Re: [EE] Small electromagnet cores?

In the USA: 4-40 sized nuts and bolts might be considered instead of
3mm threaded rod, they have a similar diameter to M3 sized hardware

On Thu, Jun 5, 2025 at 8:25 AM graham foulkes <[email protected]> wrote:
>
> Low carbon steel. >0.5% carbon, commonly called 'mild steel', is used
> extensively for screws, nails and low cost ironwork that holds stuff
> together, especially in wood. Exceptions being deck screws and fasteners
> with a grade rating,  i.e., grade 8 bolts. A quick test with a file will
> give you its approx class., soft iron files or cuts easily. Test the
> filings with a magnet for attractive response.
>
> On Tue, Jun 3, 2025, 4:54 AM Spehro Pefhany <[email protected]> wrote:
>
> > At 01:51 PM 2025-06-02, you wrote:
> >
> > Hi, Mike:-
> >
> > There's sellers for 3mm diameter 'soft iron' and for 1J50 permalloy
> > rod on Aliexpress.
> > The latter is stupidly expensive compared to the domestic price in
> > China- it's just that
> > nobody is bothering to sell it for a reasonable price overseas. There
> > you can get
> > a couple meters of 3mm diameter permalloy for a few dollars delivered
> > overnight.
> >
> > If you happen to have a friend in Shenzhen getting them to chop it up
> > into short
> > lengths and put it in a package for shipment might be an option if you
> > want a
> > material that's got a _datasheet_ and is characterized for magnetic
> > properties.
> >
> > Soft iron:
> > https://s.click.aliexpress.com/e/_oE8kZe0
> >
> > Permalloy:
> > https://s.click.aliexpress.com/e/_okGhroo
> >
> > The latter type 1J50 is a about a 50:50 Ni-Fe alloy that is hydrogen
> > annealed
> > to improve the magnetic characteristics such as permeability.
> >
> > You can get similar material to the 1J50 off the shelf at electrical
> > steel suppliers
> > in the US such as Carpenter and Fry (with different numbers) but they
> > don't generally
> > carry small diameters-- 3/16" is about the smallest and IME they
> > don't tend to be
> > enthusiastic about tiny orders even for exotic materials.
> >
> > But I'd give a cheap steel screw, nail or threaded rod a try first
> > and see if it's
> > good enough. In the US, McMaster sells 3mm threaded steel rod cheaply:
> >
> > https://www.mcmaster.com/98861A040/
> >
> > Best regards,
> > Spehro Pefhany
> >
> >
> > >Hey all-
> > >
> > >I'm trying to make a flip-dot display like this one:
> > >https://hackaday.com/2021/05/29/3d-printed-flip-dots/
> > >
> > >I'm having a hard time with the electromagnet component of the project. OP
> > >used 3mm threaded rod, and it seemed to work okay per his videos, but it's
> > >not working for me at all.
> > >
> > >I'm relatively sure the problem is in the permeability of the core.
> > >Stainless steel is not a great magnetic field conductor. I'm looking for
> > >something better.
> > >
> > >Lots of searching has led me nowhere. I'm thinking of trying a nail next;
> > >I'm wondering if anyone has any better ideas for a core? NB- I've seen the
> > >"soft iron core" that Amazon sells; it's a bit expensive for my taste ($16
> > >for 200mm; I would need four of those rods to complete the project).
> > >
> > >Mike
> > >--
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