Subject: Induction brazing from old microwave oven?

From: <[email-masked]>
Date: 29 Jul 1996 15:02:55 GMT

Has anyone constructed a homemade induction brazing coil powered from
a salvaged home microwave oven?  I think the usual oven is rated around
1000 watts, so it should provide enough power for a small coil, say maybe
1-inch inside diameter.  I want to join brass to 1/8-inch O-1 drill rod and make
a nice clean joint without any surplus squirting out the edges.  I've used
paste of silver/flux and also stick silver solder with a propane torch, but
haven't developed the skills to make a perfect joint.  According to the
AWS, for a tubular type joint, the space allowed for the filler metal should
be around 0.002 to 0.005 inches.  Any comments will be welcome. Dave

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From: [email-masked] (Peter Drumm)
Date: 30 Jul 1996 10:35:39 GMT

In message <[email-masked]> - <[email-masked]>
writes:
:->
:->
:->Has anyone constructed a homemade induction brazing coil powered from
:->a salvaged home microwave oven?  I think the usual oven is rated around
:->1000 watts, so it should provide enough power for a small coil, say maybe
:->1-inch inside diameter.  I want to join brass to 1/8-inch O-1 drill rod and make
:->a nice clean joint without any surplus squirting out the edges.  I've used
:->paste of silver/flux and also stick silver solder with a propane torch, but
:->haven't developed the skills to make a perfect joint.  According to the
:->AWS, for a tubular type joint, the space allowed for the filler metal should
:->be around 0.002 to 0.005 inches.  Any comments will be welcome. Dave

Microwave ovens use high voltage, around 4000VDC at the magnetron, so
1000 watts would only be .25 amp. Not enough to warm up much of
anything.

[email-masked]
Wausau, WI. 44d 58m 00s N x 89d 36m 45s W
All opinions are my own, even if they are wrong!

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From: [email-masked] (Paul Amaranth)
Date: 30 Jul 1996 16:00:17 GMT

>:->1-inch inside diameter.  I want to join brass to 1/8-inch O-1 drill rod and make
<snip>
>1000 watts would only be .25 amp. Not enough to warm up much of

I don't think this is possible.  There really isn't much in a microwave,
mostly a big honking transformer, a diode, maybe a capacitor and the
magnetron.  Any metal in a microwave oven turns out to be really bad news.
It generates all manner of interesting arcs, but that won't be very useful.

If I understand induction systems, you run a high power RF source through
the induction coil in which the item you're heating is in the center.
Microwaves are too short to handle in that manner; you have to run
them through waveguides.  Leaking microwaves are also rather unpleasant
since they cook food by being absorbed by water molecules and making them
vibrate (ie get hot).  This is in addition to the lethal nature of the
voltages involved.

Lindsay had a book on induction principles.  You could probably put
something together using a couple of 801s or similar high power RF
tubes (check out a radio amateur's handbook).  Still, this would not
be easy; RF work is pretty wierd and getting the power transfered to
where you want it (rather than, say, dissipating on the plates of the
tubes) is no small trick.  And, turning it on will probably get the 
FCC on your back.  They take a pretty dim view of blanking out radio 
reception for a multi-block area :-)  Still, this avenue is possible,
but I wouldn't recommend it to anyone who didn't have experience building
and handling high power RF equipment.  That stuff is pretty dangerous.
Forget the microwave though.

--
Paul Amaranth  Manager User Services - office: (810) 370 4541 (also voicemail)
               (e-mail)     [email-masked]         
               URL http://www.acs.oakland.edu/~amaranth

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From: [email-masked] (Reg H. Beardsley)
Date: 30 Jul 1996 22:31:54 GMT

A perfect joint won't be any easier w/ an induction coil.  You still
have to apply the correct amount of filler metal and flux.  The coil
just provides better heat control in repetitive operations, since you
can use the oven time mechanism to turn the current on and off.

The thing to do is strip the high voltage secondary winding and put on
a low voltage secondary in its place.  Put on a trial 10 turn winding
to find out how many turns you need for the output voltage you want.

Naturally, you'll need to size the new secondary winding for the current
it's expected to carry.  

If this is unfamiliar ground, you probably should learn more about transformers
before you tackle this particular project...

Just remember:

   1) Don't exceed the VA rating of the original windings

   2) Don't electrocute yourself.

   3) If you don't have experience w/ this stuff find someone who does to
      help you.  It's not hard to do, but mother nature is VERY unforgiving
      when you fool w/ power in the KVA range.  Even at low potentials the
      current can burn you pretty severely.  At high potentials it's so
      dangerous it's ridiculous.

The original transformer secondary output is EXTREMELY dangerous.  Don't
even THINK about applying power to it unless it's in a high voltage cage.

Any attempt to measure the voltage w/o a high voltage probe is guaranteed
to be fatal!

Have fun!

-- 

------------------------------------------------------------------------
               I am solely responsible for the contents...

Reginald H. Beardsley                                      [email-masked]

              Exploration Software Consultants Incorporated
------------------------------------------------------------------------

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From: [email-masked] (Steve Gray)
Date: Tue, 30 Jul 1996 21:21:21 -0700

> be around 0.002 to 0.005 inches.  Any comments will be welcome. Dave

   Are you sure that the frequency of a microwave (which is meant to heat
water molucules) would be suitable for heating ferrous material? I'm not
saying it is or is not, but that you should check.

-- 
Steve Gray
Gray Associates
Santa Monica CA
Algorithms, computer graphics
Mechanical inventions