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Cavity Cover?

claudel

claudel

Supporting Member
Oct 10, 2005
1,565
1,960
Further Outside Area 51
#1
So

I need a cavity cover for my seemingly endless bass project.

Body has tort binding and I have a piece of 1 ply tort plastic that matches closely enough

1 ply plastic might be a bit flexy for this.

What I'd like to do is glue the tort to a piece of sheet metal that will add strength/rigidity to the plastic, provide shielding, and attach with magnets instead of screws.

Can I use thin gauge sheet steel instead of copper and have adequate shielding?

I'm guessing "yes" but I haven't asked any dumb questions in here for a while...

Planning on shielding the cavity with conductive paint instead of copper tape, if that matters.

What glue will glue plastic to metal and not fall apart later?

TIA...
 
#2
Steel is fine for your shielding. Probably better than most conductive paint.

Epoxy is your likely adhesive of choice. Clean the steel really well to remove any oils from processing/storage, and scratch up the surface you are gluing (both plastic and steel) a bit as well.

The other glue that comes to mind is silicone, since it's more compliant for different rates of thermal expansion, but curing would be a problem in that sandwich, so I think epoxy is a better bet. There are some more flexible/compliant types of epoxy, but they are a bit hard (or impossible) to find retail, so probably not worth hunting for unless properly cleaned/scuffed up steel to plastic with easily available epoxy fails.

Oh, and: Don't use the 5 minute type of epoxy, from what's easily available retail. It's hardly ever the right/best thing, and it stinks (literally,) but it's popular with folks that want to get things over with quickly.
 
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#3
I agree with @T_Bone_TL but I'd also add that a quality CA glue can probably work too. I'm always surprised at how well it bonds metals, especially in no load situations like this. It may react with the plastic though, so worth a test. :thumbsup:
 
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#4
I guess the next steps are to find an appropriate piece of steel

Something like this?

Online Metal Supply Cold Rolled Steel Sheet, 0.042 (19 ga.) x 8 inches x 12 inches

https://smile.amazon.com/dp/B08RB4Y5B8/

and glue the plastic to it, let it cure, cut to shape & clean up the edges...

Might have to clearcoat the metal side to keep it from rusting. I'm guessing that won't keep it from sticking to the magnets

Thanks again!
 
#5
You could also use common 18-8 stainless steel plate instead of mild steel. It's not as strongly magnetic as mild steel, but it's magnetic enough that it will stick to magnets. It's conductive, fine for shielding. And no need for coating, it won't rust under normal conditions.

Like TBoneL said, a good marine epoxy like West Systems or System Three would be best for attaching a cap to it. CA glue would work too.
 
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#7
Bruce Johnson said:
You could also use common 18-8 stainless steel plate instead of mild steel. It's not as strongly magnetic as mild steel, but it's magnetic enough that it will stick to magnets. It's conductive, fine for shielding. And no need for coating, it won't rust under normal conditions.

Like TBoneL said, a good marine epoxy like West Systems or System Three would be best for attaching a cap to it. CA glue would work too.
Click to expand...

Thanks! I'd rather use stainless for the obvious reason but I wasn't sure if it would stick to the magnets
 
#9
Galvanized steel also solves the rust issue, and is dirt common. Heck, you can find plenty of nice plated (not usually galvanized, but also limits the odds of any rust) scrap in the computer junk/scrap pile. If buying new stock, "electro-galvanized" (plated) is nice and smooth and what you want (common for air ducts) not hot dip (unusual for sheet metal, and rough/lumpy.) But there should be plenty of that available as scrap, as well.
 
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#10
T_Bone_TL said:
Galvanized steel also solves the rust issue, and is dirt common. Heck, you can find plenty of nice plated (not usually galvanized, but also limits the odds of any rust) scrap in the computer junk/scrap pile. If buying new stock, "electro-galvanized" (plated) is nice and smooth and what you want (common for air ducts) not hot dip (unusual for sheet metal, and rough/lumpy.) But there should be plenty of that available as scrap, as well.
Click to expand...

I know zip regarding metalworking... I didn't even realize galvanized would stick to magnets...

I have some old ductwork laying around here somewhere that might do it.

Thanks again!
 
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