Jesse Eisenheim

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since May 28, 2020
Naturalist, gardener, amateur builder
Western Mass
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Recent posts by Jesse Eisenheim

Thanks T Hayden, I'm going to try this on a sort of model first, so I will give that a try.

I see what you mean Rufus, but unfortunately I have no way of getting my logs milled other than square. I would think laying the cuts out with pencil ahead of time should be enough? I use Sketch-up to help me get the angles right.
It seems to me that placing the beams on top of the posts makes uncomfortable joints. So, I'm trying to figure it out with the beams hanging off of the sides (such as in the diagrams). This brings up a problem of tension though, as if this were a square structure I could use a wedged half-dovetail joint - is there something similar for a 135 degree angle instead of 90? The diagrams show two different possible joins.
This is very helpful T, thank you. It is so hard to find anything about octagonal timber frame structures. Any sketches would be excellent - I try my best with Sketchup but I realize there are simply geometries I don't have in my head yet. I did work up something new for the top joinery based on your suggestions - is this the sort of thing you were talking about? Are the two joins not too close to each other?

You are right about my foundation beams, I was trying to make a short piece for the bend. I guess lapping is ok on the sill, which makes sense now that I think about. I haven't worked shoulders into my designs yet, but yes I plan to put them on the braces. Now that I think of it I was planning to flatten off the bottom of the brace tenon. I included a closeup of a brace join (without the shoulder or the flattening) since it was a little messy in my first diagram.
Mike, that is basically what I am suggesting, with a similar method to connect the post to a sill on the floor.

T, thanks for the advice, after doing some research it does seem easier to me than I thought. I have found many examples of plans out there. However, this octagonal structure seems hard, and I have found no plans that could help me make my own. Do you know of a place where I might be able to find something like that? Even a place with info on the joints I would need. I was playing around in Sketchup and came up with the following (attached), but I don't know if this is a good joint or not, for example.
I wonder if instead of inserting one large dowel I could use two smaller pegs. I would think that would decrease the chance splitting and prevent rotation?
Hi folks,

I am designing an octagonal cabin about 12' in diameter from corner to corner. I have a bunch of red oak and would like to build a timber frame, but I am intimidated by the process of making mortises and tenons - I don't have much experience with chisels and making 24 mortises (using lap joints) and 16 tenons seems beyond my capabilities.

Instead a friend suggested I use dowels - essentially drill holes into the post ends, the lap joints of the beams, and the floor, and use these to hold everything together. However, he wasn't really sure of what sizes everything should be. He thought maybe 1" dowels would be enough. I plan to use 5x5 posts and either 6x6 or 4x6 beams. There will of course be braces as well (4x4s), and the roof will be evenly octagonal with 8 3x5 rafters. I am getting the lumber rough cut so these will be true sizes instead of nominal ones. It will be green as well

Does anyone have any experience with building in this way and/or know of a guide to do it? I am most interested to know how wide the dowels should be and how deep they should be inserted. Thank you!