# How do you make an octagonal shape



## TJ65 (Jan 19, 2010)

Ok, I am planning to do another project that requires a little more from me and once again have not done anything like it before.
Anyway as my husband is seriously getting into trains he thought it a good idea since I had finished with all the xmas presents that I should make him a clock. But he wanted it to resemble a station masters clock or regulator clock. 
Now my problem is- how do I go about making the octagonal sides for the clock face. Is there a correct angle to cut them at? and how do I go about joining it all together once cut, is glue enough or is there something better that I should try/use
Thanks

Similar to these-


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## LoneTreeCreations (May 27, 2010)

You're way too nice to him. That's a lot of work, but a great learning experience. As Bentlyj said, it's 22.5 degrees for the cuts and I would try to biscuit or dowel joint the parts to add strength. The frame around the clock face really isn't going to have any stress on it as the clock is going to hang from the back panel.

Good luck and have fun with it. I'd look for a pattern to work from as well.


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## bigike (May 25, 2009)

wow i got some info from this question posted, thanks bentlyj. I never thought of breaking it down like that.
I would have just said 22.5.


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## Vintagetoni (Jan 10, 2011)

At first I thought splines might be nice in the joints….but I was thinking the case itself was the octagon shape. It appears its just a face & it already has a profile to it….not such a good spline application. Sorry….can't delete this comment.


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## richgreer (Dec 25, 2009)

To get the angles right consider the following. Make 2 squares (hardboard, plywood, cardboard, whatever) of identical size. The distance from corner to corner across the middle should the same as the distance from opposite corners of the desired octagon. Put a nail or screw through the exact center of the 2 pieces. Rotate one board 45 degrees. The resulting position of the corners will be the corners of the octagon.


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## ahohnstein (Jan 12, 2011)

Tommymac had an episode on an octagonal lazy Susan that had a jig basically as Rich mentioned. Worth a watch as it may give some ideas.


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## David175 (Jan 14, 2011)

Google this….. Segment Edge Length Estimation Table…... and it will give you everything you need

it will give you the angle and the length for any 360


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## TJ65 (Jan 19, 2010)

Wow thanks heaps guys. 
Even I understand that lot! (My mathematical skills have a lot to be desired)
But that idea about working with the squares are great.


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## mosaicwes (Sep 14, 2010)

My first question would be, what are you using to make the cuts?
Depending on what material you're cutting and the quality and sharpness of the blade etc.,
I've often found it a challenge to do without any blade deflection, on a miter saw.

My choice would be to build a sled, to run in the table saw grooves 
and create a 22.5º cutting angle on both right and lefthand sides of the blade,
so that all cuts can be made thru the face side of the material.

Is that too vague? I'm sure we could clarify if you're interested in going to the trouble.
Yes it's a bit of a hassle, but if you go to the bother, you'll have a jig that will always cut perfect octagons
for the rest of you're woodworking career without having to give it a second thought.


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## DanLyke (Feb 8, 2007)

When I did my 12 sided plate frame, I went a step further: I cut the pieces out, glued them together to make two halves, and then clamped them solidly so they would hold together and ran a saw through the middle of the joint to make sure that the joint exactly matched up. (I use a track saw rather than a table saw, although with careful clamping you could do this on a cross-cut sled.)

This may actually be harder to do with the 8 sided shape rather than the 12 sided one, because that cut will be diagonal and take off just that much more off of one of the diagonals. But I figured I'd mention the technique.


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## mosaicwes (Sep 14, 2010)

Cutting through to get a perfect joint has lots of good applications in woodwork. 
Especially hand when the angle of the cut doesn't need to be an exact division.


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## peteg (Sep 2, 2010)

Hey Theresa, my head is spinning also, I just want to see the end result, &, a big thank you from your man, youv'e got to have some brownie points with this one plus a free ticket on the next train.  good luck from Pete


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## TJ65 (Jan 19, 2010)

My choice at this stage for cutting is to use the bandsaw (as I dont have a tablesaw) . As I found with the mirror frames the blade does deflect a bit so I refined the angle on the sander and really made sure that the angle was perfect using the guide. 
Can I cut through the joint without having a tablesaw? (you mean like adding a spline??)


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## mosaicwes (Sep 14, 2010)

By cutting through the joint we mean making both sides of the cut in one pass.
Joint the pieces temporarily, cut straight through both of them at once so there's an exact match.

Band saw and sander will work it'll just be a little trickier. (I'd cut a few extra pieces just in case


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## bobsmyuncle (Jan 12, 2011)

The other question is "how long to make the sides?"

Here is a compass and straightedge method to determine an octagon:

- Draw a square the size that will enclose the octagon.
- Draw diagonal lines from the corners. The point of intersection is the center of the square.
- Set a compass at the distance from one corner to the center.
- Scribe the distance from each corner to both adjacent sides
- Those points of intersection will be the corners of the octagon.
- Measure the distance along any side.

There are more complicated ways if you don't start with a square


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## secureplay (Jun 3, 2010)

The real question is how do you want to build it? As noted above, the internal arcs are each 360/8 = 45. The other 2 angles for the triangle are the same, so they are each 45+2*x = 180 or x = 67.5.

If you were cutting an octagonal shape with a bandsaw or scroll saw, you would probably draw a circle of the appropriate size and use high school geometry to divide it into 8ths and cut carefully as noted above.

Once you've drawn the circle with the inscribed octagon, use a straight edge to check that all of the sides are the same length as you walk around the circle.

