We are working on a project that will require several hidden right angle connections of 6/4 soft Maple, approximately 6-7" wide, to 3 1/2" steel box tube. Something similar to a bed frame joint (steel tube being a post and Maple being a rail). These need to be able to be field assembled/knocked down. We'd rather not have to drill and tap the steel tubes so hoping for something we could attach via riv-nuts or similar for the steel side. Soft Maple end grain connection would be mortised and whatever fasteners needed.

Been considering using bed brackets (Selby) and have also looked at Knapp Duo (wont work due to the steel), and Star Hanger 300 green glide but Im concerned with the press-in issue with the Star Hanger. They are rated at #160 pull out but thats in PB not solids and we really need a mechanical connection on both sides of the joint to be comfortable. We could run multiples of the Star Hanger but Im still concerned with the press-in and pull out over time without a mechanical fastener.

This scenario is literally just like a bed frame connection and requires strength in vertical (shear) and pull-out (racking of the joint).

The Selby brackets seem about the best option at the moment with the rivnuts in the steel and embedding the entire fastener in the wood member.

Also looked at a product "Striplox" available through Richelieu but a fastener small enough to be concealed in a 6/4 member only looks to have 3 fasteners in plastic and gives the same concern as the Star Hanger.

If anyone knows of a good totally concealed (hidden) option it would be appreciated.

Could you weld a 2”x1/2” rod onto the steel, drill a hole in the endgrain of the maple to slip over the post, then drill and tap a perpendicular hole to thread in a machine screw?

Thanks Nate,
Avoiding any welding/fabrication (liability) and we were moreso looking for an off the shelf option.

Thanks for the input.

MarkB:

I would think that Rivnuts and the bedrail fasteners are the way to go. If the Selby bedrail fasteners are the ones I am thinking of, where the plates and hooks are about 5mm thick and the hooks are peened through the back, then the flanges of the Rivnuts will allow the peened back of the hooks a void to fall in to, and thus allowing the plate of the bedrail fastener to be right on top of the flange of the Rivnut, giving a much more solid attachment. You could add a washer or two underneath the hook plate if the void space is not enough to accommodate the peened metal. I might also use Loktite on the threads, but that is a personal preference. I also wonder whether epoxy might help in any way

I would feel better about this arrangement, metal on metal with threaded fastening, than anything else that I could think of. I don't know how many you have to do, but for the task at hand, given the possibility of numerous assembly/disassembly cycles, it is probably as quick, durable, and inexpensive a method as you will find.

The shortcoming would be the shear force on the bolts; you might consider putting another Rivnut just below where the hook plate on the steel post would end and put a hex head bolt that would serve as a stop for the downward force on the plate, acting in a manner to counter the weight put on the unit.

Hope this helps. Good luck.
TonyF

Thanks Tony,
Your outline is pretty much exactly where we are at with it at the moment. Rivnuts, Selby fully mortised into Hard Maple, and we've added a small angle bracket mortised into the bottom of the rail to eliminate lift. Only change is we are inverting the bed rail fasteners to allow them to be fully embedded in the wood rail just to avoid having to pierce/slot the steel post for the hook member on the fasteners.

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