requirements for headless guitar headpiece

[string_man]

Hi everybody, I was wondering if you had any experiences with the head design of a headless guitar (I know, it's a paradox). I am planning to you these headpieces: https://www.google.com/search?client=opera&q=abm+7010c+headpiece&sourceid=opera&ie=UTF-8&oe=UTF-8

together with a standard nut (no zero fret). How would you choose the distance between the nut and the headpieces and the height difference between these two in order to prevent strings from jumping out?

[Bizman62]

Based on an image search in Google it looks like the abm 7010c sits level to the neck, i.e. the thickness of the fretboard lower. The distance from the nut seems to be in the ballpark of 12 mm or half an inch. On a 'standard' guitar the neck break angle is usually about 10-13 degrees, yet on Fender type flat headstocks the string angle can be about 6-7 degrees. Less than that may cause the strings to fall off, yet I guess with the headpiece being so close to the nut there's not much space for the strings to fall off the grooves.

[curtisa]

The ABM dimensional drawing tells you more:

https://abm-guitarpartsshop.com/media/products/7010c_Dimensions_7010.pdf

There's 1.95mm from the bottom to the opening where the string exits towards the nut. You need some downward force on the nut for each string to seat properly in their respective slots, so the string clamps need to be at least this distance (plus a bit more) below the bottom of the nut slot.

Say you're using frets with a 1mm high crown, and your nut slot is cut about the same above the surface of the fretboard, sinking the string lock 1mm deep into the fretboard would get you your strings just kissing the bottom of the nut slots (1mm crown minus 1mm insetting of the string lock = 1.95mm, or close enough). To get some downward pressure happening you'd probably sink the string locks another 3-4mm into the fretboard again, so you're looking at insetting them pretty much all the way to the bottom of the fret board (assuming your fret board is 5-6mm thick).

Note that there are a couple of extra things to consider with these kinds of string locks too:

• The amount of downward pressure purely based on how deep you inset the string locks will change depending on how close or far you position the string lock from the nut, as it alters the angle at which the string deflects down towards the lock. If you need your string locks spaced away from the nut you'll need to inset them deeper than you would if you positioned them right up against the nut to maintain the same downward pressure of each string.
• If the truss rod in your neck is going to be adjusted from the nut-end you'll need to plan carfully how you're going to attach the string locks to the headstock. On a 6 string the screws for the D and G locks might be dangerously close to punching through the sides of the truss rod access hole, which might risk the D and G string locks being pulled out under string tension. On a 7 string it's even worse as the D string lock is pretty much directly over the top of the truss rod hole, and there's almost no timber left to put a screw in to, plus the screw itself will block the truss rod hole.
• The side-to-side spacing between each string lock needs to be considered in conjunction with your string spacing you set with the nut slots. Minimum spacing between each lock is 7mm, but if you're using a wider string spacing at your nut you might want to consider devising some way of accurately lining up each string lock so that a consistent gap is maintained between each unit, otherwise your strings will tend to go off at odd-looking angles behind the nut as the spacings between nut slots and string locks start diverging. Things get weirder if you go for equal string gaps rather than equal string centres, as the gap between each string lock needs to shrink by half the diameter of each string as you step from bass to treble.