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How many cauls for table top?

6K views 40 replies 16 participants last post by  farmfromkansas 
#1 · (Edited by Moderator)
Hi all,

I am getting ready to glue a table top. This is my first time doing a panel this large. I went back and forth on using dowels or clamping cauls to make sure my alignment is good and finally settled on the clamping cauls. So the next question is, how many sets should I prepare?

The tabletop will be approximately 40" x 78". I used a planer sled to get the two faces parallel, so I cannot guarantee that my lumber is perfectly flat, but the sled seemed to work in removing any significant twist or cup, and all are milled to the same thickness.

I've used 2-3 cauls on smaller projects, but I'm sure more would be recommended for a large panel. Those of you who use cauls, what do you do? Every foot? More or less?

Also, I've never seen a definitive statement about when to tighten the cauls. Before or after the clamps? It seems like whichever you tighten first will make it that much harder for the other…...
 
#3 ·
Speculation since I've never made a tabletop that large or used cauls, but I'd say how many cauls depends on how straight the wood is to start with.

As to when to tighten them, well, right away, no? Why wouldn't you want the boards to be aligned when the glue is drying?
 
#4 ·
As to when to tighten them, well, right away, no? Why wouldn t you want the boards to be aligned when the glue is drying?

- nickbatz
What I meant was which do you tighten first? If you tighten the cauls first, can all that downward pressure prevent the lateral clamps from sealing the joint? If you tighten the lateral clamps first, I don't think the cauls are strong enough to then enforce the desired alignment.
 
#6 ·
How did you prepare the edges square to the faces.
You don't mention what wood it is or how thick.
I don't cauls never need to because I have a very accurate jointer. I do use spring clamps on just the ends.
The thicker and wider boards get the more clamping pressure. Last thing you want is glue lines showing up 2 weeks after you last coat of finish.

Good Luck
 
#7 ·
How thick? Are you running it through a sander after or flattening it by hand?

I don't use cauls either, but not saying they don't work. I would tighten before clamps.

Panels that size, I always start in the middle and put enough downward pressure to get any little twist or bow out. Then work towards the ends. That way your working with 3' instead of 6'.
 
#8 ·
Be sure to do a test fit up using your cauls and clamps. This will give you an idea of what it's going to take to get it looking "good". You'll know if you need more and how spaced they'll need to be.
 
#9 ·
...
I used a planer sled to get the two faces parallel, so I cannot guarantee that my lumber is perfectly flat, but the sled seemed to work in removing any significant twist or cup, and all are milled to the same thickness.
...
- Travis
It takes flat boards to make a flat table top.
Or put another way: You can not clamp flat twisted/warped boards to make a flat table top.

If your boards do not lay flat to each other when laid out on table side by side, and need top and bottom pressure to 'make' them flat; will most likely have hills and dips in top when clamps are removed.
BTDTGTTS

+1 With flat boards to start, you don't really need clamping cauls. Like others posted before, I alternate my clamps top/bottom and only occasionally need to use spring clamps to keep outer ends aligned on flat boards.

Best Luck.
 
#10 · (Edited by Moderator)
I agree with Jack, cauls are not necessary. The key to a panel glue up is flat boards and perfect joints.

My technique is to gradually increase clamp pressure, and bring seams into alignment with a rubber mallet. I put clamps on the seams at each end.

If I'm dealing with some minor bows I know I can clamp out, I'll use biscuits.

That said, if you're using cauls, I would put them eveyr 12".
 
#11 ·
tighten the cauls to get it flat , then tighten the clamps…

- JackDuren
Thank you!

How did you prepare the edges square to the faces.
You don't mention what wood it is or how thick.
....
- Aj2
I used a router with a straight edge (factory edge of sheet of BB plywood) to get one good edge that is square to the face. I'm hoping to get the second edge on my TS today, but if I can't get a glue line rip with the TS, then I'll use the router on the second edge.

How thick? Are you running it through a sander after or flattening it by hand?
...
- CWWoodworking
Ash milled down to 1". I was hoping for a bit more but one of my wide planks had significant twist, I lost of lot of thickness getting that piece flat. After glue-up will be flattening by hand (ROS). So my desire for a flat, aligned glue-up is both to preserve as much thickness as possible and to minimize my labor afterward.

It takes flat boards to make a flat table top.
Or put another way: You can not clamp flat twisted/warped boards to make a flat table top.

If your boards do not lay flat to each other when laid out on table side by side, and need top and bottom pressure to make them flat; will most likely have hills and dips in top when clamps are removed.
BTDTGTTS

+1 With flat boards to start, you don t really need clamping cauls. Like others posted before, I alternate my clamps top/bottom and only occasionally need to use spring clamps to keep outer ends aligned on flat boards.

Best Luck.

- CaptainKlutz
The boards look flat when sighting them and feel flat to the touch. But when I stack two pieces on their faces, there are some small gaps, so I know they are not perfectly flat. However, they are as flat as I'm able to get them with the equipment and experience I have. I don't have dead-flat surface large enough to lay them all out side by side and fairly see how flat they lay next to each other. I don't expect the cauls will have to overpower twisting and cupping, that was taken out while preparing the boards. Just keep them in line with each other, especially as they tend to slip around with glue, etc.
 
#12 ·
How wide are your pieces and are you going to clamp them all at once?
It's easier to do 2 halves, then clamp the halves together.

