Help! Table top seams coming apart!

[malawlo]

Okay, first things first -- I'm not really a woodworker, which is probably why I find myself in this predicament in the first place. Admitting that I don't really know what I'm doing is hard but necessary, hopefully some of you skilled guys can set me straight.

Problem: I've made a few tables using reclaimed scaffolding boards mounted to 3/4" plywood. They're simply made and look really cool when they're done, but I've had a few that have started to come apart at the seams (I'll attach a few photos of finished tables). Basically, I cut the planks down to 1 1/4" thick, then glue/screw them to the plywood in a 'patchwork' fashion -- when it's done, the top is 2" thick. I add some steel legs underneath and that's it, they're solid when they leave my workspace but have been pulling apart later.

So like I said -- I really don't have much skill, I have basic tools and a humid, basement shop to call home. While the wood I use seems to be dry, I haven't checked it for moisture content and honestly, wouldn't even know how to. I'm just butting the boards together (no biscuits) and clamping them, then screwing them down underneath.

Also -- I finish the tops with water-based poly (Minwax Polycrilic), would something else be a better option.....?

So let's hear it, and be brutally honest -- I need whatever help you can give me and I need it fast. Replies will be greatly appreciated, thanks for your time.....

http://i1094.photobucket.com/albums/...o/IMG_1629.jpg

http://i1094.photobucket.com/albums/...o/IMG_1347.jpg

http://i1094.photobucket.com/albums/...o/IMG_1344.jpg

http://i1094.photobucket.com/albums/...o/IMG_0187.jpg

[tombuhl]

Your salvaged wood is solid and will expand and contract perpendicular to the grain direction, with amazing force. Plywood, being a composite with alternating grain directions is stable and will not expand and contract.

So not surprising that you have a problem. What is function of the tables? Would a expansion gap be tolerable?

Side note: Lengthwise you don't usually have to be concerned with wood movement. Looks like you have a facing edge along front and back. That in itself is not a major part of your problem. Looks like you do not have facing on the end. Good for you (if that is the case). That is a very common design "error."

I believe you need to ditch the plywood base. At least in direct and secure connection to top pieces.

Background: typically a board would be secured with screws (no glue) in one part. Perhaps front edge, or center. Then the other screw(s) is placed in a slotted (or loose) hole so that the wood can expand and contract, but is secured at the one location.

Do the boards need to be that short? Was that a design choice? My brain isn't coming up with a structure that would be suitable, given the short lengths.

One approach for starters is to make the boards move as one. That is, edge glue them together. Biscuits or dowels can help alignment, but are not really necessary. Once you have this wide board (made from many), you could screw (and even glue the very beginning edge but not sure of the necessity) the big board to the ply (other other base). Then drill/shape slotted holes in the ply from underneath into a proper pilot hole in the big board. That allows the top big board to move front to back and back again and again I guess, while holding the top to the ply base.

With the front fixed/locked into position, the top can move towards the back. I do not know the general guidelines for amount of movement to allow. Depends on species, method of milling (flat, quarter and rift sawn), initial condition and conditions experienced in its new home. Would seem that 1/4 inch would give you enough cushion. Screw slots closest to front edge would not need to be as long, but slots at the very back would experience the sum of all the movement and need to be longer. Most folks (I believe) would make the slots the same length, just because it is simpler.

Hope this helps,

Looks like a fun project if you can get the details worked out.

[malawlo]

Your salvaged wood is solid and will expand and contract perpendicular to the grain direction, with amazing force. Plywood, being a composite with alternating grain directions is stable and will not expand and contract.

So not surprising that you have a problem. What is function of the tables? Would a expansion gap be tolerable?

Side note: Lengthwise you don't usually have to be concerned with wood movement. Looks like you have a facing edge along front and back. That in itself is not a major part of your problem. Looks like you do not have facing on the end. Good for you (if that is the case). That is a very common design "error."

I believe you need to ditch the plywood base. At least in direct and secure connection to top pieces.

Background: typically a board would be secured with screws (no glue) in one part. Perhaps front edge, or center. Then the other screw(s) is placed in a slotted (or loose) hole so that the wood can expand and contract, but is secured at the one location.

Do the boards need to be that short? Was that a design choice? My brain isn't coming up with a structure that would be suitable, given the short lengths.

One approach for starters is to make the boards move as one. That is, edge glue them together. Biscuits or dowels can help alignment, but are not really necessary. Once you have this wide board (made from many), you could screw (and even glue the very beginning edge but not sure of the necessity) the big board to the ply (other other base). Then drill/shape slotted holes in the ply from underneath into a proper pilot hole in the big board. That allows the top big board to move front to back and back again and again I guess, while holding the top to the ply base.

With the front fixed/locked into position, the top can move towards the back. I do not know the general guidelines for amount of movement to allow. Depends on species, method of milling (flat, quarter and rift sawn), initial condition and conditions experienced in its new home. Would seem that 1/4 inch would give you enough cushion. Screw slots closest to front edge would not need to be as long, but slots at the very back would experience the sum of all the movement and need to be longer. Most folks (I believe) would make the slots the same length, just because it is simpler.

