Router Table - What went wrong

[greencat]

I’m looking for some advice. I’m in the middle of a project where I needed a router table. I thought this was good because it would force me to finally get a good setup. The bad part was I was in a hurry. I glued 2 pieces of MDF - 20"x24" 3/4 together then glued laminate material on top and sides. I cut an opening for a router plate and was using the clearance sears router fence. I thought all was good and was very happy. I was using the fence by clamping to the table because I didn't have time to make a permenate setup. This weekend I had some downtime in the project and I was going to install my T track for the fence. Attaching the fence is complicated by the fact that Sears changed the L bracket. The bracket has a V bottom to ride into their table. I was going to cut a v groove into some HDPE so the bracket would sit flat. Sorry for taking so long to get to the problem but here it is.

As I’m moving the fence I notice the table is not flat. It appears to be crowned. I didn’t notice this before because I thought the wobble was from the fence brackets. Could the MDF warp? Its hard to imagine since its so rigid. Could I have introduced some bumps when I glued the laminate to the mdf?

Any ideas for the new table?

[Tom Miller]

It's not overly surprising that you ended up with a little crowning, especially since you may not have been taking care to avoid it.

But, now the question is how to proceed. So, how much crowning are we talking about? Bear in mind, the amount of crowning could decrease to an acceptable level when you add the router.

Another approach is to add stiffeners underneath to pull the table flat. This would consist of a couple pieces of, say, 1x3 stock attached on edge to the underside.

Let us know what you find out.

Regards,
Tom

[ryan.s]

The warping was most likely caused because the laminate was only put on the top and sides. Most books I've read recommend that laminate be put on both the top and bottom of your surface to prevent warping.

[RayintheUK]

I'd guess that the problem may have been introduced by the clamping method used when gluing the two pieces of 3/4" MDF together. If you didn't spread the clamping pressure across the center of the boards by using cauls, or a similar way of spreading the clamping pressure evenly across the face of the boards, it's likely that by clamping just around the edges, some lack of bonding took place in the middle.

Given that scenario, when you added the laminate to the top board, the warping may have then been added to, or exagerated. I doubt that - if properly bonded - laminate alone would have the ability to crown two successfully-glued pieces of 3/4" MDF.

If the crowning is bad enough to affect the fence, there's really only one answer - start again. You might be able to achieve some flattening by removing the insert and clamping around the inner edges of the cut-out, prior to adding some stiffeners. However, if you can't clamp it flat as described first, that's headed for the bin.

Ray.

[Bulkley]

You might be able to screw a pair of L brackets below the surface (and out of the way) to flatten it. If that doesn't work, start over. When you glue the pieces, clamp them to something that will maintain the flat surface.

[kwgeorge]

Another thing to examine here is the glue you used. It may very well shrink when drying and could have added to your bad situation especially if its water based and you used an excessive amount. I personally don’t like to use yellow glue on MDF but rather prefer plastic glue. I have also been known to use contact cement but once the pieces are put together I like to put them in the vacuum press for awhile. In any case cauls and possible platens should be used for such glue up even with the laminate given your intended ends. I think I would start over if I were you instead of attempting to correct the situation as I don’t think you will ever get the flatness you will want out of what you got.

Ken

[dlminehart]

Putting laminate only on top and sides is unlikely to create this kind of crowning at all, let alone this quickly. If the bottom isn't covered, it can absorb more moisture than the top, and swell. If the bottom swells while the top stays fixed, it seems to me that it would cup at the top rather than crown. And, unless you poured liquid on it or live in a swamp, the swelling would be fairly gradual.

[greencat]

I will try to build a new top after I get my project finished and I appreciate everyone's input. The largest gap appears to be 3/32 of a crown. I hope I am describing this correctly. The edges drupe down 3/32. The crown is worse over the cutout. The area in front of the plate has very little crown. I wonder if I relieved some stress when I did the cut out. I did use titebond II glue and did not use cauls. I just placed some heavy items on top.

[SARGE..g-47]

I will second Ray on the fact that you did not caul the two pieces properly when gluing. And it you didn't get the laminate glue evenly spread and had globs somewhere, that might magnify the problem.

I have made many work surfaces glueing MDF together and no problem. I either laminate them or in the case of my router table which is 4 years old, laminate the top, poly and band the sides and 3 coat poly the bottom. I hasn't moved in 4 years and neither has any of the other tops I've made.

You might try running a piece of angle iron underneath to attach the top too to see if the crown can be pulled out. If not.. rebuild and just check each step to make sure your flat before you proceed.

Good luck...

[LarryG]

I did use titebond II glue and did not use cauls. I just placed some heavy items on top.

If the heavy items were distributed fairly evenly, this is probably not the problem.

Did you look at the MDF panels before gluing them up, to check them for flatness? A lot of folks assume MDF is dead flat and will stay that way forevermore. Neither is true. Although more stable than plywood or solid wood, MDF can and will distort just like any other material.

When you build your new top, check the two panels for crowning and, if you find any (which you almost surely will), place them together with the crowns facing each other; i.e., the middles of the panels will touch before the edges do. When you do the glue-up, the opposing crowns will counteract each other and pull the assembled panel flat. (You will still want to use some means to ensure you get good clamping pressure out in the middle ... if you're going to cut a big hole for the router, you can simply use a few screws in this area and remove them after the glue has cured.)

[scmhogg]

Mike,

I just had a similar problem with HD 3/4" Birch Plywood. I painted one side of a 2' X 4' piece. I set it aside and forgot to go back and paint the other side. In 4 days, it had developed an 1/2" bow in the 4' length. I'll admit that we have had some substantial swings in humidity here in SoCal this week.

Steve

[greencat]

I attached some pictures with a little sawdust. The bracket is for the craftsman fence. The v bottom makes it more difficult to attach. I was thinking about putting HDPE on the bottom but realized that would throw off where the bracket attaches to the fence.

[LCHIEN]

I will try to build a new top after I get my project finished and I appreciate everyone's input. The largest gap appears to be 3/32 of a crown. I hope I am describing this correctly. The edges drupe down 3/32. The crown is worse over the cutout. The area in front of the plate has very little crown. I wonder if I relieved some stress when I did the cut out. I did use titebond II glue and did not use cauls. I just placed some heavy items on top.

you don't say how heavy but I'm going to guess not enough!
20x24 to is almost 500 sq inches, if you placed a 50 pound load on top then you only hav 1/10th PSI forcing them together, you need a lot more!
even 500 lbs, is only 1 PSI, probably not enough given the span of MDF you have.

Clamps, lots of clamps and clamps that reach the center--- thus the cauls everyone mentions.