X band cavity design and microwave safety

[coppercone2]

those tend to make a super pin point flame, if you get one of those stock kits with a thin nozzle, you won't make big lap joints, thats like if you want to do copper welding, not brazing (the idea is with a copper weld, which is really like brass, you use a alloy that does not flow so well but offers strength from the actual bead), or very small area silver solder. i  think mapp gas air would be better for that (plumbers torch). It will do it I think.

I have one of those torches and I am disappointed in the oxygen bottles (they seem to leak for some reason), and I personally think for indoor storage, the fucking container those gases comes in is less safe then the acetylene MC tank. I caught those benzomatic cylinders leaking more then a few times. Replace when old and do not use the youtube trick of refilling them with wet rags and the freezer, the seal is too low quality to be reused.

When you make your holes, get yourself a 10mm reamer, start the hole out with a narrow step drill, and when you mark the hole, use calipers to scratch (not sure if you are familiar with how to use them, their carbide tipped so you actually extend it to the measurement you want, then drag it on the edge so it leaves a scribe line to the right dimension. You make 2 scribe lines from 2 faces and you get a + sign, that's very accurate. Then if you want precision, you drag a sharp hole indicator punch on it till it gets stuck on the scratch line intersection point, then you mark it, then you use a stiff drill (I like a sharp carbide countersink) to make a deeper hole, then you drill it with a pilot, then you use a step drill, then you use a reamer.

This should get you extremely precise holes in dimension and location in thin material with a hand drill.

https://www.mcmaster.com/8851A25/ - reamer 10mm
https://www.mcmaster.com/8841A21/ - step drill
https://www.mcmaster.com/2915A13/ - countersink

and I assume you have a caliper and normal drill bits.

That should reduce your error there.

[coppercone2]

the problem is the test tube is likely way less accurate then the hole I told you how to make here

if you want it to fit really nice you would need to take the test tube and grind it on a diamond wheel on a rotary surface grinding machine. Might not be hard to do if you are working with the university and they have a machine/glass shop. If they help you, when you buy parts, buy extra and give it to them (i.e. extra test tube), often they like the weird artifacts they get to keep from jobs. It makes it more cool/thoughtful then a normal machine shop if they are doing scientific things. This job is likely going to make them think a little because its non standard, you probobly need to offer some intradepartment cooperation and resources. For some reason I don't think the chemistry department is going to have this machine, unless maybe they are making their own cuvettes (little extremely precise expensive piece of glass rectangle test tube for photospectroscopy machines).

Also, if you want to put a test tube into a thin metal box and align it, you need to glue on some bushings to help align the tube (fat precise washer you can buy on mcmaster that has a precise internal diameter), or you can make the waveguide wall thicker before you drill/ream it, so you don't need two steps.  Otherwise the long test tube will try to align with 1mm thick waveguide body, rather then a 1cm thick bushing. (i.e. get yourself two 1cm thick chunks of brass, braze them on the tube, then drill it, but then you need a stiff drilling machine. If you buy and glue bushings, you can make your hole first then glue the bushing in place over a 10mm rod that you insert through the waveguide before hand, with a bit of grease on it, so the glue does not stick there. Be sure to take out the center when the glue is not completely cured because I had stuff get stuck despite applying vaseline). This will be the tricky magical not enough resources moment, to add bushings to the hole.

Likely it will be hard to align the two holes, you need a machine to do it right. ask them for help

Also, aircraft trick : if you are sure the waveguide is good, like rectangular, after you drill your top hole, you can glue a BIG tall bushing to the top with super glue, aligned over a 10mm pin, let it cure, then drill down from the top with a long drill bit to make your other hole. You can tesslate bushings, to make a properly centered but different diameter hole on the other side, so you can make both holes reamed, rather then drilling a nasty properly centered but crappy edge quality hole on the other side with a 10mm drill bit. It would mean you need to glue a bushing into a bushing after you glue a aligned bushing on. Then you take it apart with fire, you would need to make sure the two bushings fit together. But then you can do it with a hand drill pretty good. And you might need a long length drill bit if you are drilling a thin hole with a drill bit aligned by a bunch of bushings. so get a 10mm ID bushing, center and glue it over a 10mm hole with a 10mm pin, then glue a 5mm OD bushing inside of the 10mm bushing, then drill through with a 5mm drill, then do the other side like you did the first side. you can make all sorts of structures with the bushing to make it more stiff, like put a long one in there.

[ChristofferB]

My university fired all glass blowers and specialized technicians half a decade a go, because just buying from external companies would be "better"

I have a precision drill press, my plan was to drill a 3mm pilot hole with a carbide stub drill, drill out to 10mm with a step drill (last step very very slowly, maybe turning by hand with a tap holder).

I'm going to reference lenghtwise off of the waveguide flange, as I'm pretty sure that is perpendicular to the waveguide, and then drill from each side.

The test tube is actually only 6mm, my plan was to make a plastic bushing, slightly eccentric, so turning the entire bushing would spin the tube around 0.5-1 mm to be able to allign it, that would allow me to calibrate around any mechanical sloppyness.

The test tubes are going to be consumables, and should not be very custom made.

[coppercone2]

how has the lack of friendly expertise and delays worked out for them? Like, technician telling you something without trying to sell you something or further a contract?

from the sounds of things you are on your own. I managed to trade, mingle and 'help out' in exchange for skilled labor. If they wanted a paper trail, it would never happen, because it would be ridiculous, being charged for every bullshit and stuffed into a bureaucracy.

