String Instrument Truss Rod
Wednesday, June 8, 2011
How to Build a String Instrument Truss Rod
The truss rod of a guitar is inserted into a channel of the neck under the fretboard. Its purpose is to counteract the stress of the strings and is adjusted to prevent the neck from either bowing or dipping. Bowing causes the strings to be too close to fretboard in the middle of the neck, resulting in string buzz. Dipping lifts the strings too far from the fretboard, making it difficult to play, especially higher up the neck. One of the more common truss rods is the Martin-style, which features a rod inside of an aluminum u-channel and an adjusting nut on the top end.
Determine the length of the truss rod for your particular instrument. For most electric guitars, it needs to be around 18" when finished. If the finished truss rod length is 18", cut the aluminum u-channel to 16", and cut the cold roll steel rod to 17 3/4" with the hacksaw. Measure 1/2" from each end of the aluminum u-channel and make a cut 1/8" deep in the open end of the u-channel.
Using the motorized grinder, chamfer each end of the steel rod. With the 1/4"-20 die and thread-cutting oil, thread the rod about 2 inches on one end and about 3/4 inch on the other. Back the die off frequently to clear metal shavings. Spin the 1/4"-20 nut onto the short-threaded end of the steel rod until the face of the nut is flush with the end of the steel rod. Using the drill press and the 3/32 inch bit, drill a hole through the nut and rod. Tap the roll pin into the hole.
Spin the 1/4"-20 coupler on the long-threaded end of the steel rod. Place the steel rod inside the aluminum u-channel. Bend the 1/2" tabs made on the end of the u-channel over the steel rod with the vise grip pliers. Thread the Allen Head cap bolt into the other end of the coupler.
Using the motorized grinding wheel, grind the nut even with the u-channel and grind the coupler nut round and even with the Allen Head cap bolt. Using the straightedge and scratch awl, scribe a mark along the u-channel legs even with the bent-over tabs. Grind the legs almost even with the top of the steel rod. Place masking tape along the open side of the u-channel to prevent epoxy from getting onto the rod. The truss rod is now ready to install into the instrument channel.
· Moderately Challenging
Things You'll Need
· 1/4" Cold Roll Steel Rod about 2 feet long
· 3/8" x 3/8" Aluminum U- Channel about 2 feet long
· 1/4" - 20 Coupler Nut
· 1/4" - 20 Nut
· 1/4" - 20 3/8" long Allen Head Cap Bolt
· 1/4" - 20 Die with Die Holder
· Thread Cutting Oil
· Vise Grip Pliers
· 3/32" x 3/4" roll pin
· 3/32" Drill Bit
· Drill Press
· Motorized Grinding Wheel
· Scratch Awl
· Masking Tape
· Safety Glasses
· Always wear safety glasses and gloves when working with and grinding metal.
· Truss Rod
· "Make Your Own Electric Guitar"; Melvyn Hiscock and Brian May; 2003
· Stewart MacDonald Guitar Making Parts and Supplies [http://www.stewmac.com/]
· Musical Instrument Makers Forum [http://www.mimf.com/]