Flatsawn Lumber Is Not So Flat: How To Fix Cupped Wood

Quartersawn lumber stays flat, but flatsawn lumber does not (ironic, I know). Flatsawn lumber cups during the drying process and it even cups after it’s dry if not cared for properly. Wide boards are especially fussy and panel glue-ups can be a giant pain in the tuchus.

I deal with cupped lumber all of the time, and I was reminded of this common problem when a friend of mine was trying to figure out why his wide panel glue-ups had cupped. Whenever I am asked about this, my first question is always, “How did you store your panels after they were assembled and surfaced?” The answer is usually that they laid the panels flat on a table. A quick bit of logic says that a flat panel on a flat table should stay flat, but that isn’t how it works, at least not with solid wood.

Solid wood needs to expand and contract evenly, on both sides, to stay flat. If the panels are placed flat on a table, they can breathe on one side but not on the other. The bottom side will remain as dry or wet as it started, but the top side will shrink or swell depending on the ambient humidity in the room. Usually, this  problem arises when lumber is moved from a non climate-controlled environment (like a garage or barn) into a dry, climate-controlled shop, so the top of the panels will shrink and the lumber will cup up and away from the table as it dries.

This glued up panel couldn't breathe on the bottom since it was flat on a table. The top dried out a touch after processing and the panel cupped.

This glued up panel couldn’t breathe on the bottom since it was flat on a table. The top dried out a touch after processing and the panel cupped.

 

In a perfect world, rough lumber would be stored for months in the exact same, hermetically sealed environment where the processing is going to happen, but since we don’t live in a bubble, that’s not really possible. Even if you store the lumber in your climate-controlled shop and build in your climate-controlled shop, the climate still changes – in small increments from day to day and more dramatically from season to season. And, since you know that these changes will make your wood expand or contract, it is even more imperative to store surfaced lumber and panels properly to make sure your flat work stays flat.

Again, storage is the key, and there are two approaches to keep things flat. The most common way is to store the wood so that it can breathe on all sides. This is done by keeping it stacked flat on sticks or by storing it upright at an angle, perhaps leaning against a wall. The other approach is to not let the wood breathe at all and keep it wrapped or covered in plastic. I commonly use both tactics, leaning panels against the wall for short-term storage, usually during a day of processing and then covering them with a sheet of plastic for longer storage. Note that dramatic changes in flatness can happen in just hours if the conditions are right (or wrong, in this case).

From fresh sawn lumber (in this photo) to finished product, storing wood on sticks is the best practice.

From fresh sawn lumber (in this photo) to finished product, storing wood on sticks is the best practice.

For short term storage (hours to days) standing wood upright is a great choice. Make sure air is able to get to all sides.

For short-term storage (hours to days) standing wood upright is a great choice. Make sure air is able to get to all sides.

Now, let’s say you didn’t follow this advice and your panels developed a cup in them. They were planed and sanded flat and ready to be put into the door frame before you left the shop, but when you returned the next morning they had a noticeable rock. Since everything was already to final thickness, what options do you have? There is no meat left to machine flat and the wood can’t really be bent back into shape… or can it?

No, it can’t really be bent back, but it can be coerced back by doing the reverse of what caused the cup in the first place. The key is understanding the cause of the problem.

First, you need to identify the wet side and the dry side. If you are looking at a cupped panel from the end and it is shaped like a rainbow with the legs down, then the bottom side is the drier side. It is drier, tighter and smaller, and the outside edges are pulling together. The top side is wetter, looser and bigger, and its outside edges are pushing apart. These two forces, one pushing and one pulling, are working together to make a cupped panel.

After you have identified the problem, the solution is to treat the panel to the opposite conditions. This can be done by drying the wet side or wetting the dry side, but since almost all problems in woodworking are from wood that is too wet (at least around here), you should choose to dry the wet side.

I recommend to use a hairdryer for convenience, but on nice sunny days you can put the sun to work for you too. Both work fine, but the sun can fix a lot of panels at a time, quickly and quietly. The sun works great because it focuses all of the drying energy on just one side, and it focuses it on the entire side, not on just one spot like a hairdryer. (Be aware that some woods, like cherry, change color quickly in the sun and may be a better choice for inside drying).

The process is simple. Put the dry side down on a flat surface, one that restricts air movement across the bottom of the wood. The wide board or panel will be sitting like a rainbow, with the two legs down and the center up. Then just proceed to dry the top side, either with the sun or a hair dryer. If you are not in a hurry, you can simply move the wood to a drier environment, like the inside of your house on a cold winter day and let it dry out on the top side overnight. Any way to dry the top side while the bottom remains as it is should do the trick.

