Ronn W

Octagonal table

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Planning an ocatagonal table about 24" across.  Center will be veneer on plywood and will be cut to an octagon after veneering. I want to then frame the octagon with solid wood.  I can just imagine the headaches 1) cutting the center to a perfect octagon and 2) getting the 8 mitered corners of the frame to fit perfectly.   If I can do #1 perfectly then I can probably do # 2 but it would have to be perfect.  If I am a little off with #1 then #2 becomes a matter of cutting as many a 16 very slightly different angles to get the miters to fit.  AARRGH!

How would you go about constructing such a table top?

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This isn't going to help at all, but I think that table top would look great if you put the veneer on in pie shaped segments. Coarse, that opens another whole can of worms.

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1 hour ago, drzaius said:

This isn't going to help at all, but I think that table top would look great if you put the veneer on in pie shaped segments. Coarse, that opens another whole can of worms.

 

I agree it would look great.  I can do the  pie shaped segments and that is one of the options that is being considered -  16 pieces.  I can do that with the caveat that due to the fitting process, the segments will not be exactly 22.5 degrees each - they will be very, very close but joints between the veneer segments may not intersect the corners of the octagon perfectly or, if I cut the octagon so they do intersec, it may not be a "dead on the nuts" perfect octagon.

But back to my original question:  How would one go about constructing such a table top?

 

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I had to make an octagon and it was a PITA. Octagon in 4 steps using a strait edge with a center scale. You could use a regular ruler the center part might just be a bit more challenging. I made a drawing to go with the 4 steps.

1. Draw a circle the diameter you want the corners to be from the center of the table. Next put a cross through the circle meeting at a perfect 90 degree angle. I did this by putting the circle in the center of a square piece of material then used a square to get the perfect 90 degree.

2. Draw a line from the points where the circle meets the cross to each other. Make sure to mark the mid point of these lines. Draw a line from the center of the circle to the midpoint of this line. Lines are shown in red below.

3. Draw a line from where the red lines intersect the circle. Make sure to mark the center points of these lines as well. They are shown in cyan below.

4. Draw a line from the center of the circle to each of the mid points of the cyan lines making sure to extend them all the way across to cover the whole circle. These lines (green below) will be the corners of your octagon. If you want to draw the edges of the octagon just connect the points where the green lines intersect your circle all the way around until it closes into a perfect octagon.

Drawing1-Model.thumb.jpg.553919f07ffa4f99b0eb7602743a2cac.jpg

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Thanks, Chestnut but drawing and octogon is the easy part of this. Imagine another concentric octagon 1 1/2 inches outisde of the one you drew - that will be the frame. I need to figure out how I am going to cut the miters and install the 1 1 2" wide frame that goes around the 8 sides of the octagon.  I am assuming that the octagon will not be perfect. In other words, if I were to cut all the miters for the frame at 22.5 degrees I would not get a perfedt fit at the miters.

How would you build the frame to get perfect miters?  What process would you use?

Here is an example of table with frame around the octagon.

282250-438x.jpg.e5649159dedb73a0878458b1e4baa380.jpg

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Ooohh i misunderstood. Would it work to make the frame and find some way to hold it together to scribe the octagon on the table surface and then assemble it around after you cut it out?

 

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I thought about building it "inside out" as you suggest.  I didn't see how that would be any more accurate in that it moves the problem from the miters to the mating of the octagon with the frame.   When I was looking for the sample photo that I showed I did not find many pics of octagons with frames - maybe there is a good reason for that.  I have been plying with the idea of making a sled (similar to a 45 deg miter sled) where I would use the octagon to position the right and left wood fences, clamp them with toggles, remove the octagon and cut the right a  left frame pieces for each corner.  I can use each corner of the octagon, in turn, to get miter cuts specifically made for each of the 8 corners.  Sounds like a lot of work for a one time project but it just might solve my problem. or not.  I ahve been drawing it up on with cadd to try to think it through.

 No one else here has ever tried this?????   Maybe, as I said, there is a good reason why not.  I will have a lot of work into the veneered octagon before getting to the frame part of the project so I will have to know for sure that I can do it before I start.  Learn something new with every project.

