Gluing a panel and preventing it from cupping

[Meatwad]

I didn't want to resurrect an old thread:

 

 

But I am having the same issue. Lots of different ideas in there but something kept coming up about stickering the panel after you glue it up. Is this really necessary? After 24 hours shouldn't the glue have hardened all the way, excluding extreme weather shifts?

I think all was good with my panel but I left it flat on my table in the garage and then this week we had 2 days of tornadic activity here in Arkansas. Pretty sure the humidity got to it.

[Woodworking_Hobby]

I am no expert but two things I have done when gluing panels. 
1. It sound like it came out of the clamps flat and then cupped on you and did not cup when clamping. I try to use cauls when clamping to help keep them flat. 
2. if possible did you alternate the grain direction of the boards so one is up the next is down? 
3. Do you know the moisture content of your boards when you started. I have left mine in the garage and they typically do not move but the humidity does not have drastic changes? 
4. Did you give the boards some time to rest during milling? Sometimes my boards will move after the initial milling and I usually try to leave an 1/8 or so between initial milling and then taking down to final thickness.  
 

Other might have some better suggestions but that’s what I have

[Meatwad]

I had 2 leftover boards of walnut I cut these pieces from. They had both been in my garage for a year. 2 milling sessions a day apart, maybe 2. I measured very carefully before gluing and I used cauls to do the glue up and with alternating bar clamps. 24 hours later I pulled it out of the clamps and tested it for flatness. I didn't detect any cupping at all then. I don't recall if I alternated growth rings. I really suspect the monster storms that came through in the last 3 days were the culprit. But I only checked it for flatness when it first came out of the clamps and then about 4 days later. So it had 3 days of laying flat on my table.

I just never thought of glue moisture being a problem.

[Coop]

I would flip the panels over and lay them on the same table and keep an eye on them. I suspect that they received uneven moisture exposure while laying flat on the table. Sticker them next time until you get a finish on them. 

[wtnhighlander]

@Coop describes something that has happened to me, for sure. Working in a space where humidity in uncontrolled means that leaving a freshly milled board or panel lying flat on the bench is very risky. Especially with thinner stock. 

After my first incident, I took to standing all my cut parts on edge before leaving them fir the day.

[Meatwad]

On 4/15/2022 at 9:50 PM, wtnhighlander said:

@Coop describes something that has happened to me, for sure. Working in a space where humidity in uncontrolled means that leaving a freshly milled board or panel lying flat on the bench is very risky. Especially with thinner stock. 

After my first incident, I took to standing all my cut parts on edge before leaving them fir the day.

When I built a maple table frame I milled everything and got it ready but did not have the time to put it together for several weeks so I put all my pieces in a trash bag and took them in the house. I do all my work in my garage. You think just keeping them stickered or on edge would have the same effect?

[wtnhighlander]

Stickering, or on-edge storage, exposes all the wide faces to air to circulation, increasing the chance that moisture will evaporate evenly from thise faces, and reduce the risk of warping. It is still important to follow good milling practices, removing equal amount from opposing faces and so forth. Re-sawing a thick board is the most problematic, since by nature, it exposes the 'creamy middle' of the stock to the air.

[Meatwad]

Well yesterday I planed and sanded the high spot on one side and planed the high edges on the other side. Then I coated the whole thing in BLO and brought it in the house and stickered. Today it has slightly cupped back the opposite direction. I suspect maybe it was still damp in the middle piece?

I will eventually learn how to make panels but not until I have discovered every way to ruin them.

[curlyoak]

Is the wood near or at the center of the tree? The rings will tell you. Was the board milled from small diameter logs? Are the glue joints milled 90 degrees?

[Meatwad]

On 4/16/2022 at 4:53 PM, curlyoak said:

Is the wood near or at the center of the tree? The rings will tell you. Was the board milled from small diameter logs? Are the glue joints milled 90 degrees?

Not sure about the rings. I've never tried to make that comparison before. Thickness wise they went from 1 inch rough down into 3/4" on the first mill and down to maybe 5/8" on the second. Glue joints were 90 degrees and everything looked good 24 hours after glue up.

[Robby W]

I have a hunch that the boards weren't dried enough. When I make a tabletop, I place it on the base with the cupped side down, then slowly bring it to flat with a couple of screws through the aprons. That will tend to keep it flat over time. Learned the trick from Tage Freid in one of his books. They were definitely worth reading.

[curlyoak]

The center of a log is different grain. The space between the grains are wider. The tensions are different. It is the wood to be wasted, not used. You may have center cut wood.

[Tom King]

The wood that Curlyoak is talking about is called "Juvenile wood".  It's from the first decade or so of a tree's life.  It is best to avoid it, when possible.   Even when picking framing lumber, I avoid it as much as possible.

[curlyoak]

On 4/17/2022 at 9:26 AM, Tom King said:

Juvenile wood"

In the dead center of walnut is a pith. As if the center of the log was drilled from top to bottom 1/8".

[Tom King]

https://www.fpl.fs.fed.us/documnts/techline/properties-of-juvenile-wood.pdf

I try to avoid using the pith in anything but timbers, and even then, I want it in the center.  If you are buying 4x4's, 4x6's, or such, and the pith is off center, that piece will not likely stay straight.  Of course, it would be better to avoid it even then, but it's hard to do when buying those timbers these days.

[Meatwad]

Well I got it where it needs to be attached and I don't think it is juvenile wood. I think this was my mistake of not letting air get to both sides during 3 days of tornadoes. It was the last thing on my mind.

[Coop]

How did you get it back to flat? 

[Meatwad]

On 4/17/2022 at 8:37 PM, Coop said:

How did you get it back to flat? 

Well I didn't. I did do some planing and sanding. Then after applying BLO and waiting a day it was about a 1/16" of an inch cupped on both sides. I only had one "show" side because of some surface defects so flipping the panel wasn't really an option. Since this was part of refurbishing an old dresser I just used it as is. It's attached to the original top using some screws about 2 inches from the edges. I did put a little tension where the panel curled up by tightening the screws but given the width of the panel is over 18 inches I think it'll be ok.

[Coop]

Did you use elongated holes for the screws on the ends and none on the front and back, to allow for movement? And flat head screws, preferably with washers? 

[Meatwad]

On 4/17/2022 at 9:15 PM, Coop said:

Did you use elongated holes for the screws on the ends and none on the front and back, to allow for movement? And flat head screws, preferably with washers? 

Yes. The 2 at the front are stationary and the 2 in the back have elongated holes. I used phillips head and washers. When you say flathead do you mean panhead? If so, yes.

[Chestnut]

On 4/16/2022 at 11:02 AM, Meatwad said:

Well yesterday I planed and sanded the high spot on one side and planed the high edges on the other side. Then I coated the whole thing in BLO and brought it in the house and stickered. Today it has slightly cupped back the opposite direction. I suspect maybe it was still damp in the middle piece?

I will eventually learn how to make panels but not until I have discovered every way to ruin them.

I didn't respond fast enough but I was goign to say it's probably because of the storms. If you had just stickered it and put some weight on it, it likely would have reversed.  Oh well, you got there in the end.

Attaching it to it's final home is probably the best way to keep it flat. It will continue to absorb and release moisture but the dresser you mounted it to will hold it flat.

[Woodworking_Hobby]

From the picture the top does look great!