Torsion Box for a Router Table Top - What do you Think?

[Brent Ring]

I was recently watching the latest Woodwhisper episode of David Marks shop tour. I noticed that he definately has an addiction to torsion boxes:D. He is using them for resaw fences, table tops, and the one idea that I thought makes alot of sense - a router table top.

I just wondered what everyone else thinks about this idea. I have 2 -3/4" pieces of laminate-faced mdf that functions as my top, and I get an ever so small bow, so rebuilding my top id definately on the list some time this year.

I just wonder what everyone else thinks about the idea of a torsion box top.

[Jamie Buxton]

My router table is a torsion box.

[Matt Benton]

My old one was a torsion box as well. Works great. 2 layers of 3/4" mdf, with webbing from the same material. Bolted my Bench Dog Prolift to the bottom, and had a flat, consistent surface...

[Chris Padilla]

Sounds good. One can't have enough dead flat surfaces in one's shop and torsion boxes seem the best at staying flat over time.

[Dewey Torres]

Matt points out the best benefit with is flatness / resistance to warping.

[Mac McQuinn]

I built a very nice tool bench a few years back from plans in Shop Notes with 4 layers of MDF for top and it has a noticeable droop over unsupported ends. I pulled my Record Vise and gave it to my wife for her stain glass shop and she loves it:rolleyes:. Over Christmas I finished a new bench with torsion-boxed construction on legs, back and top. all glued and screwed with 3/4" MDO. I love it, it's unbelievably stiff, breaks down into 3 major components and I do not have a fortune in it. I'm certainly a believer in torsion box construction and would not hesitate to use it in the future.

Mac

[Joe Chritz]

I have two torsion boxes in the shop. A rolling assembly table and an outfeed table for the tablesaw. I have a small extension to the tablesaw and am thinking about removing it and making a torsion box for that to add a router into.

Now to complete my hijack.... what is the best way to construct that box? Just leave a big enough opening to drop the router and plate into? I would like to not use a lift since I really don't use a table router that much.

FWIW, I love the other torsion boxes.

Joe

[pat warner]

Would not use for a router table.
Way too much opportunity to have a wrinkled surface.
The structure has a substantial moment but they're rarely flat, a most important variable for fine work.

Routers (http://www.patwarner.com)

[Chip Lindley]

Depending on the thickness of the torsion box, one may experience more difficulty getting at the router from beneath the table. The router will still have to be mounted directly to the table surface or in an insert. Seems a large cutout is in order, and not sure how this will affect the strength of the torsion box.

I had good luck with a TS-mounted router extension, with a 1-1/2" angle iron screwed to the table from beneath. The extension stayed flat (I prefer slightly crowned at center, actually) along the 27" length.

[Mac McQuinn]

I was able to achieve a dead flat torsion box by running my hand picked "beams" through the planer edgewise 1st to pull everything into same thickness dimension. I removed perhaps 1/16" OA. By sandwiching the planned beams with MDO which is very consistant in thickness, I ended up with torsion boxes with good overall linear thickness.

Mac

[Alan Schaffter]

Chip has an excellent point about the thickness of the table limiting access to the router. I think it would be best to use a lift.

Torsion box engineering-

The strength and stiffness depend on the ability of the top skin and bottom skin to resist compression (top) and tension (bottom) IN THE PLANE OF THE SKINS, i.e. along the surface, not perpendicular to it. When you cut a hole (router hole) in this surface you are compromising that to some degree.

Strength and stiffness also depend on the (cube of the) height of the web- if you increase web height by 25% you increase the stiffness by almost 100%. Up to a practical limit, if you double the web height, the stiffness increases eight fold!! But then you run into the issue Chip pointed out.

Torsion boxes can be light AND strong, and have their place, but not every application is appropriate.

Here is a torsion box test I did recently. This 8' long torsion box table (bridge!) is made from a single, 4X8 sheet of big box store generic, thin, (and very floppy!) 1/8" hardboard and WW glue. In the pic I have loaded it with over 300# of bricks at mid span, yet it deflected only 1/2" there (most of the apparent deflection is optical and caused by my wide angle lens), and shows no signs of failure.

http://www.ncwoodworker.net/pp/data/1421/medium/P1080028.JPG

http://www.ncwoodworker.net/pp/data/1421/medium/P1080032.JPG

http://www.ncwoodworker.net/pp/data/1421/medium/P1080030.JPG

[Bill Hylton]

Sounds like an unnecessary complication to me. Make a simple edge frame using 2 1/2" wide material and screw it to a piece of 3/4" MDF. Include cross members flanking the router in the frame. You'll have a flat tabletop that won't cost much in money or construction time.

