Official Luthiers Forum!

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)



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?

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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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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Jim Watts
http://jameswattsguitars.com

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.

Thanks for the advice guys

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.