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Assembly of the stair flight
Single-branch flights of wooden stairs are normally assembled in the workshop and transported to the stairwell as a complete unit.
The assembly of flights of saddle stairs is relatively simple because the steps (treads) are screwed onto the sawn-out stair strings. Accuracy to size is an important criterion in screwing on the steps.
The screws should be surface-treated or be made of nonferrous heavy metal so as to avoid rusting and mean appearance when the steps are cleaned by water.
Saddle stairs assembled in the workshop are secured against displacement during transportation by means of a diagonal strip.
Figure 32 - Stair
flight stiffened with diagonal strip (saddle stairs -underside view) - 1
sawn-out stair string, 2 diagonal strip, 3 screw clamp, 4 left side of step
Screw clamps or ferrules are used for fixing the diagonal strip. To prevent marks in the wood, the lower surface of the string bottom is padded by wooden pads and the steps are padded by wedges having the shape of the rise triangles.
In the case of inserted stairs without arris for insertion of the steps, the stair foot and stair head may be inserted in the mortise (insertion slot) and the stair string be slightly drawn together with the screw rods.
To avoid displacement of the stair strings during assembly, a square-cut board with a length equal to the clear width of the stair flight is clamped between the stair strings. Such board must have a sufficient width and be clamped immediately in the area of the screw rods. This will prevent the stair strings from being drawn together too much.
Figure 33 - Stair
flight stiffened with square-cut board (inserted stairs - underside view) - 1
stair string, 2 square-cut board for stiffening, 3 drawn-in screw rod, 4
inserted step
The remaining steps are slid into the insertion slots from the front (see Fig. 7/2). The steps must tightly fit in the insertion slots. If necessary, a hammer may be used for beating in.
Be careful: Use a wooden pad when beating with the hammer to avoid beating marks.
In the case of inserted stairs with arris for insertion of the steps, the steps are inserted, one after the other, into the insertion slots until half of the tread width. Then the steps are, one by one, beaten in cm by cm. A wooden pad is to be used so as not to leave beating marks.
The procedure with mortised stairs is as follows:
- Wooden pads of equal thickness are placed on a flat workshop floor at 500 mm intervals for putting-on the stairs strings.- The two stair strings are put on the wooden pads flush with each other and with the mortised holes for holding the steps and risers showing upward.
Figure 34 - (1)
mortised stair strings put on flush with each other (2) magnified view of the
top part of the stair string - 1 stair string, 2 mortised hole for step and
riser, 3 wooden pads, 4 accommodation for the head step, 5 drilled hole for the
screw rod
- Under the second and last but one steps, in the centre of the stair string, the holes for the screw rods are scribe-marked and drilled vertically into the stair string with a diameter corresponding to the diameter of the screw rods.
- The outer string remains on the wooden pads. The screw rods are put through the drilled holes and the washers and nuts are attached between the workshop floor and the outer string.
- The steps are inserted, one by one, into the mortised holes for holding the steps and risers.
Figure 35 - Insertion
of the steps into the mortised holes - 1 stair string, 2 step, 3 wooden pad,
4 screw rod
- A board is put on the inserted steps and the steps are beaten in by a beating tool until the bottom of the hole.
Figure 36 - Beating-in of the
steps - 1 stair string, 2 step, 3 wooden pad (to avoid bearing
marks), 4 screw rod
- The risers are inserted and, if necessary, beaten-in.
A wooden pad is to be used for beating in. When beating in it is to be made sure that the risers sit 2 mm deeper on top than the steps.
- The wall string is placed on top and the steps and risers are put into the holes (not fully inserted).
Figure 37 - Placing the stair string on top of the steps and risers beaten in - 1 stair string, 2 step, 3 mortised hole for step, 4 step, 5 mortised hole for riser, 6 drilled hole for screw rod, 7 left side of step (go side), screw rod
- The screw rods are passed through the drilled holes in the wall string, the washers are attached and the nuts slightly screwed on.
- A post-piece is put on the wall string to beat the wall string tightly in.
- When all steps and risers are beaten into the mortised holes, the nuts are finally tightened and the stair flight width is checked.
- Any excessive thread of the screw rods is sawn off.
- The rosettes are screwed on.
- The stair strings, steps and risers are sanded with abrasive paper to remove any scribe-marks of pencils and to make the stairs look clean.
Building in of the stairs
First the assembled stair flight is put on the bottom stair-apron with the carved foot provided at the bottom and then it is slowly inclined towards the top apron until it contacts it.
It is to be made sure that the stair strings uniformly contact the stair aprons to avoid displacement of the stair flight. If necessary, the strings are to be recut or packed.
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