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Table Top glue up.

6K views 42 replies 12 participants last post by  DrRobert 
#1 ·
I’m working on a large harvest table and getting ready to do the top.

The lumber is one and seven-eighths inches thick, 84” long, and the four boards will be 36” wide when glued up and then trimmed. It’s some kind of softwood, likely fir or pine.

I don’t own a jointer, so to true up the edges I’ve used a sturdy pattern maker’s bit in my router, with a straight edge. I’m getting clean, smooth results, but my straight edge might have a slight curve to it.

I’ve done two edges, and when I dry clamp them they flush right up through 60” of the middle, but the ends flare away from one another such that there’s a >5/64” gap on each end. It’s easy to pull that together with a clamp. Is that something to worry about? Can I just go ahead and count on the glue to hold that together for years and years (Yellow glue, probably Woodtite II)? Or do I really need to get more perfectly straight edges?
 
#2 · (Edited)
To put it another way, if I clamp two of the boards at one end, and put a second clamp at the center of the length, the far end has a gap slightly less than 1/8” (a 3/32” drill bit slides between them a little loose, but a 7/64” drill bit won’t fit between them at all).

SO a total curve of about 7/64” across 84.” Is that too much bend to just force together and hold with glue? Or am I good to go?

FWIW, here’s an older thread about joinery for the base, with some photos.

https://www.woodworkingtalk.com/f5/hardware-no-212203/

The top boards have been planed, but I’m trying to square up the edges for the glue-up.
 
#3 ·
somethin ain't straight .....

Look down the boards to see if you see a slight curve on one or the other, maybe both? No matter, a few swipes with a hand plane will remove the curve a each end and give you a straight board. Hand tools have their place and this one, BUT you keep the sole, the bottom of the plane, square with the face of the board. Keep mating them together to see how the gap is reduced. :wink:
 
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#4 ·
Look down the boards to see if you see a slight curve on one or the other, maybe both? No matter, a few swipes with a hand plane will remove the curve a each end and give you a straight board. Hand tools have their place and this one, BUT you keep the sole, the bottom of the plane, square with the face of the board. Keep mating them together to see how the gap is reduced. :wink:
It’s a good suggestion. I’m not one of those guys who’s resistant to hand tools. In fact, before I thought of trying to use the pattern maker’s bit, I hand planed two of the edges and got fairly close.

But I also know I’m not that good with hand planes. This is so close and I fear I’d make it worse messing with it. But is is close enough, or do I have to get it better to ensure a long lasting glue joint?
 
#5 ·
If you can pull them together with clamp pressure then a spline or biscuits MIGHT be enough to ensure long term success. If you want to get them closer you could get a straighter straight edge or even using the straight edge you have you could create mirror image edges on the boards. Use a pattern bit with the straight edge on top of one of the boards and move the other board close enough to the first board so that the bit removes a whisker from each board....this will give you mirror images which even if not straight will meet with no gaps.
 
#7 · (Edited)
So the consensus is, “no, don’t just count on the clamps and glue to draw and hold these edges. Get a more perfect fit.”

The attached photo shows the size of the gap. One end is loosely clamped. The seam on the right and in the center show the gap (ignore the one on the left: a shadow makes it look a lot bigger than it is).

Anyhow, super easy to draw them together with clamps. But y’all think it’s a bad idea?
 

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#9 · (Edited)
Not the answer I wanted, but I guess it’s the answer I needed to hear. So maybe y’all can help me figure out the cause of the problem. I’m a baffled by what’s happening.

I did the first two edges using an 8’ x 1” square aluminum tube as a fence. I clamped it to the board at each end, and could tell there was a slight flex in the middle. But that should have resulted in a concave curve (cutting slightly deeper in the middle as the fence flexed away from the bearing on the pattern-maker’s bit). Instead, I have a convex curve, where the boards meet in the center but not at the ends.

For the second and third pairs of edges, I used the edge of a Formica countertop as my straight edge. This also generated a convex curve, which I find even more baffling. There’s obviously no flex to the countertop, so the curve must already exist. But I can’t find it. I ran a three-foot level along the edge of the counter which I know is perfectly straight, and there’s no gap to be found.

Here’s my best hypothesis. I don’t think either straight edge is the problem. The problem is that the boards are not actually perfectly flat, and the router is following the curve of the surface, and translating it to the edge. Does that make sense?

Since I don’t have a jointer, but I do have a planer, I milled both faces of these boards with the planer. I know that this creates a problem where if one face is curved or twisted, that curve gets transferred to the other face, creating two parallel but not flat faces.

