Architraves are decorative timber trims that are placed internally around door casings, window, and loft hatch openings, which serve to hide the joint between the wall and timberThey also conceal any subsequent shrinkage in the surrounding materials.
To cover one side of a door casing there are a total of three lengths of architraves (a set) consisting of one horizontal head piece and two vertical legs or jambs.
The return corners of the architraves are usually mitred, and in the case of a square door casing the corners are at right angles (90 degrees) so that the mitre cut is 45 degrees, half the total angle. However, if the squareness of the door casing is questionable, the angle of the mitre would be different.
When fitted, architraves are usually set back from the edge of the casing by between 4 - 5 mm, but can under certain circumstances this can be greater. Narrower margin can restrict the knuckle of the hinges and the striking plate, where larger margins can reduce the available nailing area of the door casing on the rebated side.
A margin provides a neat appearance to an opening that would otherwise have an unsightly joint line if the architraves were kept flush with the edge of the opening. After deciding on the amount of margin, carefully mark the door casing at this measurement with short margin guidelines, set about 200 mm apart, ensuring that they are all equally set back and parallel to the edge of the casing on both jambs and head as shown in the drawing on the right.
These short lines are sufficient as guides for accurately fitting the architraves, and to determine the point at which the architraves are to be mitred. For this reason, the lines at the top of each leg, and at both ends of the head should be extended vertically and horizontally so that they cross on both corners looking like the drawing to the right, so that when the architraves are offered to the guidelines, the 'Heel' of the architrave mitre cut is easily determined.
Cutting the mitres to 45 degrees should ideally be done using a mitre block, which can either be purpose made, or purchased.
As I fit quite a large quantity of architraves on a daily basis, as well as other joinery cutting, I invested in a power mitre saw, which gives very accurate cuts with the added benefits of being an useful device for a number of other joinery cutting. However, I should point out that the cheaper models of power saws do not provide the same level of accuracy and if the amount of work you intend doing is a 'one off' DIY project an expensive saw would be difficult to justify. For such cases, there are available on the market portable hand mitre saws which are also very accurate or alternatively consider tool hire.
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