Use a hair dryer (like in this photo) or put the panels out in the sun with  the wetter side of the wood up to reverse the cup.

Use a hair dryer (like in this photo) or put the panels out in the sun with the wetter side of the wood up to reverse the cup.

Keep an eye on the panels and check them regularly. With a hair dryer you will probably end up propping it up in a position to blow on the panel and check it every thirty minutes. In the sun, check the progress every hour. If you just move them to a drier environment, check them once or twice a day. Even with regular checks it is not uncommon to go too far and overcorrect. If you let the wood bake too long on one side and it starts to cup the other way, just flip it and dry the other side. Eventually, you will get a feel for how long it takes and end up with a flat panel, and now a drier panel (both good things).

Follow these guidelines for flat wood:

  1. Build with quartersawn lumber. Quartersawn wood doesn’t cup.
  2. Store lumber in the rough. If the lumber goes wonky you will still have extra thickness to machine flat.
  3. Store lumber and build in an environment similar to where the piece will end up.
  4. Quickly build with lumber after it is machined. Don’t give it a chance to move on you.
  5. If you can’t build immediately, store wide boards and panel glue-ups properly. Give them air on all sides or no air at all.
  6. Make sure assembled furniture stays flat by finishing both sides of solid wood panels the same. This is especially important on wide glue-ups like tabletops.

Remember, wood moves and changes size all of the time. It is your job as a woodworker to understand how these changes happen, how to prepare for them and how to control them. And, luckily, in the case of wide wood, you may even have the chance to correct them.

Natural Playground for Preschoolers

The final touches have been put on the natural playground structure for Immanuel Lutheran preschoolers and they have already been putting it through its paces.

The deck, climbing wall and steps are made from white oak, the posts are eastern red cedar, and all of the twisty branches are osage orange. The three species of wood were chosen for their ability to weather the elements, while the white oak and osage orange have the added benefit of being exceptionally strong.

The climbing wall is made from white oak with cedar chunks.

The climbing wall is made from white oak with cedar chunks.

In the back is a swinging piece of osage orange suspended from a u-shaped branch.

In the back is a swinging piece of osage orange suspended from a u-shaped branch.

The slide has white oak for the structure and an outdoor plastic for the top.

The slide has white oak for the structure and an outdoor plastic for the top.

The two steps are made from large pieces of solid white oak.

The two steps are made from large pieces of solid white oak.

Wind chimes hang from this corner.

Wind chimes hang from this corner.

Thanks to the staff at Immanuel for being great hosts. They always greeted me with a smile and sometimes, even with cookies.

Round Cut Tops (Almost) Always Split

All wood splits, some more than others, but it all splits. It even splits when paid professionals try to make it not split. This is good news for those of you wanting to snuggle by a warm fire, but not such good news for connoisseurs of  split-free wood. And, it is especially bad news for anyone wanting to make a round table top out of a slice of tree.

It seems easy enough to just slice a cookie, or coin, or round, or whatever you want to call it, off the end of a log and use it as a table top, but it rarely works out. The problem (especially when swimming) is shrinkage, and in the wood realm it’s uneven and unproportional shrinkage.

I talk to customers a lot about this uncomfortable subject, and even though it isn’t pleasant, someone has to do it. As woodworkers, it is critical to understand how wood shrinks (read an earlier post about shrinkage by clicking here), and as customers it is important to understand the limitations of wood.

Drying quartersawn lumber is easy, relatively speaking, and almost always produces wood that doesn’t split. Drying flatsawn lumber without splits is more difficult, but if the ends are sealed and the lumber is dried at a slow, consistent pace, it can be done reliably. Drying round cuts from the end of a log, however, is a totally different story, and almost always results in split wood, and not just a small split, but usually large, unsightly, unrepairable and often devastating splits. So much so, that I tell customers I will cut rounds for them only if they take the milled pieces directly from my sawmill as soon as they are cut. That way I can prove that I had nothing to do with them falling apart – they do that all on their own.

It all goes back to the way wood shrinks and the way it does so unevenly. As wood dries, it shrinks twice as much with the rings as it does from the center. When viewing a log at the end (not a round cut off the end of a log but an actual log), this produces cracks that resemble spokes in a wheel. Sometimes there are larger cracks mixed in with the smaller ones, but they are always in multiples. The end wood wants to split, but since it is attached to a log which is holding it in place, the end cracks with many smaller splits to even out the pressure.

When still attached to the log there will be many smaller splits.

When still attached to the log there will be many smaller splits.