So might that be the source of the problem? A slight curve or twist along the length of the face could translate to a convex curve on the edge, right?

But that also doesn’t make much sense, because I would then expect edges not to be perfectly perpendicular along the whole length, and that doesn’t seem to be the case. There they meet, they meet perfectly; where they don’t meet, they have a perfectly parallel gap, not one that tapers.
 
#11 ·
Basically the thicker and wider the board, the more perfect the jointing must be. With big tops like this, you also have to be concerned about twists, which adds a whole 'nother layer of work to getting a top flat. This is something that can be corrected after the top is done, but if several boards are twisted, you will have a tough glue up and end up with a much less thick top after correcting and flattening.

Dialing in jointing is difficult at best without a hand plane. First determine if its one board or both that is bowed. This can be difficult by eye so I recommend a long straight edge like a 6' level.

You can clamp out a small (1/64 - 1/32") gap in the middle, but not the ends. In fact, a small gap in the middle is called a "sprung " joint and is a technique that is meant to keep the ends extra tight.

As to your question about the convex curves, I'd be very skeptical about your aluminum channel being perfectly straight. Usually a factory edge on plywood or MDF will suffice.

But be sure the boards are acclimated and not moving after milling.
 
#12 ·
Thanks for your useful suggestions. I did wonder about whether the wood has been moving. The lumber sat in an attic for decades, and then in a finished basement for several years. Now it’s out in my entirely unconditioned shop for about 6 months, and it’s been beastly humid lately. Maybe I need to set it aside or find a way to store it somewhere dry before I keep going? I planed it from 2 1/4” down to 1 7/8” just this weekend, so maybe that would be significant?

I went out a little while ago and did a little experiment. I put a push pin in the very tip of the corner on each end, and pulled a piece of string taut between them (thank you once again, to the marvelous clove hitch, for being one of the more useful things I’ve learned in the past ten years).

Interestingly, the edge of the board on the far right showed a clear, even arc of about 1/8” across the full length. That’s the one I did the with aluminum tube.

The two edges in the center seam, however, appear to be arrow straight. Those are the last two I did, and I used the Formica countertop as the straight edge. I haven’t checked the bottom edges yet, so there might be a problem there.

As to the left seam, the leftmost board has a detectable twist. I’m not sure how to resolve that. I have another board I could substitute in which may be flatter. I’ll take a look.

Meanwhile, I’ll start with Steve’s suggestion and just do another, very light pass using the Formica countertop and see if that can’t close the gap.
 
#13 ·
It's also entirely possible the countertop is a little crooked. It's not intended to be that accurate.

If you had an actual jointer if the board was bowed inward in the middle you would position the middle of the board over the cutter and trim the wood to the end. Then turn the board 180 degrees and do the same. You might have to do something similar with your jointer. Set up the straight edge to slightly cut the wood on the end and nothing in the middle.
 
#14 ·
I'm in the fix it with a handplane camp but there's always another way.......

If you have a decent router bit that can cut the full depth (maybe even the pattern bit your using , then you can cut two boards at once that will fit together even if the joint is not straight. First straighten each board as you've been doing. Lets say your bit is 1/2 inch diameter. You then set the boards side by side, lined up well on the ends and sitting flat on cauls. Use a 3/8 spacer to create a space between the two boards, then run your router (off the straightedge) down the center of the gap. It will take off 1/16th from each side and they will mate even if not straight. You might have to change the gap if its way off or if your bit is a different diameter, just be sure to take something off of each board. Also take a notch out of the cauls so the bit does not hit. Countertop people do this a lot for long 45 degree joints or joining solid surfaces in showers etc.
 
#17 · (Edited)
I liked this idea. A circular saw isn’t the best choice for me because mine is a cheap-o with a crappy blade, and I won’t get clean surfaces to mate.

Here’s the set up I came up with. What do y’all think?

I clamped the two boards down to the work surface, but propped up on 2x4s so the router bit won’t groove the workbench. I used the brass 5/8” collet to set the gap between the two at each end. Then I used the collet inserted in the router base to set the aluminum fence at each end. Finally, I braced the aluminum fence in the center with a scrap of 2x4. (Ignore the steel angle iron attached to the aluminum fence—that’s not in the way and it’s there for other uses of the fence).

The router bit is 3/4” cutting diameter. So it should take about 1/16” off each side.

I have two concerns.

(1) Because the boards are only clamped on the outside edges, there’s a very slight tendency to lift in the center. I figure I should be able to minimize that by pushing the router down firmly, and clean it up later with the pattern-maker’s bit in a router table, using the edge of the board itself as the guide.

