NF4 Calibration and Adjustment

1. Level the feet

2. Mount the rotator board on its bearings

If you haven't already done so, slide the rotator board onto the pivot bearing assembly. Start to tighten the kerf bolt, until you can just slide the board in and out on the pivot bearings a fraction of an inch. If you have already mounted the rotator board, then loosen the kerf bolt, until you can just slide the board in and out on the pivot bearings a fraction of an inch.

Slide the board in or out, until the board just touches the stabilizer bearing on the rotator stop (see picture). It is better that it just miss touching it than that there is pressure between the bearing and the rotator board. Pressure introduces friction, and makes the readings less consistent.

Tighten the kerf bolt, being sure to keep the board in the position that you just set. Do not let the board slide in or out on the pivot bearings while you are tightening.

3. Set one toggle stop

The most reliable way to set the 15/8" gap is to cut a small block of hardwood with exactly the right distance between the faces. Make the controlled dimension be along the grain, so humidity has the minimum effect on it. Trim it with a very precise saw, and "sneak up" on the proper dimension. Check every trim with precision calipers; I used a dial calipers good to .001". Aim at being within .010" of the proper value. The photo shows a single block with both measurements, 15/8" and 1", that I was able to make. (The original gapping procedure for the early test models required templates for both measurements. The current improved procedures do not.)

Now use the block to adjust the toggle stop screw: Throw the toggle to the fully loaded position. Flip out the L-shaped stop. Slide the 15/8"" hardwood block between the yoke and the stop screw, as shown in the picture. Adjust the stop screw so that the block fits snugly but not a press-fit between the yoke and the stop screw. If, like me, you have a nut on the stop screw to lock it in place, be sure this fit works with the nut secured.

The L-shaped toggle stop is now set. Label and save the hardwood block. Use it from time to time, to check that this setting is still correct. If it is not, repeat the steps to set the stop screw.

Using a ruler, set the gap for the rectangular toggle stop to 1". This does not need to be very precise yet, but should be within 1/16" of the correct setting. We will set it more precisely later.

4. Adjust the rotator board angle

Set the toggle board in the profiling position (with the bolts through the lower set of holes).

Retract the rotator board stop screw. Set it to a large clearance, to allow the maximum rotation of the rotator board. Remember that this screw does not set the rotator board angle. All it does is control the slack once the angle is set. The angle itself is controlled by the height of the eyebolt.

The height of the eyebolt controls the angle of the rotator board. We will adjust the angle by adjusting the height of the eyebolt. For an NF-4, the picture on the left shows where the adjustment is made. For an NF-4.1 or later, the picture on the right shows where the adjustment is made. Adjust the nuts that hold the eyebolt, so that the eye is in the middle of its range. To do this, set it so the same amount of thread is showing above and below the hole. (In the left photo, the eyebolt is at the low end of the range, with no thread showing above the upper nut.) As you proceed, you will be adjusting this height until it gives the correct readings.

1. Place the calibration shaft in the bearings, with the tip against the tip stop. Start with a beam length of 29".
2. Take a measurement using the following procedure:
   
• Set the distance, and release the load imposed by the toggle clamp. At this point, the rotator board should be "slack". This means that there is no load on the digital scale, and the rotator board is resting on its stop.
• Make sure the shaft is sitting in the three sets of bearings, with the tip against the tip stop.
  
• Zero the scale with the "zero/tare" button. If the scale is off, turn it on and wait for "0.00" to display.
• Set the toggle to fully loaded, and "tweak" the shaft so it settles into a local NBP.
• Flip out the rectangular toggle stop, and release the toggle clamp to the profiling preload position. (The yoke should be against the rectangular stop.)
• Read the digital scale, and record the reading.
3. Repeat step #2 for beam lengths at increments of one inch down to 19". We're starting at the longest and going to shortest; this is easier than going from 19" to 29", as the tip stop will move the shaft with it as you shorten the beam length.
4. Look at the smallest reading you recorded over all the one-inch intervals. If it is between 0.90Kg and 1.00Kg, you are done. Otherwise, adjust the height of the eyebolt and repeat the steps above until the smallest reading is in the 0.90-1.00 range.
   

Now the rotator board angle is set. It is time to raise the rotator board stop screw and take out the slack rotator board motion. Raise the screw until the clearance is about 1/16"; the exact amount is not critical but there must be some clearance. It is best if there is enough clearance so you can see or hear the "click" as the slack is removed. Knowing there is slack will be a useful warning later when you are actually using the NF4.

Now it is time to do a check, to make sure the angle is OK for other types of shafts. If you have an NF4, you probably have quite a few shafts on hand. Take out a few, and repeat the measurements  you made with the calibration shaft. The minimum reading should be at least 0.20Kg. The shafts that push this limit the most strongly are very flexible steel shafts with long parallel tip sections. For instance, my NF4 has problems with L-flex steel shafts and the old Balistik combi flex. (These days, you will seldom see any of the shafts that give me trouble, which is a good thing.) If the minimum reading is below 0.20Kg, you will need to do something special to profile that shaft. Here are the possible solutions: Readjust the eyebolt, to give at least 0.20Kg as the minimum reading for the worst-case shaft. This is the simplest solution, but it has a downside. You are reducing the headroom you will have when profiling a tip-stiff shaft. If you never have to profile a stiff shaft with a stiff tip, then this could work for you. A more general solution is to use a hard tubular sleeve to measure such shafts. Place it over the tip, as shown in the picture. The thickness of the sleeve wall should take out some or all of the slack in the measurement. One of the best sources for a sleeve is a few inches cut from the butt of a graphite shaft. The next time you butt-trim about three inches from a graphite shaft, save the trimming for this purpose. It fattens the tip for measurement purposes, enough to add about 0.20Kg to the reading, which is enough for most shafts. If the sleeve is not thick enough for all your shafts (which is possible), you can cut a sleeve from a section from thicker-wall aluminum tubing or hard plastic pipe.

