[TowerTalk] [Bulk] Cutting a FT-240 type 33...in half ??

[Grant Saviers]

First, why is 393 a requirement?  RG142 silver center/double silver 
braid is rated 2000w at 50Mhz.  I've been using 142 for several years at 
QRO in 240-31 wound chokes and not had a problem.  Then the big snap-ons 
will fit.  I use the big box plastic junction boxes, Carlon or Thomas & 
Betts.  4x4x4, 6x6x4 and 6x6x6 are large enough depending on the core count.

Ferrite cutting/shaping is done with diamond tools and lots of water 
based coolant flushing.  I tile saw will cut it.  One requirement for 
the expected inductance is the surfaces mate precisely, a few microinch 
surface roughness.  I don't think a tile saw will produce flat enough or 
smooth enough mating surfaces.  Look at the flatness/finish on the big 
clamp-ons, that is what is needed.  The gap affect can be measured by 
measuring inductance cut/not cut and calculating the equivalent air 
gap.  I have a $50 Harbor Freight tile saw for cutting fiberglass stock 
and tubing - works fine for that, but does make a mess.

A surface grinder with a thin (0.035") diamond saw will make a 
satisfactory cut and finish but it is a tedious cut with usually a slow 
"plunge cut" automatic downfeed.  It is also very very messy and the 
grinder owner may reject the job on that basis.  Beside very high 
hardness, the ferrite particles are very abrasive.  In a previous life I 
was engaged in ferrite cutting and shaping for recording heads, the 
grinders only did that and were totally enclosed.  Depending on the 
ferrite composition there might be some cobalt or other hazardous trace 
elements that are a concern. Perhaps a tower-talkian knows the type 31 
composition.

At one time I rebuilt a surface grinder from a WE microwave ferrite 
making operation - quite a mess.  Another common ferrite grinding 
operation was making deflection coil armatures for precision CRT's.

Grant KZ1W


On 2/9/2015 9:55 PM, Jim Thomson wrote:
> Ok, I have a requirement where an additional  one or two x  2.4 inch OD, type 33 cores needs  to be added to  an existing choke balun.
> Since each end of the RG-393 silver plated + teflon coax is already silver soldered to a 7-16 DIN connector  at each end of the nema box,
> I would rather not have to take the entire assy apart.  Major pita.    393 coax has TWO  silver plated braids, and in this case, each of the braids has been carefully
> separated at each end, and each braid is silver soldered to a lug,  that is bolted to  the 7-16 din connector flange, via the SS  8-32 machine screws.
> IE: 2 of the 4 corners of each 7-16 din female coax connector gets a braid attachment.
>
> Can a 2.4 inch OD, 1.4 inch ID, type 33 toroid  be cut in half, edges sanded,  then  placed around the existing  4-5 turns of 393 coax, then
> held together via glue, ty-raps, both, or some other method ???   I have an excellent H-V bandsaw, made for cutting steel, hard steel, and AL.
> IE: 80-120-200 ft per minute.   It would slice through a toroid very quickly.   If what I propose is feasible, it would save me a lot of grief.
> I already checked, and the big, type 43 snap on types  will not fit, since they only have a 1 inch ID.
>
> Tnx...... Jim   VE7RF
>
>
>
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