(2) Because the fence is only on one side, I’m worried about the router’s propensity to run. I’m unclear which direction I should go to avoid having the router drift away from the fence and gouge the opposite board.

(3) Any other worries y’all see about this set up before I pull the trigger?

I’ll probably do a test run on a couple of scraps and see how it goes.
 

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#15 ·
Same concept, different tool .....

I would prefer using a circular saw with a full kerf blade and split the gap of the butted and clamped down boards. Do not clamp them together, just leave a slight gap. A straight edge may be used or if your circ sawing saws are good, not necessary. :vs_cool:
 
#18 · (Edited)
Hold the router pushed against the fence and move from left to right. i.e. toward the camera location that is taking the picture. Because you are not using a bearing guided router bit don't rotate the router in case the bit is not dead center in the base.
Did you consider using a glue line rip blade on your table saw?
Or making a guide from a long piece of plywood or hardboard with an edge guide. Glue/screw the edge guide to the plywood or hardboard and the run the router along the plywood with the router pressed against the edge guide to create a straight edge on the plywood or hardboard. Then lay the plywood/hardboard on your board and run the router along it, keeping the router pressed against the guide, to create a matching straight edge on the board. You can buy these but they are very easy to make and foolproof. This type of jig is very common for ripping plywood sheets to exact width with a straight edge using a circular saw or router.



 
#20 ·
Do your best to make each board flat to the other before routing. If after routing its not flat enough you can use a top bearing flush trim bit to correct for square, but I think you'll be fine . You be the judge. Yes, push towards the camera when you route. That's why it's important to take a minimal amount off of each side as the stress on the router and bit is minimized. Yea, you'll need to focus hard on keeping the same point of the router base against the fence, but it's not that difficult when you are taking off so little.

Its a process, leave all parts a bit oversized and then you get a second chance. Sounds to me that you are paying attention to the important things straight, flat and square, so I know you'll get this right, Good luck
 
#21 · (Edited)
Sadly, I don’t own a table saw yet. My budget is limited, so I’m operating with a make-do mindset. I’ve got a compound miter saw with an 18” reach, a crappy 10” skil circular saw, and my router with a home-made router table in a Formica countertop. Long, straight cuts are my kryptonite.

I’m going to give this rig a test run on some scrap, and if that works I’ll give it a go. If it doesn’t, I’ll buy something with a more perfect straight edge (probably birch ply). After either, I’ll give the handplane a go to tidy up as needed.

Thanks everyone for your very helpful suggestions. I’ll report back with results after next weekend.
 
#25 · (Edited)
Dylan,

You realize if you had a hand plane you'd have been done a long time ago?

I promise you're going to find your ww'ing is going to another level when you do.
I know. I do intend to hand plane the top after glue up. I’m just not confident in my skill to get two edges perfect. I did work on two of the edges with a handplane for a while (when the boards were rough sawn and hadn’t even been through the planer yet) but I just couldn’t get it to match up.

Anyhow. I got it done with the router. I used the aluminum fence, and stabilized it with blocks clamped behind it. I routed the edge of the first board, and then moved the second board next to it, separated by just less than the width of the bit. Clamped that in place and routed again. A couple of passes and some patient adjustments, and i have perfectly flush edges.

Thanks for everyone’s suggestions.

I was thinking of using dowels, not for strength, but to help make sure the top faces align when gluing up and clamping. Good idea? Bad idea?

Also, the top is five boards, currently just under 4’x8’. I was thinking of doing the glue up in phases, rather than all five at once. Glue two, wait for them to dry, glue a third on, wait, a fourth, and so on. Good idea? Bad idea?
 
#28 ·
One vote for dowels/biscuits; One vote against.

I did a dry clamp of the first two boards, and was easily able to get it perfectly flush except two short lengths that are less than 1/32 off. That’s within tolerance, I think.

But if I did decide to try to pin them, I’d have to use dowels. I don’t have a biscuit joiner.

I was thinking of using a 24” angle iron, and drilling two holes in it about 18” apart. I would use a fence on my drill press to make sure both holes are exactly the same location relative to the lip of the angle iron. Then I’d clamp the iron onto the top surface of the table, so the holes are spaced along the edge. Drill the first, put a dowel in, drill the second and put a dowel in. Then move the angle iron down the edge and pin the first hole over the second dowel, clamp in place and drill the third. Repeat to the end of the board, then do the same on the matching face.
 