Hope this helps,

Looks like a fun project if you can get the details worked out.

Tom.....

I chose the smaller boards just because that was what I had on hand -- I took a bunch of scrap off the streets and since I didn't know what I was doing, just decided to cut them down and mount them to plywood. I glue them together at the edges AND glue them to the ply at the same time, thought that was gonna be pretty solid. Having no idea what I was doing..... trouble.

Actually, they're nice and solid for the most part, they just seem to be splitting at the seams here and there. Problem is, I've started making them more and more (people really like them, then more people asked me to make them -- next thing you know, I was making a bunch) and I really need to get it figured out asap.

You said the ends don't need a 'face' board.....? Do you mean the ends where the metal is.....? Because I wrap the entire thing (plywood included) in strips of wood, thought it looked cool (and it hides the ply).

So I dunno..... guess I should give it a shot with no plywood, eh.....? Just wondering why that wouldn't stop the boards from 'shrinking', if that's in fact what's going on. If I don't use the ply base, will that stop the gaps from opening up....? Or will the expansion/contraction occur no matter what....?

Also -- if I can manage to glue up a sinle 'board' in this patchwork style, would it be okay to use some kind of cleat underneath to keep it all together....? That's part of the reason I started using the ply as well, thought it would give the top a good firm 'base', you know....?

Thanks for the help, if you've got some more advice..... it'd be much appreciated.

[areynoldsre]

It's a cool looking project but Tom is right on with his advice. The solid wood is going to move no matter what you do and the plywood isn't. Your just going to get gaps. If you're going to use plywood as a base, just let the solid wood 'float' on it. Do a small number of slotted screw hole through the ply - just enough to keep the two together.

The other question/thought I had was - did you do the metal work for the legs and end caps? If you did could you do a bit of a metal frame under the top to support it rather than the plywood? All the little pieces glued together will be a bit weaker than longer pieces but I wouldn't think that you need too much extra support. Part of me thinks that the plywood base is a bit of an over kill.

Just a thought.

[Beechwood Chip]

So I dunno..... guess I should give it a shot with no plywood, eh.....? Just wondering why that wouldn't stop the boards from 'shrinking', if that's in fact what's going on. If I don't use the ply base, will that stop the gaps from opening up....? Or will the expansion/contraction occur no matter what....?

Here's the deal. The solid wood is going to expand and contract no matter what you do. If you glue the solid wood striups together, edge to edge, then when they shrink the outer strups will move towards the center. So, the whole table gets a little narrower, but there are no gaps between the boards.

Plywood doesn't expand and contract. If you glue the table top to plywood, then when the board shrink the outer boards can't move inwards towards the inner boards, and you get gaps. Instead of the entire table getting narrower without gaps, the entire table stays the same width and you get gaps.

The trick is to support the top while still letting it move. One way to do that is use screws and oversized holes, so the top can slide a little bit. You can use screws with regular holes on the centerline, and screws in slots on the edges.

[duckkisser]

not shure if this will work so please post wether or not this will work as im planing on making a bench similar to this style. what about a tongue and groove system like a wood floor with a cross support of eather metal or wood to support the pieces below? that would allow the wood to expand and contract with each other and still remail flat. malawlo you would need a router or at least a table saw but router would be better and safer.

[Beechwood Chip]

Tongue and groove would work, and there are lots of other ways to keep the boards in line when you glue them. But you still need to allow the tabel top to expand and contract on its supports, otherwise you'll get gaps.

[duckkisser]

so a loose frame outside like a panel? or loose screw holes?

[Beechwood Chip]

yes, either of those will work. I prefer the loose screws holes for a table top, since the cracks around a floating panel can collect dust and crumbs in a horizontal table top.

[duckkisser]

would a floating top support a persons weight thinking of making a bench i would make the wood thick enough but still makes me wonder.

[tombuhl]

Malawlow, I missed the photo where you showed the metal frame at the end. Yes, that is ok, IF the bolt/screw holes allow the wood top to slide as it expands and contracts.

Cleats are a more common understructure than full dimension ply. The same issues apply though, the screw holes need to be slotted or oversized to allow movement. Advantage of the ply to my mind, is to give a bit of support to the short segments. If edge glued with your thick material it (ply support) probably is not all that necessary.

Looks like number of others have commented so I'll leave it with t he above. But if you have any other questions let us know. Maybe you can do a followup with some pix and captions of your version two of this popular table. Best wishes.

[dwacker]

I like the reclaimed tables, they have a real cool look. I dont know what you have for tools but my suggestion is to cut the staves into shop cut veneers over two layers of ply. The bottom ply can just be a frame about 5" wide glued to the top ply. This will add the thickness you want. The veneers will not move like your thick stock.

Don

[Mike M]

How about making the top out of two layers of the scrap boards. As long as the grain all goes in the same direction it will grow and shrink at the same rate. As long as the top and bottom joints are staggered you should end up with a heavy, solid top.