Fitting
Begin by removing the existing door and detachable threshold.
When the fitting procedure is complete, a 3mm gap will exist around the top, and both sides of the door. Initially though, we will only be concentrating on fitting the door into the opening, so that it's a snug fit all round.
The likelihood is that you will be fitting the new door to the existing frame, so that the recessing for hinges may not be necessary. However, if you find that the existing cut-outs are not suitable, or do not match the new hinges in some way, you may need to 'make good' the areas first by splicing-in new sections of timber.
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Personally, I first evaluate the shape of the door frame 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 that will show up any imperfections that the frame 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 also 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 frame 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 frame head and the jamb of the frame 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 frame jamb not being vertical to it, 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 door frame head. If the top of the door and frame 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 frame 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 frame 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 frame head, the pencil will scribe the required line across the door parallel to the frame head.
Leading Edge
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 3mm gap to each side, but don't forget to remove the leading edge of the door on the lock side, otherwise it may be found that the door catches when closing even though it fits correctly with a 3mm gap when 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 of the door by about 2mm. When complete it should be possible to fit 3mm packing pieces on each side of the door when closed.
Mind the Gap!
The next step is to consider a suitable gap at the bottom, however, as this is an external door with a detachable aluminium weather bar, the required space under the door can only be determined after the hinges have been fitted and the door is swinging. Therefore, it is only required at this stage that there is a gap under with would allow it to be opened.
Continued on page 4
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