Toolchests Part 6 – Key Performance Criteria Solutions 1: Durability and Longevity

It is not down on any map; true places never are.

Herman Melville, Moby-Dick or, the Whale

In this article in our continuing series about wooden toolchests, your humble servant would like to discuss the Performance Criteria of Durability and Longevity and present some potential solutions.

Durability

A toolchest should be tough as a whale because a fragile one endangers the tools we trust it to protect. Those Gentle Readers for whom durability is not a high priority should stop reading now and get back to the important task of popping bubble wrap.

When I was researching this performance criteria, I bought books and visited libraries reading everything I could find on the subject. I visited museums and was told to get up off the floor and “move along now,” by security guards more than once. I just wanted to see underneath….

I visited antique stores and the workshops of professional antique restorers and grilled them about what materials and construction details withstood the tests of time best, learning much that wasn’t written in the books.

I incorporated some of the things I learned through this investigative process into the design and construction of this toolchest, so let’s examine a few related to durability and longevity.

Wood Selection

I grew up making cabinetry and casework with my father from readily available commercial materials such as 3/4″ plywood. We would mill solid wood parts to match this standard dimension even though trees don’t grow in quarter inch increments. While the material of choice has shifted from plywood to MDF in recent years, this is still standard procedure in commercial situations. However, since my toolchest was not to be a commercial product for a Client with no understanding of quality casework beyond external appearance, but rather custom casework for my personal use, I tossed those standard procedures out the window and started with a blank page.

My examination of the available literature, museum exhibits and antiques available to me at the time combined with some structural analysis revealed that durability is heavily influenced by the mass and strength of the wood. This seems like a common-sense conclusion, but it flies in the face of conventional toolchest design, as you will see.

Many advocate making chests from lightweight, inexpensive woods such as sugar pine, poplar, cedar or cypress, and to dimension the walls thin to minimize cost and weight, and to maximize interior volume. This is the traditional approach for chests used by common folk, but anticipating the abuse my toolchest was likely to experience, and considering my longevity goals and the fact that I would never need to carry it far by shank’s mare or mule, I eschewed this philosophy and decided to use stronger more durable wood and thicker, with weight assigned a lesser priority.

One of the so-called “Genuine Mahoganies,” Honduras Mahogany is very resistant to rot and termites although some beetles will eat it if they can find it. We will look more at the sensory capabilities of bugs in a later post in this series.

HM is strong, not too heavy, easily worked, glues exceptionally well, and is phenomenally stable. Along with Cuban Mahogany, it has been the most desirable wood for luxury furniture in the Americas and Europe for centuries. 

This wood is difficult to obtain in the United States nowadays because of import restrictions prompted by environmental destruction through over-harvesting, but at the time, it was readily available as S2S clear lumber in the People’s Socialist Republic of Northern California. 

HM’s coloration varies from tree to tree. The coloration of the HM I purchased was not the most desireable dark red, but the less-expensive, less-dense orangish variety. However, I splurged and used feather-crotch boards for the lid’s floating panels and ribbon-figured HM for the tray sides.

I used no “secondary woods” except for the 5mm plywood non-structural loose dividers in the sawtill. No need to be a cheapskate.

Wood Thickness

One purpose of my research was to gain an understanding of the typical failure modes of chests. You don’t see busted, water-damaged, bug-infested, rotted-out examples exhibited in museums, listed in inventory catalogues, or written about in books, but there are lots of old broken-down chests in antique stores, and restorers are always working on them; I therefore strongly encourage you to venture away from the internet into the dark and foreboding world of reality to examine them with your own eyes and hands to determine their reactions to the challenges they faced during their lifetimes.

One very common failure mode is ruptured corner joints resulting from what appeared to be drops and impacts. Another common failure mode is cracks, gaps and warped lids resulting from differential expansion/contraction inherent in wood.

In a dovetailed chest, impact forces from drops frequently cause corner joints to fail, so the solution I employed was to use plenty of dovetails, and to make the side wall material thick enough to provide adequate surface area for glue to bond and impact energy to be safely dissipated without causing the carcass to rupture.

Obviously (or maybe it is not obvious to some) thicker walls increase the amount of long-grain to long-grain contact area at a dovetail or fingerjoint corner joint by more than the square of the thickness. A simple calculation showed the sides had to be much thicker than 5/8” to achieve the impact resistance and glue strength I needed, so I went with 1-3/16” (30mm) thick sides. And instead of using a lightweight softwood like pine, a weak but delicious wood upon which bugs and fungi dine with gusto, I went with the much stronger and more rot/bug resistant Honduras Mahogany in a medium density as noted above. This proved to be a wise decision as evidenced by the results of multiple drops and several forklift encounters during my travels. And due to its dedicated wheeled platform, the additional mass has not been a problem so far. This was never intended to be a truck-bed toolbox.

