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Wood Movement Master Calculations For Expansion/Contraction Of Headboard Panel The Trundle Bed design is complete and with this post so will the Trundle Bed Design series be. The next Trundle Bed post will be Part 1 in the Trundle Bed Crafting series where we will chronicle the build of this bed. But let’s not get ahead of ourselves and complete this post first before strapping on our shop belt. As always I will make plans for this project available to my readers on my Free Plans page.

Since the last post the only design decisions were that of choosing joinery and allowing for material expansion/contraction through seasonal changes. All panels in the bed will ride in a grove 1/2” deep by 1/4” wide. The panels must be sized to allow for seasonal expansion/contraction, and we would like the panels to be centered in the groves. To accomplish this I will use a relatively new product on the market called Space Balls. Space Balls are flexible polymer balls 0.260” in diameter to fit snuggly in a 1/4” grove. By placing a number of these all around a panel which is appropriately sized they assure the panel will always be centered, eliminate panel rattle and allow for smooth expansion/contraction. Space Balls can be purchased from a number of places, including on the internet from McFeely’s.

Expansion/Contraction Is Not An Absolute Constant Across The Panel The trick to using Space Balls and to sizing panels is to know precisely how much a panel will expand/contract over the course of a season. You have seen me make these calculations before using an application called Wood Movement Master from Kite Hill Software Inc. Unfortunately this application is no longer available and supported. So, while I will use it here, you can find similar free calculators via a search of the internet. If you want to do the calculations by hand see Understanding Wood by R. Bruce Hoadley, an excellent reference for almost anything wood.

CutList Plus 2009 Parts List Generated From SketchUp Via Cut List 4.0.7 The first picture left above shows the results of a calculation for the bed’s Headboard Panel. This panel is quite wide, 22 29/32”. The bed will reside on Cape Cod, Massachusetts, so I choose Massachusetts, Coastal as the “Ultimate furniture location” which specifies the seasonal extremes of Equilibrium Moisture Content (EMC). The species is Cherry which defines the shrinkage percentage. The other critical parameter is the type of lumber, flat sawn in this case. Flat sawn lumber expands/contracts about twice as fast as quarter sawn lumber in most hardwoods. In the lower right you can see the results. This panel will undergo a total change in width of 3/8” over the course of a season. If I cut the panel now it will be at its narrowest because this is just past the peak of the dry season in Massachusetts. Space Balls recommends that panels be undersized 3/8” overall. I suspect this is a typical number for the typical cabinet door panel width. I decided to undersize this panel by 1/2” overall, which is how I arrived at the 22 29/32” panel width. This should work quite nicely.

One other subtlety about this panel, it is not the same width across its length; therefore the expansion/contraction will not be the same absolute amount across its length. See the second picture on the right above. Most of the expansion will take place near the center of the top edge where it will place the most force on the Swan Necks. This is a place where the Swan Necks are not physically attached to anything and hence will act as a lever prying the joint at the Headboard Posts apart. This is another reason why it is important to get this calculation right, that is, to minimize that maximum force generated by expansion. It is also why I will use lag bolts and glue on this joint to make it as strong as possible.

Rough Lumber Materials Requirement Per CutList Plus Calculations. While we are on subtleties there is one more to consider. The width of the panel given is good if I cut it right now. If, on the other hand, I get lazy and don’t get around to cutting it until late summer I need to adjust the cutting width for the planned expansion. If I cut it just past the peak summer humidity I may want to cut it 3/8” wider, lest it be too narrow and create an unsightly gap next winter. It is important to keep expansion/contraction in mind throughout the course of a design and crafting of a piece. Wood is still alive even though it is cut and dried.

Finally we can generate a cut list. Thanks to Cut List 4.0.7 Ruby Script (see Cut List 4.0.7 Ruby Script Connects SketchUp & CutList Plus ) we can pass information directly from SketchUp to CutList Plus and generate a Parts List and Material Requirements as shown above left and right. The rough lumber calculations are based 20% waste, which may be optimistic for hardwood calculations. It should be adjusted for the individual work habits. In addition to the rough lumber requirements shown above, two sheets of 3/4” plywood are needed for the platforms.