4 Cauls should be plenty.
About 4" in from the edge, and a couple evenly spaced in the field.

Snug the cauls just enough to hold the planks flush with each other, (shouldn't have to bear down on them),
Then put on your clamps. I like to snug the clamps tight, then after about 10 to 15 minutes I go around and give them another crank. It's just what I do.
 
#14 · (Edited by Moderator)
How wide are your pieces and are you going to clamp them all at once?
It s easier to do 2 halves, then clamp the halves together.

4 Cauls should be plenty.
About 4" in from the edge, and a couple evenly spaced in the field.

Snug the cauls just enough to hold the planks flush with each other, (shouldn t have to bear down on them),
Then put on your clamps. I like to snug the clamps tight, then after about 10 to 15 minutes I go around and give them another crank. It s just what I do.

- LeeRoyMan
Thank you!
My pieces are variable width, I think there are 6 pieces total, final width will be 40". Range is between 5-11" wide. I was planning on doing it all in one glue-up, with the assistance of the cauls. But maybe I should do it in 2.
 
#16 ·
If you have 6 pieces, I would glue up 3 and 3 then glue them together. Actually, if it were me, I'd do 2+2+2 then glue two of those together then the final glue up. In other words, unless absolutely necessary, I don't like to glue more than two pieces together at a time. If you're doing all 6 at once though, I would absolutely use cauls. Probably no more than 18" or so apart.
 
#17 ·
I agree with the 2-step glue up, just makes things less stressful.

As to the cauls, I always apply glue to the edges, place the side clamps and after sliding things around to get a preliminary alignment, I'll slightly snug up the clamps to close the gaps. The cauls get laid on (protected on the table top edge with packing tape) and snugged firmly down. Then tighten the side clamps like torquing a cylinder head (do them all in stages, center out). The side clamps will overcome any resistance caused by the cauls.
As to a number of cauls, three minimum (ends and center).

Be sure to alternate the bars of your side clamps top/bottom. As you tighten a bar clamp, the forces will cause the bar to bow, which gets transferred to the top. The cauls will help minimize this, but alternating the clamps is good practice.
 
#18 ·
Funny! I just completed a new tabletop a couple of months back. It was a smaller kitchen table, 63" long and 45" wide. I built it using five boards. As has been suggested above, I did the following

1) I glued up two smaller glue ups then glued them together. SO MUCH EASIER, even though I had three boards in one glue up. Gluing up all your boards at once can be a stressful job, and this will help to mitigate that.

2) I used three cauls for each glue up, but I would have liked to use four. I applied the cauls and tightened them only enough to close the gaps, then I applied the standard clamps. Once they were applied I put every clamp to final pressure at the end.

3) I used a combination of belt sander to start, then a Stanley #7 jointer plane for any final flattening. I think an ROS would take quite a while, and a belt sander is a rough tool at best. It was nice to have the control of the #7 to finish the table. I know I'm crazy, but I think the #7 is my favorite plane and suggest it to anyone thinking about buying a plane as their first or second purchase

4) I gave the glue ups a SOLID 24 hours or more to cook. Oh, and i use wax paper to protect against errant glue. Dollar store is right across the street, so it's cheap for me. Packing tape works really well also. For my cauls, I just waxed them with Johnson's paste wax before clamping and everything came out suprisingly well…

Good luck!
 
#20 ·
Funny! I just completed a new tabletop a couple of months back. It was a smaller kitchen table, 63" long and 45" wide. I built it using five boards. As has been suggested above, I did the following

...
3) I used a combination of belt sander to start, then a Stanley #7 jointer plane for any final flattening. I think an ROS would take quite a while, and a belt sander is a rough tool at best. It was nice to have the control of the #7 to finish the table. I know I m crazy, but I think the #7 is my favorite plane and suggest it to anyone thinking about buying a plane as their first or second purchase

...
- Dwain
Yeah, I'm not looking forward to the final flattening with the ROS! I'm not skilled enough with a belt sander or a hand plane, and this is not the project for me to practice on ;)
 
#23 ·
Yeah, I m not looking forward to the final flattening with the ROS! I m not skilled enough with a belt sander or a hand plane, and this is not the project for me to practice on ;)

- Travis
A 4" x 24" belt sander is much easier to manage than a 3×21. The platen is almost twice the area and makes it far more stable. Add a shoe and it becomes a piece of cake to handle. Zero problems with keeping it level. You can adjust the depth as well. Another good choice for flattening a large area is a 1/2 sheet orbital sander.

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#26 ·
A 4" x 24" belt sander is much easier to manage than a 3×21. The platen is almost twice the area and makes it far more stable. Add a shoe and it becomes a piece of cake to handle. Zero problems with keeping it level. You can adjust the depth as well. Another good choice for flattening a large area is a 1/2 sheet orbital sander.

- Rich
Thanks for the tip, I'll keep my eye out for one. That certainly looks easier!

Have you looked into a cabinet shop sanding it flat for you? Would save you a lot of sanding.

I'd sand your 2 halves for a cup of coffee and a fritter if you were close. Other shops might be slightly more. :)

- CWWoodworking
If I were doing it myself,
I would use biscuits, no cauls, clamp them all at once,
Then run it through my wide belt. ;)

- LeeRoyMan
My local supplier offers use of their wide belt sander (for a fair bit more than coffee and fritter), but they cap out at 36", whereas this will be 40" wide, so I'd have to do the two halves separately, then still hand sand the final piece. Which also means transporting my two halves 30 miles each way in my minivan…. All things considered, I'm not sure it would be that much of an improvement. Who knows, perhaps after I see the results of my glue-up I'll decide they definitely need the wide belt….
 
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