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Well, I have finally started crafting the trundle bed I wrote about in the Trundle Bed Design series. Many family and unrelated projects got in the way of this project for some time. But no more excuses. The show must go on.

Headboard And Footboard Panel Details I decided to begin with building the panels for the headboard and footboard. The headboard requires a panel 22 57/64” tall by 40 1/2” wide and two panels 8 3/4” tall by 40 1/2” wide. The footboard requires two panels 8 3/4” tall by 40 1/2” wide.

The final thickness of the panels is 5/8”, but I prepare my stock for 3/4” and bring it to final thickness on the drum sander after glue up has been completed. This will allow me to take out any slight mismatches in the glue up joints which are unavoidable. In addition the drum sander can bring the finish panel to precisely 5/8” with 220 grit paper. That way, after shaping the edges, I can immediately apply several coats of finish, which I always do before affixing panels in their frames (The headboard and footboard are essentially a frame and panel construction.). Subsequent shrinkage of the panels will not reveal unsightly voids of finish.

Edges Are Always Prepared With A Hand Plane Before Glue Up Preparing stock for glue up requires the standard jointer, planner, jointer and table saw sequence to face and edge the boards. But the final step for me is always preparing the edges by hand with a hand plane. This accomplishes several things. First it removes any oils on the edge that exist from handling or are naturally secreted by the wood. This is especially important if the time from wood preparation to glue up is hours or days. Second the edge is given a glass smooth surface void of machine marks and scratches. Third I get a better edge, i.e. perfectly straight and square.

All these add up to a better looking and stronger glue joint. One of the tests I use for a properly finished edge is that I can get  a continuous, very thin shaving, of equal width all the way to the end, and the length of the shaving is the full length of the board. Notice the shaving above right. A Lie-Nielsen smooth plane is the one I use for the final cuts. But I will start with a jointer plane if the edge is close to straight, or a block plane if I have to cut short local areas to correct for a bow for example.

Headboard Panel Glue Up When I have finished preparing the edges with a hand plane I immediately glue up. If I have a number of panels to do, as in this case where I have five panels, I’ll prepare all the stock on the power tools. But only the edges for one panel at a time is prepared on the hand plane so that the time from edge preparation to glue up is short, keeping the edges from getting soiled or dinged.

I have tested glued edge joints numerous times and always found that a properly prepared and executed  joint will always be stronger than the wood itself. How long a joint will last I will never know because I won’t live long enough to see its failure. But the accelerated life tests manufacturers perform indicate these joints will still be going strong hundreds of years from now (barring abuse such as prolonged exposure to water, high heat or direct sunlight).

One other idiosyncrasy I have is that I always leave joints clamped overnight. True, the manufacture says you can work the wood after only one hour of clamping provided there are no undue stresses placed on the joint. But I am not sure what an undue stress is. This is an analog world we live in. Stresses don’t magically become undue at 10 lbs of force but not 9.9 lbs. So I am conservative but feel much more secure this way.

The Performax Pro 22-44 Is Used To Final Thickness The Panel After curing for an evening the panel is ready for final thicknessing. I do this on my Performax Pro 22-44 drum sander. To gauge when a side has been entirely sanded and flat I mark the panel with red carpenter’s crayon in wide horizontal lines. When the marks are completely gone I have succeeded in flattening the side. See the picture at right. I use 220 grit paper for this final step. I will sand it one more time just before applying finish with 320 grit and an oscillating rotary sander.

I am careful during glue up to put the good side of the panel up, i.e. away from the clamp’s bars. This allows me to clean the entire surface unimpeded by the bars of the the clamps. See picture above left. I clean the other side too, but the bars always obscure some glue. When dried the backside will have little glue hills which I level with a putty knife. Still, there is remaining glue to be removed. So the backside is the one I drum sand first. Then I turn it over, mark the good side and continue drum sanding until I reach final thickness.

On a panel this wide each pass actually requires two passes. As you can see in the picture above right, the panel is wider than my drum sander. The 22-44 in the name implies you can sand a 22” wide panel in one pass, or one as wide as 44” in two passes. One note of caution about drum sanders; you must not let the work piece stop while going through the drum sander. If you do the sander will sand a horizontal valley into your piece deep enough that you may not have enough thickness left to remove it.

