A small followup measurement. Here are spectra of the MC trans diode with and without the ISS on. The DC value of the diode (in counts) changed from 17264.2 (no ISS) to 17504.3 (with ISS), but I didn't account for this change in the plot.

There is a small inkling of benefit between 100Hz and 1kHz. Above about 100Hz, the RIN is suppressed to about the noise level of this measurement. Below 100Hz there is no change, which probably means that power fluctuations are introduced downstream of the AOM, which argues for an outer-loop ISS down the road.

Atm #2 is in units of RIN.

Yesterday afternoon, I went back into the BS chamber, and flipped both PR3 and SR3. Now all of the recycling cavity folding mirrors have been flipped.

For PR3, I followed the same procedure as SR2, setting a reference position, removing the optic, flipping it, etc.  When I put it back in, I realized that since this has a 41 degree angle of incidence, the beam going to the BS had translated north by ~1cm.  After some fiddling, Koji pointed out that the 2 degree wedge probably had a more significant effect than just the HR surface having moved back a small amount.  Anyhow, we adjusted PR3 such that we were going through the BS aperture, as well as the ITMY aperture. 

During the flip of PR3, Annalisa and I noticed that the arrow on the barrel of the LaserOptik mirrors also indicates the thickest part of the wedge.  This is opposite of our SOS optics, where the arrow's position on the barrel indicates the thinnest part of the wedge.  For both PR3 and SR3, I kept the arrow on the same side of the optic as it was originally.

I then flipped SR3, following again the same procedure.  PR3 I had done a tiny bit of pitch rebalancing, although I think it was unneccessary, since it is within what we can do with the poking/hysterisis method.  SR3 I did not do any pitch rebalancing.  With PR3 aligned at least to the ITM, Koji and I aligned SR3 and SR2 so that the AS beam was hitting the center of all the SRC optics.  We also adjusted the steering mirrors after the SRM to get the beam centered on PZT3, the last optic on the BS table, which launches the beam over to the OMC chamber.  We scanned around a bit by turning the PZT's knobs, but we were unable to see the AS beam on the camera. 

SR2 is set to go through a free swinging test at 3 am tonight. We have used this script (Git/40m/scripts/SUS/InMatCalc/freeSwing.py) reliably in the past so we expect no issues, it has a error catching block to restore all changes at the end of the test or if something goes wrong.

To access the test, on allegra, type:

Then you can kill the script if required by Ctrl-C, it will restore all changes while exiting.

[Jenne, Annalisa]

SR2 is flipped, and reinstalled.  We did that before lunch, and we're about to go in and work on SR3 and PR3.

EDITS / Notes:

I set dog clamps to have a reference position of where the tip tilt was, then I removed SR3 from the chamber.  Once out, I followed the same procedure I used for PR2 during the last vent - I removed the whole suspension (top mount, wires, optic) from the cage, and laid it down flat.  Then I loosened the set screw which pushes on the teflon nudge, removed the mirror, inspected it, and put it back in, with the HR side facing the back side of the ring.  Then I replaced the suspension system in the cage, and put the mirror back into the chamber. 

When I loosened the teflon nudge at the top of the mirror holder ring, the optic seemed to fall down a tiny bit.  I think this implies that the HR surface of the optic did not used to be parallel to the front face of the mirror holder ring.  When I put the suspension back onto the cage, the pitch balancing was very bad.  We checked the level of the table that I had the cage on, and it was miraculously pretty level, so I did the pitch balancing out of the chamber. 

Also, during my quick inspection of the mirror (not thorough, just using room lights), I noticed a small fleck of lint near the edge of the optic on the HR surface.  The HR surface is now on the outside of the SRC, but we should still blow at the optic with the ionized nitrogen to get it off.

I did not think to check the fine-tuning alignment of SR2....Koji did that after lunch (which I will elog about in a separate elog).

After the first flipping, X/Y arms were aligned and locked. Then the ASS aligned the arms.

