I built an adjustable chair for our four year old in the style of the Stokke Tripp Trapp. It’s red oak finished with three coats of shellac. Sorry for the photo rotation; they’re correct on my computer but not here and I don’t see how to correct them. I’m happy with how it turned out; my first try with angled mortise and tenon combined with my first try with drawbore mortise/tenon worked out nicely.

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He really likes it and says it’s much more comfortable than the booster seat it replaced. I deliberately overbuilt it because he’s quite active when sitting and I expected a bunch of squirming around, rocking, and so on. However, I very much underestimated his tendency to slide and kick the foot plate and slide the seat plate while sitting in the chair and I need to figure out a good way to lock them in place while maintaining adjustability.

Rabbets on the seat plate and foot plate sit in dados on the legs.
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My first thought was wedge locks to hold the plates in place by applying side-to-side clamping pressure, but the legs are too flexible. I also thought about wedge locks that would orient the pressure across the width of the dado, but it’ll be difficult to adjust the dados for an even taper (i.e. same taper for every dado) now that the chair is built. My present thought is to drill a series of holes centered in the dados and matching holes in the plates to receive locking pins coming in from the sides.

I’m not really happy with either option, so I figured it would be a good idea to submit the problem for suggestions. What are your thoughts?

Thank you in advance.

Michael Bulatowicz