If that piece is cut from the end of a log all bets are off. There is no log holding things together, so the end result is usually one large split that relieves all of the pressure at once. With wood that is known to split easily, like oak, the round cuts will not only have large splits, but will often just break in two or more pieces.

Here are some examples of dried wood cookies. All of these were cut from the end of the log when the wood was wet and then air dried slowly in the shop. They are all about 18″ in diameter and 2″ thick.

Walnut-Cracked!

Walnut-Cracked!

Pine-Split!

Pine-Split!

Maple-Busted!

Maple-Busted!

What's this! No crack? Every now and then they don't crack. This walnut is half the diameter of the others.

What’s this! No crack? Every now and then they don’t crack. This walnut is half the diameter of the others.

So, now you know that the cool round table that you were planning to build is probably going to split if you do nothing about it, but can you do something about it? Well, maybe, kinda, sorta.

One way I know to work, from personal experience and from other local sawyers, is to cut the rounds at an angle. This will reduce or completely eliminate the cracks because the stress is going more up and down than in a circle, but it will turn your round table top into an ellipse. And, while a piece that stays together is probably better than a piece that falls apart, an ellipse is not always acceptable. I personally expect to see a round piece of wood when you tell me it was cut from the end of a round log, and find the ellipse shape a bit unnatural.

This slice (from roxyheartvintage.com) was cut on an angle so it wouldn't crack. The angle cut is evident on the outside edge and by the fact that the "round" is not round. Logs that start out round, will end up as an ellipse angled slice.

This slice (from roxyheartvintage.com) was cut on an angle so it wouldn’t crack. The angle cut is evident on the outside edge and by the fact that the “round” is not round. Logs that start out round, will end up as an ellipse angled slice.

Another alternative is to remove the pith (center of the log). Removing the pith can stop the devastating splits, but it obviously puts a hole in the piece of wood, and it is still a gamble because it is hard to tell from tree to tree how much pith needs to be removed to stop the splits from happening. A larger hole is better, but at some point the missing wood in the center will demand creativity, and perhaps more wood or glass to make a complete top.

The last and most widely used solution is to use a wood stabilizer like Pentacryl or PEG (polyethylene glycol). Originally developed to stabilize wood from archeological sites, Pentacryl works well to stabilize all kinds of wood from punky wood to crotches and will help with wood cookies. It works by replacing the water in the wood and keeping the cells at their original size, even when dry. Know that while Pentacryl will reduce and often eliminate cracks, wood cookies are by far the most difficult to dry and may still crack.

Pentacryl is a good option to keep wood cookies from cracking.

Pentacryl is a good option to keep wood cookies from cracking.

Pentacryl is not perfect. It works well, but it is expensive at $60 per gallon and adds a yellow tint to the finished piece. And, wood cookies which could normally be dried relatively quickly need to be dried extremely slowly. So slow, in fact, that thicker pieces could still take over a year to safely dry.

PEG is applied like Pentacryl, but has drawbacks that make it less than perfect too. Like Pentacryl, it is also expensive and the resulting wood surface may not accept the finish of your choice. It also takes extra time to apply and may require additional equipment to make it work correctly.

The bottom line is that you can make a table out of a round end cut from a log, but you’ve got to be prepared for failure and/or be prepared to throw plenty of time and money at the problem. I still steer away from cutting wood cookies and do my best to direct customers away from them as well. And, if I do end up cutting wood cookies for a customer, I literally cut and run.

 

Siberian Elm is not Chinese Elm

It happens all the time, people call me and tell me about trees that are so big that they can’t get their arms around them and, unrelated but still slightly humorous, they tell me about their Chinese Elms. For the record, I have seen many trees that you can’t get your arms around (which doesn’t make that nutty measuring system any less ambiguous), but the Chinese Elms that I hear about have never, ever, ever, not once, actually been Chinese Elms – they have always been Siberian Elms.

I have gotten used to it now. If someone says they have a Chinese Elm, I just assume that it is a Siberian Elm. It isn’t that big of a deal, except that there really is a Chinese Elm and I often wonder if the next call about a Chinese Elm will, in fact, yield a Chinese Elm. I like both American Elm and Siberian Elm and assume that I would like Chinese Elm as well, and I don’t want to miss my chance to mill one if it ever comes along.

The elm issue moved to the forefront after a recent trip to the Missouri Botanical Gardens when I ran across an actual Chinese Elm conveniently marked with a little official sign. I have never seen one in real life, at least that I know of, and this was a great opportunity for a close-up view of a confirmed Chinese elm tree. I took that opportunity to snap some photos for comparison. Nonetheless, just assume that your Chinese elm is actually a Siberian elm, unless it looks a lot like the photos below.

