Re: [RFI] Ferrite Beads

[Jim Smith <jimsmith@shaw.ca>]

OK, Ford, I think I've got it but, just to make sure, I'll describe the 
picture I get.

I've got a machinist's vice with two smooth jaws about 1-1/2" high which 
slide along a flat bed on which you can rest stuff, as opposed to the 
usual bench vice where there's a lot of room below the jaws so you can 
get all kinds of different stuff in there. 

The metal blocks are about the same thickness, sit on the flat bed of 
the vice and are placed in contact with the front jaw, the jaws having 
been opened plenty wide enough to get everything in there.  The blocks 
have a gap between them of about an inch, the important thing being that 
the gap is somewhat less than the OD of the toroid. 

The toroid is now placed with its axis of rotation parallel to the vice 
lead screw, resting on the flat bed and symmetrically placed in contact 
with both metal blocks.

Now you hold a suitable drill bit vertical and place it against the 
toroid on the opposite side to the metal blocks and centrally located on 
the toroid while slowly closing the vice jaws.

Once the jaws are just tight enough to hold everything in position and 
you are satisfied that everything is in position, you slowly tighten 
some more until the toroid snaps.

You could do it with a bench vice but you would need 5 hands or a jig.  
A jig would be pretty easy to make if you were doing a lot of these.  
All it would have to do is simulate the flat bed.

It would be really interesting to measure the impedance of a turn of 
wire through the toroid both before it is snapped and again when 
reassembled.

Maybe you should write this up for QST Hints & Kinks.  Sounds like a 
winner to me.

Thanks Ford.  This goes into my notebook.

73, Jim   VE7FO

Ford Peterson wrote:

> > Sounds very ingenious and effective.  The only problem is that I can't 
> > picture it.  Can you give us a little more info?
> >
> > 73, Jim   VE7FO
> >    
>
> Let me try again.  I have had good luck snapping toroidal forms in two to form a home-made split suppressor at about 1/3 the cost of a commercial split bead.  Ferrite is more akin to ceramic than any other material I've handled.  It is extremely hard--almost impervious to scratching, grinding, filing, etc.  So scoring a toroid is difficult.  I have managed to score them with a sharp file (only to ruin the file I might add).  Once scored, they snap along the line every time.
>
> Since they are so hard, scoring them is also expensive (files are not cheap and the teeth are damaged almost immediately).  So I ventured into the notion of just snapping them and let the chips (pun intended) fall where they may.  When you strike the toroid, like with a hammer and chisel, they fracture into a random number of pieces, making the unit virtually worthless unless you are into jig saw puzzles with a tweezers and magnifying glass.  What I have found is that a steady pressure at a point load will snap them every time at the point load.
>
> Take an example of a 1.25" OD toroid.  Using a machinist's vice (read smooth jawed), I can place two metal blocks in the open vice, spaced about 1" apart.  Place the toroid in the vice (not yet clamped of course) with each end touching the metal blocks.  Using a 1/4" or so drill bit, I hold the shank of the drill bit vertically on the opposite side of the toroid but in the middle of the two blocks and begin to clamp the vice.  When the vice gets clamped, the drill bit puts a uniform point load on both sides (in the middle) of the toroid.  Once snug, the toroid will snap under the load right at the drill bit using a very gentle turn of the vice handle.  I have tried this several times using some junk toroids laying around here and they snap in the same spot, making two halves every time.  On a couple of them, little chips would disappear from the edges of the break, but the bulk of the mass is intact.  The fracture is very rough.  But if you take care to keep the halves matched, they will go back together again with only a minute hairline fracture crack separating the two halves.
>
>
>
> Ford-N0FP
> ford@cmgate.com
>
>
>
>
>
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