I built an almost flat table. Need some ideas.?

[keith ouellette]

I finally got time to put the pieces of my ts extension/router table together in a dry fit. It is 48" long and 38" wide. It's top is mdf set in a dado on a 4" high almost 1" thick skirt with support rails about every 10 inches made of the same plywood that is 3 1/4" high.

Its actually pretty flat. after some shimming with masking tape the top varies by .003 in some areas across its width and about the same across its length. Its a little more off that that on a diagonal. .003 or better was the goal I set for myself.

My questions are:
How much will i see this variance come out in my routing?

I want to cover the top in formica I already have. will contact cement spread so uneven that it will cause the top to rise and dip even more or would it help create a flatter surface by filling in the voids?

[David DeCristoforo]

Three thousandths of an inch? In a 48" wide top?? That's horrible. Burn it! No...really.. just kidding. Three thousandths will never be noticed. However I should add that there will be those who will swear that this will adversely affect your woodworking. I would be happy to let them borrow my new Veritas Hair Splitter.

[Stephen Edwards]

Get out the contact cement and put the laminate on the table. You're good to go. I recall a post that someone made a while back in response to a similar question. We're doing woodworking here, not building the space shuttle.

[Ben Franz]

You might want to consider laminating both sides of the MDF top - moisture absorbtion can cause noticable warping in MDF. I built an extension for my saw and didn't bother with this step. Surprise - I'm not immune to the laws of nature and now have more than 1/16" crown at the edge of the TS top. It still works okay since it's only providing support for wide pieces and the material is registered on the cast iron surface relative to the blade. Still, it's irritating :mad:.

[keith ouellette]

You might want to consider laminating both sides of the MDF top - moisture absorbtion can cause noticable warping in MDF. I built an extension for my saw and didn't bother with this step. Surprise - I'm not immune to the laws of nature and now have more than 1/16" crown at the edge of the TS top. It still works okay since it's only providing support for wide pieces and the material is registered on the cast iron surface relative to the blade. Still, it's irritating :mad:.

How about if I seal the bottom and edge of the top with sanding sealer? Do you think that would be good enough.

[David Freed]

I want to cover the top in formica I already have. will contact cement spread so uneven that it will cause the top to rise and dip even more or would it help create a flatter surface by filling in the voids?

I agree with David's and Stephen's comments. A bubble in the formica would cause a much bigger problem than your near perfect top. You might consider just waxing the mdf with Johnson's Paste Wax occasionally and forget the formica. Mdf is fairly slick to begin with. I have a couple mdf tops that I use and don't even bother with wax.

[Russ Boyd]

Even if you go ahead and laminate, I don't think laminating the bottom is necessary because of the frame you built underneath (is this what you guys call a torsion box?). On a freestanding top, yes, you MUST do both sides, but in this case you have the same situation as a countertop, where it is attached and bottom lamination is not necessary. I do agree with maybe not even laminating because of the already slick surface of mdf.

[keith ouellette]

I agree with David's and Stephen's comments. A bubble in the formica would cause a much bigger problem than your near perfect top. You might consider just waxing the mdf with Johnson's Paste Wax occasionally and forget the formica. Mdf is fairly slick to begin with. I have a couple mdf tops that I use and don't even bother with wax.


Even if you go ahead and laminate, I don't think laminating the bottom is necessary because of the frame you built underneath (is this what you guys call a torsion box?). On a freestanding top, yes, you MUST do both sides, but in this case you have the same situation as a countertop, where it is attached and bottom lamination is not necessary. I do agree with maybe not even laminating because of the already slick surface of mdf.

I don't find mdf to be very durable. I like it because it is stable as long as it stays dry but it can wear down very easy. Thats why I wanted the formica top but when i started out with this plan I didn't consider how un even contact cement could be spread.

Now I am planning to use a 3m heavy duty spray on adhesive. It says its for laminants.

Just to be on the safe side I am going to coat the bottom and the edges with fast dry poly to seal it. It can get a little humid in my shop in the summer.

[Jim O'Dell]

Keith, that's what I did for all of my torsion box tops, extensions, and the router top that is not a true torsion box (no bottom layer). 2 or 3 coats of water based poly, and I've seen no problems yet after 2 years. I just couldn't justify laminating the bottoms. I did do the sides on all of them, though.
I do have an outfeed/assembly table that I just used the poly on top. Unfortunately, there are already some gouges in it where something dug into it while assembling. I've tried sanding and filling with poly, and that helps, but doesn't bring it back to full level in those places. Eventually, I'll build a proper assembly table, then maybe I can sand this down and put a layer of laminate on it to use just for an outfeed table where it won't get scratched so much.
Russ, a true torsion box has a gridwork to separate 2 layers of material. This helps it to pull or push against itself to reduce movement. The 2 layers should be the same material and thickness, and really should be finished out the same way so that one side doesn't react differently than the other side, which could cause the box to warp. The gridwork does help, but the layers need to react to temp and humidity the same to stay flat. But as I said above, my torsion boxes only have poly on the bottoms and I've not had any problems. A top with a gridwork under it like my router table, relys on the gridwork to keep it flat. Jim.