Now that we have completed the design I will make the SketchUp model file, CutList Plus file and a complete shop drawings package in PDF format available on my Free Plans page. The shop drawings in PDF format are thanks to LayOut, a presentation package that comes with the professional version of SketchUp. Now it is time to go in the shop and build this puppy. I will see you next for Trundle Bed Crafting – Part 1.


The Final Finial Design Is Slimmer & Shorter Well, the last of the design decisions involving the look and functionality of the trundle bed is complete. Two changes were made. The finial has been redesigned and made slimmer and shorter. This gives it a somewhat more delicate look while remaining substantial enough to look at home with the rest of the bed.

The Trundle Has Been Modified To Lower One Side For Sleeping Comfort The second change was in the trundle itself. It originally had two faux drawer fronts, one on each side. The thinking was that if the trundle bed were placed in the middle of the room both sides of the bed would have the pull out drawer look. The problem is that the faux drawer front rises above the mattress and would make the bed feel like a hospital bed, not allowing the person sleeping in it to dangle their legs over the edge. I lowered one side to the height of the head and footboard. This doesn’t completely solve the problem, but it gives the sleeper one side to favor when dangling a leg.

The Swan-Neck's Overall Dimensions It is now time to turn our attention to joinery and shaping. I like to have a strategy for shaping before I go into the shop even though it may change significantly once I start. The most complex pieces to shape are the Swan-Necks, Headboard Panel and Finial, in that order. So I will start with the Swan-Neck. The first and most important thing to remember about the Swan-Neck is that there are two of them and they are mirror images of one another. The shop drawings that I have created show one Swan-Neck, the left one. The drawings are annotated in a number of places to remind the craftsman that there are two, and the second is the mirror image. I don’t know about you, but I have made several pairs of things and discovered during glue-up that they were the same and not mirrored. Be forewarned.

Swan-Neck Cross Section With Dimensions The first thing you notice when looking at the Swan-Neck’s overall dimensions in the picture above left is that the stock is 3 1/4” by 3” – very hefty. Immediately you wonder – “What kind of router bit or shaper cutter can handle this profile and how will one actually move the stock through the cut?”. I decided that it is best to make the Swan-Neck out of two layered pieces, and, after some research of router and shaper bits, use two router bits and one shaper cutter to do the shaping of the stock. The Swan-Neck S shape will be formed using the band saw and various sanders. Before moving on to the next picture notice the mortise cut in the bottom of the Swan-Neck to accept the Headboard Panel. This will be cut with a slot cutter. At the end of this blog I will list all of the router bits and shaper cutters required to shape the Swan-Neck.

Back Layer Of The Swan-Neck Looking at the Swan-Neck cross section picture above right you can more readily see how the two pieces will be shaped. The front, and smaller piece, is only 1” by 2 1/4”. This curve can be shaped with Freud Raised Panel Cutter #UP209 and the companion Rub Collar #RC101. This cut will want to be made in a number of passes, probably by lowering the blade with each pass.

The second piece of this two piece sandwich is 2 1/4” by 3”. I will use two router bits to form it. The first is a rabbet cut 1/4” by 1/4” using a rabbet bit. This will remove most of the material. Then, using a 1/4” cove bit, I can shape the remaining curve.

Front Layer Of The Swan-Neck Take a look at the Swan-Neck back piece pictured above left. You will see that it is cut from a piece of stock positioned such that the grain of the stock runs through the center line of the Swan-Neck S. This stock should be 2 1/4” thick and minimally 8 1/2” wide by 28” long. The longer the length, the better. This will provide the opportunity to slide the template up and down the length of the board to choose the best grain pattern.

Note also the mortise slot for receiving the Head Board Panel. The particular slot cutter I have chosen cuts a slot 1/2” deep. The Headboard and Footboard Panels are designed to have a 1/4” tenon. Hence there will be a 1/4” gap. This gap will be filled with Space Balls, a hard rubber like ball that will give as the panels expand/contract with seasonal changes. More on this in a later blog.

