Outdoor Workbench part 4, Wood Movement

An outdoor workbench is more likely to swell and shrink.  As a result careful construction is required.

The outside bolts holding the table to the legs, is normal.

The inside hole for the bolt is a little different so the wood can shift.

Note that the outside hole has the bolt in it already, and the hole is filled with wax mix.

This slit will allow some movement over time, and may keep the wood from spitting.    Wood swells most across the grain.  Since the legs and the top are attached along the same grain intersection,  they should match a bit for expansion and reduce the issue.

The stretcher is matched with it’s greatest expansion axis against the legs least expansion axis.  Cedar is a very stable wood, and this cedar has been seriously wax treated, but this is where a problem could easily arise.  I will be doing a bit more to improve it soon.

The base is also a big, big issue.

Two different woods, treated pine and cedar.  Both have different expansions qualities.  The pine does not expand much along the length, and the cedar will expand a bit along it’s width, so this is potentially a big problem.  If left on it’s own without compensation, it is sure to split the cedar during dry months.

This cedar is actually juniper and it’s greatest expansion axis has a maximum expansion of five point four percent.  Since between the bolts is four inches, the expansion range is a bit under a quarter of an inch.  Does not seem like much, but it can split wood and ruin what could have been a long lasting work.  So I need to modify the base of the legs and the stretcher to be able to handle a quarter of an inch stretch.

Here is where a lot of reading comes in handy, Fine Woodworking has a really nifty workbench that uses a trick that will do perfectly here.


5 comments to Outdoor Workbench part 4, Wood Movement

  • Skip J.

    Hello Bob;

    Thank you for reminding me of this issue. A quarter inch is certainly enough to split the wood. I need to consider that in the joints for my cedar bench. I guess wood pegs are not appropriate for this useage???/ I really do like drawbored M & T’s…..



  • Depends on how the wood will move. The cedar here is one of the more stable woods available, but in moisture, expansion will be at it’s worst.

    Wood movement is the first thing to consider when building to last. Classic furniture looks the way it does, because of the choices that had to be made to make things work. Modern materials allow for a difference in design. A single draw bore and peg should be fine. a single long mortise can be built with slack for expansion and still be tight in use. The tusked tenon is my favorite for this sort of thing however, especially if you use a tusk that can be compressed a bit.

    If you do a multiple joint such as the double bolt shown here or a dovetail however, it is best to match grain to grain. This is one of the reasons you will see dovetails on the sides of a box, but not typically on the bottom.


  • Skip J.

    Thanks Bob!

    I have used single M & T’s outside and they do like to work the wood peg backwards out of the hole. A good reason to not have two pegs!

    I have always liked the idea of a tusk tenon and plan to use that on my workbench upgrade. Having them outside is a whole new approach for me….. good thing I haven’t settled on my cedar bench design yet!

    Thanks again….


  • Tusks are also nice, because they can be easily tightened, and easily dismantled for moving.


  • Skip J.

    Well Bob;

    Here we go again. Tusks are on a stretcher and require extra length to stick out the other side, on both ends! I was just going to use legs attached to some supports under the shelf boards. Now it looks like another trip to the sawmill is in order, teach me to buy just enough!!

    But, on the other hand, my out-of-sight support boards are cedar and could be made into stretchers with tusks on’em. Just real thin ones…. Hmmm….


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