The free swinging test was successful. I ran the input matrix diagonalization code (/opt/rtcds/caltech/c1/Git/40m/scripts/SUS/InMAtCalc/sus_diagonalization.py) on theSR2 free-swinging data collected last night. The logfile and results are stored in /opt/rtcds/caltech/c1/Git/40m/scripts/SUS/InMAtCalc/SR2 directory. Attachment 1 shows the power spectral density of the DOF basis data (POS, PIT, YAW, SIDE) before and after the diagonalization. Attachment 2 shows the fitted peaks.

1.09

0.914

0.622

0.798

-0.977

1.249

0.143

-1.465

-0.359

0.378

0.552

-1.314

-0.605

1.261

0.118

0.72

0.403

0.217

0.534

3.871

The new matrix was loaded on SR2 input matrix and this resulted in no control loop oscillations at least. I'll compare the performance of the loops in future soon.

This morning I found that there was no light on the SPOB PD. I went looking at the photodetector and I found that the shutter in front of it was closed.

I switched the shutter driver from n.c. to n.o. which had the effect of opening it.

I guess we inadvertently closed the shutter with Rana when last week we were tinkering with the ITMY  camera.

SP table has been a mess because Q and I had let our SURF leave without cleaning up.

I cleaned up the SP table, put things back where they belong and did some sorting. I will put back the optomechanics where they belong sometime later.

For now, check out the SP table next time you are looking for a Y1  or lens or BS.

[Jenne, Diego]

The EPICS freeze that we had noticed a few weeks ago (and several times since) has happened again, but this time it has not come back on its own.  It has been down for almost an hour so far. 

 So far, we have reset the Martian network's switch that is in the rack by the printer.  We have also power cycled the NAT router.  We have moved the NAT router from the old GC network switch to the new faster switch, and reset the Martian network's switch again after that.

We have reset the network switch that is in 1X6.

We have reset what we think is the DAQ network switch at the very top of 1X7.

So far, nothing is working.  EPICS is still frozen, we can't ping any computers from the control room, and new terminal windows won't give you the prompt (so perhaps we aren't able to mount the nfs, which is required for the bashrc).

We need help please!

[EricQ]

EricQ suggested it may be some NFS related issue: if something, maybe some computer in the control room, is asking too much to chiara, then all the other machines accessing chiara will slow down, and this could escalate and lead to the Big Bad Freeze. As a matter of fact, chiara's dmesg pointed out its eth0 interface being brought up constantly, as if something is making it go down repeatedly. Anyhow, after the shutdown of all the computers in the control room, a  reboot of chiara, megatron and the fb was performed.

[Diego]

Then I rebooted pianosa, and most of the issues seem gone so far; I had to "mxstream restart" all the frontends from medm and everyone of them but c1scy seems to behave properly. I will now bring the other machines back to life and see what happens next.

[Diego, Jenne]

Everything seems reasonably back to normal:

Notes:

• the machines in the control room have been rebooted;
• the c1iscey frontend now behaves;
• I saw on nodus, which remained up and running the whole time, a bunch of   nfs: server chiara is not responding, timed out  messages, belonging to the freezing time; it may be that the sync option for the nfs share is too resource demanding, or some other network issue;
• the FSS was doing strange stuff and the MC couldn't recover the lock; the MCautolocker script wasn't running because of the lock loss of the MC and the lack of communication between the machines; so we did a sudo initctl start MCautolocker on megatron and recovered the MC too.

0.0017" OD., 500ft steel music wire ordered. Pictures of the existing roll are below. It will be on 8" OD. spool too.

The wire will arrive in 1-2 weeks. It is a new production. Brad Snook of Ca Fine Wire was suprised that we are still using the 13 years old wire.  Oxidation is an issue with iron contained steel wire.

He would not give me a shelf life time on it. He recommended to check the strenght of it before usage. It passed with safety factor of 2 just recently.

In the future we'll store the new spool in oxigen free nitrogen environment..