Sometimes local people will help because they are bored or just use it as mingling (be sure to tell the professors who helped you). Obviously don't over use them, if you have this opportunity, or people get in trouble.

on paper desk engineer projects that are delayed for 3 weeks by shipping because of the most minor of errors is the typical result, IMO. Not to mention excessive stress from documentation and proofreading because of the penalties for minor errors (good place to put the minds of creative people, making sure documents line up to optical clarity.. test tube holder turns into the fucking apollo project, IMO thats what accounting is, to make sure your money comes in on time in the correct amount). Normally it would be 'walk in at lunch time with a napkin sketch'  (not to mention having people happy to see you and making friends). I feel like excessive outsourcing turns into compartmentalization also, everything turns secret. Top level people think it makes some kind of super focused experts but its just choking.

Of course if its understaffed people want to kill you if you do any of this (might want to take it easy because of COVID).

Also, for free shop work, I would recommend just having them only do the bare minimum that you can't do with hand tools. Specifically ask not to chamfuer, deburr (your a big boy that can handle a razor), polish, or anything that can be handled with a minimum tool kit, sand paper and harbor freight. And don't bog them down with wood or paint.

[ChristofferB]

It works exactly as unwell as you'd expect it to, but hey, rather cut costs there than reduce the number of research groups right?

I think I'm good on the machining part, I'll just channel my inner Clickspring and spend 500 hours hand filing and polishing

And I can get a bit of help in other aspects of my project; I've been allowed to calibrate my newly aquired gaussmeter against the uni's EPR magnet!

I think I actually have most of the components needed now, over the last few months I've added to my lab:

 - Tunable Gunn X-band source
 - Hall gaussmeter (F. W. Bell 615)
 - Brookdeal 402 50 KHz lock-in amplifier
 - X-band magic tee, wavemeter, attenuator
 - X-Y recorder
 - Sweepable Hz to MHz generator (for modulation)
 - Slow sweep generator (up to 1000 min, between 0 and 5V

And in the works is my cavity, and the magnet.

[ejeffrey]

Sweeping frequency is tough to do with good repeatability. Sweeping a DC electromagnets current with a slow (minutes to hours) ramp gen is the option people has gone for. More recently, short bursts of RF energy and then fourier transforming the decaying echo. EPR is still usually CW swept field.

I'm curious why sweeping frequency is tough to do? The frequency of a signal is one of the things we can measure and control most precisely of all physical properties - we can generate tones in the lab that are accurate to ten decimal places or more quite 'trivially', but we need entire industries and years of expertise to create a voltage or current with have as many significant digits.

A few reasons, some historical and some still important today, mostly related to tuned circuits, at least from my limited experience with NMR.  I think ESR is similar.

It's generally easier to generate high power RF with a tuned source.  Sure you can easily get broadband power amplifiers now but they are less efficient and have more distortion.  Likewise the transmit and receive antennas are often tuned coils that don't work well with botadband excitation.

In the olden days, real time signal processing didn't exist or was expensive.  The detection was often done with bandpass filters and envelope detectors rather than an FFT.  You could still make this frequency tunable with a heterodyne receiver but that makes the system substantially more complicated.

The final issue is that you need to avoid direct detection of your drive signal.  In pulsed NMR this is done with time gating, but in CW NMR you arrange the pickup coil at 90 degrees to the transmit coil and adjust it until you get a null.  Then your receiver only sees the NMR signal not the excitation.  However if you sweep frequency the field configuration will change and you will wander off null.

For this reason my understanding is that today CW NMR is still done with field swept but pulsed NMR can be done either way but is more often frequency swept.

[ChristofferB]

That makes a lot of sense, the entire concept of sweeping is lost once we get to modern pulsed ESR/EPR, those are fixed frequency (tuned before the actual experiment to find resonance).

Maybe the field of ftnmr and epr just made CW more or less obsolete before the needed electronics was available to do freq. Sweep

[ChristofferB]

I know I just said the opposite, but the more I think about it, the more I want to try frequency sweeping first.

My gunn module is simply tuned by 5 to 35V, and has a modulation input. It would be a million times easier than doing it magnetically. It may not work, but it would be a fairly small amount of time wasted.

[LaserSteve]

Quote" Also, for free shop work, I would recommend just having them only do the bare minimum that you can't do with hand tools. Specifically ask not to chamfer, deburr (your a big boy that can handle a razor), polish, or anything that can be handled with a minimum tool kit, sand paper and harbor freight. And don't bog them down with wood or paint. "

If you asked me, a  Senior Technician, to let something out of my shop without deburring, edging, sandblasting, chamfer, whatsoever....
Well, the answer would be: We'd be having a little talk about integrity,  and I'd be upstairs, looking at your lab safety situation for a good ten minutes.
~
Rule one: Unless the prof specifies "quick junk", never make junk for a professor or researcher..
Rule two: Any "quick junk" you make, you will have to look at for the rest of your career as it remains in use for decades.
Rule three: During a public tour, the Department Chair will notice the crappy work and say something.
Rule four: Your worst piece of work ever will be transferred to an undergraduate lab full of engineering students, for critique, for decades. A parent will seek you out and ask why their son or daughter does not deserve something equal or better to the plant they work in.
~
Besides, I can deburr at the speed of summer lightning.  Most of my clientele has no idea what "break edges" means.

Care to guess how those rules came about?

Steve

[coppercone2]

sounds high end, I had a different facility/campus in mind.