Locking lidded boxes

I have really enjoyed chasing the "locking lidded box" form this past year and thought I would share a bit about my journey.  I first came across these boxes in a blog post by Jarrod Dahl, where he kindly shared pictures of "Rare Wooden Objects" that he studied during a trip to Sweeden in 2015.  Since then Jarrod has taught others how to make these boxes, including one course at Brook House Wood in Herefordshire, the UK in 2017.  It was a class for advanced turners, which you don't see much.  Owen Thomas, Sharif Adams, and Yoav Elkayam attended--all outstanding turners in their own right.  They all went on to produce their own versions of these boxes.

While there is now a fair amount online about these boxes, when I first started I had trouble finding clear images, especially of the insides of the boxes.  I knew the lid had tabs that locked under a ledge in the box itself, but the details were elusive.  How exactly did the lid "lock?"

I guessed that the ledge on which the lid sits must be carved away to form a ramp.  The ramp would gradually tighten against the flanges on the lid, thus tightening the box.  For the sake of clarity, here are a few sketches that name the parts of the box.  If you use different names for the parts of the box, let me know!

The "bowl," with "lip, ledge, ramp and notch"

The "lid" with tab, tab base, and nob

I turned a few iterations, each time gaining a bit more insight into how the form would work.  Below is one iteration, where I made two mistakes.  One was using two ramps, which you don't need.  The other was removing too much ramp material on the left notch, which leaves a gap between the bowl and the lid.

Here is another early iteration.  It worked a bit better with only one ramp.

I found that using stable wood is key in this sort of project--if the rim of the bowl warps or cups, your lid won't sit flat.  Radial, semi-dry blanks, with the radial face becoming the top/opening of the bowl, seems to work best.  All of mine so far have been beech.

Even with a relatively stable radial blank, there is going to be a little radial shrinkage (say 2-6%), whereas there will be almost no longitudinal shrinkage.  You can use this to your advantage.  In the above image, you can see how the grain is running between 12 and 6 o'clock.  As the bowl dries, it will become relatively narrower in width than in height, becoming slightly oval or even egg-shaped.  See where I started the notch and the ramp?  It is right in line with the grain direction, at 12 o'clock.  This means as lid "tightens" against the ramp, the wood is also getting narrower in width, which accelerates the tightening effect.

Another possibility with these boxes is to forget the ramps and rely solely on the shrinkage to lock the box.  Below is a still from a video by Sharif Adams.  Here the box is ready to be opened.  If you look closely, you can see two chip-carved triangles on the left lining up, one on the lid and one on the box.  You can also see the grain direction of the bowl and lid in the same orientation.

Here Sharif is locking the lid, righty-tighty.  

Notice how far the lid turns to lock--nearly a quarter of a turn, but not quite.  Since Sharif is not using a ramp, he is relying entirely on the ovalizing effect of shrinkage to cause the lid to bind against the short side of the bowl.  This takes precise turning and a real understanding of how much your wood will shrink.  Remember, if the lid does not lock after a quarter of a turn and passes that shortest width section, it will never lock at all--it will just spin.  So, props to Sharif for a really precise bit of turning.

In my case, I prefer using ramps for a few reasons.  One is I can shape the ramp to ensure that the bowl locks tightly.  The other has to do with aesthetics.  Both the bowl and the lid ovalize in drying.  If you rely on the ovalization to lock the box, it means the lid's grain direction will be at 90 degrees to the bowl's grain direction when locked. This means the oval of the lid will not sit sweetly within the oval of the bowl--they will be at right angles.  This opens up gaps between the lid and the lip and can even reveal the notch. For example, you can just barely make this out in the image below.  Sharif is such a skilled turner and his tolerances are so tight that you can only barely see the notch.  If the lid and bowl's grain goes in the same direction, it is easier to cover the notch.

However, if you use a ramp and start the notch at say 10 o'clock, you can control the tightening so that the grain of the lid and bowl line up when locked--like this:  

Lots more to share about this type of turning, especially in how to make the various cuts.  Plenty of below and behind-center turning, and big risks for catching.  Maybe more on that later.

Hope this helps.

Turn on.