How to Profile a Shaft

Dave Tutelman -- August 9, 2005

One of the primary design goals of the NeuFinder 4 (NF4) was that it should be a first-class tool for profiling the stiffness of shafts. The result is the ability to do profiling quickly, simply, and accurately. The profile is a series of stiffness readings analogous to the frequency profile readings used by Tom Wishon and others for frequency profiling shafts.

Let's look at a comparison of how NF4 profiling relates to frequency profiling. In the table below, we see an NF4 and a frequency meter doing profiling. The frequency meter takes a profile by clamping the shaft at different points along its length, and measuring the frequency of the remaining unsupported beam. The NF4 takes a profile by shortening the beam length, but keeping the tip in the tip stop next to the front bearing. As we can see, the situations are very similar, except in the actual number representing the stiffness (a vibration frequency vs a deflected load).

Frequency Profiling		NF4 Profiling
	Butt stiff- ness
	Tip stiff- ness

For both frequency and NF4 profiling:

Measuring tip stiffness is fairly "pure", because the butt is not part of the beam length; it is sticking out the back of the instrument and not being measured at all.
Measuring butt stiffness is a mix of influences; what is measured is mostly due to the butt, but has some component of the middle of the shaft and a smaller component of the tip.

The instrumentation is so similar that it should be possible -- probably even easy -- to convert mathematically between frequency and NF4 profiles. But the formulae for this have not been worked on yet.

How to do NF4 Profiling

An NF4 "profile" is a collection of readings at various beam lengths, for a single shaft. The underlined terms have precise NF4 definitions; use them. The set of beam lengths is currently taken at five-inch intervals, starting with the shortest beam length an NF4 can take: 19". So the beam lengths in a profile for most shafts are:

Most wood shafts	Most iron shafts
44"
39"	39"
34"	34"
29"	29"
24"	24"
19"	19"

The lengths are shown longest first because that is the order in which the readings will be taken. Why? Because it is faster and easier to do it that way.

Here are the instructions for profiling a shaft.

1. Use the upper position of the toggle board, as shown in the photo. A consequence is that you will use the rectangular toggle stop to set the pre-load.

2. Use the bearing side of the middle bearing assembly. You will measure the shaft's stiffness in its most stable position under load in the NF4.

3. Set the beam length at the largest beam length for the profile. That will be 44" for a wood shaft and 39" for an iron shaft, unless the shaft is too short to be read at that length. If the shaft is too short, use the longest whole-inch length that gives a stable reading, with all bearings securely on the shaft.

4. Take a reading, using a precision of 0.03Kg.

5. Unload the shaft and unlock the beam; then slide to the next smaller beam length and lock it there. Leave the tip against the tip stop, and the shaft will just slide in the front bearings, with no extra effort on your part. You may have to move the shaft a fraction of an inch to seat it securely against the tip stop, but that takes only a second.

Do not forget to lock the beam with the cam clamps before you take the next reading.

6. Repeat steps #4 and #5 until you have readings at all the lengths.

Additional Information on NF4 Profiling

The NF4 Shaft Profile Database
Coming soon, we hope.
Shaft Deflection Profiling
Some of Dave Tutelman's early experiences using the NF4 for shaft profiling. The article shows that deflection can be as good or better than frequency for "zoning" a shaft. It also introduces some data reduction (which works for both deflection and frequency) that highlights the profile differences between shafts -- which might otherwise be masked by overall stiffness differences. The same site has an article about data transforms that make profile differences more meaningful.
Relation Between NF4 Profiles and Frequency Profiles
Work to be done

Last modified by DaveT - 9/20/2016