To turn a long piece of square wood into a shapely cylinder on the wood lathe, first your going to have to chop off the corners and turn it into an OCTAGON. 
Now, I remember most of my high school trig and know a few ways of marking off corners and measuring to get that perfect octagon from a square, but oh the cosines and tangents and finding a pencil and ruler is such a bore!
Here's the absolute easiest way to do it on a table saw with an angle adjustment, like the one at San Jose Techshop.

Step 1:

Firstly, before you do anything, MAKE SURE THE SAW IS OFF! Unplug it, take out the key, do whatever you have to to ensure it cannot go off while you are laying things out. 

Go ahead and tilt the saw to a 45 degree angle. All the way over!
<p>thanks for the information on how to cut an octgon out of a 1.5x1.5. it worked out great. but four sides came out 3/4 and four sides came out 5/16. what did i do wrong.</p>
cool !
Wow - this is an awesome technique. I wish I knew how to do it when I butchered my mast in the attempt - it is now a rather ugly misshapen thing (it does the job though :) ). Now I'll be able to do better next time. <br> <br>For those advocating skipping this step. There are two good reasons for being able to make octagons: <br> <br>1) For most basic boats, you don't even need to round it; just plunk it in the partner and go. <br>2) For those of us without a lathe - this is a godsend. There is a technique for rounding a mast with a belt sander - mount the mast in-between saw horse grids as if it was on a lathe; then hold the belt sander on angle and let the whole thing spin - a round mast results shortly thereafter. If you try this technique on a square pole, you are in for trouble. On an octagon - no problem. <br> <br>Thanks again for the great ible!
Since I don't like turning a square, I love this idea and will use it. Thanks!
This is a great trick to get a perfect octagon. Why not just turn the original square piece though? You can carefully take off the corners with a gouge if you take it easy and do just a little bit at a time and keep a firm hold on the tool. This may be a little bit safer but seems like it would take a lot of extra time.
I'm admittedly still pretty new at turning. I've seen people start with a square blank, with better tools than I have, and more experience, but octagons are easiest for me right now. Setup and cutting 3 of these took 5 minutes tops.
Come to think of it, I think I recall learning to turn starting with an octagon many years ago too. Carry on and ignore me. :-) Nice Instructable!
That's how I learned it too, but now I don't remember learning why it should be done. I've done it out of habit ever since without giving it another thought. <br> <br>It's probably more useful with wider pieces of wood.
When you start square, its a bit scarier and bumpier in the beginning, not to mention, if your tools are dull you can get massive tear out i have seen entire corners get ripped off and thrown across the shop. Just use caution and more important common sense in any and all cases... Happy turning!
Ew sweet, I'll be using this tip. Ty!
It takes less time to just turn the square into a round on the lathe, no cutting required.
<br>I'm with you! Measuring isn't always the best way. <br> <br>
Very useful info, thanks for sharing it.
I've used the blade-angle trick to shave decorative (i.e., non-precision) bevels onto corners, but didn't know the trick to make them exact. Good instructable!

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