Bill

[Alan Schaffter]

Bill has the right idea (and he should know!).

Put cross bracing in the cabinet under the table right up to the plate opening. The NYW design was particularly deficient this way. Then, if you seal the bottom really well or better yet laminate both sides of the MDF so it will not absorb moisture unevenly and will not warp or sag.

I truly believe that, but as an experiment I am going another route. I will soon replace the double laminated, 1-1/4" MDF router table top with a slab of granite. I decided to seek out (and in fact found a cheap remnant piece) after I discovered a big CNC waterjet cutting table in a local shop. They said it would be no problem cutting the opening for the router plate (hopefully for a reasonable price.) I am just waiting for WoodPeckers to answer my email and confirm the precise plate size and corner radius- the WP web site says it is 9-1/4 x 11-3/4 and I measured the corner radius at 3/4". I will epoxy in a mounting ledge.

[Brent Ring]

I truly believe that, but as an experiment I am going another route. I will soon replace the double laminated, 1-1/4" MDF router table top with a slab of granite. I decided to seek out (and in fact found a cheap remnant piece) after I discovered a big CNC waterjet cutting table in a local shop. They said it would be no problem cutting the opening for the router plate (hopefully for a reasonable price.) I am just waiting for WoodPeckers to answer my email and confirm the precise plate size and corner radius- the WP web site says it is 9-1/4 x 11-3/4 and I measured the corner radius at 3/4". I will epoxy in a mounting ledge.


That is a very interesting and thought provoking idea. I had gotten a couple of scraps of marble for sharpening chisels, etc. and one of them was about 30" x 18" - Probably not sized for my table - I would need about 24" x 34" or so, but I am certain that they will get an occasional scrap or two at that, or maybe I can purchase a small remnant. What kind of epoxy are you expecting to use for the mounting ledges, and what kind of material would you use?

I have the Woodpecker PRL for the Hitachi M12V, and I like it for the most part. It racks a bit when I am raising the bit, so I have resorted to above table bit changes, but other than that I really like it.

Please keep the thread posted on the success of your granite top. Pic's would help as well

[Brent Ring]

I will soon replace the double laminated, 1-1/4" MDF router table top with a slab of granite.

How will you mount the granite to your table? Bore out holes, and use epoxied in threaded inserts with bolts? What are your thoughts Alan?

[Chuck Tringo]

David Marks' router table is a torsion box....if it works for him.....

[Jeff Todd]

David Marks' router table is a torsion box....if it works for him.....


Yeah but he doesn't build fine furniture.. :rolleyes:

I always thought about using Corian for a table top since it can be machined using most woodworking tools..

Jeff

[Alan Schaffter]

That is a very interesting and thought provoking idea. I had gotten a couple of scraps of marble for sharpening chisels, etc. and one of them was about 30" x 18" - Probably not sized for my table - I would need about 24" x 34" or so, but I am certain that they will get an occasional scrap or two at that, or maybe I can purchase a small remnant. What kind of epoxy are you expecting to use for the mounting ledges, and what kind of material would you use?

I have the Woodpecker PRL for the Hitachi M12V, and I like it for the most part. It racks a bit when I am raising the bit, so I have resorted to above table bit changes, but other than that I really like it.

Please keep the thread posted on the success of your granite top. Pic's would help as well

I have not decided how I will support the router plate. Epoxy should be sufficient to anchor a stop lip that can support the weight of the plate and the router since the force is a shear load. Other options include to epoxy threaded rod in shallow holes drilled in the the edge or bottom of the granite or use small Tapcons. Similar methods are used to attach sinks to the underside of granite counters. I will also epoxy alignment blocks to the bottom of the granite. To absorb vibration and so the granite sits flat and stays put, I will set it on a bead of silicone (I will protect one of the surfaces with plastic food wrap so it is easier to remove the top later.

