circular table from octagon-related question

[Stan Calow]

I was following the discussion in the Off Topic forum on calculating lengths for sides in an octagon. I have in my list of projects, a round table with a center glass insert. I had been thinking I would make an octagon first then round the outside and inside edges. I anticipate the width of my pieces to be about 4". How do you account for wood movement at the joints between the sides? I see miter joints on frames opening up on frames from seasonal shrink/swell. Am I missing something or is there a better way to do this?

[Lee Schierer]

I made an octagonal table with a center glass insert more than 10 years ago. The frame supporting the glass is octagonal inside and outside of the glass. There is very little seasonal movement because the frame width at the joints is only about 3-4" wide. If the outside of my table frame was round, the joint areas would still be relatively narrow. Note, each joint was reinforced with a spline for added strength. The grain of the spline was aligned across the joint, not length wise in the joint. No joint separation has ever occurred.
octagonal table.jpg
However, IF you made the entire center solid wood, in which case you would likely have problems with seasonal movement.

I also made a lazy susan from segments of red oak.
oaksusan.jpg
As you can see, the grain runs tangential to the circumference in each quarter segment. This lazy susan has not faired well over the years. The joints have opened several times.

[Stan Calow]

Thanks Lee. I have picture frames around 4" width that open up on the outside corner seasonally, so thought it might be an issue.

[Lee Schierer]

Thanks Lee. I have picture frames around 4" width that open up on the outside corner seasonally, so thought it might be an issue.

One thing that I learned a number of years ago. Miter joints are essentially end grain. As such it is wise to coat both sides of the joint with glue. This lets the end grain suck in some glue and makes for a considerably stronger joint. Try it on some scrap and see if you don't agree.