Of course, most drops and forklift kisses impact the base first, so if the bottom corner connections at the base fail all is lost. I made the base (skirt) of tough 40mm thick high-density mahogany, dovetailed the corners, and pinned/glued it to the chest’s sides. These four pieces and the assembly they comprise is the densest, toughest component of the chest. It is scratched and dinged but this is only cosmetic damage, so I feel the base has done everything I needed it to do, at least so far.

I doubt 3/4″ sugar pine sides or a 5/8” ~ 7/8” thick poplar base would have survived the first drop from a moving truck bed, let alone that incident in Bangkok when what must have been a deranged peg-legged forklift driver pushed the tool chest into the conex box with his fork tips while shrieking “From Hell’s heart I stab at theeee!” The madman damaged the toolchest but neither pierced nor cracked it. After that, I rechristened it “Moby Dick. “ Harpoon sockets and grog were not involved.

Differential Expansion & Contraction

Changes in humidity make wood expand and contract. You can ignore this natural force, as the plastic puppet people that love MDF do, or even fight it if you enjoy the tangy flavor of humiliation, but given enough time either approach will make you look the fool. Better to plan for it if your longevity goals are 200 years. If, however, longevity is not important to you, please stop reading this article immediately and get back to the important task of popping that bubble wrap.

Avoiding damage caused by differential expansion and contraction of wood is a problem humanity resolved centuries ago using well-known, but oft-ignored solutions. Some of those techniques are to use mechanical connections (e.g. dovetails, mortise and tenon joints, etc.) without relying solely on glue, avoidance of wire nails, avoidance of wide cross-grain joints, avoiding steel straps hard-connected cross-grain, and using frame-and-panel construction when wide cross-grain joints would otherwise be impossible to avoid, to name some primary solutions.

My design uses few metal fasteners, just stainless-steel screws to attach the lid’s hinges and tray shelves, brass screws to attach the brass lock and recessed tray pulls, and 4 steel bolts to attach the lifting eyes. No metal straps are used.

My toolchest employs a floating frame-and-panel lid with deep dovetailed sides made from solid 30mm Honduras Mahogany. I’ll go into this detail more in future posts.

The chest’s bottom is also frame and panel construction in solid mahogany. Frame and panel construction was used for all tray and drawer bottoms. No engineered wood materials such as plywood, MDF, LVL, OSB or veneer were used.

All glued joints in my toolchest are dovetails or pinned dovetail mortise and tenon joints, and trenails. If the glue fails, which it eventually will in some places sure as God made little green apples, the mechanical joints will still hold together. I did not use nails, screws, staples, biscuits, splines or loose tenons as structural fasteners.

Fungus, Insects and Rodents

As noted above and in Part 3 in this series, wood as a material may be economical, easy to work, have decent insulation performance, and make our collective hearts go pitter-patter, but we cannot safely ignore the fact that some fungi and insects love to eat wood, and rats and mice will chew holes in it. How can we adapt our toolchest design to deal with “the crud,” creepy crawlies, and critters? A few possible solutions are listed below:

1. Select a wood that is naturally unpleasant to chew without using toxic levels of hot sauce. God made some woods yummy, and others noxious. The later typically lasts longer;
2. Use thicker wood to make the toolchest strong and tough. This will also make it more difficult for rodents to chew holes in it.
3. Make the wood unpleasant for fungus and bugs to eat and rats to chew through the miracle of modern chemistry available in either commercial or homemade wood preservatives;
4. Seal all raw wood surfaces, both inside and outside the toolchest, so fungus spores will find it difficult to take root, and insects will be less likely to detect the savory smells of yummy wood (that is how they find it, you know);
5. Elevate the bottom of the chest above the ground/floor so there is an “air gap” preventing direct moisture transfer from below thereby keeping the wood’s moisture content at levels less than those preferred by fungus and bugs;
6. Design the base details so some air circulation underneath the chest is possible to reduce fungus growth and make cleaning possible:
7. Place vaporized fungus and insect repellent (e.g. moth balls or toilet cakes) inside the toolchest further minimizing delicious woody smells that attract insects while at the same time creating an uninviting or even hostile environment for their kiddies;
8. Combine all seven of the solutions listed above, which is what I did. You know me: Belt, suspenders, and safety harness.

We will talk about these solutions and other factors that informed the design of the toolchest in future posts.

I encourage you to give similar consideration to the design of the furniture and casework you build for your own use, at least if, like me, durability means more to you than the ecstasy of popping bubble wrap.

In the next post in this series about my toolchest, we will consider some potential solutions to the remaining Key Performance Criteria you may want to consider when designing your toolchest.

Call me Ishmael.

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