Hi Gabel,

Metal plate dies are really used to check the final size of a rived peg to make sure that it does not overfill the peg hole causing split out the cheek or tenon thus a normal tapered octagonal peg would be made and then tapped through the hole. Should any excess wood be removed then this would leave a cylindrical surface on the leading "edges" of the peg. The aim is not to completely fill the peg hole but instead allow slight edge deformation on the peg facet edges

Peter McCurdy (builder of the Globe Theatre) brings along a bag of pegs when he teaches sessions on the Timber Building Masters course at The Weald & Downland and this bag contains all sorts of rareties and oddities that tend to alter long held perceptions on the right or wrong way to peg a joint.

Some simple considerations might be as follows :-

Durability:- where a peg is exposed externally then the ability of the peg to survive weather and bug attack is important so oak and chestnut would be a good choice and ash a poor choice.

Flexibility:- pegs will deform in service and in fact need to be able to do so otherwise the tenon relish might split or pull out, worse would be when the peg is located too close to the edge of the arris causeing the cheek to split out. The likelihood of this type of failure mode being encountered is made worse by using rows of close spaced pegs e.g. as in arch braces where large shrinkage is expected. Ideally pegs should behave like springs rather than fixed restraints allowing a degree of movement but basically holding everything together. Soulace brace joints present a particular challenge for pegs.

Failure:- Pegs should fail preferentially before tenons or cheeks. Its much easier to replace a peg than repair a joint. Peg grain should be set with the annular rings parallel to the direction of developed force such that all rings are made to work together. There are differences between the crushing strength of early and late late growth wood and also differences year to year. The objective is thus to reduce the effect that weaknesses in annual growth rings might have in allowing preferential crushing or worse still ring separation potentially resulting in the loosening of a joint.

Grain:- not sloping and ideally wood species that exhibit long fibres with peg material taken from any clear wood avoiding juvenille and sap wood with clear growth areas being found between annual growth knot whorls or branches. Pine can be used along with oak, chestnut, cherry. Avoid brittle woods such as yew and elm and some (black) ashes where separation or "shelling out" can be encountered. Don't use soft pulpy woods such as aspen, willow, poplar which will yield in service.

Profile:- tapered pegs are used to draw a joint up tight that employs offset boring. Parallel pegs are used on drilled through assemblies where joints are pre tensioned by pulling up with come-a-longs or equivalent Spanish windlas. Parallel pegs are also used on centre line set tenons where a tapered peg might fail to pull the joint up tight before locking on its outside (thick) end. Square pegs are used to lock lap joints or joints where separation of both parts is to be resisted e.g. cruck blades, rafter peaks, common rafter to purlin.

I hope that this helps.

Regards

Ken Hume