Replies

1. 
   mufti | Oct 15, 2006 09:05pm | #1

              Well if you are going to cut on a tablesaw using the mitre gauge then Veritas make a simple and accurate setting tool to cover this need.

2. 
   highfigh | Oct 15, 2006 09:20pm | #2

   Is this octagonal piece going onto the end or will it be inset? If it will be inset, you can dado the ends of the rest of the box and add a strip of inlay. If you're capping the ends, it'll be pretty easy to fit it after putting it on.

   If the issue is actually cutting the shape, remember that you only need to make a 12" square and remove 4 pieces, cut at 45°. If you have a crosscut sled, you can make a jig that attaches to it so you place the 12" sq piece in a 'V', as seen from your position when you make the cuts. If you see a need to make more of these (as opposed to making one of them), you can make a dedicated jig or just something that attaches to one you already have. If you have a sled, you could also make it adjustable for different sizes by fitting a T slot rail to the face of the main fence so you can move the jig closer to the blade when making smaller pieces.

   Also, if you need to attach something at the center, you can use carpet tape or hot melt glue.

   "I cut this piece four times and it's still too short."
3. 
   user-211435 | Oct 15, 2006 09:59pm | #3

   This is confusing.  If you just need to cut a 12 inch octagon, first cut a piece square, then cut off the corners at 45 degree angles.

   Or you can cut one finished side, and one end square to it.  Then cut 45 degree angles on the side.  Then set your table saw to 12", and cut all of the opposite sides.

   Maybe I'm missing something here?  What is the hole for?

   Hal

   http://www.rivercitywoodworks.com

    

4. 
   gb93433 | Oct 16, 2006 12:39am | #4

   find the center of a square and then inscribe a circle. Then draw diagonals. Once the diagonals are drawn then draw a line which is 90 degrees to the diagonal where the diagonal intersects the circle.

   
1. 
   lare | Oct 16, 2006 02:23am | #5

   Thank you all for your responses. As I said I have a complete lack of imagination and I will very often miss the obvious and easy. The octagon pieces are the ends of the box. The sides will fit to it in a way that you will see the end grain of the octagonal pieces.So, I start with a 12" square, mark my 45 degree cuts to "knock the corners off", and run into my problem of getting 8 sides of equal length. I think the whole problem is trying to use the miter gauge. I've been getting four sides of equal length and then the four diagonal cuts would be equal to each other but not to the other four sides. I'm talking about picky small measurements here, like a 1/16" difference or less, but it is a box not house framing.Now, if I would have just started off with the cutoff sled and a V block in it I think the challenge there is going to be to get the correct distance from the blade. But once there I should be able to get the accuracy I'm after. Thank you.

1. 
   highfigh | Oct 16, 2006 08:15am | #6

   Drafting is a good thing to know for woodworking and there are many practical applications. If measuring what you need isn't accurate enough, laying it out is much better. A straightedge, compass, triangles and a protractor go a long way. Throw in a French curve and you can design just about anything, on paper. If you need it enlarged, Kinko's is usually close and they can do it to scale. Drafting books are available at any good bookstore.Remember, an octagon is just eight 45 degree isosceles triangles and if you can draw the lines across the corners accurately, then mark a 22.5 degree angle from each line, drawing from the center mark through the 22.5 degree mark to the edge. Draw a line connecting each pair of points near the corners and you'll see your octagon. Cut just rpoud og the lines and fit it carefully.
   "I cut this piece four times and it's still too short."

5. 
   John_Carroll | Oct 16, 2006 06:03pm | #7

   The length of a side of an octagon is .4142 X the length of the side of the square that it fits in. In your case, the length of each side of the 12-inch octagon is 4.97" (4-31/32"). To layout the octagon, draw a 12x12 square and find the center of each side. Now measure out half of 4.97" (2-1/2") from the center points to mark each point of the octagon. Connect the dots to lay out the octagon.

   This distance (approx. 2-1/2"), btw, can be found on most rafter squares in the "octagon scale". The octagon scale looks something like this: [....[5....1[0....1[5....etc. (pretend the brackets are straight lines). If you measure the distance from the starting point to the second dot after the 10, you'll see that it's a hair shy of 2-1/2". For the octagon you need, I'd draw the 12-inch square, mark the center points, set my divider to the distance on my square, then use the divider to mark out in each direction from the four center points.

   Yet another way to lay out an octagon is to draw diagonals across the 12-inch square. The point at which these meet, of course is the center of the square. Now set your dividers to the distance from any corner to the center. This distance is 8.485. Now, with one leg of the planted in a corner of the square, swing the divider to mark that distance out along the two sides. Do that at each corner and you'll have the eight points of the octagon marked.