Expansion - Wood vs Steel

[Lplates]

Hey Guys,

Let me just preface my question with the details of what i'm trying to achieve. I'm thinking of a lamp design that calls for a heavy base, the lamp shade is not centered and as such the base needs to be heavy enough to prevent tipping. The base would probably be in the ballpark of 400x400x15

So my thoughts were to laminate some thin wood (5mm) with some 5mm steel plate using west system epoxy. So the end product would look rather like 3ply plywood with the top and bottom piece being wood, probably some nice doug fir, and the middle section being steel.

My question is what do you think will happen in terms of expansion in warmer weather? The lamp will be indoors so the temperature would range between 10-30 celsius. I've done a quick search and found that steel has a coefficient of expansion that is two times greater than wood. I guess the real questions are, will i get away with this using relatively thin wood at 5mm? Will the epoxy provide some give and thereby eliminate cracking?

Has anyone attempted this sort of thing before and what did you find?
I suspect i already know the answers but if you have any ideas or experiences please share.

Cheers
mat

[silentC]

Never tried that and don't know how it would work but it probably wouldn't be as bad as you think.

However why not just make a wooden base and route out a hollow then fix a big lump of steel in underneath, which you could hold in place with screws in over-sized holes in the steel to allow for movement?

[clear out]

The timber will expand and contract with moisture.
The movement across the grain is about ten times the amount with the grain.
I'd expect it to come to grieve sooner or later depending on where you live.
H.

[silentC]

Whilst strictly speaking this is true, if it were always the case then MDF core veneers would fail, which they clearly don't. If the veneer is thin enough then it can't exert enough force to cause a problem.

What may happen though is that the expansion of the steel may cause the timber veneers to split. I don't know much about the properties of steel but I think that if it is not exposed to extremes, it will not move as much as you think. It would be an interesting experiment.

[Bob38S]

Like Silent said, rout the base, fix with screws but don't make the steel / timber a tight fit, leave room around the perimeter of the steel.

To minimise timber movement ensure that you fully finish all surfaces, not just the top leaving the bottom raw. Check out marine Penetrol as a base sealer, it penetrates and seals and can be over finished with your choice of finish. The Penetrol should also stop the steel rusting.

Just a thought, make sure that the steel is not proud of the base as it will mark the surface it is placed on, particularly should it be slid.

[BobL]

Id say you have nothing to worry about.
Wood parallel to the grain typically expands 4 times less than steel, while perpendicular to the grain its about ~2.4 times more than steel.

But the thing that really matters is the total movement.
On a 400 mm length, 20ºC temp change the total amount of movement will be
0.1 mm for the steel
0.24 mm for the wood perpendicular to the grain
0.024 mm for the wood parallel to the grain

[Skew ChiDAMN!!]

What BobL said, 'cept I wouldn't epoxy.

Instead I'd glue it using Silicone, which is flexible enough to cater for any movement on that scale. It's what I use to glue porcelain & china tiles into timber cutting blocks, cheese-boards, etc. (The tiles tend to crack before the wood does if a rigid glue is used!)

[auscab]

I welded up a table base out of square and rectangular hollow section and covered it in 5mm Oak , glued with epoxy . I roughed up the steel first before gluing. That was in March 2011 . No problems so far .

[Simplicity]

I like the difference between the two materials.
I think it could look quite nice especially if u polish the edge of the steel up.
So one option go with what others have said.

Option two build a hollow core box as per normally .
But fill it with lead ( Bunnings to lead sheet in I think 400 mm square sheets $30/40 I think)
I would keep adding lead till it doesnt tip over, and then a bit for comfort .
But depending on your design ,this could get quite heavy .
Would love to see some pics when it's done .
And just a thought with the lead it's quite easy to cut and work with compared to steel just tin snips will do to cut it .

[orraloon]

Never seen it done but I would be avoiding sticking two materials with differing expansion rates together. Something has to give. We allow for expansion when building things like tables, benches framed pannels and the like due to past practice showing the way.
If you like to experement then give it a go and share the results with us.
Regards
John

[Sir Stinkalot]

Just a couple of random ideas from left field .....

What about double sided tape or rare earth magnets?

[silentC]

Just out of curiosity, I did a bit of a google and found this:

http://eltongroup.com/woodwall/what-is-it/

It's basically a very thin (0.5mm) veneer which comes in sheets and is designed to be glued to surfaces like plasterboard, steel, or plastic to give a timber finish. They use it to wrap steel beams for example. It is attached to steel with contact glue.

[Lplates]

Some great feedback above and some constructive ideas too. Exactly why i love these forums.

After i posted this topic yesterday I did immediately think about the hollow base filled with loose lead option. In terms of ease that would probably be the way to go however when the idea of laminating the steel to the wood came into my mind I really started to like the idea of having an edge where the polished steel shows through (like ply). I think it could be a nice touch.

Anyway, given that we're talking about a relatively small piece i can probably make both types and just try it out. Not a lot of material wasted if it doesn't work out.

Thanks again everyone.
Cheers
Mat

[Simplicity]

They do look nice together
Well I think so
And here's one I made early lol
Well steel and timber mix that is ImageUploadedByTapatalk1414030274.703742.jpg

[rrich]

I think that you may be making an easy job difficult.

Make an attractive hollow base. Line the base with plastic wrap. (We call it Saran wrap here.) Then fill the base with something like Quick-Crete. (It is a quick hardening concrete repair product. Available at most home centers. Bunnings?) Just make your base so that the Quick-Crete is trapped and can't get loose.