#29 ·
One vote for dowels/biscuits; One vote against.

I did a dry clamp of the first two boards, and was easily able to get it perfectly flush except two short lengths that are less than 1/32 off. That’s within tolerance, I think.

But if I did decide to try to pin them, I’d have to use dowels. I don’t have a biscuit joiner.

I was thinking of using a 24” angle iron, and drilling two holes in it about 18” apart. I would use a fence on my drill press to make sure both holes are exactly the same location relative to the lip of the angle iron. Then I’d clamp the iron onto the top surface of the table, so the holes are spaced along the edge. Drill the first, put a dowel in, drill the second and put a dowel in. Then move the angle iron down the edge and pin the first hole over the second dowel, clamp in place and drill the third. Repeat to the end of the board, then do the same on the matching face.
When the glue is applied the boards can slip out of alignment quite easily. I'm a biscuit fan....you can get a biscuit bit for your router.....just a suggestion. Self centering (vix) bit for the angle iron method.....no room for error.
 
#31 ·
Anymore I rarely use alignment aids with gluing panels.



I tighten the clamps incrementally, and employ a judicious whack with a rubber hammer to bring it close.


I don't stress myself about getting it perfect. I keep the top thick, get it close, and take out any minor discepancies when I flatten the panel.


Believe me, my stress levels have definitely dropped doing it this way!!
 
#32 ·
#1: The distillation of your experience seems to be that the wood “moved” (warped/twisted/hooked/bowed) after you planed your original wood down to size. This process trims away the seasoned and stable exterior wood fibers, and exposes fresher wood with internal stored stresses to the elements, whereupon it seeks to become stabilized, so it moves after it's milled. In other words, you probably got things pretty good at first, but then it moved.

#2: Following #1 above, “dowels,” NO!! Consider how hard you’ve worked to get your edges with a relatively simple and aided/controlled tool setup. Dowels have to be controlled in 3 axes, which is not easy even for those of us who are experienced and have decent tooling.

#3: Your proposed glue up is the right approach.

#4: After the slab is all glued up you should plan on hand planing the top smooth and flat, so there’s wiggle room for the glue-up process itself, hence Dr Robert’s choice to not rely on alignment aids.

#5: As you now know, the initial cutting of the wood is the most important part to get right for our projects. Rather than spend a dime on a slot cutting router bit (for biscuits) I would save and spend the $ on a quality circular saw + quality blade, and then fabricate a cutting straight edge/track as shown earlier.

#6: Keep it simple! Please don’t take this as an insult, but reading thru this thread, it seems you are complicating your efforts rather than simplifying.
 
#33 ·
Flat top!

Thanks for all of the advice, everyone. I did not end up using biscuits or dowels. The stock is so thick, we were able to get it very close and then a hand plane did the rest.

Next step, breadboard ends I think.
 

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#34 ·
Now that you have the top, take your time with the design on mounting the top to the base and also the breadboard end. The top needs to forever be allowed to expand and contract and both mounting the top to the base and the breadboard end can interfere with the top doing that and cause the top to split.

If you just screw the base to the top it holds the outer portion of top where it is and in the event of shrinkage the top will split to releave the pressure.

Any time you attach wood with the grain running in a perpendicular direction you have to be careful to allow for shrinkage. The breadboard is normally done with a mortise and tenon joint where it's only glued in the middle. The rest of it just has pins or screws put through elongated holes to help hold it onto the top. It still allows for the width of the board to shrink.
 
#35 ·
Thanks Steve. The book that gave me the inspiration for the design (Measured Shop Drawings of American Furniture, by Thomas Moser) has good drawings of how to do the breadboard ends like you suggested. I’ve been considering if there’s a way the tenon can be hidden, so you don’t see it on the edges. I guess you would cut shoulders, and then the mortise would have to be about a 1/4” longer than the tenon so there’s room for movement and the endgrain of the breadboard does’t pop out if the top swells wider. On the other hand, my shop is not air conditioned and I live in North Carolina and it’s summer, so everything it about as swollen as it’s going to get. Building with tight tolerances might be ideal so when the table gets moved into a house it’s not too loose.

The top is ridiculously massive and is very stable on the base; I’m considering not gluing it to the base at all, in part so the table can be moved through a door more easily. To do that, I’d use a router to make a 1/4” to 1/2” recess in the underside of the top that follows the outline of the base. I may put two or three short pins along the spine, but none out on the ribs. That would keep the top from sliding if bumped hard (right now it’s heavy enough that friction keeps it from sliding if bumped or leaned-on).
 
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