LaserSaber,
That looks like a very interesting gizmo you are making for your make and break.  Hope it works well.
I have seen some other designs like that one, so it must be good.  Please keep posting, even while you are on vacation if you can.  I can't wait to see your plans.

Cap-Z-ro,
Stubblefield did say that the core could be removed for repair purposes, so why not for experimenting?  It should be fine.  It is just in the way you put the coil together.  Make sure the hole for the bolt is large enough to remove the bolt with the insulating cover on it.  If you only make the hole large enough to put the bolt through, then you cover the bolt with tape, etc., the bolt wont be able to go back through the hole.  You would only need to make the holes just a tiny bit larger than usual.  I suppose you would also have to make sure the first winding was not too terribly tight on the bolt. 

Why couldn't you use a cardboard tube with the bolt inside?  If the tube was not too thick, wouldn't that work?  Put the bolt inside the cardboard tube, then wind the coil on the cardboard not the bolt.  Leave just enough room inside the tube to be able to remove the bolt.  Does that sound plausible?   I would imagine the thin cardboard tube should not impede the properties of the coil.  Anyone know for certain about that?  Maybe you could make  your own thin cardboard tube with some layers of paper not quite as thick as cardboard but thick enough to make a tube.

I think Jeanna used a straw on one of her coils, with the bolt inside, I am assuming.

QuoteThey retain their magnetism after the magnetic field is turned off.

You are going to have some retention with soft iron. You would need an opposing field or polarity to drop it back down to zero. A ferrite core may not have the field intensity like soft iron but may be doable.   

I have been searching for ferrite rods for cores for some time now.  I think I posted this somewhere a good time ago, but now, thanks to Lasersaber, we have a good source for the cotton wire, I will bring it up again.  An alternative that is not very expensive and will allow for easy assembly/disassemble would be the 1" OD 5/$1 toroids from Goldmine.

I would not glue these in any way but, think about it, they could be stacked on a pvc or wood rod and bolted end to end to hold the stack of toroids together like a stack of pennies.  The coil could then be wound around the stack and it will be used as a solid core.

Even though the permeability of the goldmine toroids is not really known, many of us have made some really god JT circuits using them and for a really good JT circuit you need high permeability so I would guess it is pretty good.

We have been able to get some very high frequencies out of our little JT circuits with some really good back EMF spikes so I am confident that this ferrite material will easily keep up with any make/break system used in the NS coil.

If I am not clear on my explanation, let me know and I will attempt to make yet another very crude drawing.

Bill

Quote from: lasersaber on February 25, 2010, 06:58:39 AM
...  I had high hopes for those soft iron cores.  Now I have ten junk cores. I will now have to unwind my coils and make new ones with better cores in the future. ...

Just an offhand tip?
If soft (annealed) cores don't work for this application, then the typical American construction rebar hadn't ought to work any better.  The stuff is made out of soft cast iron, as far as I know.  It's easy to come by, though.

--Lee

Got my bolts and ready to make some new coils.
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Here are two good reads.  First has some good vids to watch.  Both informative.

http://www.stmary.ws/highschool/physics/home/notes/electricity/magnetism/default.htm

St. Mary's Physics Online



http://info.ee.surrey.ac.uk/Workshop/advice/coils/force.html
The force produced by a magnetic field

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My ? of the day.   

Anyone know what Rad E 4 means, or more importantly, what would it have meant to Stubblefield or those scientists of that day?