What's the best way to make the top and bottom of an octagonal box flat?

[Alan Lightstone]

I'm wondering what's the easiest way is to do this. I've built an octagonal box for a friend. The top and bottom are not attached yet, so it's an octagonal box about 12" in the long axis made of 1/2" hardwood.

I need to make the top and bottom perfectly flat. It's the edges not the faces that need to be leveled.

What's the best way to do this? I have a fairly wide selection of planes, jointer, planer, table saw, shooting plane and boards, even a Flatmaster sander (which I initially purchased for this sort of job, but find it difficult to keep things flat using it.)

[Jamie Buxton]

Can you come up with a piece of plywood that is flat enough for you? If so, cut a hole in it that is the footprint of the box. Put the box in the hole. Turn the whole thing over and add blocking to set the ride height of the plywood just below the edges of the box. If the box deforms or rocks when you put pressure on it, you might add shims to stop that behavior. Old credit cards or old business cards are good shims. With a hand plane, remove any bits of box that are proud of the plywood. Mostly ride the body of the plane on the plywood, with the blade running askew along the box edges.

[Andrew Hughes]

If your asking what I think my solution that I use for boxes I make is to glue some sand paper down to my granite surface plate with some light spray adhesive.Then pencil Mark the edge before rubbing the surface flat.It may take several sheets to get the length so don't cut your self short.Thats my guess from 2000 miles away.Aj

[Reinis Kanders]

I normally use handplane for rectangular boxes to make bottom edges flat before gluing to the bottom panel. You just basically ride plane on edges and go in circles and skew the plane to 45 Deg when transitioning on corners. This puts bottom edges all in the same plane.

[bill kaminski]

If I had one, sadly I do not,I would use a lathe. Perhaps you know of one large enough.

[Mike Henderson]

If your asking what I think my solution that I use for boxes I make is to glue some sand paper down to my granite surface plate with some light spray adhesive.Then pencil Mark the edge before rubbing the surface flat.It may take several sheets to get the length so don't cut your self short.Thats my guess from 2000 miles away.Aj
I do a similar thing. I have some sandpaper from a big machine sander. I glued that down on MDF - different grit on each side. When I need to flatten something like a box. I put the box on the sandpaper and just move the box around. The sandpaper will eventually get a flat surface on the box.

Mike