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Why don't you veneer the frame. Is there any reason you can't make that work? Do a thickened edge with the substrate and veneer the look you want. You are already most of the way there with the rest of the top. I swear frames always end up moving slightly and making the perfectly fitting seams gappy anyway.

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I have 2 ideas. Both are a bit unorthodox.

Idea 1: Find a CnC company. Or a Sign Shop or a Custom Cabinet shop, most of these companies have a CnC. They can cut you a perfect octagon. Will take them 30 or so minutes once they can cram it into their production schedule. If you lived in my area I would do it for you in my shop.

Idea 2: Steal a STOP sign. Flush trim router the octagon from the stop sign. Replace the STOP sign. STOP signs in residential neighborhoods are 24". STOP signs on busier roads are 36"

Either of those ideas would give you a perfect octagon with perfect angles. Which I think would help in making the frame?

 

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I think you're psyching yourself out.

Construction of the octagon using the method illustrated will get you a very precise shape.  Mark it on the ply with a knife, and use a block plane to sneak up on the lines.  

For the "edges", your shooting board is your friend.  

Once you have the frame made, rabbet one edge.  Drop the ply into the rabbet.  You can always fill any gaps with epoxy, but if you were careful with the block plane, I don't think you will need to.  Then, get to work on the veneer.  That's something you can really sneak up on.  

I know that's easier to write about than to do it.  Practice your shooting on a less expensive wood, and you'll get the angles right.  The other option would be a picture frame shaver, but that seems like an expense unless you plan on doing a lot of miters this size.  A dedicated 22.5 degree shooting board should be a simple thing to make, at least in comparison.  

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2 hours ago, Coyote Jim said:

Idea 2: Steal a STOP sign. Flush trim router the octagon from the stop sign. Replace the STOP sign. STOP signs in residential neighborhoods are 24". STOP signs on busier roads are 36"

Don't need to steal them make friends with a public works employee for a smaller size community and he'll give you all the signs you want for free. They tend to get weathered to the point where they need to be replaced after 10-15 years. They should have a stead inflow of scrap signs.

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I would think they would recycle the aluminum or does the sign graphics greatly reduce the number of places that will accept them ?

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On 10/2/2018 at 11:52 AM, Coyote Jim said:

I have 2 ideas. Both are a bit unorthodox.

Idea 1: Find a CnC company. Or a Sign Shop or a Custom Cabinet shop, most of these companies have a CnC. They can cut you a perfect octagon. Will take them 30 or so minutes once they can cram it into their production schedule. If you lived in my area I would do it for you in my shop.

Idea 2: Steal a STOP sign. Flush trim router the octagon from the stop sign. Replace the STOP sign. STOP signs in residential neighborhoods are 24". STOP signs on busier roads are 36"

Either of those ideas would give you a perfect octagon with perfect angles. Which I think would help in making the frame?

 

Steal a stop sign???????? You vandal you!

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On 10/1/2018 at 7:21 PM, Chestnut said:

Why don't you veneer the frame. Is there any reason you can't make that work? Do a thickened edge with the substrate and veneer the look you want. You are already most of the way there with the rest of the top. I swear frames always end up moving slightly and making the perfectly fitting seams gappy anyway.

A good idea.  in effect that woudl be the same as veneering the whole top and then cutting the 8 sides so that the corners coincide with the joints of the veneer at the corners. Fairly easy to do and it does not matter if the octagon is not perfect since know one will ever know.  I can then veneer the edges and it will look great - if I want a square edge. But if I want a rounded or routed edge (like an ogee)  I have to have a solid wood frame.  I don't yet know how the edges will be treated since we are still in the design phase.

The underlined phrase above is the key to understanding the problem since when you do a pattern of veneer, you start at the center and work your way out. Even if joints look perfect the overall dimensions and angles can be a little off and locations of the corners of the veneer octagon can be a little off.  This is especaily true if you are creating an octagon with 8 or 16 triangles that meet at the the center point.

I am waiting for some toggle clamps that I ordered to make a jig so I can practice on some MDF to see If my plan works.

I do appreciate your input.  All of you.

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