I just can't get away from joined boards cupping

[Scott Brandstetter]

Really could use some advise. I seem to have hit a bump on joining boards for drawer fronts, table tops, etc. I almost wonder if it's normal to have a bit of cupping that once installed, is resolved.

A quick rundown on my methods. On the jointer get a smooth wide side and end side. Take to the planer to get the thickness I'm looking for. To the table saw for the width I need then back to the jointer for the last end side. Put the boards together on the table to look at the fit and they are perfect.

Take the boards to the assembly table, glue on each end side, then light pressure from clamps to join the boards. Couple clamps on bottom, couple on top, not over clamping, alls good. Then a few days later, the cupping begins. It's never more than I can take care of during glue ups but frustrates me on why the heck they are cupping. What the heck am I doing wrong.

I get the wood rough sawn from the lumber mill. It is kiln dried. I keep it normally a week in my shop before I work with it to get it acclimated, what am I missing.

Really appreciate any help on this.

[Brett Robson]

Try milling your lumber in two steps. First joint and plane as you've been doing, but leave them thicker than your final dimension.

Wait a couple days and mill them again to your final thickness. This gives the board time to react to the first milling and hopefully wont move much again after you mill them the final time.

[Scott Brandstetter]

Brett, thanks for the reply. I am interested in your idea and if I'm understanding it correctly, I would do the following.

If my end result is a drawer front with a thickness of 3/4 inches I would do what I've been doing but plane and joint to 7/8 thickness. Glue up the boards and let them "rest" for a few days and then take them to the jointer, assuming there is a slight cup, then to the planer.

If I understand the jointer and the planer, the jointer would have to come first in the last step otherwise I will get the planer to smooth to the final thickness but it won't remove the cup. I hope this makes sense and maybe this is where I am making mistakes.

[Kent A Bathurst]

Do exactly what Brett said. A couple added details:

To the best you can, between the jointer and the planer, take off equal amount from both faces. SOmetimes you can't do that in detail because it would sacrifice beautiful grain, but do the best you can.

After the first rough-dimension pass, set the boards on edge. Yep - just stand them up. Some guys sticker them. That's cool. The one thing you must NEVER do is to lay them flat on some surface. Either as individual boards, or after your glue up. Never. Never. NEVER.

I wait a day. 2 certainly does not hurt.

Then - final sizing as you described. Pass one face and one edge across the jointer until they are flat [I change the infeed table height to make thin passes] then the others thru the planer and rip saw. Set the rip 1/32 wide, to allow for a final pass or 2 on the jointer to clean up blade marks.

Then - get them glued up quickly, and then assembled quickly. You cannot do that in minutes, but get organized, plan your time and move with all focused purpose. Once they are assembled, it is much harder for them to move.

[Robert Engel]

What Kent said..^.
Its all about balancing the amount of wood you take off each face.
Think of the board as made up of little layers of wood, each layer having more moisture as you get closer to center.

Stay big as long as you can is best way to ensure flat. Rejoint after each storage session.

There are other factors too, like the type of wood and how its sawn (rift, 1/4, etc.).

How you store your wood is extremely important, but it it also matters where you store your wood sometimes if you don't have a conditioned shop.
Don't stack it up on a concrete floor, or underneath a fan or strong light, for example.
Don't forget the bottom board also needs a sticker.
I usually put a heavy board on top of stack just to give a little pressure (not necessary).

If its a time of year where the humidity changes suddenly, I often shrink wrap or put the parts in plastic bags when storing overnight.
Or you can store them in a climate controlled room. Anything that will retard the sudden change in humidity.

[Danny Hamsley]

The wood is cupping because the moisture content is not stable. The wood is either drier than your shop environment and is gaining moisture or either it is wetter than your shop environment and is drying. Cupping is caused by uneven changes in moisture content, setting up the stress that results in the cupping. What Brett, Kent, and shared is the best that you can do as you allow the wood to come to equilibrium to the environment that you are working in.

[Al Launier]

All of the above plus use cauls to face clamp the boards. I like to leave the cauls on for at least 24 hrs before removing them.

[glenn bradley]

I do pretty much as Brett describes with good success. I mill to oversize, let rest, finish milling and glue-up. I try not to have a lot of glued up panels standing around waiting for assembly; glue and clamp, wait 24 hours, cut to final size and move along ;-)

[Mike Heidrick]

Tell us the history of the wood you are using. I would look at moisture content and drying technique and timings as a source of potential cause and solutions.

