Thermal Chamber Aluminum To Wood Fastener (?OT?)

[RST Engineering \(jw\)]

I'm constructing a large thermal chamber (*) that needs to fasten aluminum
strips to a wooden frame by means of threaded fasteners (please, no
suggestions of glue or epoxies). The device will be outside in the weather,
which up here means hot summers and snow winters.

The wood is pressure treated and eats steel and aluminum (even the plated
variety) for lunch. That pretty well leaves brass and stainless as the
choices. Or something that is made out of Home Depot unobtanium that I
haven't thought of.

Comments?

Jim

(*) OK, OK, it is a greenhouse, but it's going to have an antenna on top.
On topic?

 

[qrk]

I'm constructing a large thermal chamber (*) that needs to fasten aluminum
strips to a wooden frame by means of threaded fasteners (please, no
suggestions of glue or epoxies). The device will be outside in the weather,
which up here means hot summers and snow winters.

The wood is pressure treated and eats steel and aluminum (even the plated
variety) for lunch. That pretty well leaves brass and stainless as the
choices. Or something that is made out of Home Depot unobtanium that I
haven't thought of.

Comments?

Jim

(*) OK, OK, it is a greenhouse, but it's going to have an antenna on top.
On topic?

316 Stainless or titanium hardware. Both will pit aluminum, so perhaps
a insulating shoulder washer between the fastener and aluminum. 5000
series aluminum (5052, 5083, 5086 are used for boat hulls) have high
corrosion resistance and are weldable. I think McMaster Carr carries
5086 sheet if you don't mind paying a premium.

 

[John O'Flaherty]

I'm constructing a large thermal chamber (*) that needs to fasten aluminum
strips to a wooden frame by means of threaded fasteners (please, no
suggestions of glue or epoxies). The device will be outside in the weather,
which up here means hot summers and snow winters.

The wood is pressure treated and eats steel and aluminum (even the plated
variety) for lunch. That pretty well leaves brass and stainless as the
choices. Or something that is made out of Home Depot unobtanium that I
haven't thought of.

Comments?

Can you use nylon screws and nuts, larger to compensate for weaker?
You'd have less possibilities for galvanic corrosion.

(*) OK, OK, it is a greenhouse, but it's going to have an antenna on top.
On topic?

As long as it's green, you're being good...

 

[RST Engineering \(jw\)]

..
..
We use 5052H32 for the kids to make chassis out of at the college, so I've
got scrap coming out my ears. That's not a bad idea; I can use the turret
punch to stamp out dime size washers and then punch a clearance hole for the
stainless wood screw.

Thanks...

Jim

 

[Jim Thompson]

I'm constructing a large thermal chamber (*) that needs to fasten aluminum
strips to a wooden frame by means of threaded fasteners (please, no
suggestions of glue or epoxies). The device will be outside in the weather,
which up here means hot summers and snow winters.

The wood is pressure treated and eats steel and aluminum (even the plated
variety) for lunch. That pretty well leaves brass and stainless as the
choices. Or something that is made out of Home Depot unobtanium that I
haven't thought of.

Comments?

Jim

(*) OK, OK, it is a greenhouse, but it's going to have an antenna on top.
On topic?

I use small zinc screws (from ACE Hardware) for my BBQ handles so they
don't rust outdoors. I don't know if the come in larger sizes.

...Jim Thompson

 

[John Larkin]

I'm constructing a large thermal chamber (*) that needs to fasten aluminum
strips to a wooden frame by means of threaded fasteners (please, no
suggestions of glue or epoxies). The device will be outside in the weather,
which up here means hot summers and snow winters.

The wood is pressure treated and eats steel and aluminum (even the plated
variety) for lunch. That pretty well leaves brass and stainless as the
choices. Or something that is made out of Home Depot unobtanium that I
haven't thought of.

Comments?

Jim

(*) OK, OK, it is a greenhouse, but it's going to have an antenna on top.
On topic?

Sorry for asking a dumb question, but why do you want to strap
aluminum to a material that snacks on aluminum?

