Pegs

(Square or Round: Does it Matter?)

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People frequently ask what kind of pegs they should use. What diameter peg? What shape? What type of wood?

For well fit compression joinery pegs don't carry load. So - why do we use pegs? It is true that pegs carry no load when joinery is in compression, however live loads such as vibration, wind, snow, etc. cause transient loads which can put a joint in tension for short periods of time. Pegs are needed but they are typically the least likely component in a joint to fail.

Occasionally there will be a well thought out reason for using a specific type / size of peg in a specific application. However, by in large it is a matter of personal preference. This is largely due to pegs not being required to withstand pullout in modern frames. Applications that require pullout resistance in modern frames are usually handled with steel fasteners (bolts, lag screws, etc). Pegs are commonly made of a wide variety of hardwoods and come in different sizes and shapes. The most common shapes (in cross section) are: round, square, octagonal and multifaceted or hand drawn. The most common sizes are 3/4" and 1" diameter. Occasionally, they are larger for specific jobs. Tensile joinery requires properly engineered pegs.

In short; most of the time, use what ever style of pegs you desire (round, square, octagonal, multifaceted or hand drawn, etc) but know that the style of peg is for looks, because you think it's cool, and for that warm fuzzy feeling of satisfaction that you get. These are all valid reasons. After all, why do we do what we do if not because we think it's cool?

There is historical precedence for square pegs in round holes. The idea is for the square peg corners to bite into the round hole and thus make it harder to remove. There are also octagonal pegs (the same principle). This was done on joints such as rafter to plate where the rafter is just birds mouthed over the plate. The need was to resist some uplift (i.e. to keep the wind from blowing the roof off). This is now handled (much better) with lag screws. It could also have been due to pegs being made with axes.

A reference from: "The Village Carpenter" by Walter Rose (circa 1880) (page 64)

"Old Enoch also chopped his wood pins square with his axe, whereas all other of our men rounded them with chisel or plane. He said that formerly they were always left square, which I myself have noticed in very old roofs, where the rafters are fastened to the plates with wood pins instead of nails. Enoch said that square pins held better."

Notice in this quote that the "other" carpenters rounded their pins which means that their pins were first split down to size in the square and then rounded. Of course now the easy thing to do is mass produce them on lathes.

The carpenters I worked with in England used draw knives to make pegs of green oak (whereas we use turned dowels of dry hardwood). These pegs were multifaceted and anything but uniform in cross section.

An indication of one builder's state of mind concerning pegging is evidenced in the famous Westminster Hall in London (hammer beam roof finished in 1399). The joinery, where loads are transferred between timbers, is cut with great accuracy however the pegs are just any old twig that came to hand, almost an afterthought. The pegs are not necessary for the building to remain standing.

A reference from: "Westminster Hall Roof" by William Harvey article found in "The New Carpenter and Joiner" Volume 2 (page 95)

"What is even more significant of the designer's frame of mind is that several of the oak pins or trenails were found to have been made of green twigs, and to have been inserted in the most careless and perfunctory manor, although the fitting of the bearing joints was almost mathematically precise."

The shape of pegs is largely influenced by the tools available to make them. Historically pegs were split and then drawn with a draw knife on a shaving horse. This gave a multifaceted tapered shape (How to make hand drawn pegs). Many use round pegs today because they are made very quickly on automatic lathes. This technology was not available historically. Some use octagonal pegs because they have access to inexpensive material and labor. Octagonal pegs are easily made on a table saw (How to make octagonal pegs).

The draw bore technique shown (How to draw bore) works well for all except hand drawn pegs. For hand drawn pegs we use the more aggressive offset show in (How to draw bore for hand drawn pegs).

Hand drawn pegs are made of green hardwood so they can deflect around the miss-aligned tenon hole and force the joinery together (How to draw bore for hand drawn pegs). As they dry in their bent shape in the joint they become harder, stronger and difficult to remove.

All other types of pegs are made of dried hardwood. The idea is that the dry peg will take on moisture from the surrounding timber, swell, and thus be harder to extract. Turned pegs of dried hardwood work very well, they are stable, strong and pretty. The "swelling" theory sounds good but whether it is worth anything is questionable.

My experience and travels have shown that there are many different ways to get good results. In short, pick a peg style that makes you happy and get on with it.

I guess my point is "keep an open mind, take unexplained points of fact with a grain of salt, have the courage to regularly expose those beliefs you hold most dear to the harsh light of reason, and really observe the world around you as it is, not how you think it is or how you want it to be".