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Many here have used ply for their top. Use two layers for the top, MDF underneath, glued and screwed to the ply. I would also joint some trusses underneath to help keep it flat. Use Baltic Birch if you can find it. Use an aluminum mounting plate. Finish the top and and wax it.
 

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I'm about to build my mark 3 router table, but i cant find any melamine locally without buying a 10 ft x 4 ft sheet at really stupid money.
I do have some 12 mm (1/2" ) ply that is very flat and smooth.
Anyone tell me why I cant just use ply?
use it...
if you want to up the smoothness ante use grain filler...
light sanding...
and then begin the sealer/sanding/polishing between coats campaign...
smooth as glass and slick after waxing...
 

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Johnson's paste wax. Use 3/4 (18mm) for both layers, you get about 1 1/2 inch thickness (36 mm). Heavier and the MDF helps keep it flat. Stick gave you the finishing instructions. I would also add edging of some sort to keep moisture away from the MDF. The weight is substantial with the MDF, which is why I'd add the trusses. Pre drill into the mdf for screws. Put the screws through the trusses by drilling a hole bigger than the screw head to a depth that stops the screw about a quarter inch into the ply. Pre drill MDF always or you will get a bump on top, or even a split. The MDF is for flatness, not structure. That's why I'd add the trusses.
 

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I've seen so many members complain over the years that their double laminated table top warped after they glued it together that I've started suspecting that it's the water in the glue migrating into the substrates that might be causing the warping. 2 layers is not needed. I've even seen Pat Warner say so, that the frame underneath is far more important that what you put on it. I built one table, used it for 3 years, then gave it to my son-in-law who's had it for 4 years and it is one layer of 5/8" melamine with 3/8" deep grooves in it for t tracks and it's still dead flat. Despite going from -45 to plus 40 each year. The trick is a good level frame under it. Theo (Joat) has a table that is at least 15 years old that is a single 1/2" ply that is screwed to a 2 x 4 frame that is still dead level he says. Theo didn't use an insert plate he just screwed the router right to the plywood. You lose about 1/8 to 3/16" of depth doing that as opposed to using a plate. The materials have a minor importance in the build. The engineering is what's the most important.
 

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Discussion Starter #11
I had planned on a heavy sub frame of 4 cross bars, but not a full on torsion box.

The table top is only going to be just under a yard square (90cm).
from these replies I may reconsider the construction.
but of course the torsion box cant be the entire area as I have to make a space for the router, So theres a 30cm x 25cm (12" x 10") central portion that cant be double skinned. Is that area going to negate the torsion box effect?

If so maybe a compromise of a solid level base and two layers of 12mm ply?
 

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I had planned on a heavy sub frame of 4 cross bars, but not a full on torsion box.

The table top is only going to be just under a yard square (90cm).
from these replies I may reconsider the construction.
but of course the torsion box cant be the entire area as I have to make a space for the router, So theres a 30cm x 25cm (12" x 10") central portion that cant be double skinned. Is that area going to negate the torsion box effect?

If so maybe a compromise of a solid level base and two layers of 12mm ply?
no..
 

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If you use laminates (Formica is one brand), laminate both sides to keep it from warping. They have laminate without the decorative layer (which is melamine! Do you remember Mel-mac dishes?). All laminate consists of is multiple layers of kraft paper (paper bag material) glued under pressure. The laminate without the decorative sheet is called a "backer" or "balance" sheet and is used to eliminate warping of your "sandwich". (One or more layers of material.) Always use contact cement to adhere laminates.
 

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I built my torsion box into the router base, top and bottom. I do not recommend using MDF. Very hazardous you your health. Two sheets of baltic birch will work just fine.

I think I mentioned that it can get expensive making your own (melamine).
 

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Discussion Starter #15
i have no access to formica or other "do it yourself" finishes. this island is extremely limited on whats available.
I have even had to go back to the Uk to source a piece of aluminimum a foot square by 4mm.

