Yes, soft iron is generally favored over steel for magnetic
cores, because it is more responsive to magnetic flux
changes.  In particular, avoid high alloy steels (the kind
which can be hardened, often referred to as tool steels).  I
am in the model live steam hobby field where finding
reliable sources of small quantities of any metal is a
prepetual problem.  Here are some tips --

1. Hot rolled steel (the kind with blue scale still on it)
is a reasonable approximation of iron.  It is generally dead
soft and has not been worked after rolling out from a red
hot billet (thus the scale).  You want to stay away from
cold finished or cold rolled steels.  Almost any general
repair or welding shop will have a stock of this laying
around the shop.

2. Almost any reasonable sized city has one or more
organizations of "metalheads", amateur or "home shop"
machinists who love to home build model steam locomotives
and stationary models.  These people can usually give you
tips on local sources of supply such as machine shops that
will let you root around in their scrap barrel and salvage
yards that specialize in reclaimed metal.

3. Check the links posted at the following web site 
http://www.dm.net/~lughaid/ .

4. Find some copies of the "Home Shop Machinist" magazine
(there is a link at the above web site).  They also publish
the "Live Steam" magazine and both carry advertisements from
mail order companies that specialize in the sale of small
bits of metal for the hobby trade.  Some of these suppliers
offer billets of cast iron which is easy to machine (except
that you wind up with grey iron dust *everywhere*) and very
soft.

5. The core material from old power transformers should have
very good magnetic properties but would likely be difficult
to form into a useful shape which I presume to be round.

6. Root around your local electronics supply house for a
magnetically operated solenoid.  The cores of these (the
part that moves) should have very good magnetic properites. 
You should also find these in discarded dishwashers or
washing machines.

	Good luck, Bob Smith

barry lotz wrote:
> 
> Hi
>    Since it's been so quiet ....  It has been mentioned that iron makes
> a better material for sensor feedback coil transducers than steel. I
> have two questions which maybe someone can help. Do manufactured speaker
> coils have a better grade of material for use in feedback coils? I have
> looked around a little but can't seem to find a source of  iron plate or
> round stock. Any thoughts?
> Regards
> Barry
> 
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---------  Avoid computer viruses  --  Practice safe hex 
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 * * Specializing in small, cost effective embedded control
systems * *
Robert L. (Bob) Smith			Smith Machine Works, Inc.
internet   bobsmith5@.............. Lumlay Road
landline   804/745-1065	                Richmond, Virginia
23236+1004
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