[Prashun Patel]

Great advice here; give more time to acclimate, and mill in stages.

You may also want to invest in a moisture meter. I use one for green lathe work, and it's a godsend.

I've also found it beneficial to keep rough milled drawer stock on hand for months. The backs and sides are cheaper wood and don't take up a lot of space.

Last, consider using rift or quartersawn where you can afford it and the aesthetics allow it.

[Larry Edgerton]

Tell us the history of the wood you are using. I would look at moisture content and drying technique and timings as a source of potential cause and solutions.

I would be looking here first as well. If the wood is stable and dried to the right schedule your technique should be fine. I do use some of the methods mentioned above, but I have also gotten bad loads of stock that would do such things.

[Phil Thien]

I always get a little cupping, maybe 1/16" over a 24" wide glue-up. It pulls flat with little effort during assembly. The wider the boards, the more cupping I get, which is one of the reasons I haven't been too eager to invest in a wider jointer.

[Scott Brandstetter]

Thanks so much for the great info, I think I identified a few issues.

I think the biggest issue is that after I joint and plane, I lay flat on my assembly table. My thought was to keep them on a flat surface to keep from cupping but in reality, causing the cupping because I am not allowing for equal air flow thus moisture to escape from both sides. I also don't take equal amounts off both side through the planer. Thanks for the help and going to implement the changes immediately.

In regards to the wood I am using, it's rough sawn walnut from the mill, came out of the kiln, put in my shop for a few weeks before I do anything with it. Shop is temp controlled but I will start using my moisture meter a lot more now.

Thanks again for all of the help with this.

[Jim Dwight]

I would agree with Phil, solid wood moves. If you are real careful and do everything just right and then get finish on it, all surfaces, before it changes moisture content, maybe you don't get noticeable movement. But more realistically, you get a little that you deal with when incorporating the panel into the work-piece.

In addition to humidity, it moves when you remove other wood - just because you planned or jointed it. The shape the thicker board wanted to assume is not necessarily the shape the thinner board wants to assume.

I consider this just part of learning to work with solid wood - learning to deal with it's movement. Trying to eliminate it entire is futile IMHO. That is not to say that the ideas presented above are not good, but despite doing everything right, it is still going to move. It's a question of how much and how that can be accommodated.

[Steve Jenkins]

Storage between glue up and assembly is critical. Either stack flat and cover or balance on edge with a little space between panels. The goal is to not have one face exposed to changes in atmospheric humidity more than the other. Except for off the floor you don't need to use stickers if flat stacking if the wood is kiln dried.

[Anthony Whitesell]

I would also ask about the grain. Is the grain cut closer to flatswan or to quartersawn? The more arched the rings, the more prone to cupping. It has been said to go heavy on the top of the ring crown with planing and jointing, opposed to the bottom. This is supposed to reduce some of the tension causing the boards to cup. Personally, I just (try to) avoid boards where the rings make a complete arch within the board.

[Kent A Bathurst]

I think the biggest issue is that after I joint and plane, I lay flat on my assembly table.

As fas as I know - this is the one way that is guaranteed to cause your boards to cup.

Go forth and sin no more..............:D

[Scott Brandstetter]

As fas as I know - this is the one way that is guaranteed to cause your boards to cup.

Go forth and sin no more..............:D

Thanks Kent. I feel better now. Lol.

In all seriousness, really appreciate the help

[Allan Speers]

As fas as I know - this is the one way that is guaranteed to cause your boards to cup.

Go forth and sin no more..............:D



I never heard of this before. Is it really true? (And why would that be?)

[Kent A Bathurst]

Thanks Kent. I feel better now. Lol.

In all seriousness, really appreciate the help

Dude........do not think for some reason that you are special in any way here.......your heart has never sunk so low as when one walks into the shop after a weekend away, and realize he has done screwed up and left that tabletop made from veneer-grade QSWO laying flat on the TS extension/outfeed for 3 days...............choices were crying or buying a dog to kick.

Some of us have simply mistaked our way up the learning curve faster than you, or more likely we have had more years in which to make those mistakes.

Happy to share..............

So, you just mount up again, and once more unto the breach, dear friends..........

[Kent A Bathurst]

I never heard of this before. Is it really true? (And why would that be?)

Because he is a sinner.