Why don't they stay flat?

[bluedawg76]

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!

not to be overly contrarian but this seems a bit impractical from my perspective. i recently glued up 2 side panels for a dresser that were 42x20". what kind of scale should i use? how does knowing the weight/mc of the panel prevent movement? if the humidity of your shop is different from your attic, there is potential for movement as the MC of the panel changes.

 

[Matt Furjanic]

Yes, Sam, it's not practical for very large pieces, my postal scale goes up to 40 pounds - I rarely work with a piece of wood heavier than that...

 

[Bob Carreiro]

Jeff, Did you alternate the end grain growth archs during glue up? If they the curl orientation is similar, it only encourages cupping. Bob

 

[koslonc]

Jeff, Did you alternate the end grain growth archs during glue up? If they the curl orientation is similar, it only encourages cupping. Bob

No, my primary concern is the appearance of the grain matching on the top surface. However, as I stated in my original post, this happens consistently with QS lumber also.

But It occurred to me today that I omitted something from my stated glue-up process in my first post. I often wipe off the glue squeeze-out on the top side of the panel with a rag soaked in water right after I've tightened the clamps. I don't do the same on the bottom side as it is much more difficult to get at. Could it be that the moisture I introduce close to the joint lines eventually cause the top surface to swell more than the bottom surface, causing the overall cupping? (I have noticed that the cupping is toward the top face of the panel)

 

[Jeff]

Jeff,

Enlightening additional input. A few thoughts from an amateur that may help you out.

1. Wiping off wet glue with a damp rag is counter-productive, despite what's published, because it smears wet glue on either side of the line which may show up during the finishing because the finish won't take where the residual glue is. You're better off using a sharp chisel, cabinet scraper, or card scraper after about 30 minutes drying time. The glue is kinda rubbery and peels off easily. Subsequent scraping and sanding finishes up the glue line and its adjacent edges for finishing.

2. Put alternating clamps on the top of the panel as well to help equalize the squeeze and vertical distortion from the bottom clamps.

3. This tip came from a a fellow member, Dave or Dan Kepler/Keller from Raleigh. I've used it on table tops as wide as 42" and it works like a charm for keeping them flat. Basically a set of of cauls with bolts, nuts, etc. You may need 2 or more depending on the length of the top.

They're basically cauls clamped on the top and bottom faces of the panel to keep it flat while the glue dries and before the clamps are removed.

 

[dustin510]

^ Tony, I definitely tried to swipe that little bug off my computer screen :rotflm::embaresse

My experience just the same as everyones elses... wood moves. I agree with leaving it in the clamps longer than an hour, if you're concerned with clean up, a little trick I learned is to rub sawdust on the wet glue squeeze out and then it should just rub back off with most of the glue.

When gluing up, are you paying attention to the direction of the panels on the end grain? For example if they are all facing the same direction from how they were cut in the tree then the entire panel with cup together and transfer into one big cup.
If you alternate the direction, each board will cup in opposite directions and thus create a slight wavy thing happening and is less noticeable to the eye.

http://www.richardjonesfurniture.com/Articles/panel-glue-ups/panel-glue-ups.html scroll down about half way and it kind of shows it.

Wood moves, instead of cheating it, sometimes you just gotta work with it

Good luck

 

[kooshball]

Wood movement is the nature of the beast, if you want it minimized than sheet goods with veneer may be a good option (I did this for my speakers as I could not afford any movement). For solid wood projects however, you can plan on it moving over the years...this becomes part of the design challenge.

depending on what you are making it may not matter too much. For example, I glued up all the case panels for a wide dresser I built, then went out of the country for a business trip, returned to go on vacation then 3-weeks later got back in the shop to find those panels all bowed and twisted. By the time I dovetailed the case, installed the drawer rails and dividers however the structure of the joinery forced those panels flat and square.

As the previous post mentioned, wood is going to move...sometimes you just need to figure out how to move with it.

 

[Gofor]

One thing to keep in mind when gluing up panels. If all the boards have the heart side on the same surface, all will cup together as previously stated. If you are going to install a cleat, or pull it down onto a solid stretcher or cabinet side, you will remove all the cup. If you alternate the growth rings, it may become wavy, and will stay that way regardless of what you do.

Alternating the rings may work better if the panel is going to be basically free floating with little cross support.

I have found I get the best results when I match the grain features to get the best looking overall panel, pretty much ignoring the growth rings. I use the joinery to pull the panels into a flat surface as much as possible. I have been known to use a pipe wrench to "untwist" a rail or style enough to get the tenon in the mortise. Comes out fine after the glue dries if I have a snug fit.

I figure people were making good furniture way before moisture meters and humidity controlled environments by taking wood movement into consideration during the design and layout, so I just try to emulate them.

JMTCW

Go

 

[Touchwood]

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!

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

Jeff

I was looking for one key step that I did not see.

When you talk about the end grain and you're gluing up a half dozen boards 5"wide for your final width, are you alternating the grain??. If one has growth rings concave, the next one glued to it better have them convex, or you're asking for trouble.

Don

 

[kooshball]

I have found I get the best results when I match the grain features to get the best looking overall panel, pretty much ignoring the growth rings. I use the joinery to pull the panels into a flat surface as much as possible. I have been known to use a pipe wrench to "untwist" a rail or style enough to get the tenon in the mortise. Comes out fine after the glue dries if I have a snug fit.

This is a good point, I don't think I have ever oriented a board just to alternate "inside of tree vs. outside of tree"...I go for what looks best.

 

[yuenglingman]

Although I have only made a few pieces of furniture, the first thing I would ask is what is the moisture reading and how long has the wood sat in your shop so it can acclimate? then during glue up I would alternate grain pattern looking at the end grain. I just finished a Hal Taylor inspired rocker, and through the construction and in talking with Hal, he always says" wood is wood and its going to do what its going to do, you have to work with it"! Meaning no matter what , its going to move somewhat, just make sure you take as many variables out of the equation as possible. Hope that helps? Good Luck Gerry