This is one of those 'after the fact' instructables so I apologize for the lack of step by step action. I just wanted to share the idea, and maybe inspire your creativity. This is not my design of course, this is a variation on the Nineboys Delta Wedge, I just tweaked it a little. In lieu of steps, I'd be glad to help anyone interested in making one, just comment and I'll reply.
I'm using a low E string from an electric guitar with a super cheesy magnetic pickup. The base is a 3' piece of 2x6 cut down to 4", the sides of the wedge are two pieces of 1/4" pine and the top is 1/8" birch. The nut is a piece of threaded rod with a stop nut at each end, and the bridge is a can o' pineapple...hence the name 'Pineapple Express'! I could've called it the Pineboys Dole-ta wedge but hey enoughs enough.
The pickup is mounted to a piece of pine and just gets squeezed in by the string tension, the nut and bridge are held in by just tension as well. You can use any size can and "adjust the bridge" by sliding a shim under the can to change the height of the action. For that matter, you could use thicker rod with larger bolts OR shim up the bolt to adjust the nut also. At the skinny end (the nut n bolt end) the string is held by a regular guitar tuner so tuning is super easy. At the can end, the string just goes right through the plank to the bottom side where I have a penny with a hole in it as an anchor...so you just feed a regular guitar string through the penny, and the ball end of the string can't pass through the hole, voila.
It sounds really good, although I have almost no idea how to play a slide guitar (or any other guitar!). It's fun to mess around on though, and even sounds pretty decent played acoustic. If I were to change anything it would probably be to add a better pickup, this one was so cheap it can't possibly be much good. I don't know, maybe it's just the amp I have it paired to...I only have a small portable amp so I haven't heard it on a proper setup. And since I'm not a guitarist I can't see investing in a real amp just to satisfy my curiosity and make my bad music louder! Also, it may sound better with an empty can, mines still full of pineapples. I haven't tried an empty can yet, but that's what's normally used so keep that in mind. You can screw a dowel into the middle of the empty can to keep it from crushing under tension...or you could use a bottle or a pipe or coffee can, diddley bows are all about the 'use what ya got' mindset.
Thanks for looking, please share your questions or comments!