Router Table Top Question

[Larry Nall]

Thanks to all of you that responded to my last question about mounting the router to the table saw.

http://www.sawmillcreek.org/showthread.php?p=939772#post939772

Originally I was skeptical that this was a good idea but after reading your responses it looks like you can have your cake and eat it too.

So on to the next question...the top. In my reading I see that table sag is a big issue. This prompted me to take a critical look at my current table. It's just a 2x4 frame with a double 3/4" ply top covered with laminate. The router is an old PC 690 attached to 1/4" plexi. It's simple but has served well for many years. Sure enough, there is a little over 1/8" sag across the table.

So, if a PC690 can cause sag in 1 1/2" of plywood, I wonder what a PC 7518 will do. I know a cast iron top is the ultimate answer but I've already spent more $$$ than I wanted too.

I'm wondering if a torsion box approach is the answer. For example a double layer of ply or MDF on top, a narrow (2 1/2" - 3" torsion framework with a thinner skin on the bottom.

Will this work or do you have a better idea?

Thanks in advance for your help.

[Jim O'Dell]

It would help the rest of the table, that way your weak point would be as mine is...right at the opening for the router plate. I made mine out of 2 layers of 3/4" MDF, and mounted it on an open grid frame work made out of 3/4" plywood. Shimmed and leveled as I mounted it. Then routed a lip for my router plate to sit into. This left me with a little over 1" of MDF for the router to sit into, and frame around that edge. Any sag should be just what the plate would do. The open grid on mine is 6 X 8", IIRC.
I personally think that the MDF stays flatter than most of the plywood we can buy today. But ply is stronger. If you are really concerned, I guess you could combine a layer of each, or sandwich 3/4" ply between 2 pieces of 1/2" MDF. Or build your subframe out of 2" angle iron. :eek: Actually, that's not a bad idea. ;) Jim.

[Joe Spear]

I made my current router table out of two layers of 1/2" MDF, one layer of 1/4" plywood, and top and bottom laminations of formica, all bonded together with solvent-based contact cement. Then I glued one-inch wide, 1 1/4" thick purpleheart edging all around with Titebond III. It is 32" x 38" and just over 1 1/4" thick. In a little over two years it has not sagged at all, even with the big Milwaukee 5625 in it. I think that's because I cross-braced it underneath with 3/4" plywood strips cut 2 inches wide and set into open mortises in the frame of the beechwood cabinet that the top sits on.

I don't think that protection against sagging comes just from the top thickness and material--MDY, plywood, phenolic, whatever--but also from proper support underneath the top.

[Burt Alcantara]

Gary Rogowski and Doug Stowe both use a pice of 3/4 ply clamped to a bench as their table tops. Perhaps, because the router is not left in place the sag factor is reduced...???

I'm in the process of building my first table. I was planing on using a 2'x4' melamine panel from HD, perhaps trimmed a bit. Because it is my first table I don't want anything fancy until I find out what's needed and what's not.

I like all of the ideas about sandwiching. That's a good idea for any work top.

Thanks for the ideas,
Burt

[glenn bradley]

I had 1-1/2" laminated MDF sag with a 5625 in it. Some decent framing underneath cured this and there has been no repeat of the problem.

[Bill Huber]

Even though I didn't make the table I did make the cabinet under it, it is all 3/4 plywood and the widest open area is where the plate sets in and I have that just inside the plate.

I check it every now and then and it is still flat, with a Bosch 1617 in a Jessem left.

http://www.pbase.com/wlhuber/image/85312065

[Keith Outten]

The ultimate router table top isn't cast iron it is steel. I know this, now that I have had time to use the steel table that Quality Grinding made for me a few months ago. I can't begin to explain the difference in performance and quality that the new steel router table has made in my shop when measured against all of the other designs I have built/used through the years. Another major benefit is that steel like cast iron provides noise dampening that other materials don't.

