for a torsion box to work correctly it needs the bottom...
wood glue is all you need and an occasional short 23GA pin to keep things from moving during assembly......
I make mine using half lap joinery even for attaching the grid to the external frame...

 

Yes that's what I'm talking about Stick . I don't know if a guy would need some kind of jigs built to get perfect alignment on the half laps as you go across with more of them . Hopefully set the fence accurately in different increments or do a bunch clamped together .

I can see adding a bottom easy enough . Just take a hole saw and access holes to reach the bolts going threw the fence into the torsion box .

 

what bolts going through the torsion box...

 

Ok you'd think I would know this by now as its kind of how box joints work . But I like how he put an indexing pin in the mitres fence .

 

Rick I made my last table to be a throwaway as I was living in Alberta temporarily and needed a table. I used strips of 3/4 ply and some 3/4 inch left over spruce fence boards (about 4" wide) and I used them as cross members and rails and I joined them using biscuits and they were very strong.

 

Thanks for the idea Charles . I was going to use 1/2 mdf , will that be ok or is plywood better ? I prefer working with mdf for some reason . Must be the nagging cough I get afterwards lol . Just kidding , I use a mask

 

When you make those cuts, make sure you cut them a little deep. That way when you assemble the grid, the pieces will have enough room to ensure the pieces fit together flat. Right?

 

Is this what you want to build?
I drew it with 3/4 inch thick pieces.

 

Ok Stick , 3/4 it is lol

Mike thanks . Yes that's sort of what I'm looking at ,and going a tad deeper in the cuts is very good advise . I like the idea of going every six inches .
I will have to leave a few pieces out in order to make room for the router plate and lift , DC . I read it's important to have a top and bottom on a torsion box as there's far more strength that way

The incra top is 27 by 43 I believe . I have 29" between the fence so I'll have some spacers or whatever. Wish I could weld as I'd build some metal brackets to suspend it . But I'm sure there's a good wood alternative

 

Got any pictures or a link to your specific Incra table?

 

Btw Stick , is that picture you posted a younger you?

 

BTW Stick , is that picture you posted a younger you?

yup. and 35 or so of the other old geezers here..

 

Rick,

There are shortcuts that will make it more than strong enough while insuring a flat work surface. The real key is to make sure that all of the vertical elements are PERFECTLY cut the same width\height. Trying to do that with interlocking pieces can be done but adds way more complication than need be IMO. Glue will be all you need to make it a very strong structure.

Here are some photos of my take on a easy way to add torsional strength without turning the project into a test of will.

 

I found a model of the Incra table and imported it into the drawing. For some reason, the person that drew the table made it a little longer than 43 inches. But you can still get the picture, right?

Hope this helps.
Mike

 

Underside view.

 

Holy smokes Mike you have this sketch up down to an art
That's really an amazing program in the right hands . Thanks for going to the trouble , wow

 

I may go and buy some 3/4" mdf tomorrow and start this project . That's if this hangover goes away :fie:

 

screw it...
that is twice I lost everything I typed...
I'm done...
this lost of over an hour of typing simply pisses me off...

 

Ok so I'm not the only one . I posted and then seen it wasn't completed after I hit submit?
Doesn't happen enough to be a major concern though

 

Stick I was having the same Robles a while back and it wit by itself finally. Anyway, I got in the habit of copying everything I wrote before I tried to post so that I could go back and just paste if it failed. PITA but less frustrating than losing it.

 

the purpose of a torsion is to obtain strength, lightness, rigidity and flatness....
something you are never going to get W/ MDF....

¼ BB ply for the base...
½ phenolic laminated BB for the top..
½x1½ S4S parting for the grid...
T nuts or epoxied in inserts for the Incra fence...
just be sure you box where you router is going to be...

 

Stick , the top is pretty much going to be the Incra top .
I figured out what BB is (Baltic birch I suspect ) but what is "S4S" for the grid ?
Ok is that "side for side" ?

 

Sometimes glue & mdf don't work well because the glue "sits" on the surface of the mdf and you get a weak glue on glue joint. If it doesn't soak into the surface it gives you a false sense of strength. Might consider a few well place screws, with the heads below the surface.

nice drawing Mike......

 

S4S = surfaced 4 sides.

 

Ok I still have no clue what that means lol. Google I guess

Ok got it

http://www.thewoodwhisperer.com/articles/s2s-and-s4s-what-gives/

 

S4S = Surfaced 4 sides.

I think you guys are over engineering this thing.
Look at the way Ron Paulk builds his tables on you tube. That is the way I built my miter saw station. But then again, I don't measure stuff with a micrometer.

 

FWIW...
you'd be amazed at how strong of a torsion box you can get using just ¼'' lattice and Luann ...
think hollow core door...

