please help this dummy build a table top . i need a 24" octagon with a skirt. the angle to cut the skirt has me way off. looks good first 3 cuts then nothing else matches. please what is the angle and do i do this with a speed square?

should be 22.5deg the speed square will give you the angle, but not a very accurate tool to lay out the cuts you are making. what tools are you using to make the cuts?

chop saw or miter

please help me figure out how long each side should be when cutting the top.
thank you so much for your help

An octogon is a regular polygon, ie, the sides aare equal length and angles are equal. There is a general formula for finding the angle of regular polygons. Angle equals (the number of sides minus 2) times 180 degrees divded by the number of sides or angle = (n - 2) x 180 / n.

Plug in your values result equals 135.

Miter is 135 / 2 or 67.5.

Set miter box to 67.5 if square equals 90 on saw or set 22.5 if square equals 0.

try this; http://www.tfguild.org/ubbcgibin/ultimatebb.cgi?ubb=get_topic;f=4;t=000082

antlers:
if you checked out the thread which Roger mentioned, there is a method I wrote about using an octagon scale on the stanley square. If that method makes sense to you, I just set my dividers to the octagon scale at 24, and that measure is darn close to 5 inches...

" i need a 24" octagon with a skirt. please help me figure out how long each side should be when cutting the top.
thank you so much for your help"

Antlers'

With the 24" Octagon to figure the sides you can do this:

(Width) X (22.5 Tangent)

24 x 22.5 Tan = 9.941126" or 9-15/16"

All eight sides are 9-15/16" to the long point of 22.5° saw setting.

Unless you are trying to make an octogon which is 24" from point to point (22 11/64" flat to flat), then your sides are 9 3/16".