Check out this thread, (http://www.sawmillcreek.org/showthread.php?t=87932) there are some pictures of my new router table. Now that I have had time to use the new table I can definitely say it is just awesome. I am using a PC 7518 router both in my ShopBot CNC router and the new router table. In the ShopBot the 7518 is so loud it will wake the dead, this is not true in the steel router table in fact it is so much quieter I can't believe the routers are the same model. When I built my last router table I used quarter inch thick aluminum for the top and it was built for two router motors with a welded steel frame. This was a good table but it was very noisy. I have only just begun to realize the benefits of both cast iron and steel for router tables, nothing else even begins to come close if you value a flat table that will stay that way forever and a machine that is easy on the ears.

For 350 bucks a steel table is a bargain.
.

[Tom Veatch]

...In my reading I see that table sag is a big issue. This prompted me to take a critical look at my current table. It's just a 2x4 frame with a double 3/4" ply top covered with laminate. The router is an old PC 690 attached to 1/4" plexi. It's simple but has served well for many years. Sure enough, there is a little over 1/8" sag across the table...

The root cause of sag/deflection is a concentrated weight in the center of an unsupported span. The greater the weight and the greater the span, the greater the deflection. Since there is little that can be done about the weight - the router weighs what it weighs and there's no getting around that - the correction is to reduce the unsupported span.

My table top is two pieces of 3/4 MDF joined with contact cement surfaced with a Formica type laminate. Immediately adjacent on either side of the opening for the router lift are transverse supports tied into longitudinal stretchers along the front and back of the table. The top is thus supported such that the span is no greater than the width of the lift.

The lift is an Xacta branded Jessem lift and the router is a PC7518. Neither is a lightweight but after more than two years, there is no detectable deflection.

[Myk Rian]

I'm in the process of building my first table. I was planing on using a 2'x4' melamine panel from HD, perhaps trimmed a bit.
Personally, I don't like melamine. It's so thin that any scratch in it will turn into a bare spot.
I use 2 layers of 3/4" MDF glued and screwed together. You must countersink the holes where the screws are between the layers so you don't get separation. Use sheet metal screws. A good coating of furniture wax (not auto wax) keeps it slick and moisture proof.

[Wayne Cannon]

Larry,

I vote with the responders emphasizing support near the router.

If you focus on supporting the top close to the router, you won't experience much sag. Mine is 1" MDF plus laminate top and bottom. It is supported on three sides within 2" of the router plate by the vertical plywood dividers of a cabinet below, and shimmed for flatness initially. With a JessEm router lift and 7518, the sag from the initial flatness is still only a few mils after almost ten years. In addition, with close-in support, you can re-shim for flatness any time it's needed.

Note that a rigid steel, aluminum, or phenolic router plate distributes the weight and reduces sagging on its own, compared with directly mounting the router to the top or using more flexible polycarbonate or lucite router plates.

[Jerome Hanby]

I wonder if you could use two pieces of MDF and cut slots for metal strips like the Mr Sawdust RAS table to help with the sag.

[Gary Lange]

I have been thinking about how I would tackle this if I were building such a table. I can't draw it out so hopefully I can explain my idea using words.

I would cut two pieces of 3/4" MDF the size I want for the table. In one I would Dado two 1/2" deep slots on the bottom and inch away from each side of where the Router Plate of Lift will be. I would also cut two 4" wide pieces 2" shorter then the table and angle cut the ends to about 3". I would then place these two pieces in the slots and using a two inch screw and glue attach them from the top down into the braces as I would call them. I would then attach the other piece of table top to this one from the side with the braces using glue and 1-1/4" screws. The top would then be finished with a laminate of some kind.

This is my idea for the top and it is how I would do it I think and it seems to me in my way of thinking that it would be sturdy and would not sag. I should add that my wife says I get in trouble thinking sometimes.

[Joe Spear]

That would work, but you don't have to dado into the bottom of the table top. Just fasten your braces to the uncut bottom and dado the side pieces of the cabinet to hold the cross brace ends at the proper level.

[Myk Rian]

Remember to counter sink the holes where screws will be used. MDF will create a bump otherwise, and your braces won't sit flush with the bottom.

[Gary Lange]

That is just how I think I would do it if I was building one for a a Table Saw mount. I would of course counter sink the screws and adjust everything so that this section was level with the cast iron top on my 1023SL. I guess I can explain things pretty good with words.