If you are using a table saw or miter saw to cut octagonal segments, measure carefully and cut the opposite segments "stacked" so that they are identical, if possible, and then adjust:

If you count the segments around the circle 1 through 8:

First make:
Segments 1, 5
and then
Segments 3, 7

Fill in to fit Segments 2,6 and Segments 4,8

The problem is definitely different if you are using molding, cutting a segment, or cutting out an entire octagon.

After all, the most important thing is a tight fit, not a perfect octagon.


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## BertFlores58 (May 26, 2010)

It is easier to use a miter saw. I first cut the exact width with a Japanese saw (because the kerf is hairline). Then cut it on the sliding compound miter saw (setting it to half of the angle… in your case 22.5 deg) just right where cut reach the edge of the wood (outer side). This way I minimized the tearout if I cut it directly to the miter saw…. of course… kerf waste will destroy the design.. Here is the photo to prove it…










Hope this help. Bit late.


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## TJ65 (Jan 19, 2010)

All help is needed Bert. 
At the moment it is just a plan and with any luck, it will turn into a project!!!


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## dpwalker (Aug 25, 2010)

Theresa, I have an article from Woodsmith magazine called The mathematics of Miters. It gives a pretty good explanation of miter angles. I'd be happy to share it if you'd like it.


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## tswoodwizard (Jan 13, 2011)

Theresa ;this sounds like a great way to get a new table saw out of your man.


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## MTay (Jul 1, 2011)

Hi,
I am new to woodworking. I tried making the octagon shape out of crownmolding, however it came out with six sides instead of eight.

I cut the bevel and the angle at 22.5, but I was also cutting the molding laying flat on my compound miter saw.

What am I doing wrong?

Please remember I am totally new to wood working. The crown molding I am using is 6". I am try to make the center opening 20".

Any help would be appreciated.


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## Loren (May 30, 2008)

MTay:

The miter saws will usually have markers for two types of
crown moulding: mouldings with a "spring angle" of 52 degrees
and those with a spring of 45 degrees.

To cut moulding on the flat, you have to figure out what the
spring angle of your moulding is and set both the miter and
bevel of the saw to the markings for that spring angle. Many
saws have markers or stops for both spring angles. As a practical
matter the miter stop is usually pretty accurate, but the bevel
takes a bit of fiddling with test cuts.

Try not to run through too much good moulding while figuring
this stuff out. I sometimes make a flat board the same width as
the moulding and duplicate the spring angles on the table saw
so I can get the saw set up precisely.

This all may strike you as very fussy and it is. I recommend coping
inside joints because really, it's not that hard and it can be less
frustrating than trying to miter inside mouldings. The outside
corners you have to miter, but always leave yourself room on
the ends of the moulding to make mistakes and get the outside
corners right.

Here's a chart of miter and bevel angles for cutting crown and other
useful tips besides:

http://www.installcrown.com/Crown_angle_generator.html


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## buckles (Jun 10, 2011)

TJ65
I build parts for wooden clocks. I have a CNC machine that produces extremely accurate parts at reasonable prices. I am retired and don't have much overhead so I don't have many expenses to cover.
If all else fails, PM me and I will make as many or as few parts as you want. They can come assembled or separate. Guaranteed or money back
Regards
Joe


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## horologist (Feb 29, 2008)

Lots of good advice on cutting the octagonal portion of the case. 
However, before you cut any wood you want to have the bezel, dial, and movement in hand. If you are using a quartz movement it isn't as critical but if you are using a spring driven movement then it is important to size the case accordingly. The case must be wide enough to accommodate the pendulum swing and deep enough for the depth of the movement. Ignore this if you already have these things covered.


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## ArlinEastman (May 22, 2011)

I agree with tswoodwizard 
Time for him to get you a table saw
Arlin


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## Jim Jakosh (Nov 24, 2009)

I bet this program will help you make perfect shapes. Just click on Imperial under the shape you want!

https://www.blocklayer.com/polygon-templateseng.aspx

cheers, Jim


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## bondogaposis (Dec 18, 2011)

If you can draw a square then you can draw a perfect octagon. Just draw the diagonals to find the center then swing an arc from each corner passing through the center and where the arcs intersect the square are the corners of the the octagon.


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## pontic (Sep 25, 2016)

4/8=45/x solve for x =22.5
4/6=45/x solve for x=30
and so on.


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## ColonelTravis (Mar 19, 2013)

Just FYI - this question was asked 7.5 years ago.


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## AlaskaGuy (Jan 29, 2012)

> Just FYI - this question was asked 7.5 years ago.
> 
> - ColonelTravis


I guess it's time it got answered then…...............


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## ColonelTravis (Mar 19, 2013)

Ha


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## TJ65 (Jan 19, 2010)

Well you just pipped me at the post. You are correct at saying that I asked this 7.5 years ago. 
Sadly I never completed my idea but if I remember correctly, I did successfully make the octagon shape.


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## therealSteveN (Oct 29, 2016)

First I'm going to say get some cheap wood, and do a prototype, or 3 so you get a feel for this. I'd say start it bigger than where you want it to be ultimately. IF you make a goof, cut it down and make it smaller. 2, 3, 4, 5 for 1 pricing.

Ok gonna take you to left field, just give it some thought.

The following video is cutting an Octagon on a TABLE SAW. I know you have a BAND SAW. Think about this. Both saws have a blade that cuts wood. Both saws usually have a miter slot where you can use a miter gauge, which helps hold a piece at a solid angle as you move it through the blade. Your biggest difference is doing it on the right of the blade, where most people on a TS do it on the left side. Not a deal breaker.

Probably more videos than this on making an octagon. Most of them will be using a table saw. That's inside the box thinking, I'm usually outside the box.

One day I'll read more than the question….........LOL.


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