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 Post subject: hot rod split neck
PostPosted: Wed May 02, 2018 7:47 am 
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Mahogany
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First name: Damon
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I split the neck when I adjusted the hot rod. First time that's happened.

I don't really want to build a new neck if I don't have to, so I am experimenting.

I will sand off the lacquer, I'll drop some CA in the crack and take the tension off the rod to close it up. Then I'm thinking of laying some carbon fiber I have along the back of the neck over the crack and epoxying it in place, sanding the edges of the fiber and epoxy after it cures to blend as best I can into the neck. I won't lay the fiber too far down the sides of the neck toward the fretboard, maybe use a piece about 3/4" wide, so hopefully the neck should still feel very playable, it will just be slightly thicker, more of a v-shape I guess.

Edit: I may not have actually split the wood, just the lacquer as the wood expanded, but I'll see once the lacquer is off.

Any thoughts?

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 Post subject: Re: hot rod split neck
PostPosted: Wed May 02, 2018 8:23 am 
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Koa
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Lindamon wrote:
I split the neck when I adjusted the hot rod. First time that's happened.

I don't really want to build a new neck if I don't have to, so I am experimenting.

I will sand off the lacquer, I'll drop some CA in the crack and take the tension off the rod to close it up. Then I'm thinking of laying some carbon fiber I have along the back of the neck over the crack and epoxying it in place, sanding the edges of the fiber and epoxy after it cures to blend as best I can into the neck. I won't lay the fiber too far down the sides of the neck toward the fretboard, maybe use a piece about 3/4" wide, so hopefully the neck should still feel very playable, it will just be slightly thicker, more of a v-shape I guess.

Edit: I may not have actually split the wood, just the lacquer as the wood expanded, but I'll see once the lacquer is off.

Any thoughts?


I've heard of folks having this same problem with the hot rods. I personally have never had it happen. I'm curious, what is the neck material? How thick is the neck at the crack including the fretboard? Is the hot rod installed immediately under the fretboard? Sorry I'm no help on the repair but maybe I can avoid a future failure.

Thanks, M


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 Post subject: Re: hot rod split neck
PostPosted: Wed May 02, 2018 11:40 am 
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Cocobolo
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First name: Leonard
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Have you done epoxy and carbon fiber repairs before? I would think that it would be difficult to smoothly blend it into the wood.

Why not use a veneer of wood to strengthen the neck and enlarge it slightly? Blending wood into wood is easier than blending something harder than wood into wood.


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 Post subject: Re: hot rod split neck
PostPosted: Wed May 02, 2018 11:48 am 
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Brazilian Rosewood
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"I split the neck when I adjusted the hot rod. First time that's happened."

If you adjust it more do you think it will split again?


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 Post subject: Re: hot rod split neck
PostPosted: Wed May 02, 2018 12:18 pm 
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I can't imagine a truss rod cracking the lacquer without also breaking the wood.

I don't think there is a way to fix this without making a new neck that will both look/feel good and provide enough additional support to avoid problems next time the rod is adjusted. Or at least without spending as much time as making a new neck would take. That said, you don't have much to lose from trying since you can always make a new neck afterwards.

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 Post subject: Re: hot rod split neck
PostPosted: Wed May 02, 2018 12:42 pm 
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Mahogany
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Michaeldc wrote:
Lindamon wrote:
I split the neck when I adjusted the hot rod. First time that's happened.

I don't really want to build a new neck if I don't have to, so I am experimenting.

I will sand off the lacquer, I'll drop some CA in the crack and take the tension off the rod to close it up. Then I'm thinking of laying some carbon fiber I have along the back of the neck over the crack and epoxying it in place, sanding the edges of the fiber and epoxy after it cures to blend as best I can into the neck. I won't lay the fiber too far down the sides of the neck toward the fretboard, maybe use a piece about 3/4" wide, so hopefully the neck should still feel very playable, it will just be slightly thicker, more of a v-shape I guess.

Edit: I may not have actually split the wood, just the lacquer as the wood expanded, but I'll see once the lacquer is off.

Any thoughts?


I've heard of folks having this same problem with the hot rods. I personally have never had it happen. I'm curious, what is the neck material? How thick is the neck at the crack including the fretboard? Is the hot rod installed immediately under the fretboard? Sorry I'm no help on the repair but maybe I can avoid a future failure.