The key to this evolution is the cost of the CNC waterjet- too much $ and it doesn't happen. WoodPeckers sent me a PDF diagram or the router plate with the exact dimensions and corner radius, so I am ready to go talk to the waterjet guy.

Now, let me repeat, this is an experiment. If it doesn't happen or doesn't work I still need to replace the existing top. First I will definitely add additional support ribs to the cabinet, and then replace the top with another one made from laminated MDF or with a carefully engineered torsion box :D

[Dennis Lopeman]

Alan - have you been successful with this yet? I'm about to start my router table saw table project soon! I just got my 3.25 HP Triton router and aluminum insert today... Wooohoooo - I've only been looking/drooling over it it for 3 yrs.

[Alan Schaffter]

Alan - have you been successful with this yet? I'm about to start my router table saw table project soon! I just got my 3.25 HP Triton router and aluminum insert today... Wooohoooo - I've only been looking/drooling over it it for 3 yrs.

I've been busy with other projects. I got the precise dimensions from WoodPeckers, but the slab of granite is still sitting in my garage waiting for me to take it to the water jet guy. I'm not sure when I will get to it. I'm building a new prototype of a jig I have been working on for awhile and also picked up a maple top for the new WW bench I am building.

[Chris Padilla]

Alan,

That slab of granite probably needs to dry a bit more, dontcha think?!

:D

I have 120 bf of maple in 5 large planks of 10/4 that have been drying for about 4 years now...they probably need a bit more time I think.... ;)

[Alan Schaffter]

Alan,

That slab of granite probably needs to dry a bit more, dontcha think?!

:D

I have 120 bf of maple in 5 large planks of 10/4 that have been drying for about 4 years now...they probably need a bit more time I think.... ;)

I am taking a shortcut on the bench- I picked up an already laminated 3" x 30" x 72" hard maple top from Bally Block in PA. It was used and has a few small holes in it that I need to plug, but Russell at Bally ran it through the wide belt sander so the surface is like new, but only cost $75!! I couldn't even buy rough cut maple that cheap! I got some 8/4 maple from them also for skirt and vise faces.

[Chris Padilla]

Start a new thread with your future bench, Alan! Sounds very nice and you can't beat the price!!

[Alan Schaffter]

Start a new thread with your future bench, Alan! Sounds very nice and you can't beat the price!!

Will do.

The entire bench will be relatively inexpensive. I made the base with a version of the legs (http://www.ncwoodworker.net/forums/f81/new-woodworking-bench-beginning-19383) I designed for my adjustable height assembly table (http://www.ncwoodworker.net/forums/f29/assembly-table-done-w-pics-3063/), from some beech I got for free. The vises I got from Woodcraft (http://www.ncwoodworker.net/forums/f81/good-day-all-around-20822)- a Lee Valley twin screw end vise, a quick release front vise, and a sliding vise, and the bench dogs were essentially free since they were purchased with the Woodcraft gift certificate I got for winning the Wood Central/Woodcraft top shop's contest (http://www.woodcentral.com/contests/shopideas/)). I figure, when done, I will have a bench worth over $1000 that cost me only a little over $75!

[Joe Jensen]

Torsion boxes are great, and they have their place. I think for a router table a lot depends on the span you have between vertical supports.

Here are some pics of my table. It's an outfeed table for the Table Saw with lots of drawers for storage. The top is about 40" by 50". I have 4 vertical supports across the 40" span and 4 across the 50" span. The router opening itself is only 14" or so. I have 3 layers of 3/4" ply on top of the spans. I spent a bit more on plywood, but the torsion boxes I've built have been a bit tedious and time consuming.

http://i174.photobucket.com/albums/w99/AZEngineer/_NIK1422-1.jpg

Here is a shot inside below the top where the router hangs. I have a shroud for dust collection.
http://i174.photobucket.com/albums/w99/AZEngineer/_NIK3381Large-1.jpg
http://i174.photobucket.com/albums/w99/AZEngineer/_NIK3377Large.jpg

Here is where the dust collection connects to the system.
http://i174.photobucket.com/albums/w99/AZEngineer/_NIK3378Large.jpg

[Dennis Lopeman]

I like those legs! I could maybe use something like that on a outfeed table for my TS. The TS can roll around... so the outfeed table has to be able to stablize.

