The Comprehensive DIY Compound Bow String/Cable Making Guide

Automan26 and I collaborated to bring you all this information. Hopefully it will inspire and help people to star making their own custom strings.

There are a lot of guys who want to start building their own strings, but two things are holding them back: 1) They are reluctant to invest hundreds of dollars for a jig with the possibility that they might not like string building and don’t want to end up with a $350 dust collector. 2) Many guys don’t have a clue about how to build a string and are afraid the process is more complicated than they want to get involved in.

This thread is designed to take care of both of these problems so anyone can start building strings fast, cheap and easy.

This thread is going to get quite long, but I want to make sure that you have everything you need to get starts as well as some instructions on string building to make you successful.

BEFORE YOU BEGIN— All the parts on this jig have an important purpose. I had to work through a number of difficult problems that are not readily apparent just from looking at the finished product. If you leave anything off, you will run into a problem I worked hard to avoid.



Unistrut and Superstrut parts are nearly identical. I have used parts from both manufacturers simply because I had to use what my supplier had on hand. Mix and match parts as you wish, they will go together just fine.

Parts List

2, 10’ sections of 1 5/8” Superstrut channel (Flip one over and bolt it to the bottom of the other to help stop it from flexing when stretching long strings).

4 Superstrut/Unistrut corner brackets—3 ½” X 4”

2 pieces of 7” long, ¾” wide by ½” thick steel bar (If in the Kansas City area, Metal by the Foot will cut it to length)

4 Superstrut/Unistrut spring nuts

5/8” All-thread rod—Cut to make 2, 7” sections

1 Compression spring— McMaster Carr part Number: 9573K81 Medium Load Chrome-Silicon Steel Die Spring 1.5" Hole, .75" Rod, 2" L, .135" X .345"

6, 5/8” nuts—(3 for each section of All-Thread)

4 coarse thread, 1” X ½” bolts

4 coarse thread, 2” x ½” bolts

8 coarse thread ½” nuts

8” x 3/8” eye bolts with internal diameter large enough to fit the 5/8” threaded rod

4, 3/8” bolts with 8, 3/8” washers and 4, 3/8” nuts (To bolt the strut together. 3/8” because that allows you to fit a socket into the channel to tighten them down)

2, 1/4X20 X 3” Grade 8 hex bolts (handles)

2, 1/4X20 X 2” Grade 8 hex bolts (jig posts)


ASSEMBLY:
If you look at the pics above you can figure out most of the assembly, but there are a few things you will need to know:


1. Adjust the height of the eye bolts so that they keep the All-thread level when tension is applied to the jig posts. Due to the fact that the tension is not centered along the axis of the All-thread, the posts want to tilt down when under tension. This causes a severe binding problem that you will want to avoid.

2. Drill a hole through the nuts and All-thread, and then tap them to fit the bolts. This is more difficult than first appears, so if you do not have confidence in your abilities, a machine shop can do the task very cheaply. These holes need to be dead center and squared-up. I found it was easier to thread the nut on the all thread and drill through them at one time rather than drilling separately.

3. Screw the Grade 8 hex bolts down ALL the way down. You don’t want any threads from the bolt still showing as it would not be a smooth post to build on.

4. Grind a flat spot (prevents drill bit from “walking” on you) on top of the other end of the all thread 1” from the end. Drill and tap another hole in the flat spot for the “handle” screw.

5. Clamp the 7” pieces of ½” x ¾” steel bar between 2 of the corner brackets. Make sure the steel is centered, and drill them all at once if you can. If you cannot drill them at the same time, clamp them together, mark the circle of each hole in the corner brackets on the flat bar with a pencil. You may need to go around several times with the pencil. Then use a straight edge and make an “X” in the circles so that the “X” crosses dead center in the circle. Use a steel punch to make an indention where the lines of your “X” cross so there is a place for your drill bit to settle to prevent it from walking. If it walks, you may have a hard time lining all the holes up.

6. Between the two existing holes in one of the corner brackets, drill a hole big enough for one of the 3/8” eye bolts. On another corner bracket, between the existing holes, drill a hole big enough for one of the coarse thread 1” x ½” bolts. You can see on the picture which bracket has the eye bolt between the existing holes and which has the 1” x ½” bolt between the existing holes.

7. Adjust the eyebolts until they cause the 5/8” all thread rod to sit at an angle like in these pictures.

This will prevent excessive binding when you tension the string.

Tensioning the String

There are two methods which can be used to put tension on the string. First, you can pretention the tension spring and use the adjustments on the opposite head and tighten until the compression spring begins to move slightly. As soon as the stop bolt on the spring head moves slightly, the pre-tensioned spring is pulling on the string. Automan26 likes this one but I use the second method because my jig is built slightly differently.

The second method simply involves adjusting the non-spring jig head to do all the pulling and compressing of the compression spring. This allows you to use the spring as your scale. I like this one because long strings will take a different amount of adjustment to reach the same poundage as a short string. It also seemed easier since I will go up and down in weight often during the build process. To calibrate your spring, hook up a heavy scale that is capable of weighing something to at least 300lbs. Use the spring-less jig post to start tensioning the spring and watch the scale climb. When you reach 100lbs, measure the spring and record that measurement. You can also build a “jig” to that fits between the ½” thick steel bar and the washer on the outside of the spring when you reach your poundage. (That’s what I did and it works great.) Keep tightening the jig until the scale reaches 300lbs and measure or mark your jig. With these measurements or “jig” you will not need to use your scale again except to check periodically to make sure you don’t need to recalibrate. (I have not need to recalibrate for the several months I have been doing this.)

Also, keep things well lubed up. This is an inexpensive starter jig and is thus not the same quality as something you will pay $300+ to purchase. At times things may bind a bit and need a small tap here and there. It’s no big deal, but it is a small price to pay for a jig that costs as little as this one and can build the quality of string that this jig can build.


String Building Formula

Here is a good formula for determining the proper number of twists and the finished string length:
Finished Length X .75 = Number of Twists
Number of twists X .012 + finished length= Initial Jig Post Setting.
Example: 100” String
100 X .75=75 (Twists)
75 X .012=0.9”
100” + 0.9”=100.9” (Initial Post Setting)
Add 75 twists to your 100.9” string and you should be very close to your finished length.

Building the String

Note: I build all my strings and cables with the top loops on the post without the spring. This helped to keep me from getting confused about serving direction when I started and I have kept it the same for consistency. We’ll call that post A. Post B will be the stationary post that has the spring on it.

1: Set and measure you jig to the appropriate length. Measure from outside of one post to the outside of the other jig post.

2: Tie off a tag end and lay out your material so that none of the strands overlap on the jig post.