Great foil for pickguards, etc., but not much else

[rjb]

So, if I buy a roll of aluminum foil tape, and it sits in my shop for a couple years (because I'm not building that many), how oxidized was the tape when I bought it, and how much more has it oxidized while sitting there? And if I shield a cavity with overlapping edges and a cover touching those tabs under the screws, how much more oxidation will develop and open those joints? I'm going to listen to folks with electrical and chemical experience, but it doesn't seem like such a liability.

This is what I said:

The problem is that aluminum very quickly forms a thin insulating oxide "skin". When you measure one piece of tape, your probes puncture the skin and you get a reading across the Al beneath the surface. When you have "skin to skin contact" between two layers, you get an unacceptably high resistance across the boundary.

Let's try again.

When you bought the tape, it had a 4 nm layer of insulating aluminum oxide, which protected the aluminum from further oxidation.

After a couple of years, it still had a 4 nm layer of aluminum oxide.

If you shield a cavity with overlapping edges and a cover touching those tabs under the screws, without removing the aluminum oxide and treating the joints with anti-oxide compound, you will have 8 nm of aluminum oxide between the conducting layers of aluminum and you will not have continuity between the cavity and the cover.

I don't know this because I'm an expert chemist. I know this because I tried what you are suggesting, and it didn't work. I knew it didn't work because I measured the resistance between cavity and the cover. I then did a little research to figure out why it didn't work.

https://en.wikipedia.org/wiki/Aluminium_oxide

Al₂O₃ is an electrical insulator but has a relatively high thermal conductivity (30 Wm⁻¹K^−1[3]) for a ceramic material.

Aluminium oxide is responsible for the resistance of metallic aluminium to weathering. Metallic aluminium is very reactive with atmospheric oxygen, and a thin passivation layerof aluminium oxide (4 nm thickness) forms on any exposed aluminium surface.^[7] This layer protects the metal from further oxidation.

I highly doubt that the "experts" who shield cavities with scraps of aluminum foil held together with electrical tape ever bothered to confirm continuity with a meter.

[Jason Rodgers]

Ok, I'm following you, and I'm not arguing your experience and knowledge. My understanding of this is lay, at best. Forgive me if the next question is too elementary. Help me understand the difference between testing continuity and resistance in this situation. I can set my multimeter on continuity, touch a tuner post and a cavity screw and get tone. I don't know what sort of reading I would get if I did the same with a resistance setting.

[rjb]

Aluminum a PIA for pros too. All I can see, it's a poor excuse for those who will not bother to source copper, and/or afraid of soldering. Only excuse left is if you live in a part of the world where copper foil, sticky or not, is just plain unavailable.

There is one more excuse:
Belief in BL's assertion that only aluminum can eliminate light dimmer buzz.

Bill Lawrence Website

Aluminum has some strange properties, and it's the only commercially available metal I know of that can eliminate the buzz caused by light dimmers. An inch thick copper or brass shield cannot reduce the buzz caused by light dimmers but .003 thick aluminum foil can! This is known some thirty years and the reason why Belden introduced double shielded cable ( Copper braid plus aluminum foil). There is one problem for guitar cords -- the double shielding makes the cable too stiff . It helps quite a bit when you shield your guitar with copper and aluminum foil.
Try this test-- wire a single coil to a jack and plug it into your amp. Put the pickup on a table next to your amp. Take an aluminum pan from your kitchen and put it slowly on top of your single coil and watch the hum disappear!

[rjb]

I can set my multimeter on continuity, touch a tuner post and a cavity screw and get tone. I don't know what sort of reading I would get if I did the same with a resistance setting.

To be honest, it's been a while since I've shielded a guitar.

Using this particular multimeter in continuity mode, you get a beep if the resistance is below a value set by the range setting.
On the lowest setting, the threshold is 40 ohms.
How to test for continuity with a digital multimeter

I misspoke when I said "you will not have have continuity".
I should have used some waffling phrase like "you'll likely find higher resistance than you want."
In a previous thread, someone (Rick Turner?) gave a rule of thumb, something like "you're OK as long as you have no more than x ohms between any two points."
But I don't remember what "x" was. Maybe 10 ohms?

