When fitted there will be a 2 mm gap along the top, and both sides of the door, with a 6mm gap to the underside, but this gap to the underside could differ depending on the type of floor covering. Initially though, we will only be concentrating on fitting the door into the opening, so that it's a snug fit all round.
Personally, I first evaluate the shape of the door casing by offering the door up to it, and trying it in different positions. This is useful because I know that the new door has square corners and parallel sides and will show up any imperfections that the casing may have. This gives me a good indication of what will be required and the easiest way of making the door fit the opening. You may find though that the door height is greater than the opening, in which case the door will need to be reduced by sawing an appropriate amount off the bottom. Great care should be taken at this point that not too much is removed, because if you later find that the head and the bottom of the door needs scribing (which will reduce the door height), the door could end up being too short. Ideally, the door should be reduced to a height so that when it is in the opening and raised up to the casing head, the gap to the underside should be as small as possible.
When it comes to reducing the door edges to fit, the more experienced would place the door up to the opening and remove the appropriate amount until it fits, but if this is your first attempt, it would be safer to measure the width of the opening across the top, middle and bottom and transfer the sizes on to the door. The door can then be gradually reduced to the correct width by planing equal amounts from each side so by maintaining its symmetry. If it is found that the corner between the door casing head and jamb on the side that the door will be hung is not square (not 90 degrees) due to the head being out of level, or the casing jamb not being vertical, it will mean that the door head will need to be reshaped to fit. However, if this difference is minimal it is sometimes possible (and easier) to make adjustments along the edges of the door rather than at the top by tilting the door slightly as the door is reduced to fit.
After the door has been reduced so that it is a snug fit, raise it up so that it touches the casing head. If the top of the door and casing head are not parallel there will be a diminishing gap. To overcome this problem, the door will need to be scribed to fit and this can be done by placing wooden wedges under the door and measuring the size of the gap at the point were it is greatest. If for example the gap between the top of the door and casing is 5mm and on the right hand side (as shown in the drawing on the right), remove the door and place it onto the trestles, measure down 5mm from the top of the door (on the left hand side), and draw a diminishing line from this mark to the right hand side. Alternatively, leave the door in situ,
and draw a line from the top right hand side of it across the width of the door while maintaining the same 5mm distance at all times from the casing head. To aid this procedure, a simple hardboard or thin plywood guide as shown here on the left could be used, so that when the top of the guide runs along the underside of the casing head, the pencil will scribe the required line across the door parallel to the casing head.
With the door a snug fit in the opening, and the top of the door and casing head parallel, you can now confidently remove the required amount from each side of the door so as to achieve the correct 2mm gap to each side, but don't forget to reduce the leading edge of the door on the latch side, otherwise it may be found that the door catches when closing even though it fits correctly in the closed position. This problem is due to the increase radius of the door at its leading edge. When planing the closing stile of the door, this should be done so that it forms a slight angle to the full length of the door towards the outside face by about 2mm. When complete it should be possible to fit 2mm packing pieces on each side of the door.
Mind the Gap!
The next step is to provide a suitable gap at the bottom, this is usually about 6mm but can vary according to the different thickness of floor coverings. Assuming that the gap is going to be 6mm, raise the door off the floor so that a gap of 2mm exists between the top of the door and casing head and place wedges under the door to keep it in this position. Ensure that the door is parallel to the casing and measure 6mm from the floor onto both sides of the door. Remove the door from the opening and place it onto the trestles and using a suitable straightedge, draw a definite line over the scribed line ready for the cut.
Continued on page 3