Don’t Screw (up) Your Wood Top
Recently, I got a question from a customer regarding a crack forming in his solid wood countertop. He built the top out of flat sawn white oak lumber and he wanted to figure out what caused the crack and hopefully, how he could repair it. Luckily, the repair is simple (just some glue and clamps), but he really needed to address the cause of the problem or the countertop would most likely crack again.
This countertop split in the back corner because it was screwed firmly in place and couldn’t move.
This view from inside the cabinet shows how the top was attached with no room for movement.
When he sent me photos of the crack, he also sent me photos of the how he attached it to the cabinets, which was very helpful. The vintage metal cabinets have a bracket in each corner with a hole just large enough for a screw, but not large enough to allow for any movement in the top. In this case, the wood was stuck in place and had no choice but to split when it shrunk in width.
I recommended to simply make the holes in the metal bracket bigger and to add a washer or use a large-headed screw to allow the top to move side to side while still being held down. The secret is to tighten the screws just enough to hold the top in place, but loose enough to allow it to move if the wood starts to pull.
This particular solution was pretty simple, but only because I have seen it many times before, and I knew what caused it. Without understanding how wood moves, the diagnosis wouldn’t be so apparent. Even though most people don’t worry about wood movement as much as I do, I always try to get them to understand the most basic premise, which is that wood moves more in width than it does in length, and you need to allow for that movement.
In woodworking in general, this disparity in movement is referred to as a “cross-grain situation”, when two pieces of wood come together with grain perpendicular to each other, then they want to pull in opposite directions. It happens all of the time in furniture construction, and it must be addressed to avoid catastrophic failures. In the example above, the setup was the same as a cross grain situation because the metal cabinet will not change in any dimension, while the wood moves in width.
When attaching wood tops of any kind, whether it be a wood countertop to a cabinet or a table top to a table base, you need to allow the top to move or it can split. The good news is that there is more than one way to attach a top and still make allowances for this movement.
The first and most common way, as mentioned earlier, is to make an oversized or elongated hole and to make up any differences with a washer or large-headed screw. Assume that any problems will be caused by excessive shrinkage and make sure that your holes are big enough and that your screws are placed in the holes so that the top has room to shrink.
It easy to make blocks like this for attaching tops. The screw is firmly in the block, but the lip on the block can slide if the top pulls hard.
Another method, which I like to use on tables, is to make blocks to fit into dados on the insides of the aprons. They don’t take too long to make and can easily be added wherever necessary. The blocks should be made so that tightening up the screws will just pull the top snug, like a perfect fitting tongue and groove joint and placed with a little separation to make sure nothing binds. They work great, and I think they look great too.
When attaching a top with a propensity to move, understand that all of your attachment points don’t have to have play in them. For example, you can firmly attach a countertop to the front of a cabinet as long as you allow the top to move in the back. Or, on table tops, you might choose to firmly attached the top in the middle of the width and allow the outside edges to move. This is perfectly acceptable and keeps the top centered on the base.
The main point to remember through all of this is to allow the wood to move. You can only really cause a problem if you don’t allow it to move. And remember , if you find that it is moving too much for your liking you can always go back and firm things up once you understand the potential problems.
For a more thorough description of wood movement click on these two earlier posts Have Your Heard About Shrinkage? or Why Quartersawn Lumber is so Stable: The 0-1-2 Rule In Action, to read a link on the subject. I think it is probably the most important subject for any woodworker to fully understand.
How To Make A Thick Countertop Out Of Thin Wood
Lately, I have had a run on countertop orders. They have all been walnut (which is the hottest wood around right now), and all 1-1/2″ thick. These jobs could be as simple as gluing up boards 1-1/2″ thick and going home, but I don’t make anything simple.
First, a little background. In case you haven’t read much of my blog, I cut and use as much of my own lumber as I can. I get all of my logs for free and have little jurisdiction over what I get. When I mill the logs I rarely have a specific job in mind. I am cutting lumber and guessing what will sell. I tend to cut 4/4 lumber because it is the quickest to dry and the easiest to sell. It makes up about 75% of my sales, and is my fallback position.
