building an electric bell-ringer

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Just starting out as a hobbyist in this great field...!!

For whatever reason, I missed out on a lot when I was a boy, so now as
an adult learner I'm working through "The Boy Electrician", published
by Lindsay Pubs. BTW, this is a great book filled with
fun projects that you can actually BUILD.

The project is an electric bell-ringer. I've gotten most of the needed
parts so far, the only problem I'm having is securing an iron yoke for
the magnet spools and also a small rectangular piece of iron or plate
to serve as the armature. I've scoured the net and have found suppliers
selling brass, steel, alum, etc, but no iron.

www.metalexpress.net ---- sells "cast iron" but it doesn't say if its
"soft iron" -
How important is it that these parts be iron? My thoughts is that the
plans call for them to be iron since it would increase the permeability
of the magnet spools and the armature.

I've heard that rotors often use iron. Maybe I'll try one from a
junkyard if the cast iron is too costly. How difficult is it to remove
the iron pieces from the rotor? I'm thinking they may not be the right
shape or size for the project. I have no experience taking apart this
type of motor, but I'm willing to give it a shot if it means completing
the project correctly according to plans.

Any suggestions/advice is greatly appreciated.

Thank you,

Chris

 

[Homer J Simpson]

The project is an electric bell-ringer. I've gotten most of the needed
parts so far, the only problem I'm having is securing an iron yoke for
the magnet spools and also a small rectangular piece of iron or plate
to serve as the armature. I've scoured the net and have found suppliers
selling brass, steel, alum, etc, but no iron.

A piece of steel is probably close enough. Some of these things used to use
a collection of iron wires as the yoke. A steel bolt might also work OK. But
easiest nowadays might be to find some old transformers and take the
laminations out of those.

 

[default]

The project is an electric bell-ringer. I've gotten most of the needed
parts so far, the only problem I'm having is securing an iron yoke for
the magnet spools and also a small rectangular piece of iron or plate
to serve as the armature. I've scoured the net and have found suppliers
selling brass, steel, alum, etc, but no iron.

I remember having fun with that stuff.

The material is not critical at all. Any bolt or part of one will
work fine, same thing with the armature a piece of steel 1/16-1/8"
thick would be good. A somewhat harder part may be the piece of
spring steel or spring to use and the contacts. If you can find some
steel strapping used to bind lumber together that works great for a
leaf spring.

You don't have to buy any of that stuff just use what you find in the
trash.

The armature needs a spring, of course, but so do the points. If you
just make fixed (unmovable) points on the armature, you wind up with a
high pitched buzzer. There has to be another spring on one of the
contact points to allow inertia and over-travel to slow the action of
the armature and clapper.

One source of iron (steel) are railroad spikes. They are about 5/8"
square and make a great electromagnet. Almost no residual magnetism
when the power is removed. There are lots of 120 V shaded pole
induction motors with the same 5/8" square bobbin and coil. A short
walk on a track is all it takes to find a few. Hacksaw will cut them
and they can be drilled and tapped.

American Science and surplus is a good source for unusual junk and
they usually have some induction motors priced cheap - great paper
catalog too. www.sciplus.com

Love those Lindsay reprints . . . . I have a collection. I find I
have a better appreciation of electronics and history from reading and
building the stuff. I made numerous Tesla coils, a very large
induction coil, and several static generators using instructions from
the turn of the century, or earlier.

Really interesting reading Maxwell and his theories of electricity and
magnetism. (Dover Books for Maxwell and Gilbert reprints) He's
coming up with all manner of mechanical contraptions in an effort to
explain what he thinks is happening in physics. Struggling to explain
induction, inductive reactance, resonance, transformers, etc., but
without the words and conceptual framework we now take for granted.

You're not likely to find cotton covered wire, gutta percha covered
wire, hard rubber sheet, rod, or tubing, but modern wire and plastics
work just fine.

 

[Bob Eld]

Just starting out as a hobbyist in this great field...!!

For whatever reason, I missed out on a lot when I was a boy, so now as
an adult learner I'm working through "The Boy Electrician", published
by Lindsay Pubs. BTW, this is a great book filled with
fun projects that you can actually BUILD.

The project is an electric bell-ringer. I've gotten most of the needed
parts so far, the only problem I'm having is securing an iron yoke for
the magnet spools and also a small rectangular piece of iron or plate
to serve as the armature. I've scoured the net and have found suppliers
selling brass, steel, alum, etc, but no iron.

www.metalexpress.net ---- sells "cast iron" but it doesn't say if its
"soft iron" -
How important is it that these parts be iron? My thoughts is that the
plans call for them to be iron since it would increase the permeability
of the magnet spools and the armature.

I've heard that rotors often use iron. Maybe I'll try one from a
junkyard if the cast iron is too costly. How difficult is it to remove
the iron pieces from the rotor? I'm thinking they may not be the right
shape or size for the project. I have no experience taking apart this
type of motor, but I'm willing to give it a shot if it means completing
the project correctly according to plans.

Any suggestions/advice is greatly appreciated.

Thank you,

Chris

Mild steel is iron. In fact low carbon, low manganese steels, AISI 1000
series grades are purer iron than the stuff they used to call iron and cast
iron has way more carbon than virtually any steel, go figure! Aside from the
pure element iron, the irons of commerce were really a statement of
processes used to make them and their lack of purity than anything else. The
word steel implied highly refined iron, controlled process, heatreatment,
and specific alloys. For your purposes mild steel that hardware store bolts
are made of should work fine.
Bob