One Arm Endless Bowstring Jig

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. 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 unitstrut jig body will accomdate 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.

WOOD
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

HARDWARE
unistrut - 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)

TOOLS
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

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

**Metal Angle One Arm Endless Bowstring Jig**
Amended, 5/21/01
Here's the scoop on how to build a cheap and simple one arm endless bowstring jig. First, why one arm instead of the traditional two? Because you don't really need two! One arm allows for a simpler jig that will build a string just as quickly and accurately as a two arm jig. I've been using a One Arm Endless Jig for well over 30 years - it works extremely well.
Materials (all acquired from Home Depot) main beam - (2) 1-1/2"x72" slotted metal angles (zinc coated) (Note: you can use 1/8" 1-1/2" aluminum angles as well, but they're much more expensive and you need metal cutting drill bits to make the required five 1/4" holes) arm, beam separators, feet - (1) 2x4x48" fir - get one as blemish free and straight as possible string posts - (2) 3/4" diameter birch dowel - 18" minimum - get one as straight as an arrow! arm foot - (1) 1"x5"x7" - any kinda scrap wood that's between 3/4" and 1" thick beam fasteners - (5) 1/4"x2-1/2" bolts, nuts and washers wood fasteners - (8) 2-1/2" dry wall screws main arm pivot - (1) 1/2"x5" carriage bolt, 1/2" wing nut, large washer string trees - (3) #10x2-1/2" (or thereabouts) flat head wood screws string tie-down - (1) 5/16"x2" wall hanger screw and 5/16" wingnut, 2 washers string post lashing - some strong unwaxed thread glue - 5 minute epoxy to fasten in the string posts Tools Cutting the 2x4 - table saw or circular saw or jig saw or hand saw Drilling the holes - electric drill and 3/16", 1/4", 1/2" and 3/4" wood bits Tighten the bolts - box wrenches and/or vise grips Screws - a 1/16" drill bit for pilot holes is nice, screw gun, screwdriver Please Note: If you don't know it, a 2x4 is really 1-1/2"x3-1/2"! Wherever "2x4" is mentioned, those sizes prevail! Building the Jig Please Note: The full length 72" slotted angle beams will make a jig that will build a bowstring as long as 76". If your maximum string length requirements are less, you can shorten both metal beams by cutting with a hacksaw. * Measure off and cut the 2x4 for ... one 18" length (for the arm) one 9" length (for the single post end) one 7" length (for the arm support) one 3" length (for the end piece) two 4-1/2" lengths (for the feet) * You'll need to cut the 2x4x7" long main arm support lengthwise, to provide a 1-1/2" wide, 1-1/4" high, 7" long piece of wood ... The reason you need to trim off the height of this 7" long main arm piece is in order to allow the arm to be tightened to the main beam, allowing you to set the arm to whatever length bowstring you wish to spin. If you find it difficult to make this cut, ask where you purchased your lumber to make this - and all the other cuts - for you. Home Depot will usually do all of this at no charge ... See it, nestled between the pair of sloted angle main beams. * Take the 9" length and put it between the angle beams, at one end - drill and secure with three 1/4"x2-1/2" bolts - make sure the bottom of the 9" length is flush with the bottom of the angle beams. After securing, add a 4-1/2" foot to the bottom of the 9" length with the drywall screws ... * You'll need to cut the 2x4x3" long length lengthwise, to provide a 1-1/2" wide, 1-1/4" high, 3" long piece of wood ... The reason you need to trim off the height of this 3" long end piece is in order to allow the arm to pass over it - thus increasing the maximum bowstring length you can spin. If you find it difficult to make this cut, ask where you purchased your lumber to make this - and all the other cuts - for you. Home Depot will usually do all of this at no charge. Take that 3" length and put it between the angle beams, at the other end - drill and secure with two 1/4"x2-1/2" bolts - make sure the bottom of the 3" length is flush with the bottom of the angle beams. After securing, screw in a 4-1/2" foot to the bottom of the 3" length with the drywall screws... * Take the 1"x5"x7" piece of scrap wood and fasten it to the bottom of the 7" length arm support, using drywall screws ... * Take the 18" length that's the main arm, mark the exact center of the 4" wide side and drill a 1/2" hole completely through (see above pic). * About 1" from the end of the main arm support, drill a 1/2" hole completely through and insert the 1/2"x5" carriage bolt (see above pic). * Centered about 1" from from each end of the main arm, drill a 3/4" hole as straight in as you can - it must go at least 1" deep, but could also go completely through the 2x4 ... * Glue a length of 3/4" dowel into each main arm string post hole - bottom out the the dowel and cut off enough so that 4-1/2" remains above the top of the 2x4 (see above pic). * Centered about 1" from the end of the 9" length arm support, drill a 3/4" hole as straight in as you can - it must go at least 1-1/2" deep, but could go deeper ... * Glue a length of 3/4" dowel into each main arm string post hole - bottom out the the dowel and cut off enough so that 4" remains above the top of the 2x4 (see above pic). * Centered, and off to one side of one end of the main, drill a 1/4" pilot hole for the 5/16" wall hanger. Screw in the wall hanger, add a few washers and screw on the 5/16" wing nut ... * Assemble the main arm - use the 1/2" wing nut and a large washer ... * Next up is drilling pilot holes in the ends of all three string posts, screwing in the flathead string tree screws, binding the ends of the dowels with heavy thread or string, coating the thread/string with epoxy ... * On the single end post, I added a small plastic tube, that has a lip on one end, to the screw string tree - this rotates and makes turning the strands around it a bit easier - it's not mandatory ... * All done ... All set to spin an endless bowstring! Questions, comments - email Rob at

Metal Angle One Arm Endless Bowstring Jig

Amended, 5/21/01

Here's the scoop on how to build a cheap and simple one arm endless bowstring jig. First, why one arm instead of the traditional two? Because you don't really need two! One arm allows for a simpler jig that will build a string just as quickly and accurately as a two arm jig. I've been using a One Arm Endless Jig for well over 30 years - it works extremely well.