Thanks, M



Hi Michael, the neck is mahogany. I can try to measure later how thick it is, but I don't know if my caliper is wide enough. Yes, it's installed directly under the fretboard. best,

Damon

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These users thanked the author Lindamon for the post: Michaeldc (Wed May 02, 2018 1:17 pm)
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 Post subject: Re: hot rod split neck
PostPosted: Wed May 02, 2018 12:46 pm 
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The real fix is to remake the neck. Seems like the only way to prevent it from ultimately cracking again would be to add mass.
For the future...
I've seen this happen before and the problem was traced to necks that were not properly seasoned and jointed. the company was relying on the truss rod to straighten the neck for them after it was finished. There were multiple blowouts using the hot rod t rods. The design on the rod allows one to easily over torque until the neck blows out. If the neck is straight to begin with you should not have to move the rod that much.
I don't use them any more.


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 Post subject: Re: hot rod split neck
PostPosted: Wed May 02, 2018 12:53 pm 
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Mahogany
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Clay S. wrote:
"I split the neck when I adjusted the hot rod. First time that's happened."

If you adjust it more do you think it will split again?



Hi Clay, yes, I adjusted it more and I could see/feel the neck bulge out slightly, I have no doubt it would blow out if I kept going.

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 Post subject: Re: hot rod split neck
PostPosted: Wed May 02, 2018 12:57 pm 
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Mahogany
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Bryan Bear wrote:
I can't imagine a truss rod cracking the lacquer without also breaking the wood.

I don't think there is a way to fix this without making a new neck that will both look/feel good and provide enough additional support to avoid problems next time the rod is adjusted. Or at least without spending as much time as making a new neck would take. That said, you don't have much to lose from trying since you can always make a new neck afterwards.


Hi Bryan, the wood may indeed be broken and probably is, but it's hard to tell for sure until I take the lacquer off. I thought perhaps might have it bulged out just enough to stress the lacquer enough to crack it, but you are probably correct. Either way, I need to take the fretboard off and make a new neck, or try fixing it. The guitar is for my son-in-law, so he will just have to wait! :)

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 Post subject: Re: hot rod split neck
PostPosted: Wed May 02, 2018 1:04 pm 
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Mahogany
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Tim L wrote:
The real fix is to remake the neck. Seems like the only way to prevent it from ultimately cracking again would be to add mass.
For the future...
I've seen this happen before and the problem was traced to necks that were not properly seasoned and jointed. the company was relying on the truss rod to straighten the neck for them after it was finished. There were multiple blowouts using the hot rod t rods. The design on the rod allows one to easily over torque until the neck blows out. If the neck is straight to begin with you should not have to move the rod that much.
I don't use them any more.


Hi Tim, yes you may be right. Even with the frets adding a back bow to the fretboard, the neck needed a pretty good adjustment after glue up. I have read that water based glues used when gluing on the fretboard can sometime cause this, but it hasn't been an issue before, I use titebond for this job.I think I shaved too much off the neck on this one. I may start using HHG for this in the future, although it's water based as well. Don't really want to use epoxy.

What kind of truss rods do you like now?

thanks,

Damon

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 Post subject: Re: hot rod split neck
PostPosted: Wed May 02, 2018 1:15 pm 
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Mahogany
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philosofriend wrote:
Have you done epoxy and carbon fiber repairs before? I would think that it would be difficult to smoothly blend it into the wood.

Why not use a veneer of wood to strengthen the neck and enlarge it slightly? Blending wood into wood is easier than blending something harder than wood into wood.



Hi Phil, yes we once repaired a wooden aircraft wing with cf and epoxy. We had to cover some 3" access holes drilled in the plywood skin for repairing the interior of the wing. We beveled about a 1/2" edge onto each hole, and layed in circular pieces of cf in with epoxy. We did have to use some body putty to fill the slight center droop, but the edges of the epoxy/cf/wood were blended perfectly, you could not see any difference after the paint went on. That was over 20 years ago, and it's still holding up fine. It's an aerobatic wing as well, so very high stress.

I plan on using some very dark lacquer over the repair. But I take your point and will try it first on some scrap to see how it works first.

thanks,

Damon

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 Post subject: Re: hot rod split neck
PostPosted: Wed May 02, 2018 6:47 pm 
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Last Name: Lynch
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Damon
I make my own and have made them for other luthiers in Santa Cruz. They are similar to the Bennedetto t rods. Double action and lightweight but require special tooling to cut the channels inthe neck.



These users thanked the author Tim L for the post: Lindamon (Thu May 03, 2018 12:54 pm)
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 Post subject: Re: hot rod split neck
PostPosted: Wed May 02, 2018 8:05 pm 
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We've done several repairs on luthier-built instruments which used the Hot-Rod. The Hot-Rod is over 1/16" deeper than the deepest of the modern two-way rods and has a square profile in an area where there is no need for additional stress risers. We've seen enough cracks and blow-outs that we would not consider using one for any build without a very deep neck profile.

