Help me design my router table

[Rob Price]

Okay, so it's time for a dedicated routing station. I'm designing my own, but basically it's my version of Norm's table. There's enough pictures floating around out there I've been able to come up with my own design.

First of all, I'm raising it about 6" for my back (I'm tall) which gives more drawer space.

My question is about the top. Most people seem to be laminating two sheets of 3/4 stock and then covering with hardboard or laminate, etc. My concern is sagging over time, esp if I ever get a big heavy router (just a little 1 3/4 PC for now).

I'm tempted to build a torsion box, with a large space in the middle for the router. There's two reasons really, one is that the 2" webbing will directly support the router plate, and the other is that I want to build a torsion box for my assembly table, and I thought a smaller box would give me good practice before I take on a big 4'x6' bench. Plus I get a more rigid top that should reduce warping over time.

So I'm thinking 1/2 MDF for the skins and 2" strips of 3/4 ply for the webbing. Then a 3/4 melamine covered particleboard/plywood sheet for the actual top with T-tracks, etc.

My other thought, is I think I want to screw the top layer onto the torsion box, that way I can replace the top surface over time as it gets beat up. It's not as pretty with countersunk bolts on top, but if I'm going to put a good bit of time into the top, why not incorporate the ability to maintain it over time. That also gives me the ability to modify the top if I get a different router plate/lift over time. For now, I'm making my own out of 3/8 polycarb, it's easiest on the wallet seeing as how I'm about to buy a cabinet saw. It's served me well in the past. No money for a fancy lift at this point.

I'm almost done with the sketchup model, I'll post pics when I get there.

[Todd Bin]

Here ya go... One router table design. This one is fantastic. :D

[Rob Price]

I almost went that way, but milling the cast iron with my orbital sander would take all day :D

[Scott Loven]

The guy who is the guru of Radial Arm Saws suggests laminating two pieces of material together with two pieces of steel embedded vertically between them, acts like an I beam. He also puts a 1/4 inch piece of replaceable hardboard on the top.
Scott

[keith ouellette]

If you go the torsion box route I would make the ribs taller than 2" but that depends a little on the span of the table.

A 2" x 3/4" piece of ply can flex very easy along its edge even if it is only 16" long. cut a piece and see for your self.

When you are putting the table together make sure you remember when you put pressure on something you are building it can contort to the shape of the surface you are building on.

[Rick Moyer]

I don't know much about torsion boxes but I do remember reading that the height of the webbing is much more important than the thickness. I don't think you would need to use 3/4" thick material for the webs.
(engineered beams have a thin vertical pc)

[Brian Kent]

I made mine with a torsion bed - glad I did.

I put a door on the front of an insulated box surrounding the router, for noise - glad I did.

I mounted the router to the table instead of to a removable plate - glad I did.

I still managed to get the depth wrong and screw up a saw handle - sorry I did, but it wasn't the table - it was the technique (or lack thereof):D.

[Rick Metcalf]

If you are building Norm's table with only added height, it has internal support from the dividers to support the top. If you are using a router plate or lift, and worried about the deflection, simply add double ribs front to back and double ribs side to side (from added ribs) to support the plate perimeter. After I priced up the materials and hardware, templates and time to build the top of mine, and trying to get it flat during glueup, I ended up going with a Woodpecker top and fence with PRL-V2 lift. Very nice!;)

[Tom Veatch]

...My question is about the top. Most people seem to be laminating two sheets of 3/4 stock and then covering with hardboard or laminate, etc. My concern is sagging over time, esp if I ever get a big heavy router (just a little 1 3/4 PC for now).
...
So I'm thinking 1/2 MDF for the skins and 2" strips of 3/4 ply for the webbing. Then a 3/4 melamine covered particleboard/plywood sheet for the actual top with T-tracks, etc.
...

Wow! You're talking about a top that would almost work for an Interstate bridge. WAAAY overkill!!!

What's the widest span between vertical supports you're going to have? Surely not more than a couple of feet if you're going to build a cabinet under the top. What you're describing might be needed if you're going to concentrate a load at the center of an 8 to 10 foot span, but I doubt it's going to be that big.

I have a doubled 3/4" MDF with Formica laminate covering holding a PC7518 (far from being a light router) and after about 3 years, there's no detectable sag. The top is supported from beneath with vertical dividers in the cabinet so that the maximum span is probably about 22" in the direction of the fence and about 15" perpendicular to the fence.

If you simply must have a torsion box top, 1/2" MDF lower skin, 3/4" MDF upper skin and 1/2" MDF grid 1" tall would give you a top that, with a span of a couple of feet, you could jump up and down on without noticing much deflection. But you're going to a lot more effort than necessary. Using a triple layer of 3/4" MDF would give much the same stiffness with a lot less work although it would be much heavier. The benefit of a torsion box is a high stiffness to weight ratio.

