[TowerTalk] ferrites Re: Raised Radial Spacing

[Richard Karlquist]

If you add an air gap to a ferrite core, you can greatly tighten up the
tolerance, down to around 1%.  This is commonly done with ferrite pot
cores, but i have also seen it done on ferrite toroids.

---
Rick Karlquist
N6RK 

On 2025-11-03 18:19, Jim Lux wrote:

> yeah - the book by Snelling discusses all the variables.
> The Fair-rite catalog also goes into the mfr process.
> There's a reminder at the bottom of most of the pages that says "if you need better, call us, and we can talk"
> You can get better surface finish (less "flash" from the mold, for instance), better size tolerances, etc.
> 
> But for the vast majority of applications - the designer just accounts for the variability and moves on.  That ferrite lump around the keyboard cable? If it's off by 20% or even 50%, they'll still pass Part 15 and CISPR tests.
> 
> On Mon, 3 Nov 2025 18:50:06 -0700, David Gilbert <ab7echo at gmail.com> wrote:
> 
> Most of a lifetime ago I was a component engineer at Collins Radio, and
> one of the products I was responsible for was a small ferrite core.  The
> manufacturer's rep explained the manufacturing process to me, which is
> basically like making a ceramic mug, and likened it to baking a cake. 
> The process variables are many and significant, and even with automation
> the end result varies a lot.
> 
> ChatGPT provided a summary of the potential process considerations:
> 
> https://chatgpt.com/share/69095b41-ed34-8001-83ba-6c412e5e473e
> 
> Dave   AB7E
> 
> On 11/3/2025 4:40 PM, Jim Lux wrote: 
> 
>> 20-25% is actually what Fair-rite gives as a tolerance for their cores (at least for the EMI suppression family) - Chip beads are 25%
>> So if you've measured 20% variation, that's probably within spec.
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