I personally like low action on a guitar but it can be a difficult process to get it right depending on the brand and model. This is for bolt-on neck guitars only of course.
Fender guitars are versatile on this kind of set-up, usually you can get the action super low but it does not always work so well with vintage radius as the notes can 'choke' on string bending due to the frets being higher in the centre of the board.
Shimming the neck seems to scare some folks and is also sometimes seen as a bodge job (it is reversible and can cause no damage if done correctly). But in theory this is no different to the 1970's Fender Micro-Tilt System and in the 1960's some Fender guitars came with a neck shim straight from the factory. Some may still even to this day as other brands do.
Micro-Tilt System
Why would you shim your guitar neck when you can change the height of your bridge or saddles?
Sometimes, that alone is not enough and you wont get the full potential of playability from your guitar.
Here is a diagram explaining the effect of a neck shim.
As the diagram shows, it wont correct neck relief issues. This is a different thing.
What would you use as a neck shim?
I've seen everything, seriously, from steel washers to off-cuts of ply veneer, cigarette packet card, plectrums... Theoretically they all do the job but something neat that is full width of the pocket seems the way to go. Like this factory made shim on the Ernie Ball guitar.
What thickness shim would you use?
Finding the balance between the shim and bridge/saddle adjustment usually requires only a thin shim. A piece of card maybe 0.05mm will change the neck angle more dramatically than you can imagine. The only time you would need to shim more is on a major modification like fitting a TOM on an old Fender.
What material should the shim be made of?
The industry uses plastic. DIY'ers seem to use card, however, some people say sandpaper/glasspaper works better as it grips the surface eliminating any friction or movement during resonating. As ridiculous as it sounds this makes sense. I once shimmed a CIJ Jaguar neck with Rizla card and it did not sound the same, i tried sandpaper which improved it. I'll leave that one there for the Cork Sniffers.
I hope someone finds this useful, many players dont get the full potential from their guitars and this isn't all about the Malmstainz either.
