Ask HN: DIY Sit/Stand Desk

I've assembled a simple standing desk. It's a table that sits on top of my current desk and supports the keyboard tray and monitor risers.

Can you suggest a way to make it adjustable, so that I cat sit for some of the day? It should be able to adjust 16".

I don't think I can support the whole apparatus while adjusting the legs (by folding them in or loosening a knob on each leg). I'm imagining something that I can crank, like some windows, but I'm not sure how to find hardware that works like that, if it exists. What should I look for at my local hardware store (where the employees are historically useless if I want to use something not for the intended purpose), or what would such a thing be called so that I can search online for it?

Maybe there is something I just haven't found that will just work, but I look forward to some creative suggestions that will be fun to design and test out.