I started with some 3/4" stock that I had. Not sure what wood this is, but it's probably something I should have built something nice from instead of this. But it's what I had.
I used my Delta Planer and planed one board down to about 1/2" thickness. Then cut three 2" wide strips and two 6" wide pieces. They were all about 22" long.
Here, I've glued up the two larger pieces to make the base. I had trimmed the base to 8"x15".
The three 2" pieces were cut this way: four 8" long x 2" wide for the arms, and four 6" long and 2" wide for the risers (these I later cut to 5" long), and 8 small 2"x2" blocks.
The arms and risers have to have a channel routed down the center to allow a 1/4" bolt to slide thru. So I made a jig that would hold them still and put barriers at either end to stop the channel before it exited the part. No measuring here, just guestimation.
Here's one being routed:
And after the rout was cut:
I took the arms and cut a channel sideways that would allow the risers to sit in, and glued them up and clamped. I also doubled up the pieces for the blocks and glued them as well. It's funny (to me) that 2 of the assemblies were pretty well vertical, but 2 leaned a bit inward. Not really an issue, but struck me that it came out even.
The only hardware I'm using are eight wing nuts for 1/4"-20 bolts, four 1/4-20 flat Phillips machine bolts, and four 1/4"-20 Hanger bolts. I drilled 4 holes into the base for the machine bolts, and used a forstner bit to inlet the bolt heads so the base stays flat. The hanger bolts were screwed into the blocks. A hanger bolt has a threaded screw end and a threaded bolt in. I tapped the blocks with a 3/16" drill bit and flagged it so it wouldn't go thru the block. You just put two nuts on the hanger bolt, and a ratchet and screw it in until the screw threads disappear. Here's a picture of one finished and one ready to go.
The vice there was helpful for both the drilling part and the screwing in part.
After all that, I put the blocks on the risers, set the arms on the base, and positioned them close to the guitar body size.
And finally, with the guitar body on the contraption.
At some point, I'll put felt on the blocks and maybe along the risers. think the base is a bit small. I'd prefer to have more wood under where the arms and risers intersect. So, before doing another guitar, I'll make a frame for the carriage. It might call for moving the holes in the base a little further out. The guitar in the picture is Dreadnought size, so I won't be putting anything bigger into it. I also need to find something to put under the base to make it slide a bit easier. When I do that, I'm going to use some CA and glue the bolt in so that it doesn't move. Probably use sawdust to pack the recess as well.
I've seen a lot of articles on making the binding tower, but have never seen one for making a carriage. Just as there are many ways to climb Everest, there are many ways to do most anything with the guitar and jigs. This is just the way I did mine.
I hope it's helpful to someone,
Bob