Why don't they stay flat?

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koslonc

New User
Jeff
Question for the experts...

I have been making a variety of furniture items recently (coffee tables, end tables, TV stands, buffets, etc) and in most cases, I use a solid 3/4" wood glued-up top for these pieces. Immediately after glue-up they are dead-flat, but after some time (a few days to a few weeks), they develop a slight bow across the end grain. Typically I see between 1/16" to a 1/8" bow over a 24" wide panel.

This is the typical process I follow:

1) Rough Mill square stock close to final dimensions (crosscut, joint 1st face, plane 2nd face, plane 1st face, joint 1st edge, rip 2nd edge on table saw)
2) Sticker the stock for 24-48 hours
3) Mill again to final dimensions, but leave slightly thicker than final top. (I usually use somewhere between 2-1/2" to 5" wide boards)
4) Joint edge that was cut on table saw
5) Glue-up to intermediate panels <13" wide using pipe clamps (so I can run through my planer after glue-up)
6) Remove from clamps after 1 hour and scrape off glue squeeze-out
6) Wait 24 hours
7) Run through planer to final thickness
8) Glue-up intermediate panels using pipe clamps to achieve overall size
9) Remove from clamps after 1 hour and scrape off glue squeeze-out.
10) Lean up against wall (at this point the panels are still dead flat) :)
11) When I'm ready to sand and trim panel to final dimensions (this can be several days or several weeks later), I notice the panel has bowed across the end grain! :confused:

Other notes:

- My shop is climate controlled, so I don't believe it is humidity related.
- I don't pay attention to end grain orientation when selecting boards for glue-up, thought this happens even with quartersawn glue-ups.
- Most often, I can still secure the top to the piece in such a way as to remove the bow, but I don't like that I have to do that.

Is there something I'm neglecting in this process?

I'd appreciate any words of wisdom, as this issue is really beginning to frustrate me.

Jeff
 

thsb

New User
Tim
Looking forward to the answer because it has happened to me too. always flattened out when i attached it to the base though, so basically ignored the issue. hopefully someone has a better answer. One of my mentors says 'wood moves' a lot and that certainly is true.
 

nn4jw

Jim
Senior User
Being an amateur I can only guess (and probably shouldn't) that the original rough stock still had enough residual moisture in it that 48 hours wasn't enough stickering time after you cut it into rough boards.
 

kooshball

David
Corporate Member
Unless you have humidity controlled as you do temp, it is still going to swing a bit... maybe more than you would expect. Some woods move more than others...what lumber are you using? Also, do you have moisture barrier in your floor and wall systems?
 

Jeremy Scuteri

Jeremy
Staff member
Corporate Member
One trick I have heard, but have never tried myself, is to wrap milled pieces in plastic (seal with tape) until you are ready to use them.
 

bluedawg76

New User
Sam
Unless you have humidity controlled as you do temp, it is still going to swing a bit... maybe more than you would expect. Some woods move more than others...what lumber are you using? Also, do you have moisture barrier in your floor and wall systems?
my experience as well. I don't think it's an issue of acclimation or dry enough, b/c most of my stock is stored in my garage. Humidity changes equals movement, unless the panel is restrained. For me, milled boards don't cup, but glued up panels do cup from time to time. After glue up, I sticker them lying flat (not against a wall), and add some weight such as other milled boards for the project. If I remember, I flip the panel every day or 2, which sometimes helps (?). I also leave the final panel a bit thick and flatten/plane to final thickness w/ bench planes (assuming it won't fit in my 13" planer).
 

koslonc

New User
Jeff
Thanks for the feedback...

What's the moisture reading now?
I don't have a moisture meter, so I have no idea. :(

Some woods move more than others...what lumber are you using?
Mostly Cherry and Walnut, but most recently some QS white oak.

Also, do you have moisture barrier in your floor and wall systems?
No, but it is well insulated and I have a mini-split unit running all the time. It keeps the humidity pretty constant around 40%.

After glue up, I sticker them lying flat (not against a wall), and add some weight such as other milled boards for the project. If I remember, I flip the panel every day or 2, which sometimes helps (?). I also leave the final panel a bit thick and flatten/plane to final thickness w/ bench planes (assuming it won't fit in my 13" planer).
This was actually one of my suspicions. I often lean more than one panel at a time against the wall, with no space between them. Maybe the difference in air movement on both sides of the panel could have an effect. Next time I will try to sticker them and keep them horizontal to see if it makes a difference.
 

