[Jeff Kissel, Rick Savage, Timesh Mistry]
Overview:
This is a summary of progress so far on the hardware side of things as well as the lab test conducted on 20170731, a full log can be found in the text file 'NCAL_LabTest_PEM_20190731.txt' attached to this alog.
The plan was to collect PEM measurements (accelerometer and magnetometer) of the NCAL before fully dis-assembling the NCAL unit. We tripped the wall sockets multiple times when trying to set up additional equipment for PEM measurements. We discovered a wobble when running the NCAL at ~10Hz, worse that what we have seen when previously running the NCAL as well as a bad screw in the back plate of the NCAL the is attached to the main flywheel.
a) Old Plan Plan (as of 29th July 2019):
Rick, Jeff and I decided that we would completely disassemble and reassemble the NCAL. This is so that we can do the following:
a) Apply safety measures such as loctite and lock washers to the relevant bolts.
b) Clean all the parts and remove any alloy shavings, dirt and debris.
c) Using wet and dry + alcohol, sand down the bores of the NCAL to remove the surface roughness so the masses fit easier.
d) Become familiar with how to disassemble and assemble the NCAL and write up procedure.
e) Torque the bolts. The torque setting have yet to be determined. I will be going off the values found in the attached document otherwise.
f) Get PEM measurements, voltage, current and other measurements before and after re-assembly. (Suggestion from Krishna remotely)
b) New Plan (as of 31th July 2019):
a) Replace the bad screw
b) Clean surfaces of NCAL
c) Find the source of the wobble
d) Get PEM measurements, voltage, current and other measurements before and after re-assembly. (Suggestion from Krishna remotely)
e) Become familiar with how to disassemble and assemble the NCAL and write up procedure.
f) Using wet and dry + alcohol, sand down the bores of the NCAL to remove the surface roughness so the masses fit easier.
g) Clean all the parts and remove any alloy shavings, dirt and debris.
h) Apply safety measures such as loctite and lock washers to the relevant bolts.
i) Torque the bolts. The torque setting have yet to be determined.
The reason the for the above is given below for those that are interested.
1) Review from Machine Shop:
a) Long winded summary:
This follows after a visit to TK Machining where we had left the NCAL with them and asked them to machine the NCAL masses and clean up the scores in the bores (holes) of the rotor. There was a communications break down and TK Machining was under the impression we wanted a 'hammer fit'. I recall specifying a Class 4 press fit (apparently not an engineering standard as no-one knows what I was talking about).
TK did not do any machining on the parts as they found the some of the masses could be fully inserted into their designated holes with little effort at room temperature (we had not given TK Machining the heating apparatus). Furthermore, TK Machining pointed out that some of the bores (mainly #1 and #5) had significant scoring such that this will certainty cause difficulties inserting and removing the masses. Moreover, TK Machining noted that the NCAL masses had sharp edges that would also lead to increased damage to the surface of the bores if the masses were not inserted and removed perfectly. When we asked TK Machining 'How would you tackle removing material from the NCAL masses and the surface of the holes?', they responded with the following:
a) The NCAL masses would be held in a lathe, clamped at each end and centered. A hand tool will then be used to remove material from the mass while the mass is spinning, measuring frequently.
b) The rotor will be taken to a honing machine and, by hand they will hone each hole, measuring frequently.
All in all, we took the NCAL back to LHO and between Rick, Jeff and myself, we reviewed the comments from TK Machining and came up with the plan at the top of this email.
2) Issues Discovered:
a) Wobble
In the process of running the NCAL for the PEM test. The NCAL has developed a wobble.
At 10Hz (1043 counts) there is a gentle rocking motion that can be seen from from looking at the orange comms cable. When placing my hand on the shell, I can feel a wobble. This is certainty worst than than before because this time around, when spinning at ~10Hz, the table that the NCAL is bolted to is visibly shaking. there is no play or excessive resistance in the bearings. I had a thought that the back plate is misaligned slightly and that could be the cause of the wobble but I have discovered another issue.
b) Bad Screw
I have found a 10-32 socket head cap screw that does not want to fit back into the main rotor that holds the rotor base. Upon further testing, I had 1 of 2 suspicions:
a) It is a metric M5 screw
b) It is a bad quality imperial 10-32 3/8 cap screw
I consulted with Chandra and Rick and the overall conclusion was that it is a bad 10-32. This is because:
1) After 1 1/2 turns with the offending screw would 'bind' (increase resistance) when tested in other 10-32 holes in the NCAL and when testing in a screw pitch gauge.
2) When putting the offending screw into the metric M5 screw pitch gauge, it would fit but would wobble (strike one for metric theory)
3) When comparing the threads of the offending screw to a 10-32 tap and other 10-32 screws, the threads match (strike two for metric theory).
4) There are no marking on the top of the head of the screw as this is typical of metric screws (strike three for metric theory).
What I suspect is that a longer 10-32 has been cut down to the required size (I think 3-8) and has not been done properly. I am going to order more 10-32 3/8 screws and replace the bad one. In addition I have already cleaned up the threads with a wire brush as Isopropanol.I have also clean the mating surfaces of the NCAL and the back plate with alcohol wipes and cleaned the threads of the remaining good screws.
The problem of the wobble still remains.
c) Tripping the wall sockets
When trying to power the spectrum analyser, we tripped the wall socket (Serial Number: 168RP1-17). fter resetting the wall socket, tediosly, we tried each plug one by one on the wall and did not trip the wall. We found that using the we could apply no more than 3 plugs to the wall before it tripped. It did not matter if we used a power extension or directly into wall.
To get around this issue, we used a extension from anther wall socket (Series Number: 168RP1-20) in combination with the wall socket in this combination:
Socket 168RP1-20 : Spectrum Analyser, DC power supply, Oscilloscope, PC Monitor
Socket 168RP1-17 : Beckhoff motor controller
When using the power stip, we found we could only use 3 slots as plugging in a 4th plug would trip the wall socket.
