Minimum 'meat' to leave under a double-action truss-rod?

[Humphrey9999]

Designing/building my first guitar and planning to incorporate a Hot Stuff double-action truss-rod, which is 11mm tall.
That doesn't leave much intact timber under the slot.

For instance, if the neck + fretboard is about 22mm and the fretboard is 6mm as in many guitars, then the neck itself is 16mm and only 5mm is left under the 11mm tall truss-rod. I guess this is one reason why so many guitars break at the headstock near the top of the truss-rod slot. (Been looking at pics and neck profiles all day.)

I want a nice, thin neck, but this makes me nervous. Is it worth making it slightly thicker at maybe 23mm or even a touch thicker?
The current planned neck profile is oval 'C', as in the attachment below.

The (Merbau) neck/headstock will be one piece, not a scarf-jointed one, with 8 degree headstock angle and a decent-sized volute for extra strength. Headstock will be 15mm thick.

Edit: I only ever plan to use light strings.

Any input appreciated.

[Ball Peen]

If you make the neck too thick, that's the first thing people notice. Can you turn the rod around and adjust from the soundhole ? I use LMI single action truss rods. 4mm x 9mm groove and just a little beavering away around the screw area 11mm x 6mm x 6mm.

[Humphrey9999]

If you make the neck too thick, that's the first thing people notice. Can you turn the rod around and adjust from the soundhole ? I use LMI single action truss rods. 4mm x 9mm groove and just a little beavering away around the screw area 11mm x 6mm x 6mm.

Yeah, really the last thing I want is a thicker neck. I'm a small bloke with small hands, so a thick neck is a PITA.
Unfortunately, to adjust from the sound hole, I'd first need to add a sound-hole, or a decent one at least. This is a cigar-box style neck-thru guitar, and I was only planning two small 'f' holes. I like the sound of a 4mm x 9mm groove instead of a 5mm x 11mm one, but since this is my first guitar, I ordered a 2-way rod to give me a better chance of getting the neck right.
I guess I'm in between a rock and a hard place.

Can I take it then that a 'Hot Rod' 2-way truss rod is completely useless and a waste of money, if it can't be fitted to a normal thickness neck in the usual way, with the adjusting nut at the top of the neck.?

Edit: A little reading tells me that the LMI double-action rods need a shallower slot and that they can also be installed with the adjuster at either end. It seems this is a common problem with Hot Rods. A big lesson learned.
Can you point me to a good supplier of LMI rods?

[Humphrey9999]

Problem solved. Found LMI and just ordered one of their 14.25" double-action rods. Only needs a 9.5mm deep slot - much healthier than the 11.1mm needed for the Hot Rod equivalent.
Thanks for mentioning LMI, Bill.

Just re-drew the side view to suit the LMI rod. Looks much better: -


Headstock - Side View.jpg