Edit:
I found Rick Turner's post. The ROT was 100 ohms from any point to the output jack.
http://music-electronics-forum.com/t36274-2/#post343931

[Jason Rodgers]

Good reference, thank you, rjb!

[rjb]

Light Reading

Here's another reference I just found.
It's going to take me a while to digest.

Properties of Metals Used for RF Shielding
http://www.ets-lindgren.com/pdf/emctd_1293_weibler.pdf

[Fluoroscope 5000]

The diagram on the second page of the 'Stop_the_Noise...' pdf, shows that Al is much less effective at blocking RFI than Cu by ~20dB. Again, I only use Al for potential faulty rheostat noise reduction and the upper-mid “softening” effect that 0.015~0.03” thickness provides. Some of my pickups have Cu shielding on them, so there's really no point in adding more Cu to the pickup cavities, but I think I'll use Cu foil in my control cavities from now on.

[big_teee]

For shielding whole pickguards, heavy duty aluminum foil is afforable, copper foil for the most part is not.
Especially if you work on someones guitar and charge accordingly, most blue collar players will not pay for copper on pickguards.
Aluminum works great for that.
For body cavities, I like conductive paint.
It is fast, effective, and easy to use.
It can be touched up at any point in time with more paint.
Guitar manufacturers use it by the gallons.
T

[Steve A.]

For shielding whole pickguards, heavy duty aluminum foil is afforable, copper foil for the most part is not.
Especially if you work on someones guitar and charge accordingly, most blue collar players will not pay for copper on pickguards.
Aluminum works great for that.
For body cavities, I like conductive paint.
It is fast, effective, and easy to use.
It can be touched up at any point in time with more paint.
Guitar manufacturers use it by the gallons.
T

I am quoting your full post here because it all makes a lot of sense (although I personally like to use copper foil on control cavities... a very relaxing ritual as I coat the entire surface with 60/40 solder to block Superman's xray vision.)

Steve

P.S. Any suggestions on keeping the conductive paint from drying out (or thinning it if it gets thicker)? To shield, say, the pickup cavity of a tele neck pickup would you run a wire from the control compartment to it with screws on either end under the paint? BTW, I think that you would want tabs of copper foil tape under the paint going up to the screw holes for the pickguard, or do you just paint the entire shelf of the cavity as many mfgs do these days?

I have had trouble using the paint on compartments with a shiny finish so foil tape is a must for those (usually older guitars.)

[big_teee]

For strat guitars I just do the full sized heavy duty aluminum foil.
Mount the metal pots and switches on the foil, and ground the pot backs and it is all one grounded electrical unit.
I don't do any cavity shielding on strats.
If the guitar is still noisy?
If a musician wants it quieter, I use shielded cable on the Single coils, & Jack, instead of white and black single wire.
Shielded cable will always be quieter than non shielded.
Using the shielded pair cable is much easier and cheaper than all the body cavity work.
I also always use shielded cable from the strat jack to the volume pot.
If you want the guitar quieter than that, then you will have to go to humbucking strat blade pickups.
I don't mess with dummy coils, but that would be another option.
That's the way I do things.
YMMV,
T

[kmensik]

I used a 12x12" copper sheet for the cavity and 0,5mm Al sheet for the pickguard. The copper from VentureTape was not that expensive, and I am in east Europe.
kmensik | Squier shielding ? rajce.net

[rjb]

Back to the OP

I picked this up at Food Maxx "Extra strength Heavy Duty Aluminium Foil" from handi-foil. 100 sq ft.

Hey Steve, could you tell us the thickness of that super foil?
I can't find a spec online.

Thanks,
-rb

[David King]

I have to say that this thread is full of the kind of nonsense that sometimes gives the MEF a bad name.