John

 

[RST Engineering \(jw\)]

Sorry...the comment was MEANT to say that it eats aluminum that is in
intimate contact and dries slowly (like an aluminum screw an inch or so into
the pressure-treated) much more rapidly than the aluminum frame of the
greenhouse that has pretty much of an air gap (however miniscule) all the
way around.

The alternative is to use untreated wood and watch it decay in a few years.

Jim

 

[whit3rd]

I'm constructing a large thermal chamber (*) that needs to fasten aluminum
strips to a wooden frame by means of threaded fasteners (please, no
suggestions of glue or epoxies).  The device will be outside in the weather,
which up here means hot summers and snow winters.

The wood is pressure treated and eats steel and aluminum

Hot/cold will make condensation inside, and rain will wet the
outside. The corrosion problem is that wet wood attacks
the metal by electrolytic attack.

So two solutions are: keep the wet wood from contact with the
metal (use plastic washers or even just Tyvek housewrap
where the two meet), or change the materials (a stained
stick of cedar might last a long time even when wet).


There are coated 'deck screw' fasteners that tolerate treated
lumber, which are less expensive than stainless. This suggests
a layer of (for instance) epoxy paint on the aluminum where it
contacts the wood.

 

[Michael A. Terrell]

I'm constructing a large thermal chamber (*) that needs to fasten aluminum
strips to a wooden frame by means of threaded fasteners (please, no
suggestions of glue or epoxies). The device will be outside in the weather,
which up here means hot summers and snow winters.

The wood is pressure treated and eats steel and aluminum (even the plated
variety) for lunch. That pretty well leaves brass and stainless as the
choices. Or something that is made out of Home Depot unobtanium that I
haven't thought of.

A layer of sheet rubber, or roofing felt will keep the two apart.
Vinyl tubing to protect the threads where they pass through the pressure
treated material, and a little silicon grease to keep the fumes from the
threads.


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[MooseFET]

I'm constructing a large thermal chamber (*) that needs to fasten aluminum
strips to a wooden frame by means of threaded fasteners (please, no
suggestions of glue or epoxies). The device will be outside in the weather,
which up here means hot summers and snow winters.

The wood is pressure treated and eats steel and aluminum (even the plated
variety) for lunch. That pretty well leaves brass and stainless as the
choices. Or something that is made out of Home Depot unobtanium that I
haven't thought of.

Comments?

Make sure all the parts that touch each other are the same metal eq
316. Put plastic washers between the screws and the aluminum.

Paint all the parts before you assemble the thing.

Use nuts and bolts and grease them before you put it together.

Use the special fasteners for use with the lumber.

Don't use the aluminum parts.

 

[Jim Thompson]

Make sure all the parts that touch each other are the same metal eq
316. Put plastic washers between the screws and the aluminum.

Paint all the parts before you assemble the thing.

Use nuts and bolts and grease them before you put it together.

Use the special fasteners for use with the lumber.

Don't use the aluminum parts.

I vaguely remember "shouldered washers" to keep power transistor
mounting screws from shorting the case to the heatsink.

...Jim Thompson

 

[Jim Yanik]

I vaguely remember "shouldered washers" to keep power transistor
mounting screws from shorting the case to the heatsink.

...Jim Thompson

I suspect that spray-on plastic truck bed liner stuff would work well for
insulating and protecting the aluminum from corrosion.It's made to be out
in weather and sunlight.

 

[qrk]

A layer of sheet rubber, or roofing felt will keep the two apart.
Vinyl tubing to protect the threads where they pass through the pressure
treated material, and a little silicon grease to keep the fumes from the
threads.

Better to use Aqua Lube as a grease. Silicon grease washes out pretty
quickly in a wet environment.

 

[RST Engineering \(jw\)]

Thanks for the thoughts, gang. What worked best were:

(a) Duct tape to "insulate" the bottom of the aluminum greenhouse frame from
the pressure treated foundation ... and

(b) Home Depot "Deckmate" steel screws with a coating that I couldn't peel
off or cut through with an exacto knife ... guaranteed not to corrode for
life. (Couldn't get them to say my life or theirs, but what the hell {;-))
.... and

(c) The old standby dishwashing detergent as lube to make the screw want to
go into the wood easily.


Thanks again for getting my thinking cap to make it happen.

Jim