Turning tall bed posts in sections- question

[Rob Price]

Working on a loft bed for my daughter, basically a bunk bed without the bottom bunk so we can use the space under it for a dresser/desk. The posts will have a bun foot at the bottom, then the rest of the post will be about 80" tall turned in two sections. My question is about the joint between the two sections. I could turn a tenon on one end of the bottom piece and then drill a mortise on the top piece, or drill a mortise in each piece and use a floating tenon/section of oak dowel in between. I'll be starting with 4x4" posts. The joint will be at a ring in the middle of the post.

Any thoughts on the ratio of the tenon to the overall width of the piece?

I attached a schematic of what I'm thinking. There will be a bottom stretcher it's just not in the model.

[Dennis Ford]

I recently made a couple of tall bed posts for a customer. They were taller than your plan and required three pieces each. I used 1-5/8" x 3" long integral tenons for both the lower and upper joints. The mortised end was about 4-1/2" diameter for the lower joint and about 3-1/4" diameter for the lower joint (there is no load on those joints other than the weight and inertia of the posts). Had they needed to support a bed and person in that bed I likely would have turned the job down.
My concern with your plan is the side load on the joints from someone moving around in the upper bed. If one side of the bed will be near a wall; some bracing on that side would be a good idea.

[Rob Price]

It will be braced/tethered to the wall. After looking at commercially available bunk beds I feel pretty confident that 4x4 (true 4" hardwood posts- not nominal pine posts from the hardware store) posts will work. The bunk bed that I grew up on was turned 4x4 posts. We bought a bunk bed several years ago and it's 2x4 'posts' joined with a floating 1/2x2" oak dowel. And it's held up well. As this is a bit taller than most we will be securing it to the wall. There will be two beds at a right angle to each other and attached to each other as well.

[Rob Price]

I should clarify. True 4" posts, not nominal pine posts.

[John Keeton]

Dennis is about right on his measurement. In furniture construction, the tenon is typically 1/3 the thickness of the receiving member. In your case, I would make it at least 3" long.

You didn't ask for comments on the design, but the legs are the only round elements in this project. Were it me, I would leave the posts square, and have lower and upper square caps on them. Or, turn all of the balusters in the top elements.

But, it isn't my project.

[Mark Greenbaum]

When I was a kid (pre-Jurassic Period) I had a bunk bed setup that had a 1/2" diameter steel rod x maybe 5" long driven into the bottom of the top and slid into the top of the bottom leg portions. It precisely aligned the top half to the bottom half of the legs, and I am sure because it only removed a 1/2' of the maybe 3" diameter wood, it left the wood structure intact, and in shear and torsion it survived about 10 years of me growing up. If you never needed to disassemble it - epoxy it in place.

[Lloyd Butler]

My first thought was much like Mark just suggested, but I was thinking all thread of that size. Drill the hole in the end of the blocks to turn and use a cone in them to support it while turning to keep them centered. Then screw in 2.5" to 3" of thread in one side and the same in the other with the hole snug on the threads.

[Rob Price]

I like the steel rod idea. that could work. Thanks.

[Rob Price]

I've got a ways to go, but the steel rod idea was perfect. Dry fit of the first headboard:

[Rob Price]

Only one pic per post from the phone I guess. I drilled the hole first on the lathe with a Jacobs chuck in the tail stock, then use a 60 degree cone live center to turn them and the posts end up centered on the hole. After I asked this question here I saw where Rockler sells pre cut steel dowels just for this purpose. I bought a 4' steel rod and I'm cutting my own.

[James Combs]

Dennis is about right on his measurement. In furniture construction, the tenon is typically 1/3 the thickness of the receiving member. In your case, I would make it at least 3" long.
You didn't ask for comments on the design, but the legs are the only round elements in this project. Were it me, I would leave the posts square, and have lower and upper square caps on them. Or, turn all of the balusters in the top elements.
But, it isn't my project.
Like John says "it isn't my project" but if it were me and I decide to make the upper balusters round and being more or less the lazy engineer I am, I would just go to Lowe's and pickup a bunch of what ever size Poplar dowel rods(the bed looks like Poplar) I needed and just cut them to length and drill holes for them and be done with it.:D

[Rob Price]

I haven't completely decided. If I go round I'm buying dowels. With two beds to make I just don't have the time to turn intricate details on every one. If I had unlimited time I'd turn each one with a ring in the middle to match the legs. I also thought about getting some stair balusters and cutting those to length.

Right now I'm leaning towards taking a long piece of stock, detailing each corner with a bead bit on the router table like in this pic, cutting to length and calling it good. I have a few sizes, I can make them nearly round at the router table.