cutting accurate 30 degree miters

So I need to cut accurate 30 Degree miters in 2.5 x 12" old growth red cedar for a hexagon top I'm making. each piece will be 30" long. what's the best way to set up my tablesaw and ensure that I get accurate miters (off a 1/4 of a degree will mean 3 degrees out on the last cut! My mitering jig isn't accurate enough for this degree of cutting. thanks
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The table saw is best suited for ripping, not crosscutting. I'm not sayin you can't make an accurate cut with a table saw, you can. You might have better luck with a chop saw or sliding chop saw or radial arm saw.
That type of tool is better suited to the task you require. Since your boards are so wide you may have to flip the board over to complete the cut. Since it is valuable lumber you might also want to make test cuts on scrap material first. You could even do a mock-up of the hexagon with scraps before cutting into such valuable wood.
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Best way is to set a miter saw on top of it. Then cut some test pieces to be sure the angle is precise.
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I must be missing something. This doesn't seem like that challenging a cut on any table saw. The cut edge will be 13 7/8" long. That's well within the miter capacity of any table saw. You won't have to flip it over.
Bob
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Since you seem to be talking to me..... I was referring to the suggestion in my post that the OP use a mitre saw. That is what you are missing.
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You are correct, I misread context of the comment. thanks for correcting me.
Best regards, Bob
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I have a large 30-60 degree drafting triangle. That or an adjustable triangle can be used to set the miter gage.
You didn't ask, but a $60 INCRA Miter V27 with a shop made fence attached is accurate enough to make the cuts. Mine will make picture frame quality miters.
I've been playing with shooting boards and I would probably fall back on making fine adjustments with a shooting board.
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The Dubby sliding cut off sled sets up accurately to all typical angles. You have to pivot the fence 1/4" to move 1 degree setting. With that in mind you can imagine the accuracy you get if you set the fence to exactly where you want it.
Alternatively make yourself a sled with a fence that attaches to the top of the sled. Put a screw through the fence end nearest the blade side of the sled. Pivot the fence on that screw to 30 degrees or close to where you measure 30 degrees and put in another screw or two to hold the fence in that position. Make some trial cuts in scraps and check your results. The larger the scraps the more accurately you see the results.
I would advise using a straight 1x4 for the fence laid wide side down and make it as long as possible. The longer the fence the less jump it makes in degree angle as you adjust it on the pivot screw. You can tweak it until it is perfect.
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mcgyver wrote: | So I need to cut accurate 30 Degree miters in 2.5 x 12" old growth | red cedar for a hexagon top I'm making. each piece will be 30" | long. what's the best way to set up my tablesaw and ensure that I | get accurate miters (off a 1/4 of a degree will mean 3 degrees out | on the last cut! My mitering jig isn't accurate enough for this | degree of cutting. thanks
You can construct a full-size cutting template using a straightedge and the largest compass/dividers you can find (I once made a "use-once" compass to do something similar). Start with an equilateral triangle and bisect one side - connect the center of the bisected side to the opposite vertex and you'll have your 30-degree angle.
Use your cutting template to align a straight guide and make the cut with a hand-held circular saw. Dry fit the parts and make final adjustments with plane and/or sandpaper on a (long) block.
-- Morris Dovey DeSoto Solar DeSoto, Iowa USA http://www.iedu.com/DeSoto /
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Yet another way to add to the confusion.
Take a base of 'X' dimension and run a vertical (Y) (at 90 degrees) of "X" times the square root of 3 (1.732051), then connect the ends of the legs, you will have a 30-degree angle on top and a 60 degree angle on the side and the hypotenuse you have created will have a dimension (length) of exactly the base(X) times 2.
For all you trig aficionados, a similar situation occurs when you create a 45 degree angle. The base is the same as the height but the length of the hypotenuse is the square root of 2 (1.414214) times the base.
That comes in really handy... to me at least.
r
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"mcgyver" wrote in message

cedar
best
isn't
~ Buy/borrow/rent an accurate sliding compound miter saw that will allow cutting 12" wide boards at 30 angle in one pass. Futz with the angle setup on scrap until the perfect setting is locked in.
~ Buy a better miter jig for your table saw.
~ Make a specialized table saw sled like the one in the link below, only make the angle 60 degrees by using an accurate 30/60 triangle to setup the triangle used for reference edges; then make the successive cut for each joint on the opposite side of the blade, thereby taking advantage of the principle of complementary angles to insure an accurate 60 degree join.
http://www.e-woodshop.net/Jigs.htm (scroll down to "miter sled")
~ In all cases, use scrap wood to check accuracy of method and to insure hexagon closes as required.
--
www.e-woodshop.net
Last update: 2/20/07
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Use an angle sled. Build the top in halves, then joint together to finish. A large 30-60-90 draftsman's triangle will be plenty accurate to set the sled fence.
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mcgyver wrote: > So I need to cut accurate 30 Degree miters in 2.5 x 12" old growth red cedar > for a hexagon top I'm making.
As others have suggested, a 30-60 drafting triangle or use trig to lay out the line the batten line on a sled.
A 30-60 triangle has sides that are 1-2-and sq root of 3.
Tack a batten on a sled at the correct angle and have at it.
Need more help, see F Bingham's book, it's in there.
Have fun.
Lew
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Mcgyver, you answered your own question.
Set up to as accurate a 30 degree cut as you can with the tools you have and cut all but the last one. Assemble and clamp the five you've cut and scribe for the last one. Then hew to the line.
Tom Dacon

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Buy yourself an Osborne miter guage with stop block like Norm uses. Each cut will be deadon. I have one and love it.

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Tom,
I believe your technique plus the 1/4 degree error the OP mentioned would lead to a 1/4" mismatch on the inside corner where the 1st and 6th piece come together. Of course that's pretty easy to "correct" by just marking it and trimming an angled strip off of board 1 or board 6 to make them meet. If the angle error is not too bad, they eye will not be able to see it. Same goes for the outside corner - it will mismatch as well, but can also be trimmed to match.
Bob
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Exactly. My comment assumes that the raw stock is sufficiently oversize to allow for that trimming.
Tom
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Set your TS's miter gauge to 30 deg and cut 2 pieces to the correct length. Cut 4 more pieces about an inch longer than the desired finished length. Glue together 2 assemblies of 3 pieces, with a correct length piece in the center of each assembly. When dry take each assembly and run it thru the TS with the outside edge of the center piece against the fence. This will true up the final glue surfaces to be in the same plane and give you the correct length on all pieces. Glue the 2 assemblies together. The eye will never discern that your joints may be 1 or 2 deg off from each other as all joints will fit exact at the time you built it.
Be aware that you may experience the joints opening & closing a bit over time as the humidity changes. Art

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mcgyver wrote:

There's a trick here. It is not possible to hold this perfectly. What you do is cut all six pieces and then assemble three into one half and three into the other half. If you need the points to meet as points, make sure the error is slightly on the plus side. At this stage the edges are about 180 degrees. You can now joint / plane the mating edges to make them flat and assemble the two halves. The six pieces will not quite be exactly the same size but they will all look the same and the joints will all close up perfectly.
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