West System and Aluminum


I have built a mirror frame from cherry. I am planning to use two pieces 24" of aluminum J-channel with one piece reversed, as a hanger at the top - sort of a french cleat arrangement. I've recessed one of the pieces into the frame. I was thinking of embedding it in West System epoxy to fasten it. Does anyone happen to know if West System does OK with aluminum without buying that 'etching' kit' from West ? Seems like a shame to spend that much money on that kit for a 1x24 hanger. I suppose I can just screw it down but I've only got about 3/8 depth there, after routing it out for the recess.
Thanks
jim
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Oh, I think that roughing it up to give it some 'tooth' will suffice. All the etching does is just that..and it cleans the aluminum.
Use a nice paper...like 80 grit. Then wipe with Methyl Hydrate. (DO NOT confuse that with rubbing alcohol. Rubbing alcohol often contains lanolin..AKA grease.)
Drilling some small holes in the aluminum will allow some WEST to ooze through and, in fact, make their own little fasteners..mushroom-style. Let gravity do the shaping.
HTH
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"Jim Bailey" wrote:

<snip>
You have one chance to do this job and have it hold.
AS has been suggested, drill lots of 1/8"-3/16" thru the aluminum, then rough up the surfaces, front and back with some 36 grit paper on a right angle disk sander.
Next apply a layer of 6 oz glass, wet out with epoxy on both sides, allowing 24 hours to elapse between fromt and back glass.
Allow to cure are about 5-7 days, then sand smooth, trim excess glass.
You can now epoxy the cured glass to the wooden frame, and it will hold because you have trapped the aluminum in glass and then bonded glass to wood.
I wouldn't bet any real money on something else.
Lew
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Jim, bet you won't get anyone to touch this one. No one will want to be responsible if your mirror DOESN'T hold and they have given you bad advice. I cannot imagine you telling your SO that you explicity followed the instructions given to you by someone in Chatanooga for hanging your mirror.
If there is any doubt, by the etching kit. It does two things: cleans the metal to remove all traces of hand oil, manufacturing oils, dust, dirt, etc. It also literally etches the metal to provide a grippable surface for the adhesive.
I know when we put in a shower/tub enclosure and the aluminum is not properly wiped down we even have problems with out gooey sealants sticking.
Why gamble with your project? Maybe you can recess the hanger about 1/8", and then adhere your channel. I think I would feel better about that then just glueing it on. Of course, I would etch, too. Maybe you could find the etching material at one of the metal shops in your area if you feel West's is too high.
Robert
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So will some 60grit sandpaper. It's not visible. Have at it. Robatoy's idea of some holes is a good one too.
j
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A word of caution when bonding aluminum: Time is your enemy!
I believe the main purpose in etching and/or mechanically and chemically cleaning is to remove the surface oxide layer. Since aluminum is reasonable reactive, this layer will reform in a short time, therefore the important thing here is to prep the aluminum just before you apply the adhesive.
A second word of caution: Epoxy needs a gap!
Unlike wood glue, when bonding with epoxy, it's best to have a gap. If I was to bond aluminum to aluminum, I would most likely add micro spheres (about 0.005" dia.) to the mix to give me the gap. With wood, one might argue that the wood pores give you the gap, but I'm not sure. That 60 grit paper sounds like it would give some reasonably deep scratches which is a good thing.
Disclaimer: I don't have any experience structurally bonding aluminum to cherry (or any other wood) so others may give you better advice.. Now if we were just talking about beryllium....
Bill Leonhardt
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snipped-for-privacy@aol.com wrote:

I thought that went without saying. The channel should be 'let in'.
PS.. I just listened to two cuts from the Cream reunion. The 'boxed' set should be in the shape of a coffin. Clapton sounded like an old man. (Don't get me wrong here..I also aspire to become a VERY old man.)
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Clapton IS an old man.
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On Mon, 05 Dec 2005 14:37:11 GMT, "Jim Bailey"
Depends on the aluminium, the alloy and (mainly) on whether it has been anodised. I wouldn't expect it to work unless you prepare the aluminium surface first. A rub with silicon carbide (black) abrasive paper will remove the anodising - softer abrasives may not be so successful (they're only aluminium oxide themselves!)
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Sand it. It will do just as well as the etching. Yes, screw it down then use the epoxy. The epoxy alone would very likely hold it but the screws will improve it substantially.

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All excellent input guys. Thanks a lot !
I'm still in 'debating' mode with this. I've already routed the recess for the one piece of J in the frame. Unfortunately I didn't notice the the hook part of the J shape is actually a little longer than 1/2 way back to the top of the J (if you can picture this at all). That means I can't simply hook one over the other when I hang it, given that I've made the rout a pretty close fit, unless I now go back and somehow grind/cut about 1/8 off that short part of the J.
So anyway, I THOUGHT I had a good idea. Best laid plans .........
jim

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When finished, is the aluminum going to be flush with the wood surface? When you say it's a J channel - is the J part curved or squared?
The reason I'm asking is that if the top of the J channel is sitting tight against the wood at the top, the adhesive isn't going to carry much shear - that will be carried by contact with the top of the J in the recess. The resulting forces will be prying the channel out of the recess. If you cover the bottom with a thin plate of Al, you can reduce the stress in the adhesive significantly.
--------- | | <--- cherry | __| | |_______ | ||____ | <-- aluminum channel w/ squared J at top. | ||| || | ||| | ||| | ||| | ||||| | |_ || <--- thin plate | ||| | ||| -------
ASCII drawing limits details, but the channel should be a tight fit in the routed groove and a thin plate has to be tightly in contact with the channel.
It's worth the effort to weigh the mirror as assembled and get a feel for the stresses. The contact stress at the top of the channel will be the weight divided by 24Xdepth of routed groove in contact with the Al. The shear stress in the adhesive if no routed groove is used is weight/24X1. The force on the bottom of the channel pulling out can be estimated (conservatively) as the weight times the size of the J (in the direction from the frame to the wall) in turn divided by the depth of the channel (top to bottom). Divide that in turn by the number of screws holding the thin plate to see the load per screw.
BTW - you might want to include a guess at forces that someone might apply when cleaning the mirror and add that to the weight.
Compare those results with published data on contact and shear stress in cherry, the shear strength of Al-to-epoxy and wood-to-epoxy and the load capacity of little screws and make sure you're _well_ in the safe zone.
Alternatively, look at it and decide whether you will trust it. Personally, I'd prefer a mechanical connection to adhesive unless you're dealing with some exotic adhesives.
Mike
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