There are more than a few viable ways to build a unistrut one arm endless string jig. This article addresses how I built a pair of them, and to introduce the concept of using unistrut for the jig body and using one jig arm instead of two.
I've been using one arm endless string jigs since the early 60's when I designed and built my first one. They're too easy to make and use, and will build perfect length strings every time.
Study over what I've done and you'll see lots of your own on-hand material and parts substitutions that'll work just as well, if not better. As a side note, for those who prefer using a twin arm jig, the unistrut jig body will accommodate that just fine!
The unistrut I used came only in 10' lengths. Normally, I like a 6' long jig, but I didn't wanna wind up with a 4' length of nearly useless unistrut. So I cut it in half, for two 5' lengths. Using a 12" length of 2x4 for the end post adds another 5" to the extension, coupled with the overhang of the pivot arm, that allows for a 71" loop-to-loop string - more than enuf for my needs. If I wanted to make longer strings, I'd just increase the length of the end post tail arm.
While I've used both 1/4" and 3/8" pivot bolts, the more robust 1/2" is just plain better.
I like using fir for the 2x4 wood - heavier than white wood (pine), it's just more durable.
It doesn't matter much what size string end hold down screw and wingnut is used - 5/16" works just as well.
One $2.11 8' length of 2x4 fir is enuf wood for 2 jigs.
Thanks for posting that, Rob. Been planning to make an jig and your post is loaded with great tips and ideas.