Johnson Level & Tool Mfg. RAS-1 - Manual (Page 31)

29
1. Find the approximate number of steps with the following
formula:
TOTAL RISE (inches)
APPROXIMATE NO. OF STEPS = 7"
For example, let’s assume a 8' 6" rise = 102”
102"
APPROXIMATE NO. OF STEPS = 7"
= 14.57"
NOW THE ACTUAL NUMBER OF STEPS WOULD BE THE
WHOLE NUMBER, IGNORING ANY FRACTION, i.e., 14 STEPS.
Next, find the actual step rise by using the following computation.
TOTAL RISE (inches)
ACTUAL STEP RISE =
NO. OF STEPS
In our example: 102"
14
ACTUAL STEP RISE = 7.29"
2. Now find the step run (or tread width) by subtracting
the step rise from 17 1/2":
STEP RUN = 17.5" - ACTUAL STEP RISE
= 17.5" - 7.29"
= 10.21"
Thus the total run is:
TOTAL RUN = STEP RUN x (NO. OF STEPS – 1)
= 10.21" x (14 – 1)
= 10.21" x (13)
= 132.73"
Finally we calculate the inch rise (similar to the rafter inch rise):
ACTUAL STEP RISE (inches) x 12
INCH RISE =
ACTUAL STEP RUN (inches)
7.29" x 12
=
10.21"
8.57"