Materials (all acquired from Home Depot)
main beam - (2) 1-1/2"x72" slotted metal angles (zinc coated) (Note: you can use 1/8" 1-1/2" aluminum angles as well, but they're much more expensive and you need metal cutting drill bits to make the required five 1/4" holes)
arm, beam separators, feet - (1) 2x4x48" fir - get one as blemish free and straight as possible
string posts - (2) 3/4" diameter birch dowel - 18" minimum - get one as straight as an arrow!
arm foot - (1) 1"x5"x7" - any kinda scrap wood that's between 3/4" and 1" thick
beam fasteners - (5) 1/4"x2-1/2" bolts, nuts and washers
wood fasteners - (8) 2-1/2" dry wall screws
main arm pivot - (1) 1/2"x5" carriage bolt, 1/2" wing nut, large washer
string trees - (3) #10x2-1/2" (or thereabouts) flat head wood screws
string tie-down - (1) 5/16"x2" wall hanger screw and 5/16" wingnut, 2 washers
string post lashing - some strong unwaxed thread
glue - 5 minute epoxy to fasten in the string posts

Tools
Cutting the 2x4 - table saw or circular saw or jig saw or hand saw
Drilling the holes - electric drill and 3/16", 1/4", 1/2" and 3/4" wood bits
Tighten the bolts - box wrenches and/or vise grips
Screws - a 1/16" drill bit for pilot holes is nice, screw gun, screwdriver

Please Note: If you don't know it, a 2x4 is really 1-1/2"x3-1/2"!
Wherever "2x4" is mentioned, those sizes prevail!
Building the Jig

Please Note: The full length 72" slotted angle beams will make a jig that will build a bowstring as long as 76". If your maximum string length requirements are less, you can shorten both metal beams by cutting with a hacksaw.
* Measure off and cut the 2x4 for ...
one 18" length (for the arm)
one 9" length (for the single post end)
one 7" length (for the arm support)
one 3" length (for the end piece)
two 4-1/2" lengths (for the feet)

* You'll need to cut the 2x4x7" long main arm support lengthwise, to provide a 1-1/2" wide, 1-1/4" high, 7" long piece of wood ...

The reason you need to trim off the height of this 7" long main arm piece is in order to allow the arm to be tightened to the main beam, allowing you to set the arm to whatever length bowstring you wish to spin. If you find it difficult to make this cut, ask where you purchased your lumber to make this - and all the other cuts - for you. Home Depot will usually do all of this at no charge ...

See it, nestled between the pair of sloted angle main beams.
* Take the 9" length and put it between the angle beams, at one end - drill and secure with three 1/4"x2-1/2" bolts - make sure the bottom of the 9" length is flush with the bottom of the angle beams. After securing, add a 4-1/2" foot to the bottom of the 9" length with the drywall screws ...

* You'll need to cut the 2x4x3" long length lengthwise, to provide a 1-1/2" wide, 1-1/4" high, 3" long piece of wood ...

The reason you need to trim off the height of this 3" long end piece is in order to allow the arm to pass over it - thus increasing the maximum bowstring length you can spin. If you find it difficult to make this cut, ask where you purchased your lumber to make this - and all the other cuts - for you. Home Depot will usually do all of this at no charge.

Take that 3" length and put it between the angle beams, at the other end - drill and secure with two 1/4"x2-1/2" bolts - make sure the bottom of the 3" length is flush with the bottom of the angle beams. After securing, screw in a 4-1/2" foot to the bottom of the 3" length with the drywall screws...

* Take the 1"x5"x7" piece of scrap wood and fasten it to the bottom of the 7" length arm support, using drywall screws ...

* Take the 18" length that's the main arm, mark the exact center of the 4" wide side and drill a 1/2" hole completely through (see above pic).

* About 1" from the end of the main arm support, drill a 1/2" hole completely through and insert the 1/2"x5" carriage bolt (see above pic).

* Centered about 1" from from each end of the main arm, drill a 3/4" hole as straight in as you can - it must go at least 1" deep, but could also go completely through the 2x4 ...

* Glue a length of 3/4" dowel into each main arm string post hole - bottom out the the dowel and cut off enough so that 4-1/2" remains above the top of the 2x4 (see above pic).

* Centered about 1" from the end of the 9" length arm support, drill a 3/4" hole as straight in as you can - it must go at least 1-1/2" deep, but could go deeper ...

* Glue a length of 3/4" dowel into each main arm string post hole - bottom out the the dowel and cut off enough so that 4" remains above the top of the 2x4 (see above pic).

* Centered, and off to one side of one end of the main, drill a 1/4" pilot hole for the 5/16" wall hanger. Screw in the wall hanger, add a few washers and screw on the 5/16" wing nut ...

* Assemble the main arm - use the 1/2" wing nut and a large washer ...

* Next up is drilling pilot holes in the ends of all three string posts, screwing in the flathead string tree screws, binding the ends of the dowels with heavy thread or string, coating the thread/string with epoxy ...

* On the single end post, I added a small plastic tube, that has a lip on one end, to the screw string tree - this rotates and makes turning the strands around it a bit easier - it's not mandatory ...

* All done ...

All set to spin an endless bowstring!

Questions, comments - email Rob at