[keith ouellette]

Keith, that's what I did for all of my torsion box tops, extensions, and the router top that is not a true torsion box (no bottom layer). 2 or 3 coats of water based poly, and I've seen no problems yet after 2 years. I just couldn't justify laminating the bottoms. I did do the sides on all of them, though.
I do have an outfeed/assembly table that I just used the poly on top. Unfortunately, there are already some gouges in it where something dug into it while assembling. I've tried sanding and filling with poly, and that helps, but doesn't bring it back to full level in those places. Eventually, I'll build a proper assembly table, then maybe I can sand this down and put a layer of laminate on it to use just for an outfeed table where it won't get scratched so much.
Russ, a true torsion box has a gridwork to separate 2 layers of material. This helps it to pull or push against itself to reduce movement. The 2 layers should be the same material and thickness, and really should be finished out the same way so that one side doesn't react differently than the other side, which could cause the box to warp. The gridwork does help, but the layers need to react to temp and humidity the same to stay flat. But as I said above, my torsion boxes only have poly on the bottoms and I've not had any problems. A top with a gridwork under it like my router table, relys on the gridwork to keep it flat. Jim.


Thanks for the thoughts Jim. I'm going to use the water based poly. I just happen to have some on hand which is always a plus.

[David Freed]

Now I am planning to use a 3m heavy duty spray on adhesive. It says its for laminants.

That is a good idea. You will still need to be very careful when installing to avoid air bubbles between the layers. That spray-on contact adhesive is really good stuff. I underline contact because once it makes contact, whether your pieces are in the right place or not, it ain't lettin go. Don't ask how I know that.

[John Thompson]

I laminated one about 5 years ago that has not moved. I used formica on top and sealed the bottom with 3 coats of standard poly. I did use the standard formica glue you apply to both surfaces. And the advise about once you touch it down.. it's staying down.

You might want to cut some strips of wood for the formica to lay on. Then remove one and J-roll it down to elminate a bubble. Then remove the next strip and J-roll. Just continue until the entire top is down. And be sure to cut the formica a bit wider and longer to over-lap.. You can go back and trim the edge with a laminate router bit.

Good luck... BTW... you will never notice .004 variance as it is a non factor.

Sarge..

[Tony Bilello]

from a spray can. I have serious doubts about its ability to hold since the layer of cement wont be all that thick. I'm sure others have has success with it but I wouldn't be swayed by that.
I have sprayed contact cement with a paint spray gun and also have rolled it out. Even if you intend to roll or paint it on, get the "spray grade" because it is thinner and flows better.
Keep in mind that the fumes are highly flamable and give a great buzz. Be cautious but no need to get freeky about it. Just do it in a well ventilated area.

[george wilson]

I doubt that most cast iron,blanchard ground,older table saw tops are any better than .003". Some newer saws,like the SawStop,which are ground with newer technology,might be flatter.

[Jim O'Dell]

Ditto Toney's post. I use the regular glue, not the latex version. I use a roughly 1" diameter roller to roll the glue out. I do 2 coats. Be sure to wait until the glue is dry to the touch between coats, usually about 20 to 30 minutes, and then do the same before you stick the 2 together. I used old pieces of dowel rod, thin cuts from MDF, and have heard of people using the individual runs of old venetian blinds as a way to separate the 2 pieces. This allows you the opportunity to align the piece with the top. Then start in the middle, take one piece out at a time and J-roll it smooth all the way across to the sides, like Sarge said to do. This keeps you from having an air bubble in the middle. Work from the middle to one edge length wise, then go back and do the other half.
Only problem I've had is a chip of wood that got on one section of my RT top and I didn't notice it until it was too late. I had to drill out that spot with a forstner bit to get the rest of the top to lay flat. Then I epoxied in a penny to fill it in. Made the epoxy proud of the surface then used a razor blade to trim it flat with the laminate, after the epoxy had cured. Jim.

[John Thompson]

Only problem I've had is a chip of wood that got on one section of my RT top and I didn't notice it until it was too late. I had to drill out that spot with a forstner bit to get the rest of the top to lay flat. Then I epoxied in a penny to fill it in. Made the epoxy proud of the surface then used a razor blade to trim it flat with the laminate, after the epoxy had cured. Jim.[/quote]

Sounds like one of those.. "a penny for your mistakes" deals to me. :)

Regards...

Sarge..

[Stephen Edwards]

Jim, I really like the penny idea! That's a great solution for the problem that you had. Did you use a clear epoxy so that one can see the penny? If so, I bet it looks cool in the table top, too.

My technique for putting on the laminate is to use newspaper between the table or counter top and the laminate. It's easy to "feel" how much overhang you have. After it's properly positioned pick up one end and remove the paper from that end. Press it into position, being careful not to press too close to the remaining newspaper. Then, pick up the other end and remove the remaining newspaper. Roll the laminate from the center toward the edges, as OP have suggested. An old timer taught me that technique years ago. Now, I'm the old timer!

Agreed with others. Don't use the spray or the latex. Use the contact see-ment that has lots of stinky fumes, two coats of it.

[Marty Paulus]

.003 out of flat? That is less then the thickness of the average human hair (.004). A sheet of paper, if I remember correctly, is about .005. This is across a piece of 'semi precision' MDF 48 X 38? Let it go. As was said, there are comercial router tables out there that are more then that out of flat. Enjoy and be proud of the fact you are that close to being dead flat.