Actually - i was originally going to use some legs like on the outfeed for the ShopSmith... since I have some for mine... you know? I think I'll still do that...

But COOL legs anyway!! I'm sure I could think of something for them.

[Dennis Lopeman]

Oh well - I guess i better document my granite table top "making of" huh?!

[Dennis Lopeman]

http://i174.photobucket.com/albums/w99/AZEngineer/_NIK1422-1.jpg



Do you have any issues not having your T guides from the TS extend into the extension?

(DID THAT make sense!?) LOL

[Joe Jensen]

Do you have any issues not having your T guides from the TS extend into the extension?

(DID THAT make sense!?) LOL

The question makes total sense. I was originally going to put aluminum tracks in the top to align with the miter slots. I actually bought the Kreg material 2 years ago. Someday I may need to, but if I crosscut or miter with the miter gage, the bar doesn't extend past the table. This is because SawStop's top is 3" deeper than the PM66 and Delta. When I do precision crosscuts I either use my Dewalt 14" RAS or a Festool guided saw.

[Alan Schaffter]

Oh well - I guess i better document my granite table top "making of" huh?!

Yup!

If I decide the water jet guy wants too much, I will be cutting my slab myself. I thought about making a shelf under the slab and sitting a cheap wet saw on it and VERRRRY slowly feeding it under the slab and raising it a little after each pass to cut off the extra, and then do the same thing for the cutout.

[Greg Hines, MD]

I have not decided how I will support the router plate. Epoxy should be sufficient to anchor a stop lip that can support the weight of the plate and the router since the force is a shear load. Other options include to epoxy threaded rod in shallow holes drilled in the the edge or bottom of the granite or use small Tapcons. Similar methods are used to attach sinks to the underside of granite counters. I will also epoxy alignment blocks to the bottom of the granite. To absorb vibration and so the granite sits flat and stays put, I will set it on a bead of silicone (I will protect one of the surfaces with plastic food wrap so it is easier to remove the top later.


One thing you might want to consider is the Kreg system for leveling and supporting a router plate. Their corner blocks support a pair of set screws to level the plate, and it is attached to the underside of the table, without needing a rabbet.

Doc

[Alan Schaffter]

My WP lift has leveling screws.

[Chip Lindley]

David Marks' router table is a torsion box....if it works for him.....


Yeah but he doesn't build fine furniture..
Jeff

Ahemm.... I fail to see the corelation between router table construction and building fine furniture!

The photo below (FFW#37, p.62) illustrates my point, and points out the absurd notion that nothing FINE can be produced without the obsessive over-kill of ultra-tweaked EVERYTHING!

The user of the very *minimal* router table is Art Carpenter, who exhibited his work along with Wharton Esherick, George Nakashima, Sam Maloof, and Wendell Castle at the inaugural show of the Smithsonian's Renwick Gallery in Washington, D.C. in 1971.

I guess everything is relative, isn't it? Mr. Carpenter's rudamentary RT makes my angle iron stiffener indeed a far-out concept to grasp!

[Myk Rian]

The flattest surface I've gotten for a router table is 2 sheets of 3/4" MDF glued together. No need for a torsion box.
The trick to using MDF is to glue the convex sides together. That cancels out any warping and creates a totally flat surface.

[Loren Hedahl]

So now does anyone know whether a torsion box would be good construction for a router table?

[Rich Engelhardt]

Hello,

So now does anyone know whether a torsion box would be good construction for a router table?
Scroll up a bit and see what Pat Warner says.

[Doug Mason]

Speaking of Pat Warner, I modeled my router table after his (from his book). Per the picture, the top is mdf with 2x4 supports underneath--and the supports are all adjustable so I can make changes if something goes out-of-flat. Simple construction and easy to modify if needed.

114755

As an amatuer w/limited experience, my thinking on using a torsion box as a top is "why bother" - kinda like why go to all the trouble of laminating a tablesaw outfeed table with plastic laminate when a piece of mdf with wax will work fine.

[Bill White]

Not to be unappreciative of the hi-tech capabilities here, but I just made my top from sink cut-outs glued back-to-back. Set in the simple router plate from Lee Valley, mounted the router, and went to work. Have a Freud VS router in 'er now. It is as flat as I will ever need for a piece of wood that might change dimension over night.
Bill ;)