Joining timber in length – Woodworking joints
These are the most important joints for the lengthening of timbers, and the most difficult to construct. They are used where it is required to keep the section of the timbers uniform in size. The two pieces in a scarfed joint are cut and fitted to each other, so that the same breadth and thickness are retained. For jointing wide boards (Fig.A) shows the type of Scarf joint that would normally be used. Where additional strength is required (purlins or beams) then scarf joints can be bolted and plated – this is also known as a fished joint (Fig.B).
This method of jointing is used to mainly utilise short lengths of timber. It can also be used for making up curved and shaped work. Fig.C shows a glue-laminated beam used for structural work. The joints in length are staggered to obtain maximum strength. Fig.D shows the head of a semicircular frame which has been glue-laminated from a number of separate pieces of timber.
The handrail bolted joint (Fig.E) is a secret fixing for lengthening timbers. Two pieces of timber are placed together and the positions of the nuts are marked. Holes are mortised on the least important side of the timber to receive the nuts. Holes are then marked out on the ends of the timber and drilled a little beyond the mortises for the nuts. The square nut is placed in one piece and the bolt screwed into it.
The other piece of timber is put onto the projecting part of the bolt, so that the thread engages with the slotted circular nut. The two pieces of timber are then screwed together as far as possible and then the circular nut is tightened with a handrail puch until the joint is tight. To strengthen the joint, two small pieces of dowel can be used in conjunction with the bolt; this helps to prevent the joint from twisting when completed. The mortises for the nuts are then filled in with ‘timber joiners’ to hide the joint.
Sometimes reffered to as a bevelled, spliced, heading or splayed joint, this joint is used when lengthening floor boards, skirtings and mouldings and would usually be secured using either glue, nails, screws or bolts. When used to lengthen floorboards (Fig.F) then the joint must be placed over a floor joist. Fig.G shows a heading joint in skirting board.
In our next post will be looking at joints for joining timber in width.