Under the heading of “The Folding Rule Method”, a “2 meter rod” or a folding ruler/rod is used and is temporarily anchored at a point in the rod rigging or shroud cable at one end. The other end of this 2 meter ruler/rod floating or resting against the rod rigging or shroud cable in a way as to make a 5mm gap from the cable or rod terminal. This is then called a reference gap 0 (zero). As tension is applied to the rod or shroud, a stretch caused by the load corresponds directly to the desired load and then measured with a vernier caliper.
Selden Tuning Guide specifies:
Stretch per 2 Meters: (5% of braking load) – wire 1X19 = 1 mm, Dyform 0.95
mm, Rod 0.7 mm.
It is also state these values are irrespective of the diameter of the wire (1×19). I am assuming the same applies to rod as well since values are given.
It was an eye opener and interesting article worth sharing with all. It makes perfect sense that cable stretch and rod stretch to be directly proportionate to load which is in the case with a spring type stainless. I don’t know about a caliper, I would prefer a dial indicator myself to be more accurate and dial in the load as opposed to measuring. For a quick set-up measuring the distance inside the turn buckles would be also possible withing reason. How much ingenuity can be applied to tensioning the rig based on this with repeating results and measuring stretch? The idea appeals better than the LOOS Gauge with short distances between rollers! How much would a 2 meter rod with with a soft anchor in one end, a slider base plate on the other and an inexpensive dial indicator mounted to the chain plate terminals to more accurately measure and dial in the rig tension? I could probably make a set of two, one for each side to balance the load. The only question would be, is it a linear measurement or is there a ramp in either side of the deflection scale to load value? It appears to be linear within upper and lower range and proportionate to load movement, to be sure still looking for data. I think it is a great way to get the job done with more precision and repeatability.
Would be interesting to compile reference numbers and breaking loads for our rigging?
Has anyone used this method to tension their rigs?