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Discussion Starter #1
I'm experimenting with a small torsion box for a router table. It will have 1 1/4" webs and be skinned with 1/4" mdf on the bottom and 3/4" mdf on the top.

I don't have a vacuum bag setup. I've tried making cauls (I think that's what they are called) before and, although they worked fine, found them hard to use.

If I put a piece of plywood on top of the assembly and weight it down with blocks or sandbags, evenly distributed over the area, will that work? I've seen photos where some of you guys have done this with much larger torsion boxes, but haven't seen anyone do it with the smaller ones.
 

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I think you are going overboard for a router table.

Glue two pieces of 3/4in thick material for the table top. Either two pieces of MDF, or one piece of MDF and one piece of plywood, preferably birch plywood. Now you have a solid and flat top.

You do not want the top to be too thick, otherwise you have to do more routing of the space for the plate to which the router is normally installed.
 

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Yup. You have a higher risk of a non-flat top if your top and bottom panels are not the same thickness. You have a high probability of success by simply gluing together two 3/4 inch panels of MDF (one slightly larger than the other, you'll see why shortly). Stack them up, predrill lots of holes for screws, on the sides and ends and in the field. Separate them, sand down the debris from the predrilling. Slap on some glue and then screw them together. Let dry overnight, TAKE OUT THE SCREWS, flush up the edges with a pattern bit or a flush trim bit. Cover the top and bottom with high pressure laminate, trim out the edges and you will never wish you had done it differently. Mine is 10 years old and it's still dead flat.
 

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Discussion Starter #4
I want to experiment with the torsion box to see how much weight I can save and still have a reasonably flat and stiff surface. Since it has to be a knock-down table I want to minimize the weight so I'll be able to easily set it up and stow it away.

If the torsion box doesn't work I'll may try a single piece of 3/4" mdf reinforced with carbon fiber and epoxy. Or, maybe I'll just bite the bullet, keep lifting weights, and go with a lamination of 2 pieces of 3/4" mdf :yes:
 

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You don't have to land a jet plane on it...

A single layer of MDF with a perimeter of hardwood will be plenty stiff and weigh less. Overbuilding is OK, but based on your requirements, not needed here.

Torsion boxers are great but heavy. A hollow core door is strong and stiff and light, but there's only a grid of paper/card board inside. Thickness is critical on a router table because you want the router base to be as close to the bottom of the top to avoid long bit extensions. :yes:
 

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Discussion Starter #6
Yup. You have a higher risk of a non-flat top if your top and bottom panels are not the same thickness.
Curious as to why there'd be a higher risk of top being non-flat. I'll be gluing the webs to the 3/4" piece on a section of granite counter top. Seems like it should start out flat. If I then turn it over, and glue the resulting assembly to the 1/4" piece, why would that make it non-flat?
 

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Sticking with the original question, what you want to do will work. Obviously whatever surface you poilee all this stuyff on will have to be perfectly flat, but that will provide enough pressure to glue a torsion box. That wouldn't be true if you were veneering; that's when you would need the cauls. One caveat, you didn't mention what the webs were made from. I'm saying it will work, but they should be plywood or MDF. Using screws is a good idea if you don't mind filling the holes after they are removed.
 

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Discussion Starter #8
Thanks for the input guys. As I indicated, I'm going ahead with this as an experiment, if nothing else. Won't cost me anything other than some time and some mdf pieces I have on hand.

If it works, I'll post some follow up. If it's a miserable failure, you'll never hear of it again :)
 

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There was recently a thread where a member linked a page about a mobile workstation with modular sections, one of which was for a router. A torsion box was a primary feature of it for its flatness and stability.

I wish I could remember where I saw that thread; it might be of some use here.
 

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Discussion Starter #10
Well, results so far are promising - so I'll go out on a limb and give a progress report.

Attached photo shows grid glued to top. Top is 1/2" mdf (minimum size that I thought would accommodate routing groves for the "T" tracks). Grid is mostly 1/4" mdf ripped to 1 1/4" height. This will provide a total thickness of 2" (plus the thickness of the top laminate).

