece of ornate furniture. Even if there's a little
splintering, it would go unnoticed and if it doesn't, it only adds to the
rustic nature of decks. A suitably sized speed square is all that's needed
for a deck.
From What I have read:
It has to do with the force from the blade, how it cuts the kerf, and how
the wood is supported (or secured from movement.)
The force of the motor is way more than you can hold with your hand the
wood against movement. A 90 degree crosscut usually has a lot of support
by the geometry of the cut which prevents wood movement. However a 45
degree cut as a lot a force working to shift the wood due to the blade.
Vector math, resultant forces, and all that.
Step 1, therefore is to check and double check that the wood is secured
in such a way as to prevent the wood from movement during the cut. Stop
blocks do work well in this case.
Several very well written articles in Shopsmith magazine over the years
on this subject. And I believe in the results of the jigs I have built
from Shopsmith to overcome this 45 degree gap problem.
You never explained what the problem is. It is a common carpenter
"trick" to backcut all miters so that just the top finish surfaces
comes together. The amount of backcut is really small, I would
guess about 1 degree. On trim work, setting the piece up on a
nail close to the blade gives about the right relief.
Keep the whole world singing . . . .
One last thing to consider. If you are trying to come up with a particular
angle and the boards do not intersect at the correct angle the cuts will
Often a novice when trying to make a square frame with 45 degree mitered
cuts one of the joints will not close properly. This is because either the
opposite sides are not perfectly parallel or the opposite sides are not
exactly the same length.
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