Squaring The Panel On My Large Panel Cutter Once the panel is thicknessed I use a hand plane to create a square and straight reference edge. I then use that edge in my large panel cutter to square the panel to finished length. This panel cutter has been a life saver and workhorse for me. If you don’t have one I strongly suggest you make one soon. With it I can cut large panels (wider than a kitchen cabinet end panel) perfectly square every time, and with ease. The panel shown is 24” wide and 40 1/2” long. This panel cutter uses both table saw slots, has a high fence to keep your hands away from the blade and has a block that completely covers the saw blade as the fence passes it.

Inspecting The Panel With Mineral Spirits (Paint Thinner) When the panel is cut to size I wet it down with mineral spirits to inspect for any remaining glue spots. Hopefully there are none. This step also gives you an idea of what the panel will look like when finish is applied.

Of course, this being cherry, it will darken considerably with sunlight and age. Most of the darkening takes place in the first few months of exposure to strong light, but it continues for a long time. In the picture at right the wood came from two piles, one which had not been subjected to light and one which had (it was on top of the drying stack). These pieces will darken to the same color in a few weeks time.

However, you will notice some sapwood in this panel. Purists argue that you should remove all sapwood when crafting fine furniture. I respectfully disagree. I have always felt that nature does a better job of designing wood than we do. I like to expose all “imperfections” in the wood, including dark pitch pockets in cherry, or cats paw markings. I feel they add to the piece. I am sure that the Shakers didn’t throw out pieces with these imperfections, and if its good enough for the Shakers, it’s good enough for me.

A Full Scale Print Out Is Used As A Template One of the really neat features of SketchUp is that you can print drawings to scale. I printed out the headboard to full scale (1:1). It took about 23 sheets of 8 1/2” by 11” paper, though most of them were blank and I put them right back in the paper stack. I taped one side of the swan neck together and then encapsulated it with self sticking clear plastic and made a template, which I then traced on the panel. Only one side is needed for a template because the curves are mirror images and you can flip the template.

The Delta BOSS Is Used To Remove Jig Saw Machine Marks After rough cutting the swan neck curves, I used my Delta BOSS with course paper to sand away the machine marks left by the jig saw. I usually use my band saw to cut shapes like this, but a 1 1/4” re-saw blade was mounted on it and I didn’t want to take the time to change to a smaller blade. The BOSS oscillating sander does a good job, however, in the end I had to finish the job with lots of hand sanding.

This panel is rather large for the BOSS table so I used adjustable roller supports to carry most of the weight while still making it possible to easily manipulate the panel. Note that the circle in the top middle of the panel is not cut out at this point. If I would have cut it out at this point, the shaper, which will be used to shape the edges, would likely destroy the delicate points that are formed by the circle (see the first picture).

Shaping The Edge With A Large Cutter I Am Especially Alert The next task was to shape the edges. During design of the bed I chose to do this on a shaper because I could get a cutter that would form a wider shape than possible on the router. But the cutter has a rather large 5 1/2” outer diameter. Plus the shape of the swan neck is such that I had to expose most of the cutter to be able to manipulate the panel during shaping. This makes for a somewhat risky and dangerous cut. In situations like this I am always super alert, especially during the start of a cut when the shaper can grab the piece and throw it, or throw sharp pieces at you. Also, I am conscience of where my hands are at all times.

The Circle Is Cut Out With A Jig Saw Finally I cut the circle with the jig saw and repeat the BOSS and hand sanding process. When cutting pieces like this where the panel has to hang over the edge of the table, I make the cut in sections, and support the cut-off by clamping it to the panel. That way it will not unexpectedly fall an split a piece out ruining the panel. These little extra steps can save a lot of work and material and pay for themselves many times over.

The Completed Panel Ready For Finish When the panel is completed I wet it down with mineral spirits again. This time I am looking for scratches or dings. This sometimes happens due to the hard surface of the shaper and BOSS tables. If I find a mark I remove it now. If I were to skip this step the imperfection would surely show up after finish is applied and would be much more difficult to repair at that point.

This concludes Part 1 of Trundle Bed Crafting. In Part 2 I will make the swan neck frames the will encapsulate the panel. Stay tuned.

I have written a number of blog posts dealing with techniques for handling the seasonal change of wood movement and I am sure to write some more in the future. If you have crafted much in the way of furniture, or other pieces constructed from rough wood, you know you have to take wood movement into account in design. Failing to do so will ensure cracks and structural failure. If you do not believe this let me point you to two very good articles outlining the problems and solutions. First, an article that appeared in American Woodworker, 1993 issue number 34. The title is Coping With Wood Movement – How to Build Furniture That Won’t Crack or Split, pages 38 – 43 and written by Jim Cummins. If you don’t have this issue you can find it on the internet by clicking here.

