Easiest Way to Make Octagons for Wood Turning. NO MATH OR MARKING! YAYY!




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.

Teacher Notes

Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.

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!

Step 2:

Now is the "tricky" part where you really should have made sure the saw is absolutely de-powered. 
Lie your square blank up against the blade so it lies flush against it. Don't push or lean on it, just set it up flush against the blade up on one corner. 
Then, slide the fence in so its flush against the corner of the square. Lock it down.

Wallah! That's all the measuring done. Now you're set to cut the blank. Remove your block and re-establish all safeguards and power to the saw.

Step 3:

Now time to cut! Observing all safety steps, go ahead and slide your blank through one corner at a time until all four corners have been chopped, and you will have a perfect octagon, no measuring involved. 

I used a feather board, helped keeping that stray chunk of corner from skipping around and kept the blank nice and tight against the fence. Just be careful where you put your hands, as that blade does come out the left side of the block when cutting the corner. Use the push stick if you want to.

Congrats, now turn some wood!

I made it at Techshop!

1 Person Made This Project!


  • Made with Math Contest

    Made with Math Contest
  • Cardboard Speed Challenge

    Cardboard Speed Challenge
  • Multi-Discipline Contest

    Multi-Discipline Contest

14 Discussions

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.

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.

For those advocating skipping this step. There are two good reasons for being able to make octagons:

1) For most basic boats, you don't even need to round it; just plunk it in the partner and go.
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.

Thanks again for the great ible!


6 years ago on Step 3

Since I don't like turning a square, I love this idea and will use it. Thanks!


6 years ago on Introduction

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.

4 replies

Reply 6 years ago on Introduction

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.


Reply 6 years ago on Introduction

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!


Reply 6 years ago on Introduction

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.

It's probably more useful with wider pieces of wood.


Reply 6 years ago on Introduction

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!


6 years ago on Step 3

It takes less time to just turn the square into a round on the lathe, no cutting required.


6 years ago on Introduction

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!