Screwing on a solid wood top

[Steven Hans]

Hello all,
I have finished assembly of one of my nightstands. The top is hard maple and have built according to these plans here: http://www.woodstore.net/nightstand1.html
One of the tops is bowed a little, like a smiley face. When screwing the top, I have 4 screws total that screw through the plywood into the solid wood top. The back screw holes are slots according to the plans. I use washers and 1-1/4" screws. I am not sure if I can really screw the top down tight. Doing so makes the top nice and straight, but pre-loads the top and I am not sure if this would adversely affect the movement of the table during seasonal changes. Has anyone been under this situation before and if so, how did your table stand the test of time?

Thank you for any insight you can provide. FYI, this is my very first furniture project.

[John Carlo]

You have to allow for wood movement How wide is the top? Did you alternate the annual rings up and down? How wide were the boards you glued up to make the tops? Definitely elongate the holes in the plywood in the direction of the movement and don't over tighten the screws.

[Jeff Duncan]

It's going to depend on how much bow your talking about. Generally speaking you want the top to be flat so that you just snug the screws. If your having to really torque them down to flatten the top, you'll be restricting the movement and it may end up causing the top to fail over time.
JeffD

[David Epperson]

I suppose that you could isolate the top and washers from the plywood with another layer of "lubricant" film, like teflon or UHMW so that, even with the added tightening the wood could still move. But I would also suspect that after a few months inside it's final environment, you wouldn't need the screws so tight.

But I was all prepared (after reading the title of this thread) to come in and remind you that this was a family forum....:D
Whoops, It's all good.

[Bill Keehn]

Aww, and here I thought this thread was about some fun you had in the kitchen :D

[Joe Scharle]

If it were mine, I'd find where the curving starts and rip the top; joint; re-glue. A table with it's back to the wall can suffer some loss of overhang at the rear.
As a method of work, I always glue up panels before I start making anything else on a project. Gives them more time to misbehave if they're so inclined.

[Steven Hans]

Anyway, thank you for all the info. I certainly did alternate the growth rings. Smiley-Sad-Smiley-Sad (4 boards total). This was the first glued top that I ever did and the second one is pretty much dead flat. However, There was one board that was cupped and 3 that were flat. I decided to use this cupped board and that was a no-no. However, before I screwed the top on, I did check how bad the warp is and it was not bad. I could turn the top upside-down and push in the center with my hand and it would go flat with minimal pressure. Not all the way but mostly with a 1/16" gap. When I screwed the top on, I clamped the top in place flatting the top and then drove in the pan screws with washers. I used the Kreg fine thread 1-1/4" so that I didn't have to pre-drill. I also set my drill at 8 and drove the screws in. Therefore, I didn't really need to torque the screws but when I release the clamps I know that there will be more tension in the screw. I am not sure if this will hurt anything. I will let it be and see how it goes over time. I know if wood wants to move, it will and will split a very strong glue joint. The question here is, is the glue joint much stronger then the tensioned screws in the slots?

Forgot to mention, the boards are around 4-1/2" wide to make a top that is 18-1/2" depth and the width is 21". I followed the Wood Store plans closely, but did read that it is best to have your boards around 2-1/2 to 3" somewhere to remove any issue of cupping. And the holes in the back are elongated! 1/2" slot actually with a 1/2" wide counterbored slot for the washers.

[Steven Hans]

I went ahead and checked by hand to see if the screws in back are over torqued. You see I used my hand drill set at 8 to drive the screws in. I was able to turn the screw loose easily, so I turned it back a hair to snug it up. I will definitely post in the future to let you know if there are any problems. I guess in Jan when the humidity is way low and my hands start cracking.

[harry strasil]

you could fasten a batten under the top inside the stretchers to pull it into place. put your screws in the batten in the middle and don't fasten the ends.

[Stephen Edwards]

If it were mine, I'd find where the curving starts and rip the top; joint; re-glue. A table with it's back to the wall can suffer some loss of overhang at the rear.
As a method of work, I always glue up panels before I start making anything else on a project. Gives them more time to misbehave if they're so inclined.

