04-14-2013 05:30 AM
There's three issues you have to deal with.
Issue one deals with scale length. Both necks will need to be the same scale length or your bridge position will be off.
Issue two deals with the position of fret #12. When the new neck is mounted, the 12th fret needs to be in the exact same position as the old neck or your bridge intonation will be off, Most bridges will adjust intonation a bit, but the 12th fret is the key. About the most you want the neck off is maybe the width of one fret, otherwise you'll never get the instrument intonated.
Issue three is matching the neck pocket. If the original neck pocket is too deep, too shallow, to wide or narrow, if the heel is round or square, or the fretboard overhangs, all of these items need to be scoped out before you even attempt to install a new neck.
For example, if the original neck has a round heel, and your neck is square, you have to use a router on the pocket to square it up. If the pocket is too narrow you need to widen it evenly on both sides. If the pocket is too deep, and the fretboard overhangs the body, and you try and screw down a new neck without filling in the pocket, it will break the end of the fretboard off when the neck is bolted down.
If the pocket is too wide or too long, you'll have gaps where the neck is loose. Without filling in those gaps you'll have a tuning nightmare without and support from the cavity sides, and filling in the gaps will require body refinishing to make the neck look half way decent. Then if the neck mounts too deep or is not properly angled, it can cause bridge/string height issues where you can't adjust the bridge either high or low enough to be played properly.
There's also a lesser issue of neck wood types as well. Swapping a mahogany neck for a maple may make the guitar sound brighter and the frequency response of the pickups may not capture the best sound with that change.
You can see some of the issues. There are more, but those are the basics. Some guitars like fenders and generic fenders have a 25.5" neck and standard pockets which makes swapping necks easy. Ibanez has some oddball neck scales in their models so its best to measure both the scale length and the heel before buying anything.
Measure front the inside of the nut, to the center of the 12th fret, then double that and you'll have the scale length. Then measure, the width height and length of the heel, and the distance of the 12th fret to the heel and use those specs in buying a new neck. If you find an exact match, chances are you wont need to route or fill the body. If the neck is slightly smaller, What I use is epoxy putty to fill the gaps. I mix it then use a putty knife to get it in there flat where it needs to be filled. I next put a piece of cellophane around the neck heel so the epoxy doesn't stick to the neck and wang it down in place. This causes the putty to squeeze out flat and fill any gaps. If it squeezes out along the edges, I trim it up flush with an exacto knife.
Next I may install the strings and make sure the neck angle, string centering and string height is within limits. Once the putty is hardened, you can remove the neck and cellophane and sand the putty smooth or fill any additional gaps. You want the epoxy coated pocket you be as flat as possible so you have maximum sound conduction. If there's allot of air gaps, the tone will sound thin.
I use this putty which you can buy in any hardware store for filling in heels, sides and shimming necks. You can buy it in a few colors, usually gray. It wont shrink so if you sand it smooth its excellent for finishing over, much better than bond or wood filler.
If you did a neck shim, to tilt the neck back, what I do first is use thin washers placed over the back screw holes. I layer them up till I get the exact shim angle I need for the bridge height. (this isn't much different than the micro tilt many fender guitars used to have except you're using washers on the back screws instead of an Allen screw to tilt the neck.
Once I have the correct number of washers to get the neck tilted, I crazy glue them in place against the body so the screws pass through them. Next I'll remove the neck and fill the body in up to the height of those washers at an angle tilting back to the edge of the pocket like an inclined ramp. Once hardened I can use a file or wood block and sand paper to smooth the epoxy down for a firm fit.
I can also Wang the neck down to smooth it too. Epoxy is good because if there's a small gap on the sides of the neck, the putty will squeeze out on the sides and prevent the neck from skewing. Its also reversible. You can remove the putty by sanding or using a dremmil. I've even used paraffin wax in a neck pocket so the entire chunk can be chipped out without any damage to the body. It conducts sound very good as well and prefer it over shimming a neck with anything else including wood.
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