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Are Dead Flush Panel Glue-Up Edge Joints Possible?

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Forum topic by JBrow posted 02-22-2016 03:14 AM 690 views 0 times favorited 7 replies Add to Favorites Watch
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JBrow

818 posts in 385 days


02-22-2016 03:14 AM

Topic tags/keywords: edge gluing glue up panel

I have glued-up countless board into larger slabs for shelves, table tops, and raised panels. However, I have yet to achieve perfectly flush edge joints, though I have come close but not consistently. While not as critical for table tops and shelves, I often need several panels that have the same finished thickness, preferably ¾”. Flushing up a group of edge glued panels at the drum sander to the same thickness means sanding all panels until the worst of the lot is flushed up, generally yielding panels that are maybe 11/16” thick or even thinner, acceptable but not what I really want. So has anyone developed a method that consistently yields edge glued panels that have nearly perfectly flush edge joints right out of the clamps? If so, what are your secrets?

I will guess one answer for wider panels is to use curved cauls that flatten when clamped down on the top and bottom surfaces of the panel. For those offering this answer, please elaborate on the radius of the cauls and whether the convex surface of the cauls press against the panel on both the top and the bottom or just against one surface with the mating caul straight. Also, knowing the distance between adjacent cauls would be helpful.

Another question I have is how to judge when, after the glue that has been applied to the joint but before clamping pressure is applied, has the glue tacked sufficiently to prevent creep at the joint after the flattening cauls are removed? And a related question is how long should the flattening cauls remain in place before removed from the panel?

I prefer to avoid splines and biscuits – I don’t want them to show and keeping track of their location after the glue-up is too much of challenge for me.

Thanks for any tips!


7 replies so far

View bbasiaga's profile

bbasiaga

757 posts in 1460 days


#1 posted 02-22-2016 04:10 AM

I have done the last few table tops with the caul method. I planed all the boards to the same thickness first. Then used the cauls to keep them flat.

I made the cauls two ways. The first is to mark them at the center, then half way between the center and each end. I run them across the jointer from each end, only to the center, say 3 times. Then two more times from each end to the mark halfway to the center. This puts the curve in them. You may need to make another pass all the way to the center again to take any shoulders out that you left from the other passes. On a 24” caul, this will usually make it so I can get a quarter or two between the ends when paired up with its partner. For a longer caul, you may wan to make more marks so you get a more gradual curve. And YES, both the top and bottom of the pair are curved this way.

The other way is to put a quarter or two between the ends of your cauls, then clamp them together at the center so they touch. Once you’ve done that, screw a block to each side to hold the together, and remove the clamp. Now, joint the entire edge of both sides. This will also put matching curves on the pair.

I don’t remove them for 24hours, which is when my bottle of glue says it is ok to stress the joint. ‘

-Brian

-- Part of engineering is to know when to put your calculator down and pick up your tools.

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Nubsnstubs

826 posts in 1195 days


#2 posted 02-22-2016 04:37 AM

Jbrow, you are hunting for the elusive “purrrfect” that is always spouted off by the “master”woodworkers you see on tv. Almost 40 years being self employed operating a wooworking shop, and I haven’t yet made the “purrrfect’ joint. I dowel everything, including raised panels, and have always had them sanded to equal thickness….... It’s called, Doing the best job you can with an unstable media… ......... Jerry (in Tucson)

-- Jerry (in Tucson)

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JBrow

818 posts in 385 days


#3 posted 02-22-2016 03:38 PM

bbasiaga,

I never thought of method 2 for making curved cauls. That makes them perfectly symmetrical and easy to do – very cleaver.

I want to make sure I understand your statement:

“I don’t remove them for 24 hours, which…”

I remove the cauls as soon as the edge clamps are secured in place a leave the panel to cure for 24 hours before removing edge clamps. In your glue-ups do the flattening cauls remain in place until the glue is fully cured? If not, at what point do you remove the cauls? And how far apart do you space the cauls across the glue-up?

Nubsnstubs,

Your reply is a little discouraging. Using dowels, which I assume are perfectly centered and tight fitting, has to give near perfect joint lines, yet they do not. And in a couple of years, you will glue up more panels than I will in a lifetime, so I value your opinion. But before resigning myself to continually reducing the thickness panels of my glued panels, I thought I would go to the well of expert knowledge in an effort minimize sanding and retain the hoped-for thickness of my panels.

I recognize that some sanding to flush-up joints will always be required. However, a better glue-up will result in less sanding and I am trying to minimize sanding to the extent it can be minimized. About the best panel glue-up I am able to achieve requires removal of a 1/16” or maybe a hair more of material to flush up the joints. That is, my best glue-ups result in one or more boards +/- 1/32” proud of the surface of the other boards when they come out of the clamps. That seems to me to be pretty good, but since the joints in the panels seem almost dead flush immediately after clamping pressure is applied, I wonder what is going on and whether doing glue-ups a little differently might make a difference.

But then, as you point out, wood is a natural material that will do what it wants to do. A little wood movement can certainly spoil what appeared to be a perfect glue-up when clamping pressure was applied.

And Brian and Jerry, thanks for the insights!

