Calibration Shaft Variation
Dave Tutelman -- 3/9/2006
As people have been building their NeuFinders, they have been posting
the profile of their calibration shaft, as measured on their NF4. It
turns out this can be a good sanity test, and has helped in finding and
fixing bugs in a couple of machines. So let me show you a sample of six
calibration shaft profiles. Note that all are from the same batch of
Mercury Savage shafts at 300cpm. Other batches may vary from this data,
though we haven't seen much variation so far. Other models of shaft
will undoubtedly give more variation from this data; this is
significant because Mercury is going out of business, and we will have
to pick a new model for our calibration shaft.
Here is the data:
Statistic
|
Nominal
Load
|
39"
|
34"
|
29"
|
24"
|
19"
|
Stats
|
Median
|
4.535
|
2.37
|
2.84
|
3.555
|
4.745
|
7.175
|
Mean (average)
|
4.532
|
2.39
|
2.85
|
3.56
|
4.755
|
7.207
|
Standard deviation
|
15g
|
30g
|
24g
|
24g
|
40g
|
83g
|
Range
(and width of range)
|
4.51-4.55
(40g)
|
2.36-2.44
(80g)
|
2.83-2.89
(60g)
|
3.52-3.57
(50g)
|
4.71-4.83
(120g)
|
7.15-7.37
(220g)
|
Shaft
Identification
|
Nominal
Load
|
39"
|
34"
|
29"
|
24"
|
19"
|
Raw
Data
|
NF4-0 F
|
4.51
|
2.37
|
2.83
|
3.52
|
4.71
|
7.15
|
NF4-0 I
|
4.52
|
2.36
|
2.85
|
3.56
|
4.83
|
7.37
|
NF4-0 H
|
4.53
|
2.40
|
2.83
|
3.57
|
4.76
|
7.19
|
NF4-0 A
|
4.54
|
2.37
|
2.83
|
3.57
|
4.74
|
7.16
|
NF4-0 E
|
4.54
|
2.40
|
2.86
|
3.59
|
4.75
|
7.21
|
NF4-0 J
|
4.55
|
2.44
|
2.89
|
3.55
|
4.74
|
7.16
|
How to use the data:
- This is mostly intended as a sanity test of the construction of
your NF4. So you are looking to see if your NF4 is measuring your
calibration shaft in a way consistent with other calibration shafts.
The data above is useful for that purpose if the raw calibration shaft
is a Mercury Savage steel shaft with a raw frequency of 300-302cpm. If
not, don't try to use this data as a sanity test. It is likely not to
match your shaft, even if your NF4 is well-built and properly adjusted.
- Profile your own calibration shaft, and look at the profile.
- If each station is close to the median number in the table above, then your NF4 is probably spot-on.
- If each station is somewhere within the range of the table above, you have nothing to worry about.
- If your numbers are outside this range:
- Review the critical dimensions of your NF4, to be sure it was cut properly.
- Be sure everthing that needs to be secure and tight is so. That
especially includes the bolts supporting the bearing blocks and rotator
board pivot bearings. Be sure the "kerf-squeezing" bolt is as tight as
possible.
- Go through the entire calibration procedure again, just to be sure you did it right.
- Repeat the profile of the calibration shaft, and compare the
numbers again to the table above. If they haven't changed from the
first time....
- Consult the NF4 discussion group for help.
|
