# Preventing warping and cupping when gluing up table tops, etc....?



## rustictone (Oct 15, 2010)

Im looking to build a farm table for myself and a couple bar tables for friends and I was wondering if anything can be done to prevent cupping and warping when gluing up the table tops. The farm table is going to be made from barn board around 3/4 to 1 inch thick (have not bought the lumber yet, not quite sure on the thickness) and the bar tables from 2-3 inch thick stock. The last glue up I did was for my bookcase and when I glued up the top and bottems they cupped a bit (used dowels and 4 bar clamps). I was looking into buying a biscut jointer and using pipe clamps this time but is there something else I sould be doing…..use more clamps, build a jig like a veneer press? Im new to using dimentional lumber and am learning by doing and that can be expensive when buying barn board and 2-3" stock….If anyone can give me some pointers i would be very greatful!


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## IkeandBerry (Jun 18, 2009)

I have made several large panels recently and have had really good success in preventing cupping/warping. I do not use biscuits or dowels for my panels. I join the boards on my joiner and then clamp the two boards together in my bench vise with the mating faces up and use my joiner plane to get them absolutely smooth. I then use pipe clamps set about one foot apart across the span. I do try to alternate the rings if it is flat sawn lumber. If is quarter sawn I do not worry about it as much. If the end grain on the panels is going to be exposed I will also sometimes use what is called a spring joint which causes more tension on the ends of the boards than the middle keeping the ends for splitting or cracking. Tommy Mac does a good job of explaining a spring joint on his website.

For the thicker stock I would make sure the mating surfaces are as smooth as possible and again use pipe clamps. I would also recommend using calls every few feet to keep the boards even while the glue is curing. You can just use flat scap pieces with some wax to keep the glue from sticking and clamp them to the top of the panels.


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## khays (Aug 16, 2009)

I don't use biscuits or dowels either, just glue up boards. I usually try to use boards 3-4" wide and glue up 2 boards at a time. Once all those are done I'll glue up 2 boards again (which is now around 6-8" wide). I use pipe or bar claps and make sure that I don't put too much pressure on the boards. I also keep the f-bar claps around also to clamp to any ends or edges that are trying to rise or dip on me slightly.

Once that's done i'll take a small belt sander with a few quick passes to clean up any edges that aren't exactly level, but it's never anything major though.

A couple of links. I couldn't find the free version from woodmagazine.com that shows the video of the guy gluing up a panel. His wasn't the best anyway, but you got the idea.

http://www.fine-woodworking-for-your-home.com/glueduppanels.html
http://www.josephfusco.org/Articles/panel_glueups/Panel_Glue_Up.html
http://www.woodworking.org/WC/GArchive98/10_28smithglupan.html


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## khays (Aug 16, 2009)

Pretty good video.





I wait till the glue dries and take a paint scraper instead of taking a wet wag.


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## rustictone (Oct 15, 2010)

thanks guys, I really appreciate it! Thank you kevin for the websites, they helped a great deal.

YOU CAN ALWAYS COUNT ON LJ'S!!!!


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## Dcase (Jul 7, 2010)

I don't know if you can still buy them or not but I have some clamps that were designed for gluing up panels. The ones I have were made by ShopSmith and you place your boards in between two wooden bars and when you tighten the clamp it pulls the boards together as well as apply downward pressure to help prevent cupping. I don't think I have seen another company market these so you would have to look into it. They work rather well.


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## khays (Aug 16, 2009)

Anytime Anthony, glad they helped you out. It's always easier for me when I see someone do it too.

Kevin


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## dbray45 (Oct 19, 2010)

A couple rules that I live by-
If the the boards are quarter sawn, they will not cup - split, yes, cup no
If the boards are not quarter sawn, the wider the board the more chance to cup - one of the reasons that the big companies use small strips because there is so much less waste and no opportunity to cup.

If you are using wide boards, choose them carefully and make sure they are dry before you mill them. Cupping happens when the boards dry unevenly, so I am told. How they are cut off the tree make can all the difference.


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## StillTrying (Aug 25, 2018)

Cupping occurs when the moisture content of the wood changes. You're building your panel flat with wood at some moisture content, but then in use it is immersed in air at a different moisture content. It gains or loses moisture. The wood closest the to bark will expand or contract more than the wood closer to the center, causing cupping. It happens much more in flatsawn boards because more of the arc of the grain is included in the board.

Unfortunately, there is nothing in the fabrication or jointing that will stop this. All the recommendations above should produce good joints but they won't stop cupping. Look at the end of a cupped panel. The joints are tight but the boards have curved.

Before building, you need to acclimate your wood to the same air moisture content that it will live in. this can be harder than it sounds. The most reliable way is to store the wood in living space (like a spare bedroom) so the wood adjusts to that moisture level before you build with it. Or if your shop has a means to control humidity (like a dehumidifier in warmer months) that will serve. You need to know how long is long enough. A wood moisture meter will tell you when the wood stops changing. Or cut and seal the ends of a short piece with varnish (because moisture moves much more easily in/out of end cuts) and weight it periodically to see when the weight stops changing.

Once your wood is at the moisture content you need, build without leaving it sit in your shop for extended times, since it will be acclimating there. If it's at the right moisture content when you build, it will not add/lose moisture in service and it won't cup.

But then, when you move to the desert and put it out on your covered patio, it'll cup like crazy when it dries out.)

Different woods cup to different extents. This has been measure and published but I don't have a reference handy. But you can guess that the typical furniture woods are more well behaved. I've made some flatsawn douglas fir panels and found they cup a lot.

Richard


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## CrankAddict (Dec 10, 2018)

> The last glue up I did was for my bookcase and when I glued up the top and bottems they cupped a bit (used dowels and 4 bar clamps). I was looking into buying a biscut jointer and using pipe clamps this time but is there something else I sould be doing…..use more clamps, build a jig like a veneer press? Im new to using dimentional lumber and am learning by doing and that can be expensive when buying barn board and 2-3" stock….If anyone can give me some pointers i would be very greatful!
> 
> - Anthony Finelli


So there's two things here… a misaligned glue-up causing cupping across boards, and then there's boards cupping individually. Not 100% sure which one you are referring to. When I did my table top glue up recently it had a huge cup to it across the 3 boards (I glued up 3 boards at a time). But by modifying the clamping pressure with the upper clamps vs the lower clamps I was able to pull it into perfect alignment before the glue set. It would have been way, way off if I had just squeezed them all together and not checked with the straightedge.

Now if we're instead talking about the boards themselves cupping, that could be a matter of needing to do a few iterations of your milling with some time between. I took my rough stock (8/4 maple) and bandsawed and planed it down to about 1/8" thicker than I needed. And 4 days later the boards had gone from dead flat to noticeable rocking. So I jointed/planed them again to take off the final amount. They didn't move again after that. But the point being, if I had just gone from 2" thick boards to 1.25" boards and glued up same day, I think the result would have been a mess a week later, regardless of how precise my glue up was.


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