How to Take a Reading

Dave Tutelman -- August 2, 2005

Study and practice taking readings as described in this instruction page. It is the basis for everything you will do with the NF4. All the instructions for operations like shaft matching, profiling, and spine finding will be given in terms of "readings", as defined on this page. So you should know this stuff like the back of your hand.

An NF4 "reading" is a single number, a measurement of load in kilograms (Kg). These notes tell how to take an accurate and relevant reading. Here are the factors that you have to assure in order to take the reading:
Most of these are obvious, but a couple require some explanation:
The toggle board position, middle bearing position, and precision should be part of the instructions for each operation of the NF4.

Here is a step-by-step for taking a reading:

1. Make sure the toggle board is in the proper position.
Upper position:
  • For profiling
  • Bolts in lower holes

Lower position
  • For matching, spine finding, other operations
  • Bolts in upper holes

2. Set the beam length. You have two rulers you can use. Which you choose depends on the beam length you are trying to set.

If the beam length is between 28" and 36", then either ruler will do the job. For example, consider the beam setting of 31" in the photo. You can read the upper ruler at the tip of the "wand" (the aluminum extension with the orange tip), or the lower ruler at the "popsicle stick".

For beam lengths longer than 36½" or so, you must use the upper scale. Looking at the beam setting of 40" in the photo, the popsicle stick is beyond the backer board, so the only useful indicator is the wand.

For beam lengths shorter than 28", you must use the lower scale. The tip of the wand is tucked behind the rotator board in the photo, which shows a beam setting of 22", so the only useful indicator is the popsicle stick.

Note that the wand will not be able to slip behind the rotator board when the toggle board is in its lower position. The wand will bump into the rotator board pivot bolt and stop. But you only need such short beam lengths for profiling, and the toggle board is in the upper position for profiling.

3. Insert the shaft. Place the toggle in the open (unloaded) position, as shown in the photo. Slide the shaft into the bearings.

4. Be sure the shaft rests appropriately in the middle bearing block: bearing side or  V-notch side. It would be used in the V-notch in a few circumstances, all of which involve needing to take a reading with the shaft in a specific, known orientation.
5. Position the shaft in the bearings. This is almost always specified by where the tip is with respect to the tip stop.

For instance, for profiling and calibration, the shaft should have the tip resting against the tip stop, as shown in the photo.

For other operations, such as determining tip trim sensitivity, the tip would extend past the tip stop (with the tip stop rotated out of the way). In those cases, the position would be measured from the tip of the shaft to the inner edge of the tip stop.
Also, if the shaft is in the V-notch of the middle bearing block, rotate it to the desired position. The photo shows the shaft resting in the V-notch rather than the bearings.

The shaft should not rotate in the V-notch, but an occasional shaft will. This is due to a combination of residual bend and a slippery coating. If it rotates, the friction can be increased with masking tape on the shaft where it meets the V-notch.
6. Be sure the digital scale is on. There is a timeout that will turn it off if it isn't used for a minute or two, so you may have to turn it on even if this is not your first reading of the session. You must turn it on now. If you discover it is off later in the sequence, back off to this step and proceed again from here.

Note that the scale will refuse to turn on if there is too much load on it when you press the "on" button. That is not the only reason the scale must be on by this point, but it is a good one. (But see notes below.)

While you are here, be sure your scale is set to read in kilograms.
7. Load the shaft. Set the toggle to full load, as shown in the photo. If the shaft is in the middle bearings (as opposed to the V-notch), then rotate it a few degrees in each direction and allow it to find a stable position. Now leave it in this orientation for the rest of the steps.

8. Tare the scale. As soon as the reading on the scale stabilizes, press the "Tare/Zero" button on the scale. The reading should go to zero and stay there. If it does not, press it again. It may require a little practice to find a hand position that presses the button while supporting the scale body, so it consistently reads zero after you remove your hand and the scale settles.

Yes, you must tare every single time you make a measurement.
9. Back off to preload. Flip the appropriate toggle stop out, perpendicular to the toggle board.
  • If the toggle board is in the lower position then use the L-shaped stop.
  • If the toggle board is in the upper position use the rectangular stop.
The photo shows the toggle board in the lower position, using the L-shaped toggle stop.

When the aluminum yoke is firmly against the stop screw (as shown in the photo), watch the digital scale.
10. Read the load. Wait for the reading on the digital scale to stabilize, and note the reading. It will be a negative number. If you ignore the minus sign, that number is the load in Kilograms.
11. Check the precision. If there was a previous reading, and that previous reading agrees with this reading within the desired precision, then you are done!

For example, suppose:
  • The digital scale reads 4.72 Kg.
  • The desired precision is 0.03Kg.
Then you are done if:
  • You took a  previous reading, and...
  • It was between 4.69 and 4.75 Kg. That's the 4.72 that you just read, plus or minus 0.03.

If the readings disagree or if there was no previous reading, then continue.
12. Relax the shaft and repeat. Flip the toggle stop out of the way, and unload the shaft completely. Then return to step #7 and proceed from there.

See note #1 below for a "streamlined" alternative.


  1. When you are getting good enough readings that you get agreement for the first two measurements just about every time, there is a quicker "streamlined" alternative to this procedure:
    • At step #12, instead of unloading and repeating, tare the scale. (Press the "Tare/Zero" button, repeating until the scale reads 0.00.)
    • Load the shaft fully and read the measurement. It should agree with the previous measurment.
    • As soon as you have recorded the measurement, unload the shaft; see note #2.
  2. Do not leave the shaft fully loaded for any longer than is absolutely necessary. Some shafts will take a "set" (at least temporarily, for anywhere from minutes to hours) if loaded for more than a few seconds.
  3. During the steps of loading and unloading, keep an eye on the shaft tip, to be sure it is still in the proper place (for instance, firmly against the tip stop). Sometimes rotating the shaft can cause it to drift away from the stop.
  4. If you absolutely, positively have to turn the scale on under load -- under enough load that it doesn't want to start up -- there is a way to do it. But do not do this routinely; it is bad practice and could lead to inaccurate readings. With that caveat, here's the magic trick; don't depend on it too heavily.
    Press down on the rear of the rotator board, so the weight of your pressure is taking weight off the scale. With the other hand, turn on the scale. Keep pressure on the board until the scale is completely on and showing a reading.

Last modified by DaveT - 8/14/2005