I only cut thicker lumber when I have a really good log that will produce high-quality thick boards or I have an order for it, and then only when I am not in a hurry (thicker lumber takes longer to dry). So, that leaves me with a lot 4/4 lumber that needs to magically grow to 1-1/2″ thick when a countertop comes along. Martin Goebel (a friend and fellow woodworker) would call me an idiot and tell me to cut all of my wood thick, that there is no substitute and anything else I do is just nonsense. I am OK with that, but that isn’t the real world.
In the real world, regular woodworkers (and even irregular ones) are often asked to make some magic happen from time to time. Often, it involves stretching lumber to make a project even possible. And, so it was on my latest countertop, when I was asked by a customer to make a large island top out of their small walnut tree.
In this case, I didn’t have enough lumber available in the logs to cut them thick and still get the coverage I needed. I also needed to get the top installed in just a couple of months and thicker lumber would have made that nearly impossible (without my dream vacuum kiln).
I pulled out a trick that I “invented” years ago when I had a similar situation with lumber that was too thin for the job. In that first attempt, I reassured myself that I could do it because the room it was going in had little light and no one could look at it closely anyway. It so happens that it turned out great and now it is my go-to move (much to Martin’s chagrin).
The concept is simple, but until you see a finished piece you may be as skeptical as I was on my first one. Keep an open mind and be sure to look at the final pictures, and I think you will be a believer.
It all starts with picking out the lumber and laying out the boards to be about 1-1/2″ to 2″ wider than the finished piece on all four sides. For the countertop in the photos, the finished size was 42″ x 96″, so my final glue-up was about 46″ x 100″. After the top is glued up and sanded, it is time to lay it out and trim it to the final size.
The top was glued up with extra wood on all four sides. 1-1/2″ to 2″ is the perfect amount.
A circular saw with a straightedge (3/4″ plywood in this case) is all it takes to trim the top to size.
As you trim the top, keep track of the offcuts and their relationship to the countertop. All of these pieces have to be flipped under the top to make up the extra thickness, and they need to line up with their original position. Start with the end grain pieces because they are the most critical as far as alignment goes. Miter the corners, flip them over and glue them on.
The ends of the top are trimmed to length, the offcut is mitered to width and flipped, so the end grain is bookmatched. This view is of the bottom side.
After gluing the end-grain pieces, do the same thing with the long-grain pieces. The grain alignment is less critical on these pieces, so focus more on the fit of the miters and making sure that the corners look good.
The long edge is trimmed to width. The offcut is mitered to length and the piece is flipped so the outside edges are bookmatched. This view is also of the bottom side.
After the glue is dry on all of the edges, it is time for more sanding. I use a 6″ random orbit sander for this task. Spend enough time sanding to make sure all of the saw marks are gone on the edge. If you are doing a top with a square edge, it is time to do the final overall sanding and finishing.
After the glue is dry, it’s time to sand everything flush. This photo shows how the end grain would look if the edge wasn’t profiled.
The top I did got a profiled edge, which helped hide the glue lines even more. Look at the photos below to see how the endgrain on flatsawn and quartersawn lumber looks.
On this corner, the end grain from the flatsawn boards has opposing arches, but they still blend well.
On this side, the end grain is more vertical and helps hide the glue seam.
After profiling the edge, just a little more sanding finishes up the woodworking portion of this top. Next, it is on to the finish.
The walnut countertop is sanded and ready for finish.
When finishing walnut, I usually put on a coat of walnut stain (yes, walnut stain on walnut). It is a 50/50 blend of Minwax Special Walnut and Minwax Dark Walnut to maintain the dark color, since walnut lightens with age. The stain does a great job of enhancing the rich color without hiding the grain. Waterlox, which is easy to apply and repair, was used as the topcoat.
Now, it’s time to bask! The walnut countertop is finished and the cooktop fits without incident. Whew!
After all is said and done, I think you’ll agree that the top looks great, and appears to be made from thicker lumber. I even ended up with a few extra boards.
What’s Going on at WunderWoods
Everyone always asks what I do. Here's the answer. Click on the photo above for a short video tour and see all of the steps it takes to go from a tree to finished furniture.