Before buying a new door measure the height and width of the frame to determine the size of the door needed. To enable the door to close smoothly allow a clearance of 3mm at the top and sides and 6mm at the bottom of the door. Doors come in various sizes so choose a door which is close to the size you require, chances are that you won't find a exact fit so buy a door slightly bigger, this will allow it to be cut to size.

If the door comes with stiles which are used to protect the door in transit, use a try square and draw a pencil line flush with the bottom and top of the door.

Remove the stiles with a hand saw, make sure the saw is kept to the waste side of the pencil line and keep the saw perfectly upright to ensure a square cut is made. Use a plane to to finish off removing the stiles up to the pencil line. Plane from the outside of the door inwards to prevent splintering the edge of the door.

Place the door against the frame and place wedges (chisels will do) underneath to raise the door by approx 6mm to allow for floor covering. Draw pencil lines on the door allowing for a clearance of 3mm at the top and sides, then trim the door up to the lines. If there is a lot of waste use a saw and finish off with a plane, work along the grain on the sides of the door and work from the outside of the door towards the middle at the top and bottom of the door to stop the edge of the door splintering.

When you are happy the door fits with the right amount of clearance place the door within the frame wedging it until it is in the right position, once you are satisfied take a hinge and hold it in position approx 150mm (6") from the top and 225mm (9") from the bottom of the door and mark the top and bottom of the hinge on the door and frame.

Remove the door and support it with the hinge side upwards. Hold a hinge in place so that its knuckle projects just past the face of the door and draw round it with a pencil. Do the same on the door frame again with the knuckle projecting just past the edge of the frame ( not the architrave).

Cut out the recess for the hinge using a sharp chisel. Cut along the vertical lines first and then make a series of cuts across the width of the marked area to the depth of the hinge. Make shallow angle cuts removing the waste until the required depth is achieved. Repeat for all hinges on both the door and the frame.

Place a hinge in the recess on the door and using a bradawl make small pilot holes for the screws then fasten the hinge to the door. Repeat for the other hinge. Place the door up to the frame and use wedges to raise it to the correct height, then fit one screw in each hinge flap, remove the wedges and test the operation of the door. When you are satisfied insert all the screws making sure the heads lay flat otherwise the door will not shut properly.

With the door out of the way unscrew and remove the striker plate, again if it has been painted over you may need to chip the paint from the slot in the screw. Put the striker plate to one side as we will need to refit this later.

The recesses that are left from the removal of the hinges and striker plate now need to be filled. This can be done by either cutting pieces of wood to size and glueing into position, or an appropriate wood filler can be used. These come in all sorts of colours and can also be stained, painted or varnished.

Now we can remove the hinges from the door, as they will need refitting on the other side. With the hinges removed fill in the recess, again using wood or an appropriate wood filler.
Use a try square to line up with the old hinge position and mark the top and bottom of the new hinge position. Cut out the recess for the hinge using a sharp chisel. Cut along the vertical lines first and then make a series of cuts across the width of the marked area to the depth of the hinge. Make shallow angle cuts removing the waste until the required depth is achieved.

Place a hinge in the recess on the door and using a bradawl make small pilot holes for the screws then fasten the hinge to the door. Repeat for the other hinge. Place the door up to the frame and use wedges to raise it to the correct height, then fit one screw in each hinge flap, remove the wedges and test the operation of the door. When you are satisfied insert all the screws making sure the heads lay flat otherwise the door will not shut properly.

To find the position of the striker plate, partly close the door and mark the top and bottom position of the door catch on the frame, now fully close the door and measure the distance from the catch to the edge of the frame. Using the marks and measurement line up the striker plate and draw round the outer and inner edges, using a chisel cut the recess to the depth of the striker plate, then cut the centre hole to the depth of the catch and screw the striker plate in place.

Determine the height that you want the lock to be, then place the lock on the side of the door draw round its body and mark the spindle hole and any key hole. Using a try square draw lines across the edge of the door in line with the marks for the top and bottom of the lock body.

Measure the thickness of the door and half it, then draw a vertical line where the lock is going to go. Place the back of the lock on this centre line and draw round it, this is the bit that will need to be removed to fit the lock. Drill a row of holes, the same width as the lock. Measure to make sure the holes are deep enough.

Use a chisel to straighten the sides and remove the bits left in between the holes. Clean out all the splinters and try the lock to see if it fits. Chisel out as required until the lock fits, then with the lock pushed fully in draw around the face plate. Chisel a recess for the face plate to the required depth.

Drill out the spindle hole and the key hole if it has one, using appropriate size drill bits. Fit the spindle to test the lock and also test the key if fitted.

Once you are happy that everything lines up and works freely, use a bradawl to make small pilot holes for the screws then screw the face plate in place and fit the handles.

To find the position of the striker plate, partly close the door and mark the top and bottom position of the door catch on the frame, now fully close the door and measure the distance from the catch to the edge of the frame. Using the marks and measurement line up the striker plate and draw round the outer and inner edges, using a chisel cut the recess to the depth of the striker plate, then cut the centre hole to the depth of the catch and screw the striker plate in place.