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Quince
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[*] posted on 2-10-2006 at 05:34
Microwave drill


As someone already pointed out in another thread, http://www.eng.tau.ac.il/~jerby/microwave_drill/index.html
Note specifically this photograph: http://www.heise.de/tp/r4/artikel/13/13450/13450_2.jpg
(a larger version of the image is in some of the papers)
Looks like the magnetron is just sitting on top of a waveguide with some matching knobs. Looks very DIYable.

Now, in some images in the patent, he discusses a version where the working end is separate from the source. What type of coaxial cable would be suitable for the typical consumer magnetron? How would one go about optimally coupling the cable to the magnetron, and what is the exact nature of the matching adjustment things such as 66 in patent fig.9?




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Mr. Wizard
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[*] posted on 2-10-2006 at 05:52


An Aluminum foil hat, and outfit might be real useful while playing with that rig. Throw in a pair of aluminum screen goggles with three layers of fine wire screen. I don't recommend any DIY experimentation until you get your cornea transplants lined up ;)

No doubt it works, but how much leakage is there from the tool to work interface?

People who used to work in the vicinity of radars have told me they used to attach an old fashioned flash bulb to their work clothes to warn them if they strayed into a microwave beam. A small neon bulb would work, but it doesn't get your attention like a flash bulb.
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Quince
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[*] posted on 2-10-2006 at 06:21


This device is not intended to be operated in the open: from the patent, "Regarding microwave safety, its radiation emission can be limited to strict international standards by use of grid screens, graphite absorbers and the like as required for each application." Photographs of the device in operation always show it in a safety enclosure.

So, getting back on topic to my questions...

[Edited on 2-10-2006 by Quince]




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12AX7
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[*] posted on 2-10-2006 at 06:25


Sounds like high voltage and dielectric loss heating to me. The advantage to microwaves, of course, is the high voltage and loss reached at such a point. Unfortunately, low loss coax at that frequency and power isn't easy to come by (not to speak of flexibility!).

Tim




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[*] posted on 2-10-2006 at 07:09


Okay then, as to the topic of "your questions".

Basically, they're ridiculous. Given that the patent is dated 2 days short of 6 years ago, combined with the fact that there is no commercial unit available, STILL.

Methinks that this problem is not about to be solved with some simple back of the envelope calcs, nor asking somebody to say "Here comes the aeroplane".

Btw - I think I hear Ray, Lucy and Trinity calling for you. Better get back to SunnyVale..
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Quince
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[*] posted on 2-10-2006 at 19:24


Who cares if there's a commercial unit? The prototypes work fine and the research was accepted in peer reviewed publications; that's sufficient for me to consider building one. Thanks for contributing absolutely nothing but your lame trolling to this thread.

[Edited on 3-10-2006 by Quince]




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[*] posted on 2-10-2006 at 19:45


Okay, fair call. Sorry for being such a shit.

Though, to be serious - you appear to have quite some considerable knowledge concerning Xrays and the like.

I know practically nothing of them except the pain it causes my wallet whenever I've one taken.

Annyway, I'm too stupid to know and too lazy to look - but what sort of frequency are they running at? I seem to remember an Xray machine that had the generator seperate from the emmitter. Perhaps it would be possible to snare an old co-ax from one of those babies. A decommisioned dental or vetinary unit??

Once again, I'd like to apologise for being downright rude and unpleasant. Perhaps it would be more helpfull for me to explain my reasoning. The only reason I mentioned the lack of a commercial unit was that if indeed the unit is as great as proclaimed, i.e Cheap hardware, no fast rotating parts, cheap to operate, small, quiet and dustfree and FAST, if it were in fact this good (which I have no reason to believe it's not) then there'd be a hell of a lot to be gained commercially from such a device. The fact that it had not yet been realised led me to believe that it wasn't for a lack of trying, rather (currently) insurmountable technical issues - i.e Sufficient radiation shielding. That the unit does not drill a hole that is dimensionally accurate, nor the fact that material is only softened as opposed to being vaporised and immediately evacuated from the hole.

Though from an analytical standpoint, perhaps all it would require would be a faraday cage large enough to accomodate the work-piece and the unit. Not quite so portable anymore, however I imagine that there would be a degree of loss perpendicular to the hole being drilled - i.e one would need to shield the top, bottom & sides of the workpiece. This clearly would become an issue with parts of large fixed structures.

