Flattening Large Slabs with Router

[Danny in Houston]

I've purchased some very large slabs for delivery in a few months, and I am now in the planning stages of building a jig to flatten them. One slab is 3" by 42" by 14 feet long. I have several others that are curved, about 6 feet long and 3 feet wide.

I've flatten a couple of smaller slabs before, and was able to build a sled on my workbench. I was going down the route of building large torsion boxes when I cam across this photo on the web:



I like this approach, much easier. As long as the slab is shimmed to the floor in a stable position that cannot move, and the box is shimmed and leveled correctly, I see no need to build giant torsion boxes. Might be a good idea to hot glue (a lot of hot glue!) the slab and the jig to the floor. The fail would be if something came loose during the middle of the work, it would very very difficult to get everything re-aligned.

PS - My goal is to keep the slabs as thick as possible, with one surface very flat, the other only flat enough to provide for fastening a metal base.

I'm also thinking about making the sled long enough to mount the router tight on the sled, then mounting a pole on the sled so I don't have to be bent over for so long, just move it back and forth using the pole while standing.

Thoughts?

[Big Dave]

I kinda like this approach.

Just a thought, if you built this set-up on a plywood subfloor it seems to me everything could be secured more easily...

Dave

[cputnam]

Working on the floor, even just shimming would be very impossibly painful for me. I'd be thinking about a knock down set up that could be mounted on sawhorses. A wood I-beam(s), split in half or not, would support the slab nicely and give you room to shim.

Random thoughts.

[PaulC]

Practical, but my back hurts just looking at that.

[Danny in Houston]

PaulC said:

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Practical, but my back hurts just looking at that.

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The problem with having a large slab off the floor is you have to build a substantial structure to keep it rigid. I think I'll just focus on the router jib, make it almost like mopping the floor with a long handle so I can do it standing up?

If I were going to be doing lots of these in the future, I would build a dedicated table and jig, but for only 3-4 slabs.....

[CLETUS]

Danny in Houston said:

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I think I'll just focus on the router jib, make it almost like mopping the floor with a long handle so I can do it standing up?

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You're going to need some downward force on the router.

[Danny in Houston]

Does this make your back hurt?

I'll definitely want to include dust collection.



https://www.youtube.com/watch?v=D-JwkF1FwpM

[CLETUS]

The first thing that jumped out at me was the cord... suspend it from the ceiling so you don't have to keep moving it.

[bennybmn]

CLETUS said:

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The first thing that jumped out at me was the cord... suspend it from the ceiling so you don't have to keep moving it.

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Ditto!

[David G]

I'd try to get the slab to a workable height. Two short metal sawhorses, shim and secure the slab to the sawhorse. Two long jointed 2x8 on edge resting on the sawhorse parallel to the long side. Connect the short sides any method. the short ends aren't necessary. The 2x8 should be stiff enough to avoid sagging in the middle.

Not that I have ever done this.