We have indeed seen numerous tarnished/rusty points along the wires, and just tried to choose lengths free of any of these. I wonder if this can explain the brittleness/ease with which we've been breaking it. My feeling is that we should use the newer wire if feasible.

Not really true that it passed. That's just an arbitrary margin. Best to throw away all the old wire. We have no quantitative estimate of what the real torque should be. Its just feelings.

Stress Relieved 0.0017"  Music Wire  CFW P/N: CFW2035025,   Made 08-17-2016                                

GBL (grams breaking load )         

UTS (ultimate tensile strength)                                 

YTS (yield tensile strength) 

ELONG (elongation)  

Two SOS suspensions for the ETMs were disassembled and packed for cleaning and baking by Bob.

These suspensions have been stored on the X end flow bench long years, and looked quite old.

They have some differences to the modern SOSs.

- The top suspension block is made of aluminum and had dog clamps to fix the wires.
- The side bars are not symmetric: the side OSEM can only be fixed at the right bar (left side in the picture).
- EQ stops were made of Viton.
- One of the tower bases seems to have finger prints (of Mike Zucker?).

I found that the OSEM plates had no play. We know that the arrangement of the OSEMs gets quite difficult
in this situation. Therefore the holes of the screws were drilled with the larger drill.

We decided to replace all of the screws to the new ones as all of the screws are Ag plated and got corroded
by silver sulfide (Ag₂S). I checked our stock in the clean room. We have enough screws.

Important note: Use stainless screws in aluminum / Silver-plated screws in stainless
There exists some study about galling: LIGO-G020394-00-D

I opened the packages send from Syracuse.

- The components are not vacuum clean. We need C&B.
- Some large parts are there, but many parts are missing to build complete SOSs.

- No OSEMs.
- Left and right panels for 6 towers
- 3 base blocks
- 1 suspension block
- 8 OSEM plates. (1 SOS needs 2 plates)

- The parts looks like old versions. The side panels needs insert pins to hold the OSEMs in place. We need to check what needs to be inserted there.

- An unrelated tower was also included.

[Yehonathan, Paco]

We put away most items used / involved in SOS assembly and characterization. Many were stored in the left-most cabinet in the clean area. The OpLev test setup and optics were stored in the upper cabinets above the microscope area, and several screws and other general components were collected in clean bags or wrapped in foil, labeled and put away.

Atm 1, It's right arm is perfect.

Atm 3-4, The left one has bended (dropped) end.

Atm 2, Our ruby wire stanoffs will fit the jig. Ruby OD 1.27 mm vs. old Aluminum OD 1.0 mm. Length ruby 6.4 mm vs Al 4.8 mm

Atm 5, The fixture translation stages are a bit loooose. Careful use of the micrometer is needed to be precise

Betsy agreed that the 40m will keep SOS fixtures.

One of the possibilities that we see a large low-frequency digital noise is due to Foton. I've checked the SOS coefficients that saves Foton with a Matlab coefficients. I used a 3 order low-pass cheby1 filter cheby1("LowPass",3,0.1,3) 

In matlab I generated SOS model using 3 approaches 

[A,B,C,D]=cheby1(3,0.1,3/1024) % create SS form

[sos,g]=ss2sos(A,B,C,D)  % convert to SOS form

[z, p, k]=cheby1(3,0.1,3/1024) % create ZPK form

[sos,g]=zp2sos(z,p,k)  % convert to SOS form

[b, a]=cheby1(3,0.1,3/1024) % create TF form

[sos,g]=tf2sos(b,a)  % convert to SOS form

As this is a 3 order filter, in the SOS representation we'll get 2 by 6 SOS - matrix. It is presented below. In each matrix place there 4 numbers - from the Foton file and obtained using these 3 methods.