Also notice the annotation that suggests that cutting and shaping the ends of the Swan-Neck may be a hand cut and sanding operation rather than using router or shaper bits. This is to avoid tear out ruining the entire piece. Better safe then sorry.

A similar picture of the Swan-Neck front piece is shown above right. This time I will use a piece of stock 1” thick by minimally 8 1/2” wide by 28” long. Again, the longer the better so that I have a choice of best grain direction. Also, as with the back piece, the ends will likely be shaped by hand to avoid tear out ruining the whole piece.

I promised a list of the shapers and cutters I plan to use to shape the Swan-Neck. These can very well change as I begin working the wood, but at this moment here is the list:

Freud UP209 Raised Panel Cutter
Freud RC101 Rub Collar for UP209
CMT 835.502.11 Rabbeting Bit Set
CMT 837.722.11 1/4” Cove Bit
CMT 822.364.11B 1/4” Wide by 1/2” Deep Slot Cutter
Freud UP207 Raised Panel Cutter for the Headboard and Footboard Panels

 

If you don’t have a shaper you can use similar or equivalent router bits. But they will have large radii which will require slow cutting RPM and they may not cut as cleanly as a shaper cutter.

In the next blog in the Trundle Bed Design series I will cover the shaping of the Headboard and Footboard panels.

Sneak Preview – Possible LayOut Tutorial

A Sample Of A Shop Drawing In LayOut As I mentioned earlier I purchased a SketchUp 7 Pro license and I am using LayOut to generate my shop drawings for this project. When they are completed I will make them available to you from my Free Plans page. I am also thinking of (quite seriously thinking of) creating a tutorial series on how to use LayOut. If there is enough interest I will get to work on it. To see how much interest there is I have a polling question at the top of my blog page. Please vote whether you are interested or not.


Isometric View Of Bed & Trundle The Trundle Bed design is almost complete. The joinery still needs to be added to the SketchUp drawings and I am not happy with the finial design at the top of the headboard. Also, I may dress up the faux drawer fronts a little to make them stand out more. The overall dimensions are 4’ 6 1/8” tall by 6” 11” long by 3’ 10 1/2” wide. The trundle will accommodate a twin platform mattress of 39” wide by 75” long by 8” thick. As it stands now the bed will accommodate  a twin platform mattress or a combination mattress & box spring of 39” wide by 75” long by 12” thick. Because the bed sits over the trundle its platform is necessarily longer, just barely enough to squeeze an X-Long mattress of 39” wide by 80” long by 12” thick, but with no margin for slipping a fitted sheet over it. The design could easily be modified to accommodate a few inches of margin.

Isometric View With The Trundle Pulled Out The trundle rolls out on non-turning casters aligned to make rolling out and in easy. The faux front drawer pulls also help. I debated using knock-down hardware to assemble the trundle instead of glued dovetail joinery. It certainly would make moving this bed easier. But in the end I couldn’t bring myself to abandon hand cut dovetails on a piece of fine furniture for knock-down hardware. The movers will just have to suffer. The overall trundle dimensions are 3’ 7 3/8” wide by 6’ 6 1/2” long by 12 1/4” tall. The faux drawer front is cock beading 1/4” thick with a 1/8” radius bead. The swan-neck cap on the headboard is rather thick, 3 1/4” in cross section. I may need to dress up the drawer front with more substantial and decorative trim to provide balance of attention garnered by the bed and trundle.

The Headboard - Notice The Swan-Neck Profile The shaping of the swan-neck will be done on my shaper using shaper cutters. The profile shown is an estimate of what I desire. In reality I will have to research my inventory, and on-line, to see which cutters I need to approach my desired profile. I have already done this for the shaping of the panels. They will require a Freud UP207 Raised Panel Cutter. Since I don’t have one I will purchase it on-line for about $140 plus tax. Shaper bits are not cheap, but in order to get a larger cut on the raised panel, I need to use shaper cutters rather than router bits. The Freud UP207 is designed for 5/8” panels which is what I have used in this design.

