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I'm building a router table based on on this FWW video series: http://www.finewoodworking.com/item/57006/build-a-router-table

It has a MDF top with countertop laminate glued on (with solid maple stretchers to hold the lift and keep the MDF from bending).
My question is this: in the video and plan they have you laminating countertop material onto both the top and bottom of the MDF. I can't figure out why it makes sense to do the bottom and thought I might try to save a bit of time and work by just doing the top. But maybe I'm missing something, so I thought I'd ask here.
Thanks.
 

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I believe that they have you do the bottom too guard against the top cupping or bowing. Although you're using mdf so I don't know if that's really a concern. MDF tends to sag overtime I think so perhaps the laminate material helps prevent that. I made my own router top a few years ago. Actually I did it twice because the top warped (I can't remember now if I laminated both sides or not). For the second top I did this: made it out of two sheets of 3/4 ply, ran hardwood edging around it, laminated both sides with a formica-like material, then had a machine shop weld an angle iron frame with drill holes countersunk into it that I screwed right to the underside of the top. It might be overkill but this sucker is never going to move. It's flat for ever now. If you're interested I'll post a pic. The only drawback is that the angle iron obstructs your access to the router a little bit but it's not that big a deal. I like how heavy the table is too; there is no vibration or movement.
 

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Discussion Starter · #3 ·
Thanks for the reply. I'm not worried about it sagging, since the router and lift are supported entirely by 2×4 hard maple stretchers and the MDF only has to support its own weight (you can kind of see how at about 1:30 in the intro video with the link above for non-members to FWW). You're probably right that controlling moisture and avoiding warping is the reason, like finishing both sides of a table. Like you I'm not entirely certain that this kind of thinking really applies to MDF, but I suppose it's worth the extra bit of work, especially since I don't think I can buy the formica in smaller than 8×4 sheets (although I'm going to check countertop places to see if they have scraps).
 

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It has been my experience that when MDF decides it wants to absorb moisture it does so in a big way. For the cost of laminating the bottom side it is worth it.

Also, I found white laminate is best since I can mark on it with a pencil. A quick mark to help with setup or returning to a previous setting.
 

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I am also building a router table, and one of the gurus over at the local Woodcraft store advocated the same thing, laminating both sides of my MDF top. The reason being to minimize moisture absorption as WoodNSawdust pointed out.
 

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Discussion Starter · #6 ·
Thanks WnS and Chris. I guess it's unanimous that it'd be stupid to try to save $20 and a bit of time by laminating only one side. I'll be off to HD this evening to buy some laminate.
 

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Hi there,
it is not so much about moisture absorption, since wood is hygroscopic it is just what it does, MDF and Chipboard beeing no exception. However you have to make sure that the tension moisture absorption creates is balanced and that is why you have to laminate both sides, ideally with the same material and same thickness. Try this, have a piece of Mdf lean against a wall. after some time it is bend because the weight is creating an unbalanced tension and with the moisture absorption, or the opposite, the board is changing form. Just keep it balanced and it will stay staright.
 

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If the laminate on the bottom is just to keep it from absorbing moisture, seems it would be easier to just seal it with some paint or poly.

Cheers,
Brad

PS: I really hate gluing and trimming laminate :)
 
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