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jumbojack

1667 posts in 2089 days


#4 posted 02-22-2016 04:39 PM

While I would not call the job impossible, it is rather improbable. When glueing panels I set my perpendicular clamps rather loose and try to get the best grain match. Then I put clamps snug at the ends of each joint. I do use slightly curved cauls, top and bottom across the panel. On a 6’ long panel I would probably use three pairs. It is imperative the the individual boards be as flat as possible, also the same thickness. Even’ off the rack’ lumber can vary enough from board to board to be a problem. Thicker material, say over 3/4” get biscuits, dowels or splines. I prefer biscuits or splines as I can get a little lateral wiggle room.
I normally leave the cauls on for a least an hour in good weather (+65 degrees) longer in cooler weather. I will leave the main clamps and end clamps on for two to three hours. I take the cauls off to clean up the squeeze out. Except for dropping a panel after decauling, the boards have never moved but think gentle movement when flipping the panel to get the other side.
All that said, out of the many panels I have glued up only a few have not needed work to true up. A few, all that was needed was a card scraper.
Good luck I hope this and the above advice helps.

-- Made in America, with American made tools....Shopsmith

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pintodeluxe

4858 posts in 2278 days


#5 posted 02-22-2016 04:51 PM

My boards for panel glueup have usually been freshly jointed and squared. Then I take a very light edge jointing pass (alternating orientation against the jointer fence) to ensure that any deviation from 90 degrees will be negated by the adjoining board. I batch plane all my boards to the same thickness. This is a critical step.

For most panels I use a large caul in the middle, and small “F” clamps at the ends. The small clamps hold the boards flush as the clamping pressure is applied. Start at one end and apply gentle clamping pressure top and bottom, checking for flush frequently. If it starts to come out of alignment, bend the board slightly until it is flush at that clamp. Continue until the whole panel is flat.

I get most panels within 1/32”, but usually send the whole works through the planer to clean up the glueline. It’s much easier than sanding.

If you are stuck working with home center 3/4” stock, then I would expect regular issues with glueups. If you want thicker finished panels you will have to start with thicker stock. My rough 5/4 stock usually yields finished panels 1” thick.

Good luck with it.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

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JBrow

818 posts in 385 days


#6 posted 02-23-2016 03:34 AM

jumbojack & pintodeluxe

Thanks for the insights. For the sake of brevity, I did not review the steps I take to get to the glue up. I do not use home center lumber stock for the reasons both of you mentioned plus its cost. I flatten one face of the 4/4 rough lumber (I normally use) at the jointer. I then batch surface plane the lot to the same thickness to achieve flat stock, trying to leave the stock a little thicker than the finished panel thickness – a real challenge with the 4/4 lumber I have. I also follow pintodeluxe insightful method for jointing the edges. Light passes, alternating faces against the jointer fence to eliminate the 90 degree problem. With the lumber planed flat and the edges jointed, I then proceed to glue-up.

In the end, if I end up with panels that require removal of a total of 1/16” to flush up the joints, well I guess that just the nature of wood. If I could consistently achieve this result, I would be happy.

jumbojack,

Thanks for the info regarding cauls. The vast majority of my glue-ups strive for a finished thickness of ¾”. On thicker finished panels, I will probably go with biscuits – a little more convenient that splines.

You answered a question I had and revealed a mistake I began to suspect I was making. I was wondering whether my problem was removing cauls too quickly, allowing the creep or even slipping that seems inherent in the PVA glue to move the panel surfaces out of alignment. If you are getting good results by leaving the cauls in place for a while, then so will I. I will just make some more cauls. I will solve the problem of cauls sticking to the panel by using wax paper at the glue joints. I will also apply a coat of polyurethane to the cauls as a little extra insurance.

pintodeluxe

My method was to start with edge clamping pressure in the center of the panel and then work outward to each end. The edge clamps are not tightened until the flattening cauls are fastened down. I will try your method of working from one end to the other. It seems more manageable.

I like the idea of flushing up the joints at the planer rather than using the drum sander. Unfortunately, I only have a Woodmaster 12” planer. Most of my glue-ups are wider than the planer will accommodate.

View JBrow's profile

JBrow

818 posts in 385 days


#7 posted 02-23-2016 03:35 AM

jumbojack & pintodeluxe

Thanks for the insights. For the sake of brevity, I did not review the steps I take to get to the glue up. I do not use home center lumber stock for the reasons both of you mentioned plus its cost. I flatten one face of the 4/4 rough lumber (I normally use) at the jointer. I then batch surface plane the lot to the same thickness to achieve flat stock, trying to leave the stock a little thicker than the finished panel thickness – a real challenge with the 4/4 lumber I have. I also follow pintodeluxe insightful method for jointing the edges. Light passes, alternating faces against the jointer fence to eliminate the 90 degree problem. With the lumber planed flat and the edges jointed, I then proceed to glue-up.

In the end, if I end up with panels that require removal of a total of 1/16” to flush up the joints, well I guess that just the nature of wood. If I could consistently achieve this result, I would be happy.

jumbojack,

Thanks for the info regarding cauls. The vast majority of my glue-ups strive for a finished thickness of ¾”. On thicker finished panels, I will probably go with biscuits – a little more convenient that splines.

You answered a question I had and revealed a mistake I began to suspect I was making. I was wondering whether my problem was removing cauls too quickly, allowing the creep or even slipping that seems inherent in the PVA glue to move the panel surfaces out of alignment. If you are getting good results by leaving the cauls in place for a while, then so will I. I will just make some more cauls. I will solve the problem of cauls sticking to the panel by using wax paper at the glue joints. I will also apply a coat of polyurethane to the cauls as a little extra insurance.

pintodeluxe,

My method was to start with edge clamping pressure in the center of the panel and then work outward to each end. The edge clamps are not tightened until the flattening cauls are fastened down. I will try your method of working from one end to the other. It seems more manageable.

I like the idea of flushing up the joints at the planer rather than using the drum sander. Unfortunately, I only have a Woodmaster 12” planer. Most of my glue-ups are wider than the planer will accommodate.

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