GAIN

1.582261654653329e-07

1.582261654653329e-07

1.582261654653329e-07

1.582261655030947e-07

SOS-MATRIX

1              1.0000000000000000      #           0                                              #       1      #         -0.9911172660954457     #       0

1              1.0005663179617605      #           0                                              #       1      #         -0.9911172660954457     #       0

1              1.0000000000000000      #           0                                              #       1      #         -0.9911172660954457     #       0

1              0.9999894976396830      #           0                                              #       1      #         -0.9911172660997303     #       0

############################################################################################################

1              2.0000000000000000      #          1.0000000000000000         #       1      #        -1.9909750803252266      #      0.9911175825477769

1              1.9994336820732397      #          0.9994340026283055         #      1       #       -1.9909750803252262       #     0.9911175825477765

1              2.0000000000000000      #          1.0000000000000000         #      1       #       -1.9909750803252262       #     0.9911175825477765

1              2.0000105023603174      #          1.0000105024706190         #      1       #       -1.9909750803209423       #     0.9911175825434912

It seems that smth analog to zp2sos is used in Foton. We can see that due to representation error we have derivations in the 4 and 6 digits for SS and TF forms. This means that a pretty big mistake can run due to digital transforms even using double precision as in the Matlab test.

Alex Ivanov said that he'll fix that single precision problem and in the 2.5 release we won't have any FLOAT variables. Though we still do not understand how that variables declared as FLOAT can cause filter calculations. 

The SOS coil drivers (Atm2) were moved from 1X1 to 1Y2 location. Is this the best place to locate the  IOO Tip-Tilt steering that will replace the PJ-PZT ?

See 40m wiki T-T

The SOS centering target is 1.9 mm lower than it should be! 

The hole is 10mm for the  ~6 mm beam

For the upcoming vent, we'd like to rotate the SOS towers to correct for the large YAW bias voltages used for DC alignment of the ITMs and ETMs. We could then use a larger series resistance in the DC bias path, and hence, reduce the actuation noise on the TMs. 

Today, I used the calibrated Oplev error signals to estimate what angular correction is needed. I disabled the Oplev loops, and drove a ~0.1 Hz sine wave to the EPICS channel for the DC yaw bias. Then I looked at the peak-to-peak Oplev error signal, which should be in urad, and calibrated the slider counts to urad of yaw alignment, since I know the pk-to-pk counts of the sine wave I was driving. With this calibration, I know how much DC Yaw actuation (in mrad) is being supplied by the DC bias. I also know the directions the ETMs need to be rotated, I want to double check the ITMs because of the multiple steering mirrors in vacuum for the Oplev path. I will post a marked up diagram later. 

Steve is going to come up with a strategy to realize this rotation - we would like to rotate the tower through an axis passing through the CoM of the suspended optic in the vertical direction. I want to test out whatever approach we come up with on the spare cage before touching the actual towers.

Here are the numbers. I've not posted any error analysis, but the way I'm thinking about it, we'd do some in air locking so that we have the cavity axis as a reference and we'd use some fine alignment adjust (with the DC bias voltages at 0) until we are happy with the DC alignment. Then hopefully things change by so little during the pumpdown that we only need small corrections with the bias voltages.

Some remarks:

1. Why the apparent difference between ITMs and ETMs? I think it's because the bias path resistors are 400 ohms on the ETMs, but 100 ohms on the ITMs. 
2. If we want the series resistance for the bias path to be 10 kohm, we'd only have ~800 urad actuation (for +10V DC), so this would be an ambitious level of accuracy. 

 Green welding glass 7" x 9"   shade #14 with 40 mm hole and mounting fixtures are ready to reduce scatter light on SOS

PEEK 450CA shims and U-shaped clips  will keep these plates damped.

{Yehonathan, Paco}

{Paco, Yehonathan}

Today we suspended SR2 (E1800089) which Anchal has loaded into the thick optic adapter. Attachments 1,2 show the height and roll balance adjustments.

