Question: attaching aluminum to plywood

[Benjamin Maggi]

My plywood boxcab engine is coming along slowly but surely, and I am nearly to the point where I can start adding the cosmetic details that make all engines- especially boxcabs- so unique. The body is 5/8" thick birch plywood with a 1/4" thick plywood bent roof. The interior is already completely painted in Kilz primer, and by the end of the week will also have a thick coat of Rustoleum black to better hide from view the goofy-looking roof braces and such. The exterior plywood will be painted with Kilz as well, but I won't finish paint it until the engine is ready to get a nice spray of quality automobile enamel.

To dress out the boxcab (and keep it from looking like a "Generic Electric" or a "Lil Pumpkin" copycat) I plan to use alumimum angle-iron on the exterior corners and aluminum bar stock to make horizontal and vertical trim pieces. For rivets I purchased some 14g escutcheon pins. I plan to drill the aluminum holes slighly oversize the diameter of the pin, then drill the plywood slightly undersize the diameter of the pin. Then, tapping the pin will grab the wood and not deform the aluminum.

I was wondering if you guys thought it might be necessary to use epoxy or something else on the back of the aluminum to help secure it to the plywood?

[ccvstmr]

Ben,

If you really want the aluminum to stick, you might consider contact cement. Cleans up easily enough with Acetone (just make sure your area for cement application and cleaning is ventilated..unless you really want to get "a buzz"). Else, if you're installing the escutcheon pins on 1/2 or 3/4" centers, that will be enough to hold the aluminum angle or flat in place.

I've attached many a trim piece with the method you described for over 20 years. Typically, I use 16 or 18 ga pins...14 ga seems large. I countersunk the hole in the alum strip slightly so the head still protrudes to show the "rivet detail" after painting. Something new...I put a dot of Superglue on the pin heads after they're set. Capillary action will draw the glue into the crevices (do not use gel type Superglue) and thereby hold the pin in place. Otherwise, climate changes, wood expansion and contraction, etc...allow the pin to pop. Time will tell if this method holds the pin in place for more than 15 years. Hope that gives you some ideas. Carl B.

[Goose]

On my diesel-switcher, which is build from Multiplex (that's the material, which is used for the floor in trucks and trailers, very hard and waterproof) I used contact-cement rubber-type to add the aluminum and other parts. For the angles, they where rivited by "prototype", so I drilled the aluminum and the Multiplex and used grooved pins with round head as rivet. I tipped them in carpenters white glue and glued them into the drilled holes.

And that worked very well.

[makinsmoke]

Somebody must have put something in my coffee. That outside braced boxcar looks upside down.....

I have built a couple of cars with differing materials, specifically a steel underframe stock car, and a drover car.

The drover car was furniture grade plywood sealed and sanded to look like metal, then the sides were screwed to the steel under frame and aluminum angle on the interior at the corners. I used 2-56 screws on the ends and those as well as a few 8-32 and 10-32's from the sides into the steel frame at the bottom. I put the nuts out if they were that way on the prototype. The rest of the car I used escutcheon pins as you suggest, but I was not holding anything with them. Undersized holes and paint keeps them in place.

The stock car was even more of a challenge. I bought upteen boxes of 2-56 x 1" screws and nuts from McMaster Carr. They sell a smaller nut than normal that looks more scale. I glued and clamped the upright and diagonal braces to the horizontal boards, then drilled them and installed the screws from the back. On stock cars the nuts are to the outside to keep from damaging the lading. After tightening everything up I cut off the excess with a Dremel and again paint holds everything tight. No reason this would not work for you. The Santa Fe stock car in Pawhuska, Oklahoma has bolts through the outside bracing and the horizontal boards above, with again the nuts to the outside. You could use any round head screw that was the size you need, tighten everything up, then fill the slots or Phillips with epoxy or Alumilite if they bother you. Simple enough at that point to prime and paint.

Brian

[ccvstmr]

Somebody must have put something in my coffee. That outside braced boxcar looks upside down.....Brian

You're right Brian...the photo IS upside down. It was flipped to "capture the moment" and show the car right-side up. As for your coffee...nobody knows what's in there except you. The car was upside down while I was refurbishing it. That was the easiest way to work on the lower door rails. By the time the car was flipped right-side up, I had already started to prime and paint. The escutcheon pins still went in...pointy end first! lol Carl B.

[boaterri]

In place of escutchen pins how about using "drive pins" or "drive screws" (i think thats what they are called). The things used to attach dealer tags to machine tools.

Rick

[mjahn]

I like Rick's idea since its a mechanical fastener. That said, I did glue some aluminum window frames to my caboose with 5 minute epoxy. It holds so tight I probably couldn't pop the windows off without taking some of the ply along with it, the tubes usually have s nozzle with a fine tip so you can get a small bead where you want it, and it dries clear in case you make a mistake.

[Kevin_S]

Ben, before you mount the aluminimum, I would sand and apply etch primer before you attach it to the box. Also I found for applying automotive paint to wood. Start off with automotive primer and over reduce it a little and spray a couple of coats over the wood. After it dries sand it down lightly then apply another coat of primer mixed properly, sand then apply the top coat. The over reduced primer will draw the primer into the wood to act like anchor for the second coat of primer. Also I don't think the Kilz primer is compatable with automotive paint.
-Kevin S.

[mjahn]

The thinned primer is basically a wash, right?

[Benjamin Maggi]

Thanks for the posts guys. As for the pins, it is true that they will generally be holding the aluminum on but I didn't know if something more would be required. Maybe not. I picked the larger size (14g) instead of the smaller ones because it is for an engine and I want to emphasize the bolts... they might be too large but from a distance they will be seen and not lost in the mix.

As for the priming the aluminum beforehand, I used Kilz on the inside (and planned to use it on the outside) because I didn't want my body to warp. As the interior is already primed with it there is no going back. As for the outside, I have read other posts on other forums where people used Kilz to seal their wooden cars. For my exterior, what other options are generally available that will look good? It is supposed to look like a metal enginer, not a wooden boxcar.

[Bill Wilkins]

Ben,
I liked the idea of drive pins. I have used them. Drill the holes undersize. You could use epoxy as you put the pins in or before you put the pins in use thin Super Glue in the hole. It will soak into the wood and harder it. If you use super glue when you put the pins in they won't be coming out, and probably not with epoxy either. In light of getting one in partway and the SG sets I would use super glue on the hole ahead of time. And with drive pins you may not need anything.
There are also miniature lag bolts out there. Maybe someone will have a link of where to find them.
Is it picture time yet ?

Bill W.

[ccvstmr]

There are also miniature lag bolts out there. Maybe someone will have a link of where to find them.

Try Micro-Fasteners in NJ. They can get pricey ($6-8 per 100 count) if you need a lot of 'em. Not to mention, better get a small hex driver with a swivel end...'cause your fingers are going to get sore putting in so many lags (been there...done that). Don't forget to pre-drill the hole. Carl B.