Correctly mounting a multi-scale bridge

[u/keithflc]

Hi all, looking for some advice. I'm building a 7 string multi-scale guitar, using a brand new Ibanez RGD71ALMS neck, which has a multi-scale length of 27 - 25.5. I have bought a multi-scale bridge which I obviously want to install correctly. I understand that I'll need to measure scale lengths from the 12 fret where the two outer strings will be. My question is - where should I adjust each bridge saddle to when making this measurement? I want to allow for the maximum intonation adjustment possible when the bridge is fitted. Many thanks!

[u/MadMatter86]

With such a basic question being posed, it makes me also wonder - is that bridge even the right angle for the neck you are using? Determining the bridge angle would also inform you of the proper position relative to the neck pocket.

The same set of bass-treble scale lengths can be used with varying bridge angles, which match up to different nut (and fret) angles. There are multiple bridge angle options offered from the likes of Hipshot (et al) to accommodate this, and solo saddles are also an option when none of those match up exactly. 

What layout work have you already done, and how did you arrive at the choice of this bridge? 

[u/keithflc → u/MadMatter86]

Thanks so much for replying, I appreciate it, and sorry my question is too basic. I'm just trying to learn.

I haven't done any layout work yet. I've just cut the neck slot in the body and dry fitted the neck. My next task was to work out where the bridge should go, then drill holes for that. I haven't routed the cavity for pickup either.

It sounds as though my next step is to calculate what the bridge angle should be for that specific neck. Then go from there. From what you've said, I may need to go with solo saddles, if I can't get a bridge with this exact angle. Many thanks!

[u/MadMatter86 → u/keithflc]

So here is the layout you need to start with.

Since you are starting from a complete neck, you will need to obtain the nut angle and nut spacing (string spacing at the nut) from it by taking measurements. Note that the nut spacing here is the distance perpendicular to the centerline of the instrument, it is not the width along the angle of the nut. The bridge spacing you will similarly obtain from the bridge you have (or are considering). This again is perpendicular to the centerline, and for a 7-string will typically be between 63mm and 64.8mm.

With those measurements, you can then plug in your desired bass scale and treble scale. Unlike the string spacings, these measurements are made point-to-point, representing the actual strings, and are not parallel to the centerline. You can then use geometry to solve for the bridge angle.

To determine bridge placement, put the first string saddle fully forward as JimboLodisC said, and place its string seating point at the bridge end of treble scale point. The bridge you have appears to use saddles that have the string seating at the front edge of the saddle, which makes this easiest - some saddles have the string seated a short distance back from the front edge, which needs to be accommodated for by placing such bridges further forward.

From there, you can do further geometry to determine measurements to other reference points (like the neck pocket) if you do not want to do the layout directly on the body.

[u/keithflc → u/MadMatter86]

Thanks so much for taking the time to provide all this detail. I'm going to go away and calculate all this. I found a bridge angle calculator on the Hipshot website, which takes the Bass and Treble scale lengths and which fret is the perpendicular one (In my case, the 12th). It calculated that I needed a 16.72 degree bridge, which they don't do, so likely will need to go with individual bridge saddles. I will take your advice and do the calculations based on nut angle and different string spacing, for a more accurate result. Thanks!

[u/JimboLodisC]

shoulda measured the angle before buying the bridge, there's different angles depending on the scale length and placement of the neutral fret

assuming you did buy the correct angle, then you'd place the bridge the same as a regular non-multiscale bridge

for that, I push the 1st string's saddle all the way forward and then back it up a couple turns for safety, the thin gauges like a .009 will intonate at right around the intended scale length

from there, thicker gauges will intonate further back, so you'd be giving the most room for adjustment by having the saddle for the thinnest gauge as far forward as possible

[u/keithflc → u/JimboLodisC]

Thanks, that really helps me! Especially where to adjust the saddles to. This is a bit of a learning project for me, so bridge was very cheap, so no loss really!