Must I laminate both sides of everything to avoid warping?

[Andrew Pitonyak]

I am building a router table to place in my table saw wing. My intent is:

1. Build an oak frame that is roughly 2" x 7/8".
2. Cut the top from 1" MDF
3. Laminate the MDF bottom.
4. Attach the top into the frame so that the top is flush with the frame.
5. Laminate the top and the frame.

Two questions:

Question 1: If I do the steps above, then the top of the frame is laminated and the bottom is not, is that a problem? I assume not.

Question 2: If the top is flush with the frame, do I need to laminate the MDF top and frame? I intended to do this to make sure that the wood never caught on the frame lip. It does make it marginally more difficult to mount the table.

[ian maybury]

Can't say for sure, but there's likely quite a difference in rate of expansion/contraction with temperature and humidity between the laminate and the MDF - and despite the pretty thick MDF laminate can be pretty strong stuff. My personal instinct would be to play safe and make sure that the construction of the top and the bottom is the same. i.e. of the same materials, same thicknesses, same exposure to the atmosphere and both laminated...

[Bill Orbine]

The oak frame..... is it gonna be the 7/8" edge flush with the top? Or is it gonna be the 2" face flush with the top? I'd say you're fine with the 7/8" edge flush with the top even though I would rather rabbet the oak so that the oak edge doesn't appear as wide. And just what is this laminate? Formica or wood/ something else? If it's formica or something airtight, you might run the risk of the edges of plastic laminate delaminating in the future if you lamininate on the 2" face of the oak. The point of all this is that I'm concern of the movement of the wood in humidity related situations.

[Andrew Pitonyak]

The oak frame..... is it gonna be the 7/8" edge flush with the top?

Yes, I meant the 7/8" flush with the top of the MDF without laminate and then laminate the entire top.

And just what is this laminate? Formica or wood/ something else? If it's formica or something airtight, you might run the risk of the edges of plastic laminate delaminating in the future if you lamininate on the 2" face of the oak. The point of all this is that I'm concern of the movement of the wood in humidity related situations.

Standard counter-top laminate from Lowes, so, certainly airtight. Did not intend to laminate the 2" face portion, but I had intended to laminate the entire top so that it is uniform. I can certain crown / round the 7/8 top just a wee bit so that the top is flush with the laminated MDF and not use any laminate on the MDF. Based on Steve's recommendations, I will probably apply some poly to the 2" faces (and the 7/8" faces if I do not laminate the entire top and bottom).

I'd say you're fine with the 7/8" edge flush with the top even though I would rather rabbet the oak so that the oak edge doesn't appear as wide.

Hmm, no particular reason I need to embed the top into the frame, I could place the entire MDF top onto the frame...

[Frank Drew]

Andrew,

It's always best practice to laminate both sides of a panel with similar material. Not doing so sometimes works out, but sometimes it leads to unhappiness down the line.

[Steve Ryan]

You need to laminate both sides to prevent warping. P-lam and MDF are very close to the same as far as enviormental change movement. Remember, both are wood products. Problem is that moisture/humidity will enter the raw MDF side a lot quicker than the laminated side. Once the table is made it would be a good idea to put some poly on all raw edges to seal them.

[Andrew Pitonyak]

Thanks for that Steve.... I will certainly do this.

[Tim Sproul]

The way you describe it, you can skip the bottom laminate. Attach 1" mdf to frame and then laminate the top. Contact cement and plastic laminate don't present huge problems with a supported top. A free floating panel is a different beast.

When you build the frame, I'd recommend you crown the top ever so slightly - say 1/32" or so for a table in the 24 inch range. It it very easy to do precision routing with a crowned top, difficult with a flat top and nearly impossible with a bowl top.

[Howard Acheson]

Yes, it is always best to laminate both sided when you really want it to remain flat. The rule is to treat both sides the same.

[Chris Fournier]

I'd avoid using the oak as it moves differently across it's cross-section, introducing seasonal changes to your table insert. Why not build a torsion box entirely out of MDF?

[Bob Falk]

As stated, whenever laminating, you should balance design (same veneers top and bottom) to minimize warping. I can't tell you how many products have been sent to our lab for analysis that warped (skateboards, table tops, etc.) because this basic design criteria was ignored.

Bob Falk
Research Engineer
USDA Forest Products Lab
Madison, WI

[Scott T Smith]

Bob, let's say that there is a situation where you cannot use the same veneers on both sides (such as when working with a very costly burled veneer or a rare material), what rules should one follow when choosing a veneer for the 'back' side?

I presume that rule #1 would be to use a veneer with the same thickness as the display side, and rule #2 would be to use a material with a similar specific gravity? Or are there different rules that should be followed?

[Bob Falk]

Bob, let's say that there is a situation where you cannot use the same veneers on both sides (such as when working with a very costly burled veneer or a rare material), what rules should one follow when choosing a veneer for the 'back' side?

I presume that rule #1 would be to use a veneer with the same thickness as the display side, and rule #2 would be to use a material with a similar specific gravity? Or are there different rules that should be followed?

Scott,
You are correct. The best bet would be to use the same specie and thickness. I would suggest a balance design (same number/orientation of veneers top and bottom from the neutral axis (center of section)) and if you use a walnut burl on top, use a walnut veneer on the bottom. Where you can't use the same specie, I suggest trying to match both SG and shrinkage characteristics, if possible. Also, I would also match grain orientation top and bottom (obviously there is no orientation to match with burl).

Our Wood Handbook Tables 4.3 and 4.4 list the shrinkage values for various species and Tables 5.3-5.5 provide SG values. See www.fpl.fs.fed.us for download. Note that cross grain in peeled veneer is the tangential direction (greatest shrinkage in tables). Depending on how sliced, much veneer is akin to lumber and will be cut across both the radial and tangential directions (I would use an average of the radial and tangential values from the tables in this case). If the veneer is radially sliced, then you would use the radial value.
Hope this helps. Cheers, bob

[Scott T Smith]

Bob, that's great info - thanks much.

I manufacture a sawn veneer, so the data is very applicable.

Regards,

Scott

[Alan Lightstone]

Can you laminate one side of MDF and seal the other side (and edges) with shellac and avoid problems, or is laminating both sides necessary.