Help in Making an Octagon

[GrayFox]

I have a 4" square piece of wood that is 15" long. I need to make it into an octagon. A table saw with blade tilted at 45 degrees won't do it. How do I cut the corners off?

[CW]

Why?

[Jody]

I'll second that.... Why would it not work?

[Markem]

Cause it is eight sided, divide 360 buy 8 then by 2 and your answer lies there. (Hint there are 16 ends to eight sticks)

Mark (sixoneeight) = 618

[Scott]

[CW]

[Markem]

Well let see an octagon has eight sides not four. Perhaps the angle is

22.5? Or is your mind totally stuck in the box.

(Hint 45 + 45= ?) and #2 (22.5 + 22.5 = ?)

Mark (sixoneeight) = 618

[The Davenport's]

If you are trying to make a 15" long part that is octagonal in cross section, than I don't see why tilting the blade to 45 won't do it...if fact, it's the only way I can think of to do it without breaking out the hand planes.

IF, on the other hand, you are trying to make a FRAME that has eight sides and the pieces that make up the frame are 4"square, than you wouldn't tilt the blade, rather you would set you miter gage to 22 1/2 degrees and cut the end of the blank off, rotate the part 180 degrees and make a cut to get your first segment. Rotatecutrotatecut repeat...you should get the picture

Oh...the segments really need to be the same length and exactly 22 1/2 degrees to come out right.

OK...I just did a little layout in AutoCadd and unless you have a way to cut with zero kerf, this won't work because you don't have enough stock.

However, if you take your stock down to 3 3/4, you can just make it, if you use a thin kerf saw blade...your segment s will be a little under 3 1/8" wide...3.1066" to be precise.

Good luck Mike

[Markem]

Nope just need to recalibrate the visual thought processes from making a octagonal box to an octagonal solid stick.

(Been under the kitchen sink with a rodder and it is still stopped up)

Yep that would work.

Better?

But I think I would use the bandsaw.

Mark

[Lee Gordon]

Yes, an octagon has 8 sides and it has 8 equal angles. The angles in a polygon have to add up to 360 degrees. Divide 360 by 8 and you get -- wait for it -- 45 degrees.

If the O.P. wants to turn a length of 4" x 4" (true dimension) stock into an octagon, he needs to measure one inch from the edge, tilt his table saw blade to 45 degrees and set the fence so the blade hits that one-inch mark, run the piece, then repeat the cut three more times, rotating the piece 90 degrees each time. If he's using a 4x4 (IOW, a piece that's actually 3.5" x

3.5") he needs to make his mark at 7/8" instead of 1".

Lee

[CW]

45 it is.

[J T]

Sat, Apr 14, 2007, 11:22pm (EDT+4) [e-mail] (GrayFox) doth sayeth: I have a 4" square piece of wood that is 15" long. I need to make it into an octagon. A table saw with blade tilted at 45 degrees won't do it. How do I cut the corners off?

I 'guess' you could call that an octagon. Then set the table saw at some other angle. Or you could plane it. Me, I'd probably make a planer sled to do it, more fun that way.

From The Collaborative International Dictionary of English v.0.48 (gcide) Octagon \Oc"ta*gon\, n. [Gr. ? eight-cornered; 'okta- (for 'oktw` eight)

• ? an angle: cf. F. cctogone.] 1. (Geom.) A plane figure of eight sides and eight angles. [1913 Webster]

1. Any structure (as a fortification) or place with eight sides or angles. [1913 Webster] {Regular octagon}, one in which the sides are all equal, and the angles also are all equal. [1913 Webster] From WordNet (r) 2.0 (wn) octagon n : an eight-sided polygon

JOAT I have anal glaucoma. I can't see my ass going to work today.

[Leon]

Have you ever cut a bevel on a TS??? I am not sure what your formula represents but it has nothing to do with cutting an octagon out of a square.

8*45=360. Since cutting 1/3 width off at the corners creates 2, 45 degree angles, you need only rotate the piece 90 degrees 3 times and cut after the first 45 degree cut.

[Leon]

Actually you want the 45 degree bevel to begin at 1-11/64" from each corner, leaving 1-21/32" in the center for actual 4x4.

[GrayFox]

Because when the blade is tilted at 45 degrees, the diameter of the blade is not big enough to reach thru the top of the 4" square cross section.

[GrayFox]

I probably didn't really make myself clear on my setup. My table saw blade tilts to the right and my fence is on the right.

Perhaps I'm missing something, but if I try to run the stock through the table saw and cut off the lower right corner of the cross section, that seems like an extremely dangerous cut to make. The cutoff piece would be against the fence.

If I can move the fence to the left side of the blade, it would be a much safer cut. But, I don't think I can do that. :(

[DJ Delorie]

If you have eight sides, you have *sixteen* cuts (two on each board - one at each end). Divide 360 by 16 and you get 22.5.

Plus, the angles of a polygon do not add up to 360. They add up to

180(n-2) where n is the number of vertexes. The *bevels* add up to 360, with '0' meaning unbeveled (square cut end).

[Leon]

OK, that makes much more sense. Most right tilt saws will let you move the fence to the left side of the fence 8-12" and that would be the way to do it.

Or use a 45 degree chamfer bit on a router.

[Robert Haar]

Personally, I wouldn't sue the fence in that situation, at least not having the work piece running continually along the fence. I would use either a miter gauge with an extension fence and a stop block to get the length, or a cutoff sled. If you want to use the fence for position, I would add a temporary fence piece that is entirely in front of the blade. Hold the work against the miter gauge with the end touching the temporary fence and then move through the cut. As you bring the work to the blade, the cutoff would no longer be against the fence and there would be less chance of it binding up.

[Markem]

Do you have access to a bandsaw with a fence? Or perhaps a new tool is needed.

Mark