I realigned the opLev setup and balanced the suspended mass. Attachment 3 shows the motion spectra on the QPD. There are major peaks at 723 mHz, 832 mHz, and 996 mHz. I inserted OSEMs and tightened them in place. I adjusted the OSEM plates to make sure the magnets are at the center of the OSEMs, then I tightened the OSEM plates to the SOS tower.

The optic was locked keeping the alignment fixed on the center of the QPD.

Again, we should apply some glue to the counterweight to prevent it from spinning on the setscrew. Is there a glue other than EP30 that we can use?

Related: Peek nuts, screws and washers were ordered from Mcmaster.

Vacseal in the freezer. It could have been expired sooooo many years ago, We need some cure testing.

Can you release the part numbers of the ordered components (and how/where to use them), so that we can incorporate them into the CAD model?

Yes,

For the thin optics adapter design, we want Peek 1/4-20 screw (part # 98885A131) to replace the lower back long EQ stop. On it, we will have a Peek washer (part # 93785A600) fastened between two Peek nuts (part #98886A813).

For the thick optics adapter design, we want Peek 1/4-20 screw (part # 98885A131) to replace both the upper and lower back EQ stop. On the upper stop, we need a single Peek nut (part #98886A813).

I will cure-test the Vacseal.

I handed the Peek parts we got from McMaster to Jordan for C&B.

[yehonathan, paco, anchal]

We continue suspending PR3 today. Yehonathan and Paco suspended the thick optic in its adapter. After fixing some nominal height and undoing any residual roll angle (see Attachments 1,2 for pictures), we noticed a problem with the pitch angle, so we insert the counterweights all the way in. Nevertheless, we soon found out that we needed to shift one of the two counterweights to the back of the adapter side (so one on each side) in order to tare the pitch angle. This is a newly experienced maneuver that may apply for further thick optics.

After taring the pitch angle roughly, we noted another issue. The wedge (~ 1 deg) on the optic made it such that the protruding socket heads on the thick side bumped against the lower clamp (not the earthquake stop tip itself). Attachments #4,5 show the before/after situation which was solved provisionally by replacing the socket head screws with lower profile (flat) head screws in situ. Again, this operation was highly delicate and specific to wedged thick optics, so for future SOS we should keep it in mind.

Another issue that we had with the new thick optic adapters is that for some reason there is a recession in the upper backside of the adapter (attachment coming soon). This makes the upper back EQ stop too short to touch the adapter. We replaced it with a longer screw. When inserted it doesn't really hit the back of the adapter. Rather, it touches the corner of the recession, stoping the optic with friction.

While all this was happening, Anchal started mounting AS4 on its adapter. After one of the magnets broke off, he switched to another one and succeeded. This is the next target for suspension. We still need to check the orientation of the wedge. Furthermore, we started a gluing session in the afternoon to prepare as much as possible for further SOS during the week. 3 side magnets were glued to side blocks. 3 magnets were glued to 3 adapters that were missing 1 magnet each.

In the afternoon, Yehonathan and Paco set up the QPD and did all the usual balancing, and then Anchal took the data of which the result is shown in Attachment #3. The major peaks are located at 723mHz, 953mHz, and 1.05Hz. Very similar to the case of the thin optic adapters.

Anchal progressed with OSEM installation, and engraving and yehonathan glued the counterweight setscrew in place. After securing the EQ stops, and wrapping the wires in foil, we declare PR3 is ready to be installed.

{Paco, Yehonathan}

Today we suspended LO2 (E1800089) which Anchal has loaded into the thick optic adapter. Attachments 1,2 show the height and roll balance adjustments.

I realigned the opLev setup and balanced the suspended mass. We figured that if we use 2 counterweights we will be 1 short. We decided to use 1 mass at the back of the adapter. This has the additional advantage that the Viton tip on lower back EQ stop can touch it and act normally. The optic was successfully balanced in this way. Attachment 3 shows the motion spectra on the QPD. There are major peaks at 712 mHz, 854 mHz, 876 mHz, and 996 mHz. As expected using only 1 counterweight raised the center of mass and lowered the pitch resonance frequency. The optic was locked keeping the alignment fixed on the center of the QPD, OSEMs were inserted and the SOS tower was engraved.