An End View Showing The Headboard & Footboard I am not real happy with the finial design. Though the bed has a substantial look, the finial seems to be too large and not delicate enough. I have changed it numerous times and still have more work to do. it is possible I might eliminate it all together and replace it with a reading light. One of those old style desktop lamps with the thick shade, dark green on the outside and white on the inside, might look good mounted on the pedestal. Alternatively a bedside table style lamp with a decorative shade might also look good. I have to check with the boss.

In the next installment of this series I will show the joinery and explain why I chose the joinery I did. One of the reasons for leaving the joinery to last is so that I can get accurate measurements of various components and then calculate the expected expansion and contraction during the course of a year. This drives the choice of joinery. In addition, leaving the joinery to the end allows for easy changes in design. Once the joinery is added, changes are much more complicated and require more work. Stay tuned.


Trundle Bed Sketch Minus Joinery & Panels After reviewing the styles and design criteria with Willow a few decisions were made. First, she fell in love with the Swan Neck headboard style shown in the third picture in Trundle Bed Design – Part 1. The second decision required a quick budget analysis of the component parts that made up a trundle bed’s height. This was aided by a few SketchUp drawings like the one shown at left. The total height of the bed from floor to the top of the top mattress was 30”. That included two 12” thick mattresses. Thirty inches was too tall because it was 4” above the sill of the window it would reside next to. Reasoning that a trundle is seldom used except as guest overflow, and that futons are often 4” or less, we chose to reduce the allowance for the trundle mattress to 8”. It should be rather easy to find a very comfortable platform, single  mattress, that is 8” thick or less.

This trundle bed SketchUp drawing is incomplete. It has no joinery included, the headboard and footboard have no panels to hide the trundle, and the faux drawer fronts have no trim to form the false drawers. In addition, the shape of the Swan Neck profile is simply a quick selection of geometric shapes, but I haven’t done a search of the shaper bits available to create them, so they are subject to change. This drawing took little time to produce, but it is very helpful in viewing the concepts and determining dimensions. From here I can try a number of design options.

Trundle Sub-Assembly Showing Dovetail Joinery One quick piece of joinery, and joinery decision, is shown at right. In almost all my projects there is a good size helping of dovetail joints. My favorite joint, and one I love to produce by hand. All that is missing from the trundle sub-assembly is the trim that will provide the faux drawer front look. The platform is 3/4” plywood. I almost never use plywood in my projects, but this is an application that screams out for it. Plywood is strong, it is almost warp proof, takes a finish well and it is cheap. In this application it will not be seen, but fits all the criteria. So I reluctantly submit to its use.

X-Ray View Of The Trundle Sub-Assembly - Note Casters & Dovetail Joinery I am an avid SketchUp fan and use it for all if my drawings. You by now have probably seen my beginner and advanced SketchUp tutorials. One of the really helpful features of SketchUp is the one click X-Ray. The picture at left is the very same drawing shown right above but with the X-Ray Icon selected. In this view the casters are clearly visible as are the platform support pieces. This view is not only helpful to see hidden joinery and hardware, but it also aids in the drawing of components when it is necessary to attach a primitive drawing element to an otherwise invisible point. SketchUp also has a companion sectioning tool that helps to make slices though any plane, for example a cross section down the length of the bed if desired.

Trundle Bed Sans Trundle Sub-Assembly Another feature of SketchUp is its ability to define views. A view can be from any angle, distance or several drawing representation (e.g. Isometric or Perspective). This helps when dimensioning a drawing or showing sub-assemblies such as the trundle above. At right is the bed minus the trundle sub-assembly. The number of views that one can create are virtually limitless, even in the free version of SketchUp. Recently I purchased the Professional version which includes SketchUp LayOut, at full featured presentation package. As this project proceeds I will use LayOut to create professional looking shop drawings and describe how this is done in this blog series. So stay tuned.


