Second try for flat table top - Woodworking Talk - Woodworkers Forum
 
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post #1 of 13 Old 02-20-2014, 06:34 PM Thread Starter
Dan Gallagher
 
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Second try for flat table top

I glued up 1x8s for a 4' round table top. I didn't have enough long clamps, my radial arm saw was off, (I've since adjusted it), and yes, I wasn't patient enough. As a result, I wound up with a warped table top. I thought I'd try to use pocket screws and glue on my second try with 1x6s. What are the pros and cons of using pocket screws? Any help would be greatly appreciated?
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post #2 of 13 Old 02-20-2014, 07:48 PM
where's my table saw?
 
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nice bird bath...

Sorry, I couldn't resist. It's not as easy as it looks to get a flat surface from a plank glue up. But the basics are making certain the edges are square to the faces of the planks .... and you sight the boards for straight before gluing.... and letting them acclimate to the shop before gluing.... and use a finish on both sides of the top.
Some recommend alternating the curve of the end grain on every other plank before gluing.

Pocket screws may tend to tighten a misformed edge without being squared true, rather than clamps and cauls across the entire glue up, I donno, I don't use 'em.

Here's how I made a large surface like a table top from planks:
http://www.woodworkingtalk.com/f2/do...1-4-ply-55717/

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #3 of 13 Old 02-20-2014, 08:15 PM
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With a top that size and shape there is the potential of cup warp even if you used clamps. I think you might be able to salvage that top. If you would strip the finish off of the top of it you could soak that side with water to make it swell causing it to flatten. At the same time if you would screw some strips of hardwood to the underside across the grain it would tend to hold it flat. The pieces you would screw to the underside you would have to make elongated holes to allow for wood movement. Then finish the table back and be sure there is a finish on the underside as well.
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post #4 of 13 Old 02-20-2014, 08:37 PM
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In my opinion this isnt the right application for pocket screws. Theyre more useful for small joints like 'rail to stile', or 'shelf to side panel'. Some people use them for edge joining but i dont think thats gonna help you here.

As mentioned above, boards on edge screwed underneath would probably work. There are a variety of brackets and fasteners u can use to allow for wood movement while still holding the top flat. I like the figure 8 fasteners personally.

Good luck!

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post #5 of 13 Old 02-21-2014, 10:33 AM Thread Starter
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LOL at the bird bath comment! It's good to keep a sense of humor. Not sure if the old top is really salvageable but I may try. Already bought and cut the wood for the new top. If I can salvage the old top I may use it for another table. This one is for my daughter. (Note the Celtic Knot carved into the door panel representing Father / Daughter relationship.) I'm going to take off this weekend and think about it some and decide next week.

Thanks for the insight.

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post #6 of 13 Old 02-26-2014, 06:07 PM Thread Starter
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Salvaged

Cut kerfs on bottom of table, clamped it and screwed and glued hardwood supports (elongated holes) to pull out the cupping. Hope it holds.
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post #7 of 13 Old 02-27-2014, 10:22 AM
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For a top like that and a base that small, I would do the following - this is just me of course...

Assuming you have a good jointed edge first) Rip your boards in 3" to 3 1/2" strips

Alternate ring directions

Cut channels to use splines

Glue panel up

I rarely have to use cauls on panels like that. A good square edge, thinner strips which really can't cup, the alternating ring direction and the splines should be enough to check cupping, bowing and twisting.
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post #8 of 13 Old 02-27-2014, 12:14 PM
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If it were me, I'd probably have taken a #7 hand plane to it.

Last edited by Chris Curl; 02-27-2014 at 12:16 PM.
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post #9 of 13 Old 03-01-2014, 10:22 PM
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Pocket screws should not be needed if you have long enough clamps.
If the boards were jointed square the panel should be flat after glue up.
Unless you use perfectly quarter cut boards, a wide board or glue up of boards is going to warp when there is a humidity change. It can be aggravated by finishing the sides unevenly like putting more or only Finnish on the top.
It is almost vital to have cleats across the table as the cleats mentioned above or the more common use of a table apron.
If you need a flat table without an apron you need to use plywood or some other more stable material.
Pocket screws can be used but take time while the joint is being held flat. If used close together, they will work and can be removed after the glue is dried. The wide glue up table will still warp if not held flat. You should see even squeeze out of glue along both sidesof the entire joint.
Glueing up pairs of boards and clamping till dry then planing and glueing the pairs together. Wedges at the end the right length 2x4s can replace long clamps.
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post #10 of 13 Old 03-31-2014, 02:51 AM
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And don't clamp too tightly...only enough so you see some glue squeeze out. Use an even number of clamps above and below and remember that no amount of clamps/glue will save a project from poor joinery.
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post #11 of 13 Old 03-31-2014, 07:49 AM
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I wouldn't use pocket screws. When using clamps above and below the outer edges of the boards, if the pressure point on the edges isn't centered, pressure will cause some grain compression in a direction to form a cup.

For example...lets just say that you have clamps with the pressure more along the top edge, than centered, the boards will have the tendency to pull up on the edges. In this case it may not be immediately noticeable but you will likely have squeeze out at the top, and that seam will look tight, while on the bottom the boards may not be tight. With many glue ups the boards are on a bench, and you may not be able to look underneath, or find it necessary. It takes some care to center the pressure.





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post #12 of 13 Old 03-31-2014, 08:28 AM
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From what I can tell from the picture on post 6 the top was kerfed cross grain and a piece of wood was laminated with the grain to the underside. The way it was done the screws wouldn't hurt anything.
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post #13 of 13 Old 03-31-2014, 09:17 AM Thread Starter
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Thanks for the tips. Final photo. I'm pleased with the final product. Now working on the dinning room hutch.
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