The bending flexibility of the internal grid without the skins is immaterial. The grid contributes so little stiffness to the overall structure that you can ignore it from the bending stiffness perspective. Think of a honeycomb sandwich structure. The honeycomb is about as "wiggly" as you can get, but bonded into a structure with even thin skins, the assembly is very stiff. The grid is there for shear resistance, not bending stiffness. The height of the grid is the important thing and for the loads you're going to see, even a 1" high grid is overkill. You wouldn't see a significant difference in stiffness in the completed structure using 1/4" versus 1" thick material for the grid as long as the height was the same.

[keith ouellette]

Wow! You're talking about a top that would almost work for an Interstate bridge. WAAAY overkill!!!

What's the widest span between vertical supports you're going to have? Surely not more than a couple of feet if you're going to build a cabinet under the top. What you're describing might be needed if you're going to concentrate a load at the center of an 8 to 10 foot span, but I doubt it's going to be that big.

I have a doubled 3/4" MDF with Formica laminate covering holding a PC7518 (far from being a light router) and after about 3 years, there's no detectable sag. The top is supported from beneath with vertical dividers in the cabinet so that the maximum span is probably about 22" in the direction of the fence and about 15" perpendicular to the fence.

If you simply must have a torsion box top, 1/2" MDF lower skin, 3/4" MDF upper skin and 1/2" MDF grid 1" tall would give you a top that, with a span of a couple of feet, you could jump up and down on without noticing much deflection. But you're going to a lot more effort than necessary. Using a triple layer of 3/4" MDF would give much the same stiffness with a lot less work although it would be much heavier. The benefit of a torsion box is a high stiffness to weight ratio.

The bending flexibility of the internal grid without the skins is immaterial. The grid contributes so little stiffness to the overall structure that you can ignore it from the bending stiffness perspective. Think of a honeycomb sandwich structure. The honeycomb is about as "wiggly" as you can get, but bonded into a structure with even thin skins, the assembly is very stiff. The grid is there for shear resistance, not bending stiffness. The height of the grid is the important thing and for the loads you're going to see, even a 1" high grid is overkill. You wouldn't see a significant difference in stiffness in the completed structure using 1/4" versus 1" thick material for the grid as long as the height was the same.

I have to disagree with that statement because of personal experience. The extension wing that came with my jet table saw had a 3/4" melamine and mdf top with ribs made of 1 3/4" high 3/4" wide plywood strips to support it. It was supported by steel rails on both side and legs at the end. It was flat when I installed it. In the 9 to 12 months I was out of my shop I had my all steel tenon jig (probably a little heavier than a router) sitting in the middle
of the table and the table is no longer flat.

This table did not have a bottom skin, only a top skin, so I don't know how much difference that would make. I also don't know to what extent the mdf top was secured to the ribs as that would make a difference also.

I wanted to test a piece of 2" high plywood I was thinking of using as webing for my table to see if it would flex and a 16" long piece supported on edge flexed very easy.

Thats just what my experience has been.

[Todd Hyman]

This table did not have a bottom skin, only a top skin, so I don't know how much difference that would make. I also don't know to what extent the mdf top was secured to the ribs as that would make a difference also.

I wanted to test a piece of 2" high plywood I was thinking of using as webing for my table to see if it would flex and a 16" long piece supported on edge flexed very easy.

Thats just what my experience has been.

From what I remember from college, both the bottom and top skins add a lot to the strength and rigidity (sp?) of a torsion box. You have to have both a top and bottom to get the full benfits and they don't have to be too thick to make it work.

[Cliff Rohrabacher]

Any wood construction presents the risk of changing shape over time. Have you considered Concrete?
You can cast steel flat stock in it as guides for your miter gauge.

[Tom Veatch]

...This table did not have a bottom skin, only a top skin, so I don't know how much difference that would make. I also don't know to what extent the mdf top was secured to the ribs as that would make a difference also....

Both of those make all the difference in the world. Without a bottom skin, the strength and stiffness of the assembly is DRASTICALLY reduced. It's like an aircraft wing with the lower spar cap missing. Also, unless the shear web (grid in a torsion box) is secured to the top and bottom skins, you don't have a unified structure, you have several parts acting independently of one another.


Say, Todd, just noticed your Auburn logo. I graduated from there in '68 and went back for graduate school in '71. And what you remember is correct.

[Rob Price]

I need to go back and find the article in one of my magazines, but their point was the strength comes from the glue surface between the webbing and the skins. Both skins are critical- to get the thing to warp you have to break all the glue lines simultaneously.

They had a picture of the author standing on a 24" shelf he made with 1/2 skins and 1/2 webbing and it supported him.

I have plenty of 1/2 ply lying around.

I may change and go with the double layer mdf, but I still want to practice on a smaller scale before I do the assembly table.

