Prepare for fixing
With the door now recessed for the hinges, mark the position of the screw holes, but before inserting the screws, use a bradawl to form pilot holes that will assist correct insertion and help prevent the timber from splitting. If the door is hardwood, then a pilot hole will be needed to be drilled first. For 75mm hinges, use number 7gauge, 25mm screws.
With the hinges fitted to the door, their position will now need to transfer from the door onto the door casing, so that when the hinge flaps are recessed into the casing they correspond to the door and, at the same time position the door so that the 2mm gap between the top of the door and casing head is maintained.
There are two methods that can be used to do this, the first is by using a staff, which is usually used for repetitive work where a lot of doors require fitting. This requires a suitable staff with a square cut top end, (a length of timber, 25mm x 10mm for example) at the door's prepared length. Using a square, draw a line 2mm down from the top of the staff, and place the staff onto the door edge, with the 2mm mark to the top corner of the door's edge (the 2mm excess will overhang). This overhang provides the required 2mm 'top gap' for when the door is hung. Holding the staff in this position, mark the position of the hinges onto it. Now, place the staff onto the door casing where the hinges are to be fitted, with the top tight up to the casing head, and using a sharp pencil, carefully transfer the marks from the staff to the door casing.
The second method is by using the door as the 'staff', by placing the door in the opening, and with the aid of wedges, set the door to the correct position by raising it so that the top gap is 2mm. With the door held in this position, mark the position of the hinges directly from the door to the door casing. Lines can now be drawn, about 20mm long from the marks, which should be square off the casing.
The next step is to position the vertical lines between the two horizontals that have been drawn for each hinge, as when fitting the hinges to the door. However, in this case, not only does this line mark the position of the hinge flaps, it also governs the position of the door when closed in relation to the shoulder of the rebate. If set too far in towards the shoulder, the door will rub against it preventing it from closing properly. If set too far from the shoulder, the gap between the shoulder of and the face of the door will be too wide when the door is closed. Getting this position correct then is quite important, but actually simple.
Measure the exact distance from the edge of the door to the edge of the hinge as shown here on the right. Then, add 2mm to this measurement, and transfer it to the door casing (measuring from the shoulder of the rebate) using this mark as the position of the vertical line.
Recessing the Door Casing
Using the same procedure as with the door, cut out the recesses for the hinges into the door casing, testing the fit as you proceed. Having a spare hinge for this job is also a good idea.
Hanging the Door
With the door in the open position, raise it up so that the open hinge flaps correspond to the recesses that you have formed in the door casing. Beginning at the top, ensure that the top hinge fits correctly up to the vertical line, and with a bradawl, make a pilot hole for one screw only, preferably the centre, and inset the screw. Do the same for the bottom hinge, but do not at this point insert the remaining screws as the door may need slight adjustments. Try closing the door and check for fit, in particular the distance from the closed door surface to the rebate shoulder. Secondly, check the overall fit to the sides and top. If you are happy with the fit, inset the remainder of the screws.