A Double Bed I Crafted - The Design Adapted From Workbench Magazine, Heirloom Bed, March/April 2001 Willow has been after me to design and build a trundle bed for the Cape House guest bedroom for some time. I am finally ready and I thought it would be a great opportunity to write a series of blog posts chronicling the design and build of this bed. So this is Part 1 in the design phase series. The crafting phase will also bring a number of posts in a series.

I will start with the bed’s requirements. The guest bedroom is a rather small room with a window opposite the entry door. Because of the small room size the bed design is limited to a twin (or single size).

A Simple Elegant Design - The Trudle Would Be Faced With A Faux Double Drawer We get a lot of guests on the Cape, especially grand children, and we need all the bed capacity we can get. So this bed needs to be a trundle. Also the window it will go against is rather low so there cannot be a mattress/spring combination, but rather two platform bed mattresses.

Twin or single bed mattresses come in two sizes: twin size 39” wide x 75” long or X-Long 39” wide x 80” long (same as the length of a queen or king mattress). The size of the room again dictates the normal size of 39” x 75”.

The Headboard Features A Grandfather-Clock-Like Swan-Neck Pediment With One Finial While the length and width of a mattress is standardized, thicknesses are not. However, a twelve inch assumption is plenty of thickness to acquire a comfortable platform mattress. So now I know I need to accommodate two mattresses, each 39” wide by 75” long by 12” thick. These box dimensions representing the mattress size will drive many of the trundle bed’s design decisions.

With the design constraints in hand it is time to consider bed styles. If you are the really creative type you might do this by sitting in front of a blank sheet of paper with pencil in hand and begin sketching. I am not that creative; I need a starting point for my designs. So I run to my desktop and begin a search for “trundle or twin bed” pictures to look at. There are thousands, but the trick is to narrow interesting and general styles to a few.

A Sleigh Bed Headboard & Platform Bed Footboard There are four that interest me that are represented by pictures on this page. In the first picture left above is a double bed I crafted with a design adapted from an article in Workbench Magazine, Heirloom Bed, March/April 2001, page 52. I like this design and one benefit to sticking with it is that the bed shown is already in the Cape House. Another benefit is that drawing it would be a matter of simple modifications to my current drawings. On the other hand, I like to choose projects and designs that are different one from another. But there are pieces of this design that might get incorporated in the final design.

The second picture above right is another simple and elegant design. I like the simple single curve of the headboard top. The double drawers would serve as a nice faux front for the trundle. The footboard could remain the same or raised to the level of the mattress and allow for slats that match the headboard. Alternatively a matching curve could be incorporated into the footboard. There are a lot of possibilities with this design.

A Simple Sleigh Bed Design Incorporated Into Both Head & Footboard The third picture above left incorporates a grandfather-clock-like swan-neck “pediment” with one finial forming the top of the headboard. The swan-neck is rather tall and the curves are a little severe, but the narrowness of the bed may dictate that. I would attempt to alter it. The overall design, especially the footboard, could have simpler lines; I don’t like the footboard design shown at all. An American Colonial flavor might be just right for this style. There is also the possibility of adding a swan-neck to the footboard.

The last two pictures above right and left are variants of a sleigh bed. The last picture is more traditional in that both the head and footboard are sleigh bed shapes. The second to last picture uses a platform bed footboard. The last picture is actually a trundle bed design. There are lots of possibilities for modifying both designs into one. The footboard in the last picture exposes the “trundle” which I find distracting. Also the footboard height is well above the mattress, which is traditional for a sleigh bed, but not a feature that will be accepted by Willow. She believes one should be able to lie in bed and look at nature with nothing blocking one’s view.

The bottom line is that my opinion and taste means little. I am simply attempting to give the customer (Willow) some ideas. She will make the final decision of style selection and modifications. In the end it may be that she has a completely different idea. But this is the beginning of the design phase. Stay tuned for follow-on posts on this topic.

Note: All but the first picture was copied from a JCPenny.com website page and are used simply as an architectural example. Any design that I might extract in part from them will not be used for commercial purposes. If you like one of these beds and wish to purchase it I recommend visiting JCPenny.com.


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