Reddit mentions of LFA / Reichel Hardware 5220L-1/2-20 Keyless Light Duty Double Sleeve Locking Chuck, 1/16-1/2 - 1.5-13mm Capacity, 1/2-20 Threaded Mount

So I've started buying the parts to see if I could make this thingamabob as well. It looks so useful!

One thing I think I've discovered while researching: I think it might not be absolutely necessary to buy the exact same chuck that the original maker used. I'm thinking any 1/2" threaded chuck would do. Here's my reasoning: I thought at first that the threaded rod coming off the lever piece would screw directly into the chuck (and thus it would be important to match up the threading of the lever shaft with the threading inside the chuck. But now that I look at the step-by-step instructions on the original maker's webpage, the lever shaft is screwing directly into the nut he's epoxied onto the chuck. I think the lever shaft screws into the nut and then just moves deeper into the chuck when he adjusts the height of the piece, never actually touching the threads of the chuck itself. I ordered the same lever you did, and after taking it down to a hardware store and playing with that little gadget that helps you determine threading sizes, I found out the lever shaft on this one is threaded M8 1.25 (metric). That's definitely narrow enough to fit into the 1/2" thread inside the chuck.

I came just 'cause I was thinking if you were getting impatient about the delivery time of the chuck you ordered, I think you could get a different (but still cheap) 1/2" chuck on Amazon with Prime and get it lickety split. This is the one I got, but it appears to be out now. :(
https://www.amazon.com/gp/product/B00LDSSNP2/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1
This one looks like it might also work:
https://www.amazon.com/Eyech-Keyless-Universal-Replacement-Electric/dp/B078H9N23D/ref=sr_1_26?s=hi&rps=1&ie=UTF8&qid=1525220991&sr=1-26&keywords=1%2F2+keyless+chuck&refinements=p_85%3A2470955011
Anyway, just a thought. As it turns out, I'm not using the one I bought, because I remembered I had an old . drill of my dad's, and I just took off the chuck and am using that one.

For epoxying the nut to the chuck, I ended up buying Original JB Weld at the local Home Depot, simply because it was the strongest they had. I haven't tried it yet.

Speaking of the nut, I held up my M8 1.25 nut to the chuck, right where the guy showed he epoxied his, and wow, there's just a tiny TINY about of metal-to-metal contact available there. I'm starting to think about how difficult it will be to get that nut on there centred, and how well it will stay. As a possible solution, I bought some flanged nuts of the right size, in hopes they'll provide more surface area for the epoxy. I went to two stores in my area, and they didn't have a bunch of metric hardware, so I just ordered these on Amazon. Fingers crossed.
https://www.amazon.com/gp/product/B077HSXHPV/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

I'm now wondering how to get a threaded shaft that screws into both the lever and the nut. The lever assembly I got just has a bolt screwed into the end, so threaded one end and a hex cap on the other end. What I really need is a threaded rod. What I might do is just get a M8 1.25 bolt and hacksaw the cap off. There's a big fingers crossed moment.

Hope your build is going well! Thanks again for this great post!