S4S Parting.... Surfaced 4 Sides
go to the molding department at your big box and you'll find vertical grained boards smooth on 4 sides in 3/8 and 1/2'' thicknesses and a in a variety of widths...
using S4S gives you strength, better glue bonding, ease of tooling and a whole lot less weight...

the purpose of a torsion is lightness, flatness, strength and durability...

MDF fails on all accounts accept for flatness...

use ¼ for both surfaces,,,
install space blocks where your bolts need to be...

 

Here's a video I watched , but it's not the way I really want to go about it

Build a Torsion Box Assembly Table - Fine Woodworking Video

How come?

 

I'm really not liking how he cut a ton of separate pieces and airnailed them into place . I like the idea of using a dadoo to interlock long pieces into one another instead .



I just seen a problem .Because the Incra top is 1.5 inches thick , the bolts will not go threw the fence rails into a torsion box but more or less come into contact with the side of the Incra table top . So luckily there's almost a spare inch on each side . This way maybe I can buy some angle iron and attach it to the fence rails and hopefully secure the Incra top and torsion box to the angle iron .
Will have to take a picture to demonstrate the issue . I'm sure there's a simple solution though. Would be nice to make micro adjustments to change the extensions height to

 

Rick...

what if you were to keep the front rail of your saw "as is" and then bump out the rear saw rail to accommodate the additional width of the table (bend or cut and weld). Use some heavy angle under the table top between the two rails for support?.....

 

Bill I should take a pic to help . It's all good as the Incra top is actually smaller in width . Sorry if I conveyed it wrong . I've got almost an inch each way , so that should provide me with a way to attach additional angle iron sections to the inside of the factory table saws rails with out modifying the table saws itself .
Wish aluminum was more available around here .
I was going to remove the saws factory extention and then prop the Incra table in its place to help me think threw an idea . I think if this added ange iron is deep enough , I may be able to attach bolts threw there bottom horizontal section which could allow me to make critical height adjustments .
I'll go out and start taking this apart as soon as I can and provide a pic

 

Rick, what kind of saw do you have? I thought 27 inches was the standard for most saws.

The poor old Craftsman I used to have was only 20 inches deep. UGH.

 

I have to recheck but I thought it was just shy of 29" . The RT is 27" . In the picture where it's just test fit you can see there's a gap on each side of about an inch . This is good news IMO as otherwise there would not have been an easy way to attach it .
I think are local company that sells steel has all but left town

 

I'm following ya now....

ok, how bout some 1" square stock? alternating mounting holes. Kinda like the tablesaw fence that you posted a few days ago...odd holes to the table top, even holes to the rails?...

just spit ballin' here for ya...

 

Ok guys after looking at this a little more this morning , I think it's going to look like a dogs breakfast , as the width difference is just not going to look right IMO .
The table saws inside width between the fence rails is 29.25 and the width of the Incra top is actually less than 27"s . So I'm thinking instead of taking the easy way out I am going to use the top for a seperate router table similar to TimberTailors (although I can't build anything that complex drawer wise ) ,
and build a new router top to replace the factory table saws extention . This way the new top can have a torsion box built underneith it and I can use the side of the torsion box to attach directly to the table saws fend rails as a thinner 3/4" top will allow for bolts to go threw below it.
I think I'm going to kibosh using an Incra fence to , not sure .

It's to bad no one likes mdf for a build as its so darn flat to begin with . I'd like to use 3/4" mdf for the router table top and put white Formica on the top surface , then use mdf for the torsion box build and then coat all the bottom area with fibreglass resin so that moisture cannot be an issue in the future ?
I have to find some miter guides and fence guides now .

Or maybe use two layers of mdf . This way you could use the bottom as a platform and install seperate pieces of mdf on its top around the perimeter of the rails instead of dadoing them in ? Cut the area out on the bottom where I need access for the bolts sticking threw from the fence rails

 

NO FIBERGLASS. You think MDF dust is dangerous, look up Silicosis Cancer. Fiberglass dust is the devil's fairy powder!!!!!! The last thing you want is to have it settle on EVERYTHING and get disturbed every time you move a box or pick up an exposed tool.

Take a box of donuts and a thermos of coffee with you to your equivalent lumber yard and ask for Baltic Birch specifically.

You can get quality birch plywood from a good lumber yard (do not even think big orange or blue). I have a Kilgores. A small mom and pop lumber yard that only sells quality material. And, it s not much more than the other guys. Remember, these types of lumber yards usually cater to LARGE commercial orders. You are just a waste of time for them for the most part. Hence, the coffee and donuts.

Here is a good article if you want to learn more.

Ultimate guide to Baltic Birch Plywood

When you laminate two sheets of this remarkable quality plywood together on a flat surface (I use my table saw top), you get something that makes you wonder why MDF was ever conceived. NO screws, NO nails, just some wood glue and clamps or some heavy objects.