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PostPosted: Thu May 12, 2016 5:18 pm 
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Koa
Koa

Joined: Wed Feb 17, 2016 8:54 am
Posts: 854
State: Texas
Country: United States
Focus: Repair
So I feel kind of stupid for asking this but if you don't know ask right?

Regarding the addition of neck reinforcements I have a 1936 Dobro M32 that simply is unplayable (action at the 12th fret is measuring out at nearly 1/4") due to the neck needing to be reset as well as the permanent relief. With this instrument I am not concerned with the vintage value, I really only care about it's musical value at this point.

Compression fretting did exactly jack squat for the previous owner (he might not have had done it correctly but that's beside the point) so I'd like to add some stability to the neck and straighten it.

What I would like to do is simply add a cf rod (only 1) down the middle of the neck to give it some resistance against the pull of the strings. It has nothing as you can see from the photo below (and yes the removal should've been cleaner, that's my fault)

Image

My question is, after the channel is routed for the carbon reinforcement, is it necessary to add a shim to the top of the cf rod under the fingerboard or is it safe to simply have the cf rod flush with the top of the neck and make direct contact with the fingerboard?


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PostPosted: Thu May 12, 2016 9:25 pm 
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Walnut
Walnut

Joined: Fri Mar 25, 2016 4:54 pm
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First name: Finn
Last Name: Tobias
City: Sacramento
State: California
Zip/Postal Code: 95864
Country: United States
Status: Amateur
It's a matter of preference. It will look nicer if there is a shim between the rod and the Fret Board but it won't increase or decrease the functionality since the rod won't be pushing upwards towards the fretboard under string tension.


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PostPosted: Thu May 12, 2016 10:54 pm 
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Contributing Member
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Joined: Thu May 12, 2005 5:46 am
Posts: 2969
Location: United States
It'll be a lot easier to get a good gluing surface if you use a shim than it will be dealing with wood and carbon fiber on the bonding surface. But as was pointed pout above it's a matter of preference. I've done it both ways.

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PostPosted: Sat May 14, 2016 2:03 pm 
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Brazilian Rosewood
Brazilian Rosewood

Joined: Thu Feb 12, 2009 10:27 pm
Posts: 2109
Location: South Carolina
First name: John
Last Name: Cox
Focus: Build
Status: Amateur
In ye olde days.... The shim on top of a one way adjustable trussrod was a lot thicker in the middle than on the ends. This establishes the bend in it so that when you tighten the rod - it pulls the headstock down. They aren't straight.

Then - with Martin rods adjusting through the sound hole - your shim takes up the top thickness so you don't have to cut a groove in the top to thread the trussrod in.

If none of these apply - then you don't need the shim.


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PostPosted: Mon May 16, 2016 8:50 am 
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Koa
Koa

Joined: Wed Feb 17, 2016 8:54 am
Posts: 854
State: Texas
Country: United States
Focus: Repair
Thanks for the advice guys


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PostPosted: Mon May 16, 2016 10:03 am 
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Brazilian Rosewood
Brazilian Rosewood

Joined: Tue May 13, 2008 10:44 am
Posts: 6256
Location: Virginia
My understanding of CF rods is that they are most effective the deeper they are in the neck, further away from the neutral axis... So I would go as deep as you can, say 1/8th inch of exposed wood from the bottom of the channel to the outside of the rod, then shim any airspace on top of that.


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