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Steel Suggestions for Threaded Rod

Dickie Frank

Plastic
Joined
Jun 13, 2023
Location
Toronto, ON
I'm designing my own guitar truss rod and I'm debating what steel to use. The rods we use now are listed from the supplier as "Mild Steel". The rod is 3/16" diameter and approximately 19" long with a 10-32 RH thread on one end and a 10-32 LH thread on the other end. It will have a corresponding threaded nut on each end (plus an hex adjustment nut). When the rod is turned right it will stretch and when it is turned left it will compress.

I suppose I'm looking for a steel that has good yield strength, good tensile strength and good comporession strength. It will be turned somewhat frequently (a few times a year), so the threads also need to hold up. Rust is not a huge concern since it's inside a guitar neck...people generally keep their guitars pretty dry and in good humidity conditions :).

I've included an image of my design. I didn't come up with this concept so I'm not really worried about IP, hence including the picture of the model 🤷‍♂️

Please let me know what material you think would be ideal for this application (for both rod and nuts).

Thanks in advance!
Nick
 

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I've gotten high strength threaded rod from fastenal. I forget the grade but it was equivalent to a grade 8 bolts, and is genuinely quite strong.

Another option is to use a regular, short high strength bolt, and thread a tube that spans the entire length. If you want to get fancy, thread the OD of the tube at the stationary end to thread into the mounting block.

EDIT: why turn the entire rod instead of just a nut at one end? If you do want to turn the rod due to accessibility or something you may consider making something like a turn buckle out of square or hex stock, and a carriage bolt on each side keyed in the mounding blocks.
 
I would think PH 4140 would work pretty well for what your asking.
Awesome. Thanks for the sugestion!

I should've mentioned, I was planning on having the threads rolled instead of cut. The thread rolling company suggested C-1018 Steel. It's got a lower yield strength and is softer than PH 4140 though.
 
Awesome. Thanks for the sugestion!

I should've mentioned, I was planning on having the threads rolled instead of cut. The thread rolling company suggested C-1018 Steel. It's got a lower yield strength and is softer than PH 4140.
1018 is just mild steel. If you want stronger rolled threads, I would expect you to have to roll the steel while it's annealed and then harden it, like they do with bolts.

I should have mentioned, with the approach I stated of using female threads and a strong bolt, is that you can have longer thread engagement to compensate for the softer threads.
 
I've gotten high strength threaded rod from fastenal. I forget the grade but it was equivalent to a grade 8 bolts, and is genuinely quite strong.

Another option is to use a regular, short high strength bolt, and thread a tube that spans the entire length. If you want to get fancy, thread the OD of the tube at the stationary end to thread into the mounting block.

EDIT: why turn the entire rod instead of just a nut at one end? If you do want to turn the rod due to accessibility or something you may consider making something like a turn buckle out of square or hex stock, and a carriage bolt on each side keyed in the mounding blocks.
This type of design is known as a dual action rod and can compensate for upbow and backbow. It's more versatile than a single action rod, which is just a nut that turns at one end, with the rod remaining static. A single action rod only stretches which adds backbow to the neck (or in most cases straightens the neck to compensate for string tension).

One consideration is the diameter of the rod. We don't want to remove too much material out of the neck. Not sure what size tube you had in mind...interesting conept though! Another consideration is if having a hollow tube inside the guitar neck would affect the sound of the guitar.
 
The real question is...how much stress is on the rod? I doubt it is significant so most all steels are likely strong enough for for this job, especially since mild steel is commonly used. Some people like to over engineer things but strong enough is strong enough, more adds no value for this. However, maybe using stainless steel adds some visual appeal when adjustment is needed.
 
The real question is...how much stress is on the rod? I doubt it is significant so most all steels are likely strong enough for for this job, especially since mild steel is commonly used. Some people like to over engineer things but strong enough is strong enough, more adds no value for this. However, maybe using stainless steel adds some visual appeal when adjustment is needed.
Agreed. These need to function really well, and last forever. I experimented with stainless with a different rod design and had some break at the anchor point. The only part that is visible is the adjustment nut at the end, so aesthetics is not really a consideration.

I don't know exactly how much stress is on the rod. Typically the rod gets tightened a maximum of 1.5 turns. That would result in a fairly significant adjustment in the guitar neck.
 
I'd make a few to test out of 17-4. It's really nice stuff, reasonably strong, looks good, not too expensive, readily available, corrosion-resistant ... it's hard not to like it as a general-purpose upscale material.

If you want to go crazed and specs-waving is useful for sales, vascomax 250.
 
very conservative a 10-32 has roughly 1000 pound shear in mild steel (cold roll 1018). You want titanium for sound enhancement-and pretty anodizing.
 
I like 17-4
Get it in condition A so the ends can be rolled. (Actually, ask the thread rollers, just in case for some reason they would prefer N)
Then easy and non distorting to HT @ 900 - 925F.

Most of us like 4140 prehard for all kinds of apps where toughness and moderate hardness is useful - like yours.
If the thread rollers don't like it, see if the stress works ok with plain 4140 normalized. It is still a lot tougher than mild steel.

smt
 








 
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