Ditto to Joe's suggestion! I learned that the hard way.

[Richard Dooling]

Another school of thought says you should not alternate annual rings because you risk ending up with a washboard effect. Aligning the rings in the same direction is more likely to result in a simple arch, which if turned concave side down can be controlled using a batten in the way that Harry describes.

I can’t remember where I read this but I’m pretty sure it was from Tage Frid.

[Steven Hans]

Hi Richard,
What do you mean by washboard effect?

[Chris Tsutsui]

I always alternate the grain and would prefer a washboard than a smiley face warp. heh

Lee valley sells figure 8 washers for cheap that I use for attaching solid wood tops to an apron to allow lateral movement of the top.

http://img.diynetwork.com/DIY/2003/09/18/wwk201_4cb_e.jpg

[Richard Dooling]

I found the article I was thinking of on the FWW site.
It’s called Textbook Mistakes by Tage Frid.

http://www.taunton.com/finewoodworking/FWNPDF/011002037.pdf (http://www.taunton.com/finewoodworking/FWNPDF/011002037.pdf)

There are those who advocate flipping orientation of growth rings and those who feel they should be all orientated the same way. I think there is room for both approaches depending on the circumstances and priorities of the project.

In this example using flat sawn wood:

If you keep the rings orientated in the same direction and the boards end up cupping you get an arch. An arch can be held flat by anchoring at the center with the edges simply riding on the rails or a batten. This lets the wood expand and contract across its width.

If you flip every other board one will cup up, the next down and so on resulting in a S shape, or washboard, which will be difficult to keep flat.

The degree of cupping of course depends on many factors.

Heck.
Never mind – just use quarter sawn.


120308

[Tim Cleary]

Perhaps I should post this as a new question, but just following on here I was wondering a related question: if a tabletop is small (just 13" across grain), does it need to allow for wood movement, or can I just screw it in on both sides and with minimal movement it will be OK? It is 6 foot long but just 13 inches across, pine, will be painted, is being attached to carcase/face frames below.

Should have figured out before the cabinets were assembled of course, but that has not been my woodworking style -http://www.sawmillcreek.org/images/smilies/smile.gif- so at this point I really appreciate any suggestions.

Thanks,

Tim

[Steven Hans]

That is interesting with the washboard effect. I thought by alternating the growth rings that this would not happen though.

[Richard Dooling]

As I mentioned there are different opinions about this. As you may have noticed woodworkers often tend to be a tad opinionated. :eek: What’s the best way to sharpen and hone a blade? Should I cut dovetail pins or tails first?

I don’t fret over this stuff too much – but I try to be aware of the dynamics involved. The “wash board” effect would probably be most pronounced when gluing up wide flat sawn boards. It may be advisable to glue up a lot of narrow boards flipping the ring pattern.

There are many factors to consider including:

Grain direction is important if you are going to plane the glued up panel.

Different species of wood have different characteristics as regards movement.

The particular board you are working with. Even different boards from the same tree may act different. Many people rough mill a board and sticker it to let it reach a new equilibrium before proceeding to final milling.

The area you live in – maybe it’s so dry that you do not anticipate cupping will be a problem.

Cupping may not be your main concern. If you have two boards bowed along their length you may want to flip one so it helps control the bow in the other.

What looks best may be the ultimate decider. All heart wood up?

In the end there are so many factors that you can’t have a check list – IMHO you need to understand wood and it’s dynamics. I’m still in the steep learning curve and have so much to learn. I suggest R. Bruce Hoadly’s Understanding Wood: A Craftsman's Guide to Wood Technology. Again – I never worry about this so much that woodworking stops being enjoyable – I’m just trying to understand my material.

Here is an interesting tool to help estimate wood monement.
http://www.woodworkerssource.com/movement.php

[Bill Keehn]

Forgot to mention, the boards are around 4-1/2" wide to make a top that is 18-1/2" depth and the width is 21". I followed the Wood Store plans closely, but did read that it is best to have your boards around 2-1/2 to 3" somewhere to remove any issue of cupping. And the holes in the back are elongated! 1/2" slot actually with a 1/2" wide counterbored slot for the washers.

