Why does it have to be so small I.D.? It'll barely fit, hmm, maybe five turns at the required ampacity?
You're welcome to ask mfgs for custom parts but don't be surprsed if they roll their eyes at your quantity or budget.
There is a machinable powder material, that I'm familiar with through its use in induction heating coils. Don't remember who makes it, but maybe it has low enough losses you can make use of it.
As others mentioned, this is an X-Y problem. You should not be asking "how do I make this fuckoff massive inductor?", when the obvious uestion is "how can I avoid using a fuckoff massive inductor?"
You didn't mention voltage, but if it's modest (10-100V?), this is very much in the realm of a multiphase, full wave, forward converter. Push-pull is preferred at low voltages, full bridge in the middle, half bridge at high voltages (say >800V). Phase interleave is preferred at low voltages. The point is to reduce the peak current any given switch sees, keeping the inverter impedance reasonable (above an ohm at least). Which makes layout tractable, and keeps switching losses down. Phase interleave also saves on ripple current seen by the input and output filter caps, another savings not to be underestimated.
Resonant can also be considered at the power level, but it's probably not a big deal because the inverter impedance will be so low, i.e., stray inductance will dominate the dynamics, not switch capacitance. Well, an inverted resonant might be okay, but current-fed inverters and upside-down topologies aren't exactly beginners topics.
If isolation is not actually necessary, boost or SEPIC is perfectly reasonable of course. Multiphase is still desirable for all the above reasons.
With these changes, you should also find commercial offerings are very available. You probably won't find transformers this size, or whatever ratio you're looking for, but that's easy enough to custom order.
And yes, multiphase repeats a lot of stuff, it's a PITA to hand build. Consider making a common module and ordering assemblies in quantity, then make one common control/distribution board to plug them into. Much cheaper when engineer proto hours are considered.
Tim
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/
"Hul Tytus" wrote in message
news:qvsipk$30i$1@reader2.panix.com...
>
> I've been looking for a toroid with a cross section area (one side) of
> probably 2 or 3 square centimeters and an id of about 10 or 12 mm. The
> intended inductor is about 14 micro henries and will handle between 40 to
> 80
> amps in a flyback power supply at, again probably, 100 kc.
> Fair-Rite, Micrometals, and Magnetics show, at the desired id, cross
> sections typically less than 1 sqcent. Greater cross sections show greater
> id's and consequently greater lengths. These toroids would result in
> windings
> using only a portion of available space with the rest of the toroid doing
> nothing but dissipating power.
> Anyone know of some suppliers that have the bulky type of toroids that are
> required in this case? Or, perhaps, another approach to limit the
> dissipation?
>
> Hul