Basic wood construction materials are plentiful, but finishing touches are not.

without spending silly money, ply is my only option.

I can make a torsion box with 12mm ply top and bottom, but it will have to have the middlle section as a single layer to allow the router to work.
 

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Both my tops are lam'd 3/4 ply, with hardboard both sides then formica both sides. The 2nd top was built in 03/04, I didn't truss either up, it might not be an issue if it were a small router or a big one and or base were removed after use. But who does that? I just checked mine and have a 3 1/2" long .022 gap center front of the base. While I don't have issue with the almost 3/128", (sag it should not be there), others might be vexed with not perfect. If I bought a factory built table I would expect absolute.

When I replaced my RAS table 18+ yrs ago I did embed chain link fence tension bars in the lam, I was doing lots of arbors, trellises and flower boxes on the side PT and cedar can be heavy. It has held up, although it doesn't maintain 20 something lbs. of dead weight. I'm slobby sheik, had I contemplated sag when fabricating either RT top I probably would have thought "Meh, how much could it sag". After 12 yrs, of a 3 1/4hp PC and Bench dog lift 3/128 aint so bad.
 

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Discussion Starter #17
I've already learnt the hard way that table sag affects small pieces of wood. A long run of a foot or more passes over any valleys. But I do mainly small box sides, 8" and less, and they are small enough to ride up and down the surface.
Thats how i found my table wasnt flat,when a set of box joints came out angled downwards.
 

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I've never built a torsion box for a router table and probably never will. Theo didn't with his either. Neither of us have had issues building that way. You're talking about hanging a 12-15 lb/ 6-7 kg router from it, not park your car on it. A different VOE speaking. Never doubled the top lams, never sealed both sides. Still no issues ever in 40 years. If you attach the top to a solid, level sub frame with enough cross members to prevent sag then the top can't move. It is physically impossible. The construction is no different in principle from installing the floor in a house. If you use a wide enough joist on close enough centers and not over too long a span then it doesn't move. Just because it is a router table doesn't make it different.
 

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Discussion Starter #19
The router plate is faulty, 100% unarguable. Thats why I'm working on this. As Kreg have sent another, i want to beef the table so this one doesnt warp.
The table top, which is white melamine, has some very small rise and falls, discovered only after checking with the best straight edge I have. If I wasnt working with the plate, I suspect this would not impact my work, but as I'm going to work on it, I might as well do it properly.

My thinking is twofold.

1, this table was made when I had a lot less knowledge than I have now, so I can see a couple of ways of improving it.

2, I dont want to spend hundreds making a construction that will become a family heirloom. I just want it to perform better than it does now.

I think I will compromise between the two extremes here. I'm not going to build a complete torsion box, it just seems too excessive for a table barely a yard square. But I will run 4 joists front to back across the base (much more support than it has now), on which I will lay 2 x 12mm ply sheets, glued and screwed. My garage doesnt suffer from damp, so I wont make any edging, just use a couple coats of wipe on poly to seal it.

Maybe a couple coats of wipe on poly on the top surface?

Its good to get other peoples viewpoints, thanks.
 

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I've never built a torsion box for a router table and probably never will. Theo didn't with his either. Neither of us have had issues building that way. You're talking about hanging a 12-15 lb/ 6-7 kg router from it, not park your car on it. A different VOE speaking. Never doubled the top lams, never sealed both sides. Still no issues ever in 40 years. If you attach the top to a solid, level sub frame with enough cross members to prevent sag then the top can't move. It is physically impossible. The construction is no different in principle from installing the floor in a house. If you use a wide enough joist on close enough centers and not over too long a span then it doesn't move. Just because it is a router table doesn't make it different.
but Charles!!!!
you did build a torsion box... aka floor joist w/ blocking.. aka your frame...
a torsion box build made w/ half lap joinery adds skill set..
you can halve the frame member thicknesses too..
 
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