CrealBilly

Jeff
Senior User
Thanks for the feedback...



I don't have a moisture meter, so I have no idea. :(



Mostly Cherry and Walnut, but most recently some QS white oak.



No, but it is well insulated and I have a mini-split unit running all the time. It keeps the humidity pretty constant around 40%.



This was actually one of my suspicions. I often lean more than one panel at a time against the wall, with no space between them. Maybe the difference in air movement on both sides of the panel could have an effect. Next time I will try to sticker them and keep them horizontal to see if it makes a difference.
Best advise i can give is to store fresh glue up so air movement is the same on both faces or shrink wrap in plastic till you get ready to use it. personally ive found that gluing up right after milling also help. wood is wood its gonna do what wood does... sometimes thats just the way it is... Sometimes people forget that Wood is a living thing not man made
 

scsmith42

New User
Scott Smith
Jeff, one thing that you did not mention is if you attempt to remove the same amount from each side of your boards when jointing/planing.

It sounds to me like your problem is related to the airflow around the pieces after glue up, due to the fact that all boards - irrespective of species of milling pattern - exhibit the same problem.
 

CLetts

New User
Carl
1.) +1 to Jeremy. I always wrap panels up until I'm ready for them. (I use a 55 gal. trash bag if they'll fit, otherwise I use stretch film like they wrap pallets with. I get mine from UHaul on line but you can also get 30" wide rolls at places like Staples. Just make sure you leave enough overhang on the ends to seal them also)

2.) Always wait until the last possible minute you can, to cut (joint, plane, sand, saw), pieces to final dimension.

3.) +1 to Scott. Take equal amounts off each side if at all possible.
 
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Willemjm

Willem
Corporate Member
IMHO if you are looking for less than 1/16" movement across 24" in an unsupported panel, solid wood and even most sheet goods will not deliver your needs.
 

Jeff

Jeff
Corporate Member
A few thoughts. I assume you're using kiln dried lumber which should be about 8-10% MC and pretty well acclimated to your shop environment before and after milling. Air dried may be 14-19% so it'll move more with lower humidity.

+1 to storing the intermediate and final glued up panels flat and stickered to ensure good air movement across all faces. Your observation that the QS panels also cupped is important and points to your method of vertically storing the panels which may be ok... IF... the bottom end of the panel is stickered so that it's not in direct contact with a concrete floor.

Glue time: Dead flat after 1 hour clamp time. Well, that glue across a 3/4" t surface is still wet internally so maybe you should extend the in clamp time for several more hours. Squeeze out is still easy to clean up with a cabinet scraper or card scraper.

General wood movement considerations. Note a little subtle cupping in these "ideal" panels. The zoom pic shows a random mixture of flat sawn, rift sawn, and quarter sawn pieces.

http://brownellfurniture.com/2012/11/18/factors-contributing-to-glue-creep-in-woodworking/

The wood should be acclimated to both the shop environment and its in-use environment so wrapping it in plastic defeats that purpose. When it's unwrapped it gonna do what it wants to do despite your best efforts to control it. Example: Hardwood flooring is delivered 1-2 weeks before installation and stored in the house. :confused:
 

CLetts

New User
Carl
....The wood should be acclimated to both the shop environment and its in-use environment so wrapping it in plastic defeats that purpose. When it's unwrapped it gonna do what it wants to do despite your best efforts to control it. Example: Hardwood flooring is delivered 1-2 weeks before installation and stored in the house. :confused:
In this thread he's talking about glued up panels rather than individual boards. Wrapping in plastic prevents air flow across the panel. This air flow causes moisture to evaporate, however minuscule. When one side of the panel loses more moisture than the other, cupping results. When attaching a top to a base, expansion/contraction must be taken into consideration but the panel is still held flat to the base even though it is expanding/contracting seasonally.
 
