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» Trad » Topic Archives » How To - Resources » Build a Unistrut Endless String Jig

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Author Topic: Build a Unistrut Endless String Jig
Rob DiStefano
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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!

Some comments on the jig design and build parameters ...

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.

18", 2x4 - pivot arm
12", 2x4 - tail arm
12", 2X4 - jig feet (optional)
18", 3/4" birch dowel - posts
12", 1/2" ply - pivot and tail blocks

unistrut (SuperStrut)- jig beam (home depot, 10', $19)
3", 1/2" bolt - pivot arm
1/2" id washer - pivot arm
1/2" id lock washer - pivot arm
1/2" id wingnut - pivot arm
1-1/2" dry wall screws (3) - tail arm
2" flat head screws (partial thread) (3) - pivot arm
2", 1/4x20 machine/wood screw - string end hold down
1/4x20 wingnut - string end hold down
1/4" id washers (2) - string end hold down
1" dry wall screws (4) - jig feet (optional)
1/4" id washers (4) - jig feet (optional)

wood saw (table, circular, jig, hand) - cutting all wood
metal saw (metal cutting bandsaw, hacksaw) - cutting the unistrut
drill (electric, hand) - drilling all wood
3/4" speedbore bit - pivot/tail post holes
1/2" wood bit - pivot bolt hole
1/8" wood bit - wood screw holes

slow set epoxy (30-45 minute) - posts, pivot bolt, post binding
binding for string posts (carpet thread, floss, string fiber)

There's more to come as I'll show just how I use the jig to spin up a string, but for now here's some jig pix ...

One Arm Endless Jig on the bottom, most of the jig parts on the top ...

The pivot arm ...

Pivot arm bolt system - a scrap piece of plywood is used to secure the pivot arm ...

The scrap plywood's width just allows it to slip into the unistrut, but it's held in place by the unistrut's lip ...

The end post attachemnt - just like the pivot arm, it's fastened by a slat of plywood with 3 predrilled holes (see inset pic) that's held in place by the unistrut's lip, using dry wall screws into the endpost block of wood ...

Post dowel, string screw, hole ...

String post w/screw and dowel thread binding ...

Easily make from a 24" to a 72" string ...

IAM ~ Black Powder Gang ~ TANJ ~ NRA Patriot Life ~ NRA RSO

Posts: 10180 | From: NJ | Registered: Mar 2003  |  IP: Logged | Report this post to a Moderator
Trad Bowhunter
Member # 15276

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Thanks for posting that, Rob. Been planning to make an jig and your post is loaded with great tips and ideas.


Posts: 3247 | From: Colorado | Registered: Feb 2008  |  IP: Logged | Report this post to a Moderator

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