Once again, sorry for being such a shit.
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[*] posted on 2-10-2006 at 22:43


LOL, I don't care so much about it's utility as the novelty factor. It's just a toy I want to build and play around with for a little while.



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[*] posted on 2-10-2006 at 22:48


Quote:
Originally posted by 12AX7
low loss coax at that frequency and power isn't easy to come by

How about http://cgi.ebay.com/ANDREW-fsj4-50B-1-2-Heliax-Sureflex-Cabl...
The connectors themselves are rated at 2.5 kW, but I don't know about the cable. I'm having trouble figuring out how to properly search for cable, and I'm mostly getting data for connector ratings.

And again, I'm not clear on how the impedance matching is accomplished.

[Edited on 3-10-2006 by Quince]




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[*] posted on 3-10-2006 at 08:14


I think the reason this hasn't been explored commercially is that for home/domestic use, obviously all sorts of shielding would be needed that is impractical to say the least, and for industrial use, mankind has done a pretty good job of honing the art (and it IS an art)of industrial tools, from the English wheel and simple hydraulic lathe all the way to wire EDM and AutoCAD laser cutting, where developing one more way to turn electricity into cut metal/material seems irrelevant without a specific purpose or specialization of this particular technology.



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[*] posted on 4-10-2006 at 00:19


2.145 GHZ is too low a frequency to drill very small holes, so I think an oven magnetron is a poor choice. A good military surplus unit 18 GHZ or higher would be more useful for super precise small holes in my opinion.

Try cooking gnats. You can watch them fly around in there on full power, and after a minute open the door and watch them fly right on out. I see this all the time in this part of the country in the summer, damn annoying little things. They are so tiny (maybe also so dry inside?) they just do not absorb enough radiation to feel it. In fact hot water vapor inside the oven is the only way to take them out. I have not been able to fry a single one from the microwaves alone. No I am not sadastic towards our tiny annoying friends, it is simply impossible to turn the oven on after shutting the door without one or more making their way inside.

I used to have a one megawatt pulsed klystron from a Navy ship, too bad I let it go long before I learned about building a drill. That would have been a fun project.
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[*] posted on 4-10-2006 at 02:42


Drilling small holes in hard materials is easy -- I have jeweller's diamon bits and they last well if you do it under water.

I'm still wondering about the cable, and matching impedances, and those questions are why I started the thread. If you can't address those specific questions, please don't divert my thread any more.

[Edited on 4-10-2006 by Quince]




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[*] posted on 4-10-2006 at 09:58


"please don't divert my thread any more"

Your topic was microwave drill, and my post was precisely on topic. If you don't want people saying anything about it don't post it in an open public forum.

Your topic should have been titled "don't talk to me about microwave drills, just tell me how to hook it up as I am a whining floosey"
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[*] posted on 4-10-2006 at 13:51


IrC, not a bad title suggestion given the nature of our present protagonist. ;)

Might be able to Google for attenuation and ratings of said coax. If nothing else, ask around ameteur radio places (including reality, there is such a thing), IIRC there's a 10cm band or something that's pretty close to 2.4GHz.

As for gnats, they are less than 1/20th the wavelength, a ratio generally considered acceptable for "frequencies staying in the wires". Which is exactly why all the 2.4GHz crap in your computer has to be onboard the chip itself, things get smaller for things to behave like voltages and currents on wires and transistors.

Tim




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[*] posted on 4-10-2006 at 17:47


Quote:
Originally posted by IrC
"please don't divert my thread any more"

Your topic was microwave drill

The fuck it was! That's the title of the thread, a short and generalized version of the topic; the full topic, contained in the first post, was obviously the specific questions there.

[Edited on 5-10-2006 by Quince]




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[*] posted on 4-10-2006 at 19:10


It does help when you want others to provide you with help or information to not have the personality of a rope.
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[*] posted on 13-10-2006 at 19:28


I'm fairly sure I've seen microwave cable in the Farnell catalog - though its wasn't terribly flexible. It consisted of a solid copper tube (sliver plated), teflon dielectric, and silverplated iron (?) center conductor.

Matching/coupling: I think you will still need a section of waveguide to couple to a commercial magnetron, add the stub tuner to this (I think its just 3 screws poking into the waveguide), then the co-ax coupling at the other end. This involves poking the centre conductor into the guide at 1/4 wave from the end and terminating the shield on the guidewall.

I'm no expert on this, its just the few bits I've gleaned over the years - should help with your google searches though.




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