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Jeff

Jeff
Corporate Member
Yes, I understand that difference. The panel is supposed to behave like a single 24" w board not its individual components, but the components do indeed affect that behavior. Restricting air flow and moisture gain/loss across and within those surfaces doesn't do anything to change the final behavior and the panel will still do what it wants to do when it's exposed to wherever it is. :argue:

I can't dispute your experiences but have a different opinion based upon my understanding of wood movement and what drives it.

Flat sawn table tops of many dimensions will usually cup/warp and that's the nature of the beast. The common methods to minimize that are:

1. Cleats across the glue lines for narrower tops.

2. Breadboard ends for wider tops.

Christian Becksvoort presents a good discussion of the methods at FWW March/April, 2006.
 

chris_goris

Chris
Senior User
I think if you notice the cupping direction from your "stacked" or leaned panels, they probably are cupping away from one another? This would indicate moisture trapped between the boards and as we know, moisture causes one side to grow, cupping the opposite side. Stacking them horizontally and stickering them is key.

Thanks for the feedback...



I don't have a moisture meter, so I have no idea. :(



Mostly Cherry and Walnut, but most recently some QS white oak.



No, but it is well insulated and I have a mini-split unit running all the time. It keeps the humidity pretty constant around 40%.



This was actually one of my suspicions. I often lean more than one panel at a time against the wall, with no space between them. Maybe the difference in air movement on both sides of the panel could have an effect. Next time I will try to sticker them and keep them horizontal to see if it makes a difference.
 

Jeremy Scuteri

Jeremy
Staff member
Corporate Member
Yes, I understand that difference. The panel is supposed to behave like a single 24" w board not its individual components, but the components do indeed affect that behavior. Restricting air flow and moisture gain/loss across and within those surfaces doesn't do anything to change the final behavior and the panel will still do what it wants to do when it's exposed to wherever it is. :argue:

I can't dispute your experiences but have a different opinion based upon my understanding of wood movement and what drives it.

Flat sawn table tops of many dimensions will usually cup/warp and that's the nature of the beast. The common methods to minimize that are:

1. Cleats across the glue lines for narrower tops.

2. Breadboard ends for wider tops.

Christian Becksvoort presents a good discussion of the methods at FWW March/April, 2006.
The way I understand the use of wrapping the piece in plastic isn't to prevent the wood from ultimately moving, but to delay the movement until you have done what you want with it. Just as cleats and breadboard ends can minimize movement, attaching a given piece to other pieces of structure can also help minimize movement. Not to mention, that if you have some joinery left to do, it is easier to do it before a piece has moved (i.e. dovetails on a large panel).
 

Woodmolds

Tony
User
For me, milled boards don't cup, but glued up panels do cup from time to time. After glue up, I sticker them lying flat (not against a wall), and add some weight such as other milled boards for the project. If I remember, I flip the panel every day or 2, which [STRIKE]sometimes[/STRIKE] helps (?).
My experience is the same. I glue panels weekly at work and for my self at my own shop. Generally flipping the panel every day or two works for me(at work) whether they are horizontal or vertical. I stick them if they are in my shop and will be laying for a few days.

For me more importantly than what Scott said about taking equal amounts off each side, is if the panels are sanded, both sides have to be sanded with the same grit to stay flat. Sanding with a coarser grit on one side will have more area to absorb humidity and expand = bowing.

Note this is just my observations based on my experiences.

Tony
 

Howard Acheson

New User
Howard
>>>> Best advise i can give is to store fresh glue up so air movement is the same on both faces

Storing glued up panel flat on another flat surface is the number one cause of panel warpage. Either sticker the panel(s) or store them upright on edge in an area where air can freely flow.

Many times you can flatten the panels by stickering them now with a weight stickered on top. The freely flowing air will cause the two surfaces to equalize in moisture allowing the panel to become flat.
 

Matt Furjanic

Matt
Senior User
Hi Jeff, Even a moisture meter will not do you much good on a finished panel. You must make a fresh cut into the wood to get an accurate reading with a meter. Here's a better way: Weigh your wood before and after. Get a postal or other accurate scale. Weigh your wood, then give it a few days and weigh it again. If it has lost weight, it has lost moisture. I weigh most of the good stuff I buy as soon as it is acquired - write the date and weight on it, then put it in my attic - it gets pretty warm up there. If when it is weighed after a few days and it has lost weight (moisture), back into the attic it goes. I will not use it until it ceases to lose weight!
 
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