We should apply some glue to the counterweight to prevent it from spinning on the setscrew.

{Paco, Yehonathan, Anchal}

Today we suspended AS4 (E2000226-B). Anchal mounted Lambda Optic mirror with an RoC closest to AS4 in a thin optic mount. He noted that this optic as well as AS1 don't have a wedge angle. The specs claim that the wedge angle is 2 degrees what should have been clearly seen by inspecting the optic with a naked eye. All the ghost beam deflections probably come from the curvature of the mirror.

We did all the height and roll balancing using a camera (Attachment 1,2). We balanced that pitch of the adapter using a QPD not before we realigned the OpLev setup.

We measured the motion spectra (attachment 3). Major peaks are found at 755 mHz, 964 mHz, and 1.062Hz. I locked the counterweights setscrew and observed that the pitch balance doesn't change. I locked the EQ stops such that the alignment of the mirror remained the same by monitoring the QPD signals. I clamped the suspensions wires to the suspension block.

The only thing remaining is inserting the OSEMs.

I set up a working area on the table next to the south flow bench (see attachment). I also brought in a rolling table for some extra space.

I covered all the working surfaces with a foil from the big roll between 1x3 and 1x4.

I took the SOSs, SOS parts and the OSEMS from the MC2 table to the working area.

I cleaned some LN Allen keys with isopropanol and put them on the working table, please don't take them.

You can remove the components of the optical table enclosure (black ones) and use the optical table as your working area too.

I gathered all the components I could find from the SOS towers and the cleanroom and put it all on the table next to the flow bench (See attachment).

I combed through the cleanroom cabinet for SOS parts but didn't find all the parts listed in the procurement spreadsheet. I did find some extra items that were not listed.

This table compares the quantities in the spreadsheet to the quantities collected on the table. Green rows are items I found more than in the procurement spreedsheet while red rows are items I found less.

Gautam pointed out that there are extra Sm-Co magnets stored in the clean optics cabinet.

I took the magnet box out and put it on the rolling table next to south flow bench. The box contains 3 envelopes with magnets.

They are labelled as following:

FLUX 94 - 50 parts

FLUX 93 - 10 parts

FLUX 95 - 40 parts

(What is FLUX??)

The box also contains some procurement documents.

The clean and bake dcc says :

1. Ultrasonic clean in methanol for 10 minutes

2. Bake in vacuum at 177 C° for 96 hours

Should we go ahead with the C&B?

The curie temp of SmCo seems about x2 (in K) of the one for NdFeB. i.e. 600K vs 1000K. So I believe 177degC = 450K is not an issue. Just make sure the curie temp, referring the specific property for the magnets from this company. (You already know the company from the procurement doc). It'd be great if you upload the doc on the 40m wiki.

Done.

Also, the magnets are nickel-plated. I guess that doesn't matter for the baking (Curie temp of 355 °C)?

A summary of things that need to be fabricated/purchased/done:

I measure some of the dowel pins we got from Mcmaster with a caliper.

One small pin is 0.093" in diameter and 0.376" in length. The other sampled small pin has the same dimensions.

One big pin is 0.187" in diameter and 0.505" in length. The other is 0.187" in diameter and 0.506" in length.

The dowels meet our requirements.

We got some dumbells from Re-Source Manufacturing (see attached). I picked 3 in random and measured their dimensions:

1. 0.0760" in diameter, 0.0860" in length

2. 0.0760" in diameter, 0.0860" in length

3. 0.0760" in diameter, 0.0865" in length

In accordance with the Schematics.

Today I assembled the skeleton of 6 towers, without clamps and sensor assembly (attachment 1).

Some of the side plates have this weird hole that doesn't fit any of the suspension blocks (attachment 2). I didn't notice when I counted the parts and now there are exactly enough side plates to assemble 7 towers.

