The difference between a wax soak and vacuum potting.

[CRU JONES]

Very interesting thoughts Scott!

I agree. But, at the same time, I really have gained an admiration for the guys who only use their ears for test equipment. Bigtee, for example. If you chat with bigtee, you realize the bare minimum you need to wind pickups. His pickups sound really good! ...I guess that makes sense though, as he used his ears

[ScottA]

Very interesting thoughts Scott!

I agree. But, at the same time, I really have gained an admiration for the guys who only use their ears for test equipment. Bigtee, for example. If you chat with bigtee, you realize the bare minimum you need to wind pickups. His pickups sound really good! ...I guess that makes sense though, as he used his ears

Don't get me wrong, I'm not discounting ears. I've used mine quite a bit in the development process.

I'm defending the use of science and engineering right along side the ears. While I do agree that it probably is true, you can't measure everything you can hear, you also must agree that listening tests are notoriously unreliable. I find ears tempered with data to be the best approach.

And while YMMV, and one may choose not to utilize the science behind it and have pretty good results, you should never discount it.

[CRU JONES]

Don't get me wrong, I'm not discounting ears. I've used mine quite a bit in the development process.

I'm defending the use of science and engineering right along side the ears. While I do agree that it probably is true, you can't measure everything you can hear, you also must agree that listening tests are notoriously unreliable. I find ears tempered with data to be the best approach.

And while YMMV, and one may choose not to utilize the science behind it and have pretty good results, you should never discount it.

Do you feel like there is an "anti-science" thing going on with pickup makers? I feel like its the opposite. I see many discussions get dominated by people that don't wind.

[ScottA]

Do you feel like there is an "anti-science" thing going on with pickup makers? I feel like its the opposite. I see many discussions get dominated by people that don't wind.

No, not universally. There's a strong contingent of people who are interested in and trying to advance the understanding. Many of them post here regularly. There's also a strong contingent of people who cling strongly to misinterpretations of the physics and cloak them in physical terms, then there is an undercurrent of anti-science. A fair amount of the anti-science comes from winders. I see some winders doing both, depending on the context.

[rhgwynn]

“It would be possible to describe everything scientifically, but it would make no sense; it would be without meaning, as if you described a Beethoven symphony as a variation of wave pressure.” -Albert Einstein

[Joe Gwinn]

Yes, if you leave the pickup in the pot with the molten wax long enough, the wax will penetrate from gravity. This takes so long because the air has to escape, and this happens very slowly if the air in the pickup has to come out through the wax without a pressure difference. The pressure difference from the pump gets the air out quickly, and then the wax gets pushed in by gravity.

It's true that gravity will eventually work, but when you release the vacuum after the bubbling has stopped, 15 psi of air pressure forces the wax into all the nooks and crannies. This would actually work in zero G.

[Mike Sulzer]

It's true that gravity will eventually work, but when you release the vacuum after the bubbling has stopped, 15 psi of air pressure forces the wax into all the nooks and crannies. This would actually work in zero G.

Yes it would; that is the fastest way. Any idea what the time constant for gravity would be? I think molten wax is less viscous than water, and so I would expect it to go in pretty quickly.

[Joe Gwinn]

Yes it would; that is the fastest way. Any idea what the time constant for gravity would be? I think molten wax is less viscous than water, and so I would expect it to go in pretty quickly.

Well, in round numbers, we can assume that molten wax and water have about the same density (actually, wax is less, but never mind). If one pulls a vacuum in a vertical tube with its bottom in water, the water will rise about 33 feet in the tube. The is also the maximum height a water siphon can overcome.

The pickup in the wax bath is maybe 2 inches below the surface, so the ratio is 33*12/2= 198, call it 200 to one.

[Mike Sulzer]

Well, in round numbers, we can assume that molten wax and water have about the same density (actually, wax is less, but never mind). If one pulls a vacuum in a vertical tube with its bottom in water, the water will rise about 33 feet in the tube. The is also the maximum height a water siphon can overcome.

The pickup in the wax bath is maybe 2 inches below the surface, so the ratio is 33*12/2= 198, call it 200 to one.

Yes, I agree that it will take a bit more than 200 times as long. Anyone know how long it takes to go in with the full pressure difference?

[Joe Gwinn]

Yes, I agree that it will take a bit more than 200 times as long. Anyone know how long it takes to go in with the full pressure difference?

Molten wax is pretty thin. I'd bet no more than ten seconds.

Capillary action will speed the gravity method up a bit, so long as the air can escape.

[Mike Sulzer]

Molten wax is pretty thin. I'd bet no more than ten seconds.

Capillary action will speed the gravity method up a bit, so long as the air can escape.

That is kind of what I was thinking, too. But there is one more factor also, that might not have been mentioned, heating up the coil. Not sure how fast heat penetrates through fine insulated wire, but I bet the delay is significant. So the wax might cool and thicken as it penetrates, and the pressure provided by opening the system up to air pressure might be necessary. I do not really know.

[rhgwynn]

That is kind of what I was thinking, too. But there is one more factor also, that might not have been mentioned, heating up the coil. Not sure how fast heat penetrates through fine insulated wire, but I bet the delay is significant. So the wax might cool and thicken as it penetrates, and the pressure provided by opening the system up to air pressure might be necessary. I do not really know.

Exactly why I do 2-3 vacuum/release cycles over 5-10 minutes. It will cool and thicken, you can see this happen, when you first drop the coil in, it will solidify around the magnets until they heat up.

-Rob

[kayakerca]

That is kind of what I was thinking, too. But there is one more factor also, that might not have been mentioned, heating up the coil. Not sure how fast heat penetrates through fine insulated wire, but I bet the delay is significant. So the wax might cool and thicken as it penetrates, and the pressure provided by opening the system up to air pressure might be necessary. I do not really know.

I haven't cut open any coils I've vacuum potted, but the visual look of the fury of bubbles during the vacuum potting process seems very similar regardless if I preheated the coils or not (as in it still looked like a jacuzzi running full out either way). The difference I did notice however is that it is a lot easier to clean off the excess wax if the coils were preheated. If I put them in at room temp and vacuum pot for 15 seconds, the wax solidifies on the outside of the coil before I can get it set them down on wax paper after I removed them from the pot. I use a variable temperature heat gun to melt off the excess wax off the coils when that happens which does a really nice job of it.

[Stratz]

I preheat all of the pickups that I pot to a certain temperature. This way they only need stay in the wax for a very short period of time. I can also un-pot a pickup that's been over saturated. Works great.

[Joe Gwinn]

That is kind of what I was thinking, too. But there is one more factor also, that might not have been mentioned, heating up the coil. Not sure how fast heat penetrates through fine insulated wire, but I bet the delay is significant. So the wax might cool and thicken as it penetrates, and the pressure provided by opening the system up to air pressure might be necessary. I do not really know.

I was implicitly assuming a preheated coil to achieve full penetration in ten seconds.

As for the thermal resistance of a coil of very fine insulated wire, it's actually the air between the insulated wire strands that is the main thermal barrier, just as in textiles. The hot wax will penetrate a bit before thickening, displacing the air, the heat will penetrate, warming things up and thinning the wax, and so on. Removing air allows the hot wax to penetrate further before thickening. If one starts with wax on the hot side, it all happens pretty fast.