Fixing a Sagging Router Table Top

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Blog entry by Karson posted 09-10-2008 12:18 AM 7675 reads 3 times favorited 12 comments Add to Favorites Watch

The router table that I use is attached to my table saw. It sits on an angle iron support attached to my Incra TSII fence system (Upgraded to LS). To the right of the table surface.

The top surface is two layers of mdf glued and screwed together, with Formica on top, bottom and 4 sides. The surface is 40” X 36.

But since it is very heavy and especially with the 3HP router hanging in the middle with a Version 1 of the Jessem Router Lift, it sages.

The table always sagged, so a while back I laminated a beam of OSB boards 3” thick and 4” wide and Pocket Screwed them to the under surface of the table top. It was OK for maybe a week or more or less.

I was at a friends this week and was telling him about the problem and he showed me his solution.

He was using a Sprung Joint Wikipedia Definition and a Fine Woodworking article on Joinery

So I took the beams off and marked the edge with a bowed line.

I then used the bandsaw to cut to the line. and then smoothed the edges with an electric hand plane.

I got 4 – 6” X 1/2” bolts, nuts and washers. I brazed the nuts to some fender washers so that I wouldn’t have to use a wrench to hold the bottom.

The brick that I’m using is a result of my looking for some fire brick. What I was looking for was some brick that is used in a fireplace. When I went to a brick MFG company and told them what I wanted he said follow me. He took me to a brick kiln that they were going to rebuild and he pulled some of their bricks that line the kiln and handed them to me. These things weigh about 6 oz apiece, very light. I liken it to the tiles on the space shuttle, they can get red hot, but the brick itself stays cool on the sides and bottom.

I got 5-6 of them and they work great.

I drilled a hole in the top surface of the router table and put the washer and bolt through that hole. I got my spacing and drilled the laminated beams. I then took the drill and realigned the holes so that the bolt would go through.

I then drilled a hole for a pocket screw to go through the washer to keep the nut from turning when I tightened the bolt on the table surface.

Here is the gap between the beam and the underside of the table top.

Turned the top over and screwed down the beams to make it flat.

I then put in the router and checked the sag. It was maybe 1/32 to 1/16”, so I tightened the bolts some more.

Very nice and flat, but just one problem The router table is just a little below the surface of the table saw so I’m going to cut some shims from some soda cans and bend the Aluminum so that I get them flush. I’ve used washers before, but never got a critical flush fit.

I’m going for the flush fit this time.

-- I've been blessed with a father who liked to tinker in wood, and a wife who lets me tinker in wood. Appomattox Virginia [email protected]

12 comments so far

View lew's profile


13534 posts in 5218 days

#1 posted 09-10-2008 12:32 AM

Great Idea, Karson!

I have never heard of the “Sprung Joint” but I can see some definite uses!

Thanks for the information.


-- Lew- Time traveler. Purveyor of the Universe's finest custom rolling pins.

View Karson's profile


35300 posts in 5863 days

#2 posted 09-10-2008 12:37 AM

The original thought behind the ”sprung joint” was to have a low spot in the middle and when you glued it tight then you wouldn’t have a gap form at the end of the board at the glue line. The spring of the wood would keep the gap closed.

This design is just the oposite. I have the gap at the end and the middle of the board is resting on the underside of the router table top and so when you close the gap at the end, it will raise the middle.

-- I've been blessed with a father who liked to tinker in wood, and a wife who lets me tinker in wood. Appomattox Virginia [email protected]

View dalec's profile


612 posts in 5351 days

#3 posted 09-10-2008 01:46 AM


Thanks for the explanation and pictures of your “sprung joint”. One of the great things about LJ is the sharing of learning.


View Lee A. Jesberger's profile

Lee A. Jesberger

6883 posts in 5442 days

#4 posted 09-10-2008 01:54 AM

Nice post Karson.

Great solution to a relatively common problem.


-- by Lee A. Jesberger

View mleedix's profile


63 posts in 5013 days

#5 posted 09-10-2008 02:03 AM

Interesting joint. Thanks for sharing this super idea.

-- - Michael "Over 300000 species of trees, yet we take the credit for their beauty..."

View Grumpy's profile


26811 posts in 5314 days

#6 posted 09-10-2008 02:12 AM

Some great ideas there Karson. I have a similiar setup & had the same problem. I solved it by glueing button magnets in the mdf. The router table insert has grub screws which can be used to adjust the levels. The magnets attract the grub screws & hold the insert down.

-- Grumpy - "Always look on the bright side of life"- Monty Python

View cabinetmaster's profile


10872 posts in 5021 days

#7 posted 09-10-2008 03:12 AM

Thanks Karson. I learned something new tonight. I’ll keep this in mind the next time I have one of those problems.

-- Jerry--A man can never have enough tools or clamps

View Karson's profile


35300 posts in 5863 days

#8 posted 09-10-2008 05:42 AM

It took .033 Thous to raise one side and .048 Thou to raist the other side.

It now seems very close to the cast iron table saw top.

-- I've been blessed with a father who liked to tinker in wood, and a wife who lets me tinker in wood. Appomattox Virginia [email protected]

View Jeff's profile


1010 posts in 5557 days

#9 posted 09-10-2008 06:05 AM

Thanks for the idea Karson. Brilliant.

-- Jeff, St. Paul, MN

View Douglas Bordner's profile

Douglas Bordner

4074 posts in 5526 days

#10 posted 09-10-2008 06:13 AM

Old school engineering to the rescue again!

-- "Bordnerizing" perfectly good lumber for over two decades.

View John Gray's profile

John Gray

2370 posts in 5348 days

#11 posted 09-10-2008 05:50 PM

Great post!!!! Thanks for the information, I favorited it.

-- Only the Shadow knows....................

View Bob #2's profile

Bob #2

3810 posts in 5484 days

#12 posted 09-10-2008 05:58 PM

Great engineering Karson.
For leveling the router insert I used 1/4 nut inserts under the table and 4 machine screws that I can level the insert to the table with.
If you can access them from you set up the work great.


-- A mind, like a home, is furnished by its owner

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