Chinese elm is more oriental in shape. In this case, the tree has a short trunk with a lot of taper and crooked smaller branches.

Chinese elm is more oriental in shape. In this case, the tree has a short trunk with a lot of taper and crooked smaller branches.

The bark on a Chinese elm looks nothing like other elms and unlike any domestic species. It is flat and scaly with multiple colors from silver gray to rusty orange.

The bark on a Chinese elm looks nothing like other elms and unlike any domestic species. It is flat and scaly with multiple colors from silver gray to rusty orange.

The bark has the same scaly texture throughout the lower portion of the tree.

The bark has the same scaly texture throughout the lower portion of the tree.

Thanks to the Missouri Botanical Gardens for clearly marking this Chinese elm.

Thanks to the Missouri Botanical Gardens for clearly marking this Chinese elm.

 

Using an Adze to Make a Hand-Hewn Finish on Wood

I was working in the shop last week doing some adze work on a couple of hollow beams and remembered back to my frustrating first days using an adze. I recalled a couple of tips that I wanted to share in this latest Quick Tip video:

For an extended description of the hollow beam making process and more adze fun click here to read  How to Turn New Wood Into Antique Beams.

Easy Sign, Difficult Customer

At the end of May, my daughter and pickiest customer Mira, turned eight and planned to have a mermaid swimming party at Grandma’s house. Grandma has a swimming pool and we knew that she would be willing to heat it for an early-season swim, so it was an easy choice. The difficult part was finding mermaid themed items that met with Mira’s approval and weren’t for little girls (Ariel, A.K.A. The Little Mermaid, is not cool when you are eight).

While searching for party decorations, my wife, Chris, came across a little sign that she thought was cute and asked if I could make one for the party. It said, “Mermaid Lagoon” and it was pretty simple, and since it was right up my alley, being made of wood and all, I said “Yes”.

I dug out some cypress that had lots of knots and a good rustic look and started cutting. I wanted the sign to be bigger (who wouldn’t) than the one in the photo, so I cut the boards about two feet long to make the height. I trimmed the ends at random lengths, some at a slight angle, until I had enough to make the sign about three feet wide. It went quick, especially since I had no formal plan. If a board didn’t look right, I just trimmed it more or flipped it around or just grabbed another board. I love that kind of woodworking; no tape measure, no pencil, no worries.

After I nailed the boards together, I painted them with a wash of blue/green paint. I already had some bright blue paint in the shop and added green Transtint to get the color right. I thinned the paint down with water and brushed it on as quick as possible. While it was still wet, I wiped it off like it was a stain to show the wood below.

Once the paint was dry, I did the lettering, which I laid out and printed from the computer. I cut out the words with an X-acto knife and used a light coat of Super 77 spray adhesive to hold it in place while I painted it. A light mist of white spray paint did the trick, making the words legible but not too pronounced.

After the sign panel was assembled and painted, I needed to come up with a post. My first attempt was a weathered piece of oak 2″x4″. It had the right look and feel since it was old and gray, but I thought that Mira might not approve since it just looked like an old board, so I continued to search for a better way to display it.

A quick walk to the other end of the shop revealed a piece of driftwood that was perfect. It was the right size and height, and with just a little block added to the bottom, it sat up beautifully crooked. Plus, I wouldn’t have to pound it in the concrete-like ground since it would stand up on its own. That piece of white oak driftwood couldn’t have worked out better.

All that was left to do was screw the sign to the post, which took a grand total of 30 seconds. If it was going to be for long-term use I would have been more serious about it, but two 3″ deck screws worked just fine and quickly put this job to bed.

The perfect piece of white oak driftwood and cypress lumber teamed up to make this sign for my daughter Mira's swimming party.

The perfect piece of white oak driftwood and cypress lumber teamed up to make this sign for my daughter Mira’s swimming party.

I was pleased as punch. I showed it to everyone within shouting distance of the shop and couldn’t wait to bring it home and show the girls. They were pleasantly surprised at how it turned out and I was pleasantly surprised that Mira quickly approved it (I was still a bit worried that my unauthorized driftwood addition might have been a bit aggressive in her mind (even though it was perfect)). We capped the whole thing off with hot glue, a few seashells and then perfect weather for a “Mermaid Lagoon” swimming party.

The sign now resides in my shop, where it generates many inquiries, but as of today, no more official orders for driftwood mermaid signs.