Also found that one of the stiffener plates has a broken threading.

We will need more parts to go beyond the necessary 7 SOSs. I will do the recounting later.

Things to do next:

1. Find the capped spring plungers and send them to C&B.

2. Assemble the clamps onto the suspension blocks.

3. Push some Viton tips into the vented screws we got to make safety stops.

4. more C&B: Magnets, dumbells, dowel pins, OSEMs.

5. Push clean dowel pins into the last suspension block.

6. Assemble 7th Tower.

7. Assemble safety stops and clamps.

8. Glue magnets to dumbells.

Today, I screwed the plungers on the sensor plates and installed them on the Towers. I also installed the wire clamps on the suspension blocks (attachment).

I ran into problems in 2 separate suspension blocks: one had a dowel pin that was slightly too fat for the wire clamp. In another, the tapped holes were too short so that the 4-40 screws couldn't be screwed all the way.

I found a "vice" in the cleanroom (attachment 1). I used it to push dowel pins into the last suspension block using some alcohol as a lubricant.

I then assembled the 7th and last suspension tower (attachment 2).

Things that need to be done:

1. Push Viton tips into vented screws and assemble the earthquake stops.

2. Glue magnets to dumbells.

I tried to push the clean Viton tips into the vented screws just to find out that the vented holes are too small. We need to drill 0.1" diameter holes about 0.1" deep into these screws and clean them again.

Can you just cut the viton tips smaller? If you cut it to have some wedge (or say, taper), it can get stuck with the vent hole.

Today I glued some magnets to dumbells.

First, I took 6 magnets (the maximum I can glue in one go) and divided them into 3 north and 3 south. Each triplet on a different razor (attachment 1).

I put the gluing fixture I found on top of these magnets so that each of the magnets sits in a hole in the fixture. I close the fixture but not all the way so that the dumbells get in easily (attachment 2).

I prepared EP-30 glue according to this dcc. I tested the mixture by putting some of it in the small toaster oven in the cleanroom for 15min at 200 degrees F.

The first two batches came out sticky and soft. I discarded the glue cartridge and opened a new one. The oven test results with the new cartridge were much better: smooth and hard surface. I picked up some glue with a needle and applied it to the surface of 6 dumbells I prepared in advance. I dropped the dumbells with the glue facing down into the magnet holes in the fixtures (attachment 3). I tightened the fixture and put some weight on it. I let it cure over the weekend.

I also pushed cut Viton tips that Jordan cleaned into the vented screws. While screwing small EQ stops into the lower clamps I found some problems. 4 of the lower clamps need rethreading. This is quite urgent because without those 4 clamps we don't have enough SOS towers. Moreover, I found that the screws that we bought from UC components to hold the lower clamps on the SOS towers were silver plated. This is a mistake in the SOS schematics (part 23) - they should be SS.

Then, can we replace the four small EQ stops at the bottom (barrel surface) with two 1/4-20 EQ stops? This will require drilling the bottom EQ stop holders (two per SOS).

According to the schematics, the distance between the original EQ tap holes is 0.5". Given that the original tap holes' diameter is 0.13" there is enough room for a 1/4" drill.

On Thursday, I glued another set of 6 dumbells+magnets using the same method as before. I made sure that dumbells are pressed onto the magnets.

I came in today to check the gluing situation. The situation looks much better than before. It seems like the glue is stable against small forces (magnetic etc.). I checked the assemblies under a microscope.

It seems like I used excessive amounts of glue (attachment 1,2). The surfaces of the dumbells were also contaminated (attachment 3). I cleaned the dumbells' surfaces using acetone and IPO (attachment 4) and scratched some of the glue residues from the sides of the assemblies.

Next time, I will make a shallow bath of glue to obtain precise amounts using a needle.

I glued a sample assembly on a metal bracket using epoxy. Once it cures I will hang a weight on the dumbell to test the gluing strength.