I had to check carefully that this wasn’t an April Fool’s deal, but it is apparently real. Neat trick:
[youtube width=”800″ height=”540″]http://www.youtube.com/watch?v=LVODJm05plw[/youtube]
I gotta say, it’s a pretty slick idea that I’m dying to try on my wife’s microwave.
This one about balancing rotating machinery is also interesting:
[youtube width=”800″ height=”540″]http://www.youtube.com/watch?v=pMxtYRdbjwI[/youtube]
I’ve got a crazy idea we can predict chatter frequencies with a rig like that and do it very cheaply. Will have to try some experiments.
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I don’t know that I’d trust a microwave for that application, it’s not intended to heat metal and I’ve seen more than one ruined by spoon or metal object left in a bowl or cup of something. I’ve got a better & cheaper alternative if using your stove burner or oven isn’t convenient. There are an abundance of single burner induction hotplates out there for sub $100. They are intended to heat ferrous metal and magnetic stainless and would probably be better suited to the application than trashing the microwave. Here’s link to an example, plenty more on Amazon.
http://www.amazon.com/Aroma-AID-506-Induction-Plate-Black/dp/B0044WWBGG
On a positive note, it would be great for keeping a coffee pot warm in the shop with little fire hazard to be concerned about. Having an induction cooktop, I can tell you first hand that when I cook greasy or splattering foods, I lay a sheet of parchment paper on the cooktop, put the pan on top, cook, then toss the splattered paper in the trash. No greasy clean up. Try THAT with your gas or electric range.
Like the induction plate idea, Charles!
Hmm. this is not the same as a spoon in a microwave. If the rag is damp there won’t be a problem. The microwave is not heating the metal directly, it is heating the water in the rag and the steam heats the metal so it is still doing what it is designed to.
Actually, the method shown is quite safe for microwave ovens as long as you keep the cloth both thick and wet. The hazard to microwave ovens is that using them without something to absorb the microwave radiation results in the energy being partially reflected back into the microwave tube and overheating it. As a result the cloth should be thick to hold a significant amount of water, and you also need to ensure that you don’t cook the cloth to approaching a dry state.
It is relatively easy to determine if enough microwave energy is not being absorbed when the contents of the oven is metallic – you will rapidly get arcing. Anytime that you hear or see arcing you should immediately stop the oven are redo the loading in a much better manner that includes a microwave absorbing load. A purely metallic load gets high frequency currents induced into it by the microwave photons (limited by skin depth) and the voltage buildup is what causes the arcing.
By wrapping the metallic part in water soaked cloth the microwaves barely “see” the metallic object since the water absorbs the incident microwaves before they reach the metallic object. Hence, the complete wrapping is also quite important. The video author has actually done his homework (I’m a recently retired research electronics engineer).
What is much less obvious and more difficult to do is to empirically determine how much weight and where to put it to dampen vibration. Automotive tire balancing machines do it but I have yet to see a way to do it on a motor (for example). It all seems to be trial and error. If you could figure that out then you’d really have something I could use.
If by “motor” you mean an electric motor, you could fabricate a couple of collars that fit on the motor shaft ends (assuming that the motor has a double ended shaft). A tapped through hole going through both sides of the collar (this hole is perpendicular to the collar bore) allows for installing either different length set screws or short bolts. Try to minimize the vibration at the resonant frequency at one end of the shaft first, and then proceed to the other end. Some iteration may be required. If you meant an internal combustion engine (which many incorrectly call a “motor” – motors have 1 or less moving parts while engines have more than 1 moving part), I cannot offer any advice since imbalances could occur in several rotating components.
Since I have the appropriate instrumentation I accomplish this quite differently. A variable frequency strobe light can also be used to good effect for balancing rotating components (I have a couple of these, one recent and one antique).
Firstly, make a visible mark on the rotating component to be balanced, such that you can identify a unique rotational orientation. We can arbitrarily call this the 0 degree reference. Now get the rotating component operating at its fundamental resonant frequency using the technique shown in the video.
Then adjust the strobe light frequency upward (starting at a low frequency) until the 0 degree reference mark freezes in place. If you see more than one reference mark you are not matching the fundamental frequency with the strobe light, so readjust the dial until you see one strong reference mark (“strong” to ensure that you are not at a sub-harmonic).
Once you can achieve a relatively stable reference mark simply compare the position of the leaf spring to determine if the imbalance is high or low relative to the resting state of the leaf spring and adjust the dial to achieve the maximal high or low displacement. The difference between the up or down displacement and the zero degree mark indicates the orientation of the imbalance.
To make the latter more clear, I will use a hypothetical example. We will start with a perfectly balanced motor. If I now attach an additional mass to the rotating shaft and the shaft will try to rotate around the new center of mass, which is slightly displaced towards the additional mass from the original center of rotation.
The displacement will be proportional to the center of mass imbalance (multiplied by the “Q” of the resonance state) and the direction for a compensating mass location will be on the opposite side of the original mass imbalance. If the maximal displacement is high (above the resting position) then the compensating mas need to located at the rotational orientation of the high position of the shaft.
The compensating mass location may sound “backwards” but it isn’t. You want to more the rotating component back to its static resting location and to do that you need to move the center of mass back.
Note that if you are actually achieving balance by removing material you will need to subtract that mass from the opposite side from that described above.
You might not want to try the microwave trip with an older non-inverter microwave. Most of the newer inverter types have short/open circuit protection. I don’t know that that thin layer of damp cloth will really be enough to protect the microwave.
Why not just use an oven/toaster oven?
As long as the paper is wet, which it will be for the short time required for heating, it will provide more than enough protection, the microwaves won’t even see the metal. The nice thing about the method as mentioned in the video it that it guarantees temperatures that are hot enough but not so hot that they will have any metallurgical affect. Another advantage is that many people have one already. Personally I have a super cheap microwave that I use for everything but food so I’d use that but I would not be scared to do it in my home one.
what will the steam do to the grease inside the bearing?
Seems like there might be trouble if the cloth dries out too much. Would water vapor condensing on or inside the bearing be a concern?
The inductive heating plate seems like a safer solution so long as the bearing temperature is monitored.
Sorry about all of the typos, it appears that autocorrect didn’t have a clue about what I was trying to say. “stop the oven are redo” should be “stop the oven and redo”. Likewise, “then the compensating mas need to located at”
disengarbled would be much closer to “then the compensating mass needs to be located at”. And similarly for any that I failed to spot.
Forget the microwave and sous-vide the bearing. Zip-lock bag, bring to a boil in water (almost). Use a thermometer and you’ll be spot on temp. Heck, make some pasta while your at it!
If you want just 100°C and dont trust a microwave you can just fill a pot with water make it boil, put your bearing into a smaller pot and put that into the hot water.
I just tried heating an aluminum part this way to drop a bearing into it ( instead of a press fit ) and it worked great.
I did it in the break room microwave though, not the one at home, just it case it all went wrong.
-Rob
For chatter, try an accelerometer. While you could make a magnet / coil setup that would work as above, on a machine tool where you can’t put the entire thing on a beam and let it wave around wildly you’ll probably want a more sensitive device to measure vibration – thus accelerometer. Other than that, you could probably do basically the same thing – run the output into Audacity or similar to look at the spectrum. Also you could try tapping the system with a hammer to see what frequency it rings at. If I remember correctly, you can get the level of damping as well by looking at how long the system takes to ring down. Highly damped systems will have their resonance decay towards zero quickly. Systems without much damping will ring for a long time after you tap it (like a bell).