Where do you guys get the laminate to put on top? I may use that on plywood instead of the particle board shelf stuff at the BORG.

[Tom Veatch]

... Where do you guys get the laminate to put on top? ...

I started to buy a sheet from the blue borg, but they didn't have the desired color in the rack so I decided to check with one of the local lumber/hardware places. Turns out they had 4 4'x8' sheets in their "scratch and dent" outlet that were exactly the right color. They were a special order for someone who never picked them up. I bought all 4 sheets for about what one would have cost at the borg.

Be prepared, around here, at least, that stuff ain't cheap!

[Rob Price]

I may have to look into that.

I found my old article on Torsion boxes. According to the author, the most important part is the glue-line. The height of the core is not that important, just make it tall enough where you can work with it.

He uses 1/4 skins and 1/2 core material and makes a 2" x 8" x 24" shelf that bears his weight when he stands on it.

I may try that to see how it works out. I have those materials lying around in my scrap bin.

My new SS ships out today, sounds like a good first project...

[Russ Kay]

Just one thought here. If you use 1/2" for the top and bottom, that's not thick enough to be able to mortise in a miter slot or T-track if you want. So you might want to think about using 3/4" for the top skin of the torsion box.

[Andrew Joiner]

I like a router table to have a slight crown to the top. The stock will then contact the cutter and the table at the point of cut.

I'm making a new router table. A single thickness of 3/4" MDF is all thats needed if you make adjustable.

I would make it adjustable with a steel (or hardwood) bar under the top. A screw will bend the top up a hair as needed, but it will never sag. Yes that's it simple, cheap and sag proof.

[Rob Price]

very interesting, a good idea, any pics?

[Andrew Joiner]

Not yet. I added a second story to my shop building and it's next on the list.

[Don Morris]

Don't know about the torsion stuff, but the two router tables I've built with two 3/4" MDF glued together held my PC 7518 rock solid. Simple, but you could easily add a beam or two of some sort if you were paranoid.

[Rob Price]

I started to buy a sheet from the blue borg, but they didn't have the desired color in the rack so I decided to check with one of the local lumber/hardware places. Turns out they had 4 4'x8' sheets in their "scratch and dent" outlet that were exactly the right color. They were a special order for someone who never picked them up. I bought all 4 sheets for about what one would have cost at the borg.

Be prepared, around here, at least, that stuff ain't cheap!

You're not kidding, almost $50 for a sheet. I'm going to try some local cabinet shops for scraps.

[Steven J Corpstein]

This is how I did mine with a set of drawings I purchased from Jointech. Used the heck out of the fence to build the cabinet.

Jointech Router Center (http://www.datasystemsltd.com/router)

[Jeff Dege]

I thought the primary purpose behind a torsion box was to combine stiffness and light weight. A lot of the torsion boxes I've seen have webbing and skins so thick that they aren't anything like light weight. Which makes me wonder if they're worth all the effort.

The torsion box for the "Ultimate Tool Stand" - http://christophermerrill.net/ww/plans/UTS/Tool_Stand_1.html - uses 3/4" MDF for both the webbing and the skins. Which I am sure results in a very stiff box. But if I run the numbers right a three-layer laminate of 3/4" MDF would be just as stiff, and would actually weigh less. (And it'd be a lot less work).

You can always get stiff, if you throw enough material at the problem. It's always seemed to me that the extra work involved in making a torsion box would only be justified in situations where you have to keep the weight down.

[Bruce Wrenn]

You might want to get hold of a copy of Kregg's plans and video for a router table, using pocket screws. Easier to assemble than Norms.

[Louis Rucci]

Who's that? I'm going to restore an old 8" Dewalt RAS and can use all the information I can get.

[Rob Price]

Got some scrap laminate from the local counter company. It's not pretty but it will work.

I have an old fence lying around I made for adjustable slots in my work bench. It's two 3/4 pieces of melamine laminted together, 3" tall. It's rigid, I can't flex it, and it's been sitting around in the shop for a few years now.

So I think with the frame of the cabinet supporting it, two sheets of 3/4" material will suffice. If I can find some flat plywood I'll use that, I just don't like working with MDF. I'll probably run some additional supports under the router plate to be sure, I like the idea of an adjustable bolt to put a slight crown on the table.

[Ron Bontz]

Well I have read a couple of these and still think the torsion box is to much work for to little gain. If any. 2 layers of 3/4 MDF laminated on both top and bottom, (wilson art on top and balance backer on bottom) is not going to sag over time if you build the cabinet right. Remember the box around the router will be supporting the table as well. I put 1/8" thick 1.5x1.5" alum. outside corner around my 36 x 27 as well. Mainly to protect the outer edges. After years of use I layed my machinest straight edge across it and it is still flat. oh yes. I use one of those big routers in it. Best of luck to you.