The second article is titled The Shrinking and Swelling of Wood and Its Effect on Furniture by Carl A. Eckelman. I will make this and other references available via Adobe PDF download at the end of this blog. Both of these articles outline specific construction situations, the effects of moisture and resulting wood movement on them, and techniques to avoid the problems that can arise. In both articles the author points out the importance of knowing how much movement to expect and that is the focus of this post.

Wood Movement – The Basics

SEM View Of Poplar - Photo Courtesy Of N.C. Brown Center, SUNY Let’s start with a short explanation of why wood moves. (For a comprehensive coverage of this topic I have listed a number of articles and books at the end of this post.) When wood is alive and green it is made up of soda straw like vessels that tend to run end to end along the length of the tree. These vessels are made up of thin walls consisting of specialized cells. (See the scanning electron microscope photo of Poplar at left.) Both the vessels themselves and the cells that form their walls contain water. When the tree is cut and sawn the vessels begin to lose water and continue to do so until all the water is out of the vessels. At that point the cells that make up the walls still contain moisture. This point is called the Fiber Saturation Point or FSP. It is the point where the tree has given up all its “free water” but the cells are still saturated with “bound water”. This point is very similar in most trees and represents a point at which the tree (lumber at this point) still has a moisture content of approximately 30%. (Moisture content is the ratio of water weight contained in the specimen to its oven dry weight, i.e. no water weight. Many trees, when live, have moisture contents greater than 100% which means that water accounts for more the half its live weight.)

The drying process from green moisture content to FSP, while making the lumber less dense or heavy, does not cause any shrinkage and in fact the lumber is still in its weakest state when it reaches FSP. As the tree (lumber) continues to dry from FSP to 0% (called oven dry) it gives up bound water from the cells, shrinks and becomes stronger. The shrinkage is quite linear from FSP to oven dry and the total shrinkage, expressed as a percentage, can be measured in three dimensions: radially, tangentially and longitudinally. Longitudinal shrinkage, which occurs along the length of the lumber in the direction of the grain, is very minimal and is generally neglected.

Flatsawn (Plain Sawn) Versus QuartersawnTangential shrinkage occurs along a line tangential to the tree’s growth rings and radial shrinkage occurs along a radial from the center of the tree. These two factors are called tangential shrinkage factor (expressed in percent) and radial shrinkage factor and can be related to two common types of lumber: flatsawn and quartersawn respectively. Tangential shrinkage is usually about twice as large as radial shrinkage but they each vary widely from species to species. In real life no lumber is cut exactly quartersawn or exactly flatsawn (also called plain sawn). As a craftsman you have to make a judgment call. If in doubt you might want to consider treating your lumber as flatsawn because that would be worse case.

Map Of Regional EMCs For JanuaryOK, so we know that wood shrinks as it loses water from FSP to oven dry. But the reverse is also true; it expands as it takes on moisture from oven dry to FSP. So what makes wood give up and take on moisture? Its environment. Relative humidity and temperature, and both change throughout the year, usually from dry air in the winter to moist air in the summer. If lumber sits long enough in a given environment it will reach equilibrium with that environment. Suppose for instance that the average temperature and relative humidity have been 80 degrees Fahrenheit and 70% relative humidity for the past two months. It is likely that lumber stored in this environment will come to equilibrium at a moisture content of 12.9%. Clearly higher than one would like if one intended to build a piece that would reside in Arizona. This is why we bring lumber into our shop and let it sit for a few weeks; to let it reach equilibrium.

Map Of Regional EMCs For JulyMost homes do not have humidity controlled environments and are subject to seasonal moisture changes. There have been a number of studies that have measured the outdoor monthly averages over the course of many years. Through the use of computer models, these studies produced maps and tables of indoor seasonal ranges by region of the country. The Department of Wood & Paper Science at North Carolina State University produced such maps in 2003 which you will find by clicking here. These values are called Equilibrium Moisture Content or EMC and represent the moisture environment a piece of furniture would be exposed to, on average, for each month and by region.