 

How to Make Realistic Worm Holes in Wood

If you want to make something look older, just add some worm holes. Sounds simple enough, but there is a major difference between just poking holes in the wood and making the holes look authentic. Now that the all natural, rustic wood look is in style, even new, or at least not very old wood often benefits from more character, and I am here to show you how to really do it.

First off, let me assure you that I have a lot of experience in this field. I often build pieces that need to be “wormed up” in some regard, either to make new wood look old or to make old wood look even older. Especially on projects like beams and mantels, worm holes help add a lot of age to a piece.

Much of the wood that I use already has worm holes in it because I let the logs sit awhile outside before I mill them into lumber (sometimes even on purpose), so I have a head start, but there will still often be spots without bug holes where the wood needs a little extra love, like in the following video:

To get things started, it helps to first look at truly worm-eaten wood. There are consistencies even in what looks to be very inconsistent patterns. Here are a few principles that hold up in most wormy wood:

1.) Hole sizes vary: Even similar-sized holes are not the same. Your method for creating holes should easily produce random results.

2.) Worms tend to focus their efforts: Holes will usually have an area of focus, with more holes in the center of an infected area fading out to fewer holes.

3.) Not all holes are perpendicular to the surface:  While most holes are just that – holes, many are oblong and some are more like trails.

4.) The bugs that make the worm holes often enter around defects in the wood: Soft or punky wood, spalted wood, cracks, and sapwood are all areas that will focus worm activity. Good, strong, solid heartwood is the last area to be bug infested.

5.) Small holes outnumber the big ones: Older wood that has been attacked by multiple insects will have lots of tiny holes (1/16′ diameter), some medium-sized holes (1/8″ diameter), and just a few big holes (up to 1/4″ diameter).

Here are some photos of authentic worm holes. If you can copy any these patterns you will be off to a good start.

This section of pine shows a nice array of hole sizes from large to small. Notice how the long holes follow the grain.

This section of pine shows a nice array of hole sizes from large to small. Notice how the long holes follow the grain.

This section of hickory has holes that make short lines. They are also very dark and almost seem stained.

This section of hickory has holes that make short lines. They are also very dark and almost seem stained.

This section of maple shows a mix of holes and short trails.

This section of maple shows a mix of holes and short trails.

The holes in this white oak are larger and have stains around them where the wood has started to decay.

The holes in this white oak are larger and have stains around them where the wood has started to decay.

 

Here are some of my tricks for achieving realistic results:

  1. A scratch awl, normally used for marking projects, is the perfect tool for making small to medium-sized holes, after being sharpened to a long, tapered point.

    A scratch awl, normally used for marking projects, is the perfect tool for making small to medium-sized holes, after being sharpened to a long, tapered point.

    Small holes. You’ll be tempted to use a drill bit for the smallest holes, but it isn’t the best choice. Tiny drill bits break easy and the size is too consistent. Plus, they pull out wood fibers that make the edge of the holes fuzzy. Instead use a nail or a scratch awl sharpened to a long fine point. A scratch awl is the best choice because it can be used without a hammer and produces speedy results. The long point will make different sized holes depending on how deep it is pushed into the wood. Push the scratch awl in the wood at different angles and different depths.

  2. Large holes. Use a twist drill bit for the larger holes. Be sure to drill deep enough that you can’t see the bottom of the holes and to vary the drill angle. Put the bigger holes in the softer wood. Sapwood, punky wood and areas around defects are a good place to start. Mix up the sizes in the 1/8-3/16″ range for a more natural look.
  3. Oblong holes. Some of the larger holes tend look like small jelly beans. Drill in fairly deep and then use the side of the drill bit to cut a short trail. The result is similar to two holes drilled right next to each other.
  4. Trails. Trails are often left just under the bark in bug infested logs and sometimes inside the log. Use a twist drill bit about 1/8-3/16″ in diameter and drag the bit in different lengths of crooked lines. Be sure to make some of the areas have more depth. Think of the trail as a river with shallow areas and deeper pools. Trails can have one, both or none of the ends finishing in a hole. Mix it up and have a few ends disappear into holes made with the same drill bit.

One of the most important things to remember when making worm holes or using any other techniques to age wood is to really go for it. You won’t destroy a piece of furniture by adding a few more holes or dents, and you can only miss by doing too little to the surface.

I often see furniture, especially mass-produced furniture, that will have some sort of distressing that looks like it was just phoned in. Usually, someone quickly takes a chain to the surface or pokes a few holes and calls it a day. Don’t do that. Pay attention to Mother Nature’s work and try to duplicate it. And, most importantly, have fun doing it.

 

 

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