Fixing Aluminium to end grain plywood

[Muggnz]

help pluh-ese

How do I best attach Aluminium sheets to end grain plywood?

Do I squirt an epoxy glue on the tip or shaft, before tightening it down? And a dab of sealer under the head? Or will only sealer hold it in place?

Also I'm wondering how big to make the screw holes. How much gap, if any, should there be between the screw shaft & ali? I've been told to have no gap. But after reading about ali heating up during the day & shrinking at night, I feel that there should a small gap. Otherwise the movement will cause the screws to come loose. Am I right? Or . . . ?

thanks
david

[toypusher]

I would advise you to use epoxy (or fiberglass resin) on the end grain an let it dry first, then predrill and use the longest screws that you can without getting too large of a diameter.

[synaps3]

http://tnttt.com/viewtopic.php?t=33920

[Muggnz]

I would advise you to use epoxy (or fiberglass resin) on the end grain an let it dry first, then predrill and use the longest screws that you can without getting too large of a diameter.

thanks

Do you know if the holes in the ali need to be over sized? to allow for temperature fluctuations. Or just right ?

david

[madjack]

David, I use an 1/8" drill for the holes and a #8 SS screw...this makes an adequately sized opening for the screw without it being too large...
madjack

[Muggnz]

Jack,

thanks.

I'm more worried about making the hole to tight and not leaving enough room below the head for the ali to stretch & shrink a little during the day & night. Thereby causing the ali pull the screws out of the end grain ply . It may help to know that my corner ( angle ) pieces are 3mm & the end grain ply is immediately below the 1.2mm ali roof.

Hopefully I explained that right. It seems to me to be such a simple yet important thing. That I'm surprised that it hasn't been asked & answered before. Even the power of google struggles. Perhaps it's not as important as I think.

Call me paranoid and/or pedantic, but I'm probably only going to get one chance at getting it right. So that it lasts a while or 2.

david

[madjack]

...all I can say, I've done two this way with no problems from the hot Southern US sun...I don't know how the numbers translate down there but the 1/8" drill leaves just a big enough hole so the #8 screw does not grab at the Ali on it's way into the wood...I use a 1" long screw and have had no problems with it pulling out...........
madjack

[Muggnz]

Jack,

thanks, I'll give it a go.

As I guess that I can always widen the holes later, should the need arise.

david

[afreegreek]

if you're worried about expansion problems you could use a product like Sika-Flex 291 or 292 to bond the strip. it will hold the aluminum to the wood all by itself and if you want to add screws you can drill sloppy holes and use pan-head or (I suggest) K-Lath screws.

K-Lath screws have a wider, thinner head than pan-heads and are available in stainless steel.

http://www.mcfeelys.com/ss-k-lath-screws

http://www.sikaindustry.com/ipd-ma-products

[Muggnz]

I'm using a similar version of those screws. With the same size oversized head, but with a normal thread ending.

They're doing a good job.

I didn't know about Sika-Flex until it was to late. If I build another, I'll consider it.

david

[Shadow Catcher]

Hang with me this gets to the point. I am looking to glue ABS plastic solar mounts to the Filon FRP outer skin of our MM and really did not want to use West System Epoxy (allowable with out harming the Filon) but it is so permanent. So when I got an add for 3M VHB tape (structural) I was intrigued and started looking into it.
http://solutions.3m.com/wps/portal/3M/en_US/VHB/Tapes
I spent an hour discussing the specific application with one of their engineers and will be using it. It is visco elastic and bonds well and might be a solution,

[angib]

I don't think epoxy is a good choice for bonding almost any thermoplastic. ABS will probably get a better bond than polyethylene or polypropylene, which are awful. VHB tape is an excellent choice for any of these.

And while discussing epoxy bonds, I've mislaid the thread where the bond to metals was discussed, because I should add that epoxy bond to stainless steel is poor, unlike most other metals. Aluminium and epoxy work very well together.

Andrew

[Muggnz]

http://www.thistothat.com/

might help

david