Wood Expansion Calculator

An Opening Centric Analysis Of Cherry In The Massachusetts Interior This brings me to the real topic of this post – a SketchUp Plugin tool called Wood Expansion Calculator. I created Wood Expansion Calculator to estimate just how much expansion and shrinkage you might expect in a given structural situation. I developed this tool because I have for years used a stand alone application called Wood Movement Master by Kite Hill Software which does precisely this. You have probably read some of my articles where I used this tool. Unfortunately, it is no longer available or supported by Kite Hill Software or its developer. I decided to pick up the gauntlet and provide the same capability in a SketchUp tool. So here it is: Wood Expansion Calculator ZIP File.

One note of caution. In my professional life (I am now retired) I was an electrical engineer and engineering executive. I started my career when CAD tools were nonexistent and you had to figure things out with paper, pencil and a slide rule. The advantage of this was that you developed a close feel for what you were designing. You knew the expected behavior intimately. Years later, when I was an engineering manager and CAD tools were ubiquitous, it drove me nuts to see a young engineer model a circuit, run the tool and take the results as Gospel. He/she had no feel for, or personal intimacy of the expected results. Don’t use this tool that way. It is meant to give you a quick, efficient, and yes accurate result so long as the input and assumptions are correct. If, for example, the temperature is 100 degrees Fahrenheit today at 90 percent relative humidity, and expected to be 30 degrees Fahrenheit and 10% relative humidity tomorrow, don’t expect wood stored in this environment to respond to that change no matter what this tool might indicate. Moisture takes time to enter or leave a specimen; that’s what equilibrium accounts for. So use judgment as well as the tool.

The tool itself is quite simple to use, and has Help notes for each input. To install the tool use WinZip to extract the one Ruby file and one folder to the SketchUp Plugins folder on your system. When you open SketchUp you can access the tool via Tools/Wood Expansion Calculator or go to View/Toolbars and check Calculators for a toolbar and icon (a tree). What you need to know to use this tools is the stocks current moisture content (best to use a moisture meter to measure this), the region of the country where you expect the final furniture piece to reside, the wood species, the stock type (flatsawn or quartersawn) and the construction situation you want to analyze (board centric, opening centric or breadboard end).

A Printer Friendly Results Of An Analysis If you don’t know the stocks current moisture content you can use a Relative Humidity and Temperature mode to calculate it. But be careful. Consistent with two paragraphs ago be sure to use average temperature and average relative humidity of the environment the wood has resided in for a period of time long enough to reach equilibrium. Do not use seasonal or daily maximums. The wood’s moisture content will not respond to fast or temporary changes.

One other note; board centric, opening centric and breadboard end are not a specific construction method but a representative method. For example, opening centric includes drawer fronts that fit flush in an opening, but could also mean a panel that is framed to make a door. Breadboard end could represent any cross grain situation such as a mortise and tenon. Don’t let the labels limit your use of the tool. Understand what is being analyzed.

This tool currently works only with Imperial or US measurements.

For example 3′ 7 1/64" is a valid input. More precisely, the following are the only valid inputs:
i n/d"
f’ i"
f’ n/d"
f’ i n/d"
where i, n, d, and f must be non-zero integers who’s leading
digit also is not a zero, e.g. 0123 is invalid.

In the future I will expand it to accept metric measurements. The region table is the contiguous US only. In the future I hope to get data for other regions of the world. But you can still use this data by selecting regions that you know are close to environmental conditions in your area. Also, in the future are plans to let the user build their own environmental tables or to add their regions to the existing table. Lastly, I plan to add persistence to the tool so that it remembers the last set of conditions analyzed and uses them as the starting point when the tool opens.

Please report all bugs directly to me, and include the conditions that resulted in the bug. Thank you in advance, and I hope this tool serves you as much as Wood Movement Master has served me in the past.

Related Reading

Centennial edition of the Wood handbook : Wood as an Engineering Material. This is an excellent reference book. You can download individual chapters in PDF format. Chapter 04: Moisture Relations and Physical Properties of Wood is particularly pertinent to this blog post.

Understanding Wood – A craftsman’s Guide To Wood Technology by R. Bruce Hoadley is a book that ought to be on the bookshelf of any serious woodworker. Chapter 6: Water & Wood is particularly appropriate to this subject, but the entire book is directed at the woodworker.

The Shrinking and Swelling of Wood and Its Effect on Furniture by Carl A. Eckelman was mentioned at the beginning of this post. It is an excellent article on designing for wood movement.

Download Wood Expansion Calculator Here

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