Mr. Morelli worked out a good repair strategy which we subsequently borrowed:

- Remove the neck
- Remove the fretboard
- Remove the Hot-Rod and deposit in the nearest active volcano
- Repair any cracks as needed
- Using a fresh 3/8" diameter ball-end straight bit, re-mill the channel just a bit deeper than the original to get rid of the block areas
- Mill a neck material filler strip and glue in using epoxy
- Mill the insert for new truss rod
- Fit and install the rod and reglue the fretboard
- Touch up neck and body as required

I think we have some shots of the original repair...despite the massive split, all went well. I have no idea why StewMac still sells these rods - heavy, too deep, and the end blocks rotate when tensioned, further concentrating the loads in the nut to first fret area.

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These users thanked the author Woodie G for the post (total 2): Lindamon (Thu May 03, 2018 12:54 pm) • Clinchriver (Thu May 03, 2018 3:54 am)
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 Post subject: Re: hot rod split neck
PostPosted: Thu May 03, 2018 3:35 pm 
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I had a hot rod truss rod blow out and it was my fault cause a guy (prospective buyer) told me he would like the neck thinner. I didn't do the arithmetic before taking material off the bottom of the neck and got the bottom of the channel too close to the outside of the neck. After the autopsy I saw it was at 0.12". I learned a couple of things:
1. You need 0.18" or better (my own "made up" figure)
2. Think about what your about to do before you try something like this.

I took the hot rod out, installed a strip down the bottom of the channel, put in my own homemade single action rod, refinished the "blowout" and evImageerythings' good.



These users thanked the author surveyor for the post: Lindamon (Fri May 04, 2018 2:15 pm)
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 Post subject: Re: hot rod split neck
PostPosted: Fri May 04, 2018 2:18 pm 
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surveyor wrote:
I had a hot rod truss rod blow out and it was my fault cause a guy (prospective buyer) told me he would like the neck thinner. I didn't do the arithmetic before taking material off the bottom of the neck and got the bottom of the channel too close to the outside of the neck. After the autopsy I saw it was at 0.12". I learned a couple of things:
1. You need 0.18" or better (my own "made up" figure)
2. Think about what your about to do before you try something like this.

I took the hot rod out, installed a strip down the bottom of the channel, put in my own homemade single action rod, refinished the "blowout" and evImageerythings' good.



I agree with the 1/8" measurement. I measured another neck thickness on one that did not blow our and it was exactly 1/8". I will measure the thickness on this one when I get back to the shop with it.

thanks, Damon

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 Post subject: Re: hot rod split neck
PostPosted: Fri May 04, 2018 2:50 pm 
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So here is the crack in the lacquer, and possibly the wood.

Attachment:
IMG_0586.jpeg


Here is what I am going to try. I epoxied some cf on a dowel, and sanded the edges, feathering fairly carefully, though I can do better, I did go into the wood a little more than I meant to, the sanding block I used was too big, I will use a smaller one and take my time, this was done too quickly.

Attachment:
IMG_0577.jpeg


I will need to fill the pinholes from bubbles in the epoxy.

The side view shows the profile. You can also see below the patch where I took a screwdriver and pressed into the wood as hard as I could to make a dent. I wanted to compare it to the same in the cf, to see if it would be strong enough for the truss rod. You might be able to see the very slight dent I made in the cf in profile here, however I included another profile of the patch in the last picture, with the dent in the marked oval area. Compared to the dent in the wood, I believe it will be strong enough, however I have nothing to lose by trying this, if I don't like the results I will take the fretboard off and put it on a new neck, so nothing ventured, nothing gained, right? The guitar is for my son-in-law, so I can keep an eye on it to see how it goes.

Attachment:
IMG_0578.jpeg


Attachment:
IMG_0581.jpeg


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 Post subject: Re: hot rod split neck
PostPosted: Fri May 04, 2018 6:57 pm 
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I used a hot rod once, never again. It takes up too much height in the neck and requires a non-standard bit to cut the channel. I’ve heard of blowouts several times.

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 Post subject: Re: hot rod split neck
PostPosted: Fri May 04, 2018 9:11 pm 
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I've had a Hot Rod blow out the neck right under the first fret area. Guitar is an OM with a mahogany neck. The Hot Rod is just too tall in that area. I pulled the fret board, glued the crack, and put a filler strip (maple, I think) in the bottom of the truss rod slot. Then I put in an Allied rod and a new fret board. Been playing that guitar ever since. Won't use a Hot Rod again, they're just too tall - a sub-optimum design in my opinion.

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These users thanked the author SteveSmith for the post: Lindamon (Sat May 12, 2018 2:35 pm)
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