The 3/4 mdf grid pieces form a base for the "T" tracks, mitre slot and aluminum router plate as well as backing for plate attachment and leveling screws.

The 1/4" mdf top is shown, ready for glue-down.

I used scraps of mdf for locating pieces on the top and bottom. The locating pieces and grid were hot-glued to keep all in alignment.

So far seems pretty flat and stiff. I'll wait and measure after gluing down the bottom.
 

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It's often hard to discern scale in a photo, but that opening for the router seems a little small. But it does look like you're on your way, should work well.
 

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Discussion Starter #12
It's often hard to discern scale in a photo, but that opening for the router seems a little small. But it does look like you're on your way, should work well.
The outside dimensions of the 3/4" mdf "box" are 8 1/4" x 11 3/4" - designed to support the Rockler plate. The portions of the table top and bottom within the "box" will be routed away to allow the router to mount flush against the plate. The inside dimensions are 6 3/4" x 10 1/4" - which will fit the top end of the router I plan to use.
 

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Discussion Starter #13
Forgot to mention, the sides of the grid are 1/2" mdf - to allow enough thickness for using some biscuits to align the edging (maybe oak?) that will be added.
 

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Discussion Starter #14
Finished the bottom glue on. The table top, pre-router cut-out, pre-edging, etc. is 2" thick and weighs 21.6 lbs.

Based on the weight of a same-sized piece of 3/4" mdf, if I made a table of solid mdf, 2" thick, it would weigh 38.9 lbs. Hopefully I've achieved a 44% weight reduction with approximately the same stiffness.

I'll see when I do the cut-outs for mounting the router.
 

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Discussion Starter #15
OK, all glued up, maple edging on, laminate gluded on top and opening for Router carved (routed) out. Time for a test.

Checked across long dimension with Rockler precision 2' straight edge (either side of router opening). My smallest feeler gauge is 0.006". Couldn't fit it under straight edge at any point.

Next, put cinder block on top, over router opening. Weights about 37.5 lbs. as I recall, way more than my router. No observable sag against straight edge (see photo).

Not concerned about sag over time since the table will spend most of its time stacked against the wall of my garage.

Encouraging so far.

Expect my Rockler router plate any day now. Next steps - rout recess for plate and attach mounting legs.
 

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Discussion Starter #17
Moving along. Finally got router plate (was back ordered). Practiced routing rabbit on scrap mdf and then, after a few deep breaths, routed out the rabbit on the table top.

Fits nice and tight - no motion in any direction, yet sets in place without much effort. I used the strip method of forming a template (see my post on "how tight should a router plate fit") and provided a little clearance by sticking a couple of pieces of masking tape on two adjoining edges.

Photos show rabbit and table top with plate in place. Plate fits about 3/64" low, to allow for leveling screws.
 

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OK, all glued up, maple edging on, laminate gluded on top and opening for Router carved (routed) out. Time for a test.

Checked across long dimension with Rockler precision 2' straight edge (either side of router opening). My smallest feeler gauge is 0.006". Couldn't fit it under straight edge at any point.

Next, put cinder block on top, over router opening. Weights about 37.5 lbs. as I recall, way more than my router. No observable sag against straight edge (see photo).

Not concerned about sag over time since the table will spend most of its time stacked against the wall of my garage.

Encouraging so far.

Expect my Rockler router plate any day now. Next steps - rout recess for plate and attach mounting legs.
Did you glue on the laminate first, and then rout the opening?
 

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Discussion Starter #19
Did you glue on the laminate first, and then rout the opening?
I did. Subsequently I read that if I'd routed the opening first it would have eliminated potential air pockets in the middle of the table when gluing the laminate down. Nevertheless, it seemed to work out OK. When I routed the rabbit for the plate I looked closely at the laminate/mdf interface at the edge - no sign of air pockets.
 

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Discussion Starter #20
And, here's the construction of the box section support legs and the assembled table attached to my knock-down, adjustable height tool stand. Ready to route the grooves for the "T" track.
 

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