Calibration Course

How did / do you judge pull tension at the far end?

A small, portable "fish scale" works. Then when you learn what a "Newton" feels like pulling the tape with the scale attached, it becomes easy to pull it just as hard or harder than required just by feel.

But how do you hold the other end where there is nothing but nylon clad steel tape to grab onto?  After I asked the question I tried this and it seems to work OK at up to 24 pounds of pull. Cut 2 pieces of 1 1/4" flat stock (one 1 3/4" long and the other 3 " long). Bolt them together with 3/16" machine screws and nuts.  Drill a 3/8" hole at the far end of the 3" piece.   Lot of other better materials but that is what I had.

You're a better engineer than I, Oscar. Aren't most steel tapes equipped with a loop end? Just hook your DE-LIAR onto this loop, pull, and mark your tape appropriately.

OK, I pulled the reel cover plate and there is a loop of pure tape but to make that loop the tape necked down to about half.   Pretty sure though that the loop would deform plastically with a direct hook up to the thin metal De-Liar hook.   You could pretty easily rig up a clevis arrangement though and use the loop.  I have been "calibrating" my hand with a 20 pound weight just before measuring and directly pulling on the tape.

This is a gizmo to make tape pulling with a DeLiar convenient.

Then, tried an experiment.: The “zero” end of a 200’ CST Berger 82-20010 B tape was nailed to the pavement of a walking trail. Then the tape was stretched out 200’ and allowed to relax.  An alcohol thermometer was set out in the shade of the tool.  Then a piece of masking tape was marked with a line at the 200.000’ point of the tape.  First, the tape was stretched using one hand “calibrated feel” tightness and a dot was put on the tape at that point.  It was awkward both holding the tape with one hand and marking with the other.   Next, pull forces of 5, 10, 15, 20 and 25 pounds were applied using the De-Liar which is over 50 years old.  A dot was made at each point.  A temperature of 83 F was noted at about 8:05 pm.

A passer-by asked if I needed any help so the experiment was repeated but this time two hand pulling was possible.  A second piece of tape was put down right next to the first tape and the 200’ point marked.  It was noted that the 200’ relaxed point was not even .005’ past the first set of measurements.  I pulled and she marked the particular pull points.

This is a table of results:

A few days later, I tested the 50 year old Deliar against a 20 lb dumbell and got only 18.5 lb.  That means 20.0 lb indicated was really 21.5 lb applied.  AND that the calibrated hand applying 20 lb force was almost dead on what it should have been.

Oscar

Pete Riegel is smiling from above to see someone conducting and reporting on experiments in this forum. Thanks Oscar.

Like most people I'm guessing, I tension the tape by feel when measuring a cal course. I do occasionally get my fish scale out to check what 10-11lbf feels like though, just as kind of an ad-hoc calibration. I think there is a tendency to pull harder that you should, so it's a good idea to check yourself every now and then.

The stretch of the tape should be linear as a function of pull force. The fact that your data does not show this just indicates it's hard to be precise with this, and there is going to be some scatter. The hope, which I think is justified, is that the scatter of multiple tape pulls will tend to cancel itself out.