# Cupping after glue up



## rookiewoodworker (Sep 10, 2012)

Just glued this together and it is slightly cupped. I alternated clamps and clamped boards on top and bottom and once all clamps were on I checked in multiple spots and it was flat. Once I took the clamps off tonight it has a slight cup. Anyone know a good way to fix this?

I thought maybe screwing boards underneath but the wood is 2.25" thick so not sure it would work. 

Any help appreciated!


----------



## hwebb99 (Nov 27, 2012)

How bad is it cupped? There is a shadow across the bottom of the level, and I can't tell.


----------



## woodnthings (Jan 24, 2009)

*turn it over*

Let the light and heat get to the other side for a few days and then see how bad it is. 

It looks like it was made from 3 built up laminations, so the wood movement isn't the issue, more like the glue up process OR as I mentioned, just an environmental issue.


----------



## rookiewoodworker (Sep 10, 2012)

There is about 1/4" underneath the level in that picture. It's not going to impact the use of the table it is just going to bug me!!!

I'll give it a couple days and see what happens. Any way to fix this?


----------



## mengtian (Nov 8, 2012)

Are you sure your level is not bent:laughing: j/k....

I had that happen to me once. Everything looked good until 3 hours later. The boards, under pressure must have shifted ever so slightly. That is when I learned the value of using cauls.

BTW: Did you use cauls during the glue up?


----------



## pinwheel (Jan 17, 2010)

Bowling alley lanes repurposed?

I'd lean towards you didn't have your edging perfectly square instead of cupping if the 3 lamination's were flat when you started.

If it is the wood actually cupping, flip it over on the shop floor & put some weight on it for a few days, see if it don't flatten back up. Cupping is caused by moisture imbalance from one side, to the other.


----------



## GeorgeC (Jul 30, 2008)

Are all three sections cupped equally? If not how many are cupped.

In the picture it visually looks like the right section is twisted. That could easily be an optical illusion.

George


----------



## was2ndlast (Apr 11, 2014)

Just run it across your 48" jointer


----------



## woodnthings (Jan 24, 2009)

If the edges that were mated together were not square to the faces, it would appear to be "cupping" but that's not the issue. 

Laminated sections will not cup as a rule, but a improper joint will create that same impression. Are the sections at different angles to the center or is the cup a smooth curve all the way across?


----------



## Stevedore (Dec 28, 2011)

I don't know how you jointed the glued surfaces, but when I'm doing a glue-up like that, I alternate which surface of each section, i.e., top or bottom, is against the jointer fence. So if my fence is off at all from square, the error gets canceled out. This wouldn't help if your problem is due to temperature or moisture though.


----------



## rookiewoodworker (Sep 10, 2012)

I used cauls on the glueup and the cup is fairly consistent in the both of the edges are higher than the middle, the picture is a little bit of an illusion because both sides are higher me than center, not just the right side. I didn't joint the edges, they were already tongue and groove and these were planks that were the flooring in railroad cars about 100 years ago. 

I guess I will have to live with the cupping. Oh well.


----------



## GeorgeC (Jul 30, 2008)

You do not have to live with it. You can make a jig and lever the top with your router. Or find a shop in your town that has a sander that can do the job.

George


----------



## was2ndlast (Apr 11, 2014)

I think the joint caused the cupping


----------



## Crick07 (Nov 14, 2012)

I second using the router and jig method to level.


----------



## rookiewoodworker (Sep 10, 2012)

Thanks for all the tips. The issue with leveling with router is that I wil lose a lot of the grooves and scratches that give it character that my wife loves. 

You aren't going to believe this.....I randomly decided to see what would happen if i put the cauls back on it and it flattened back out! See the picture. So my plan is to simply do this before I attach the legs and the base support structure. My question is what will be needed on the bottom to maintain that it stays flat? If I use 3 pieces of 8" red oak on edge and screw to the underside of the top with lag screws, do you think this will be strong enough??? Thoughts???


----------



## rookiewoodworker (Sep 10, 2012)

Correction...not 8"...I meant 8/4.


----------



## was2ndlast (Apr 11, 2014)

Just make sure the screws don't prevent wood movement across the grain. If the top doesn't cup too much, hopefully there isn't enough pressure on the screws to prevent movement as the wood contracts and expands.


----------



## woodnthings (Jan 24, 2009)

*it will work ....*



rookiewoodworker said:


> You aren't going to believe this.....I randomly decided to see what would happen if i put the cauls back on it and it flattened back out! See the picture. So my plan is to simply do this before I attach the legs and the base support structure. My question is what will be needed on the bottom to maintain that it stays flat? If I use 3 pieces of 8" red oak on edge and screw to the underside of the top with lag screws, do you think this will be strong enough??? Thoughts???


Any pieces whether wood or metal, that you attach across the bottom whether cauls , braces, OR aprons must allow for expansion and contraction of the top. This can be done using metal "Z" clips or elongated holes on the wood and screws that allow movement because they are snug, but not reefed down tight.


----------



## FrankC (Aug 24, 2012)

Are you going to have an apron, if so run a couple stretchers across from side to side, put grooves in them as will as the apron for wood or metal clips and lock the sucker down. With the clips expansion will not be a problem.
http://benchnotes.com/Fastening Table Tops/fastening_table_tops.htm


----------



## rookiewoodworker (Sep 10, 2012)

Thanks for the help I will certainly elongate the jokes for the screws or lag screws to allow for wood movement. 

One final (maybe haha) question......since I know that clamping the cauls back on the table top eliminates the cupping and flattens it back out, and I will do this before I attach the legs and underneath support structure, should this impact when I apply finish? In other words, do u think it is okay to apply finish to the top while it is cupped and then apply cauls and bottom support structure? I know that finish is flexible so I presume this will work out just fine but just wanted to verify with some of you. Thoughts??


----------



## woodnthings (Jan 24, 2009)

*if it were mine ....*

I would seal the back first with shellac or other fast drying sealer. Then install your cauls,waiting to see if the sealer helps flatten it out. Then seal and finish the top with your topcoat.

If you remove the cauls, does it immediately cup back?


----------



## rookiewoodworker (Sep 10, 2012)

Yes it does. I left them on for 2-3 days and roved them and it cupped as soon as I removed them.


----------



## tom d (Oct 23, 2013)

Did you by any chance have moisture on the bottom side of these boards? (or hot lights on top) If so you experienced differential drying on the top, or wetting on the bottom which caused the "cup" If you allow full circulation I think this may correct itself.


----------