If it were me, I'd be focused on which face of the board looks best and how well the grain matches. If I'm going to compensate for cupping, I'd rather modify the construction in a way that doesn't place aesthetics second.

I'm a little suprised nobody asked this, but did you finish the underside of the tabletop too? You can greatly reduce the amount of moisture aborbed by the wood by finishing both sides. Try removing the top and let it sit out in the sun with the underside exposed to see if it flattens out again. If it does, put some finish on it. If that doesn't work, consider ripping a series of kerf cuts on the other side so that the top can easily be flexed. Then you should be able to flatten it and use battens to reinforce the top and keep it flat.


you could fasten a batten under the top inside the stretchers to pull it into place. put your screws in the batten in the middle and don't fasten the ends.

I think better still, instead of screws, use a sliding dovetail. This is something I saw on the seat/lid of an antique piano bench I once owned. When I first saw it, I thought it was a very clever idea for strengthening the seat and keeping it flat. Also, I am sure it made alignment of the boards in the seat much easier during glue-up. Of course, this won't work if the top is already cupped. You need to flatten the top before cutting the dovetail slots.

On the bottom side, route a pair of dovetail slots, across the grain about a 1/3 from each end of the top, starting at the back. Stop the slot before exiting the front. Then using scraps the same thickness as your table top, rip battens to fit the dovetail slot, adusting the blade pitch to the dovetail angle. You can adjust the thickness and width of the dovetail to get the strength you need. It should be a snug fit, and you'll need to tap them in place. A little bit of glue at the blind end of the slot should be all you need to hold them in place.

[harry strasil]

Sliding dovetails was how all 3 battens were fixed to the top of this wedding chest, the outside battens are also the hinges. No metal used in its construction.

[Bill Keehn]

Sliding dovetails was how all 3 battens were fixed to the top of this wedding chest, the outside battens are also the hinges. No metal used in its construction.

Good example! I like it. What's it made from?

On my piano bench, the battens were not as thick as those. The craftsman had also rounded over the edges that stood proud and had chamfered the ends. I think the chamfering had been done so that the batten could continue out past the edge of the "chest" part of the bench without preventing the lid from closing.

Even with the chamfer, the battens still stood slightly proud and it was these that made contact with the chest when it was closed. This caused an eighth inch gap or so under the front lip of the lid. I don't know if this was done to fine tune how the lid fit between the side pieces, or if it was to prevent little fingers from getting crushed. What I do know is that the thing held up really well.

[harry strasil]

the frame is salvaged Burr Oak from a corncrib, they were grooved with a stanley 45, the panels were a board that was stained, either from chemicals from the ground while growing or spalted, no one wanted it so I got it cheap, the panels were all raised with a woodie panelraiser. The top is some old barnboard I bought at the lumber yard years ago, the battens each have one 1/4 dowel on one end to keep them from sliding out should the material shrink, the hinge pivot are also dowels. Something I really didn't want to do, but a good friends daughter requested that I make her a wedding chest for her wedding present from Mom and Dad. I gave them a bag made from an old sheet that was full of cedar chips, I had originally wanted to make the panels from cedar. Its their pride and joy I think, her dad told me they use it for a centerpiece/coffee table in their living room.

[Steven Hans]

I did finish both sides. I have some pictures so you can see the top on the nightstand. Please note that I built this from plans and it is the first project I have done. I built shelves and drawers for my garage, but felt it important to follow plans as written for my first project.

[Bill Keehn]

That looks great Steven. Pretty impressive for your first project. I see the wood movement you were talking about, but I honestly wouldn't have noticed it if you hadn't mentioned it.

[Steven Hans]

Thank you Bill. I don't think I am too worried about the top because when I was placing into position I actually was able to nudge the top on the nightstand. I then nudged it back into position. Would this be a good check to see if the top is screwed on too tight? Or perhaps there could still be problems of wood movement. Bill, I should mention that I took the photo at an angle that really accentuates the flaw. And this is towards the back.