5. Calibrate

Before we begin the calibration procedures, let's look at the calibration shaft. It has quite a few markings on it in the vicinity of the butt. Here is what each one refers to:

What it's called	Example in photo	What it means
Mfr Info (optional)	302 +/- 1CPM	Information that the manufacturer of the shaft chooses to put on the shaft. In the case of the current calibration shafts, the manufacturer is Mercury and they put the measured frequency on a butt label.
Serial # (optional)	F	The person who turns the shaft into an NF4 calibration shaft may choose to keep track of the individual shafts. For the ten generation-0 shafts that I made, I gave them designations from A through J, and have recorded who received them and the calibration load for each.
Model	NF4	It is possible that future designs of NeuFinder will require calibration shafts that are incompatible with the NF4. I expect and hope that does not happen, but just in case we have reserved a field to indicate which NeuFinder the shaft works with.
Generation	0	This indicates how many generations of calibration shafts were used to get to this one. I built generation 0 in a half-hour session on my NF4, so they are as close to one another as an NF4 can possibly measure. A calibration shaft made from a reference of a generation-0 shaft is a generation-1 shaft. While I don't expect the need to arise, a calibration shaft made from a reference of a generation-1 shaft is a generation-2 shaft. Etc etc etc. With each increasing generation, the calibration shaft tolerance increases by about ½ percent.
Calibration	4.51	When using the shaft to calibrate your NF4, set the machine to this load in Kilograms.

Now let's use the calibration shaft to calibrate an NF4.

5.1. Coarse calibration

1. Put the toggle board in the matching position (the T-slot bolts go through the upper holes in the toggle board).
2. Set the beam length at 35", the normal length for matching iron shafts.
3. With the toggle clamp completely unloaded, place the calibration shaft in the three sets of bearings, with the tip against the tip stop.
4. Throw the toggle to fully loaded, flip out the matching preload stop (the L-shaped stop) and release the toggle so it is firmly against the preload stop.
5. Set the digital scale to zero with the "zero/tare" button.
6. Throw the toggle to fully loaded, and read the digital scale. It should be somewhere not far from the calibration load marked on the shaft.
7. Repeat from step #4, until you are convinced that the reading you get is stable and repeatable.
   
8. If that reading is within 0.10Kg of the target load marked on the shaft, you are done. Your NF4 is coarse-calibrated. If not, proceed to the next step.
9. Remove the shaft from the bearings.
   
10. Loosen the nut that holds the upper scale bolt in the slot, as shown in the picture. Loosen it until you can slide the bolt along the slot.
11. If your reading was too high, slide the bolt a little to the left. If your reading was too low, slide the bolt a little to the right. Tighten the nut.
    
12. Go back to step #3, and proceed from there.

5.2. Fine calibration of the L-shaped toggle stop

1. Leave the toggle board in the matching position, and the beam length at 35".
   
2. With the toggle clamp completely unloaded, place the calibration shaft in the three sets of bearings, with the tip against the tip stop.
3. Throw the toggle to fully loaded, flip out the matching preload stop (the L-shaped stop) and release the toggle so it is firmly against the preload stop.
4. Set the digital scale to zero with the "zero/tare" button.
5. Throw the toggle to fully loaded, and read the digital scale. It should be somewhere not far from the calibration load marked on the shaft.
6. Repeat the previous step until you get the same reading twice in a row. You want this to be spot-on, so it is worth taking the time to be careful about it.
   
7. If that reading is anywhere with 0.01Kg of the target load marked on the shaft, you are done. Your NF4 is calibrated. If not, proceed to the next step.
8. Remove the shaft from the bearings.
9. Adjust the screw in the L-shaped toggle stop. If your reading was too high, turn the screw a little to the left. If your reading was too low, turn the screw a little to the right. If you use a nut to secure the screw, tighten the nut.
   
10. Go back to step #2, and proceed from there.

5.3. Adjust the rectangular toggle stop

1. Leave the toggle board in the matching position, and the beam length at 35".
2. With the toggle released, insert the calibration shaft so that the shaft tip rests against the tip stop.
3. Take a reading, using the L-shaped toggle stop and a precision of 0.01Kg.
   
4. Multiply that reading by 0.61. Call the result "X".
   
5. Without changing the toggle block position or beam length, take a reading using the rectangular toggle stop. Again, the precision should be 0.01Kg.
6. If the new reading is within 0.01Kg of X, then you are done.
7. Adjust the screw in the rectangular toggle stop. If your reading was too high, turn the screw a little to the left. If your reading was too low, turn the screw a little to the right. If you use a nut to secure the screw, tighten the nut.
8. Go back to the step #5, and proceed from there.

Maintenance

• Save the hardwood blocks you used to adjust the toggle stops.
• Save the shaft measurements you made to adjust the rotator board angle. That way, you will know which shafts at which beam lengths were the most critical, and can minimize the time it takes you to set it again.
  

Modification history