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:



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

[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.

[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?

[Andrew Pitonyak]

I want to be clear about what I mean to do.

The bottom blue portion is 1/8" plastic laminate that I will attach to the bottom of the MDF so that the MDF will not warp.

The dark brown is 1" MDF that is the primary router top.

The light brown is the oak frame. I intend to install the MDF into the oak frame flush with the top of the oak frame. The oak frame is 2" tall and the MDF is 1" thick (plus 1/8" for the bottom laminate).

My intention was then to laminate the entire top, which includes the oak frame and the MDF.

I intend to use pocket holes to attach the MDF into the oak. I have done some tests so that I know a know how much pressure I can use without crushing the MDF.

I used an oak frame that I will attach to my table saw table top and to my fence rails. I think that I can easily attach the oak frame to the table saw but that it would be difficult for me to attach the MDF to the table saw.

Note that although they are not shown here, I intend to run a support structure (like a torsion box) under the MDF with support as close as possible to the section where I install the router lift and also where I run a T-Track for accessories.

I have practiced threading MDF and then strengthening the threads using CA glue. I intend to use this method to secure the top to the supports that I place under the top.

My concern was that the top of the oak frame would have laminate and the bottom would not. Based on the comments here, I have a few more questions:



It was mentioned that oak is not a good material to use for my frame because it is not dimensionally stable. I cut the frame using straight grained quarter sawn oak. If Oak is a bad choice here, what would be a good choice? Chris, I did not think about using only MDF because I think that it would be difficult to connect to the table saw.
So do I understand correctly that the plastic laminate may come off the 7/8" portion on the top? If so, then I assume that I should ONLY laminate the MDF and NOT laminate the frame.
It sounds like I should apply some sort of sealer (poly) along all portions that are not laminated. I had been wondering about that (thanks Steve).
Based on a comment by Bill, I wonder if I should simply build a bottom support and then attach the entire MDF top to the frame from underneath (rather than sliding the MDF into the frame). This would be pretty easy to do..... Hmmm, no... With the laminate, the top is 1 1/4" thick. The saw top is 1 1/2" thick and the screw holes are centered 3/4" down, so, all support members would then be placed directly into the MDF, which I expect would not hold.

[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...

[Andrew Pitonyak]

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

[Bill Orbine]

179498Andrew, pictures are worth thousand words. Maybe this drawing will help you see my thinking. Of the two, the bottom is better the more I think about it! I saw an issue with the top one. You have to also think the there is expansion and shrinkage of the oak along the thickness of the top, too! I see too much of that in the top drawing and I think the lower drawing is a better way to go!

[Frank Drew]

I don't think you'd have problems by applying the formica over both mdf and oak frame, assuming the top edge of the oak is nice and flush with the surface of the mdf, but I do think that both sides of the mdf need to be treated the same, oak frame or no oak frame. And that applies to finish, wood veneer, plastic laminate, whatever. I have seen applications with man-made sheet goods plastic laminated on only one face, but I don't think it's a good idea.

[Andrew Pitonyak]

179498 I see too much of that in the top drawing and I think the lower drawing is a better way to go!
A 9/16" height rabbit on the oak, a 5/8" rabbit on the MDF (both 1/2" left to right), should leave the oak 1/16" proud. I can then use trim bit to bring the oak to exactly the same height as the MDF and apply the top laminate.

[Andrew Pitonyak]

Good.... Easy to laminate both sides of the MDF. I did not want to laminate the bottom of the Oak. Do not mind a bit of poly though.

[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 (http://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.

[Mike Gager]

most prefab kitchen counters are particle board with laminate on only one side and they stay flat...

[scott vroom]

For $150: http://www.woodpeck.com/rt2432p.html

[Jamie Schmitz]

If you make the edge of the oak flush with the laminate (not under it) it will help protect the edge of the laminate from de-laminating or breakage from use. I like the idea of a torsion box but maybe a bit much but hey never enough right. Another thought which I am about to embark on (because mine warped, I did not seal or cover) is to mount the bottom to 2 rails made of angle iron. I actually just checked H. Depot for some stock and they had some steel with pre-drilled holes along the entire length which might be nice for hanging tools and save drilling. These pieces were very strong I tried to bend them and they did not budge and were very straight. Did you say 1/8 inch laminate? I have never seen it that thick.

[Don Alexander]

most prefab kitchen counters are particle board with laminate on only one side and they stay flat...

no they don't they appear to be flat and stay that way if they stay dry and are screwed down well enough but they are not flat like you want a router table top to be flat also particle board in that application is "good enough" for the majority of the construction industry you can also use MDF for countertops the same way also not as flat as you want a router table top

if you want laminated panels to stay flat and the back /bottom isn't visible then its common practice to put backer laminate (brown or black and thinner / cheaper than the laminet you want to look at on the top/outside) on those surfaces (look at laminated table tops for example)

as to the OP's question, the best practice for what you are wanting to do would be to laminate top and bottom of the MDF and poly the exposed oak
and seal the edge of the mdf where the cutout for the router is just don't soak that mdf edge or it will swell and mess up your top i often seal those edges with contact cement put on with a small roller for smoothness

HTH

[Andrew Pitonyak]

Did you say 1/8 inch laminate? I have never seen it that thick. I did not measure it, so I am only guessing. It seemed pretty thick to me, but it rolled up pretty well, which would indicate thinner. OK, now I am curious.... OK, it is less than 1/16" (pretty close though). Used a tape measure...

[Andrew Pitonyak]

as to the OP's question, the best practice for what you are wanting to do would be to laminate top and bottom of the MDF and poly the exposed oak
and seal the edge of the mdf where the cutout for the router is just don't soak that mdf edge or it will swell and mess up your top i often seal those edges with contact cement put on with a small roller for smoothness

HTH
In response to your "HTH", yes, it does.

[Phil Phelps]

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.

If you are securing the laminated MDF, such as a table top, you don't need to laminate or shellac the other side. If it were a stand alone, then yes I would treat both sides. Like a laminated counter top, there is no treatment to the back side.