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ID Date Author Type Category Subjectdown
  8822   Wed Jul 10 14:49:00 2013 SteveUpdateGreen Locking more fiber protective tubing layed

Quote:

Craig, Gautam and Steve,

Single mode fiber 50m long is layed out into cable tray that is attached to the beam tube of the Y arm.

It goes from ETMY to PSL enclosure. It is protected at both ends with " clear- nylon slit corrugated loom tubing " 1.5" ID

The fiber is not protected between 1Y1 and 1Y4

 Installed 0.5" ID 10 ft long protective tubing at the PSL end of the  ETMY fiber this morning. Here I had to cable tie a bunch of cables at the east side of the PSL enclosure.

They were hanging off the table blocking space were the sliding doors move.

 At the ETMX end of the X-arm fiber received the same protective tubing.

  3505   Wed Sep 1 10:54:15 2010 steveUpdatePEM more crane balancing

Crane balancing at the south end is continuing today.

  3288   Mon Jul 26 08:51:31 2010 steveUpdatePEM lowering AC setpoint by 2F makes PSL happy

Quote:

The control room temp is warmer than usual. The heat exchanger Office Pro 18 set point was lowered from 70 to 68F yesterday.

The MOPA headtemp is higher also. The Neslab chiller bath temp peaks around 21.6 C daily. This should be rock solid 20.00 C

It did not have any effect.

Now, I have just lowered the thermostat setting of room 101 from 73 to71F  I  hope Koji can take this.

 Little change in the AC set temp can make wonders. Neslab chiller bath temp 19.99C is back to normal and daily variation of PSL are much better.

  3745   Wed Oct 20 16:41:41 2010 steveOmnistructureGeneral laser chiller leaving for MIT
  12227   Wed Jun 29 14:32:22 2016 SteveUpdateSUS how to remove epoxy from optics

 

Hi Steve -

I found the doc I was looking for:

https://dcc.ligo.org/LIGO-E1200821

Specifically, you might find guidance in Section 5 and the pictures at the end of the doc.  This should work for Vacseal as well.

Good luck - it will take some time (hours to day or 2)...
I'll be interested to know how it goes.

GariLynn helped us develop this procedure so you could also ask her to cast an eye over the setup if you are worried.

-Betsy

ps: there is no existing fixture to hold SOS optic while soaking it
 

  12231   Thu Jun 30 10:03:16 2016 SteveUpdateSUS how to remove epoxy from optics

Proposed Acetone soak dish for SOS epoxy softening.

It has good acces through 5" top ID. The set up is stable and teflon lined.

Materials: glass jar with SS cover, teflon bricks, 0.008" teflon wrapped "high density Drever bricks" and aluminum

Drever brick: I beleive it is a Tungsten alloy. We used it as vac-bat savor at the coffe can. It has high density, heavy and hard, it was never identified.

I will soak one brick  to see if it has any reaction ability with acetone.

 

NO means that only Glass and Teflon can be used for this fixture in  Acetone. We can not take a chance on the coating!

I guess the small surface area Aluminum dumbbell, guide rod and-or wire standoff, magnet and epoxy does not degrade the acetone such way that it effects our coating.

Not ot mention, that only the very edge of the coating would in this solution.

              

 

  12241   Tue Jul 5 09:25:31 2016 SteveUpdateSUS how to remove epoxy from optics

Glass soaking dish with teflon guides.

Quote:

Proposed Acetone soak dish for SOS epoxy softening.

It has good acces through 5" top ID. The set up is stable and teflon lined.

Materials: glass jar with SS cover, teflon bricks, 0.008" teflon wrapped "high density Drever bricks" and aluminum

Drever brick: I beleive it is a Tungsten alloy. We used it as vac-bat savor at the coffe can. It has high density, heavy and hard, it was never identified.

I will soak one brick  to see if it has any reaction ability with acetone.

 

NO means that only Glass and Teflon can be used for this fixture in  Acetone. We can not take a chance on the coating!

I guess the small surface area Aluminum dumbbell, guide rod and-or wire standoff, magnet and epoxy does not degrade the acetone such way that it effects our coating.

Not ot mention, that only the very edge of the coating would in this solution.

              

 

 

  9643   Tue Feb 18 10:10:07 2014 SteveUpdatePEM floor cleaning under racks

Quote:

 Keven, Steve

 

The floor was cleaned under the east arm tube with hand held wet towel. We moved staff around and mopped. I did at the bottom of rack  1Y1, 2  and 3. 

Last week we did the south arm tube floor.

Next week we 'd like to clean under rack 1X1,2,3, 4, 5, 6 and 7 

 Keven, Steve

1Y4, 1X1,2,3,4 & 5 instrument racks floor space were cleaned.

  9689   Tue Mar 4 17:07:27 2014 SteveUpdatePEM floor cleaning under racks

Quote:

Quote:

 Keven, Steve

 

The floor was cleaned under the east arm tube with hand held wet towel. We moved staff around and mopped. I did at the bottom of rack  1Y1, 2  and 3. 

Last week we did the south arm tube floor.

Next week we 'd like to clean under rack 1X1,2,3, 4, 5, 6 and 7 

 Keven, Steve

1Y4, 1X1,2,3,4 & 5 instrument racks floor space were cleaned.

 Keven, Steve

 

1X6, 1X7 and 1X9 instrument racks floor space were cleaned today

  9623   Tue Feb 11 16:49:36 2014 SteveUpdatePEM floor cleaning

 Keven, Steve

 

The floor was cleaned under the east arm tube with hand held wet towel. We moved staff around and mopped. I did at the bottom of rack  1Y1, 2  and 3. 

Last week we did the south arm tube floor.

Next week we 'd like to clean under rack 1X1,2,3, 4, 5, 6 and 7 

  7999   Tue Feb 5 09:08:11 2013 SteveUpdatePEM exterier doors to be painted

Quote:

The wood exteier walls, gutters and doors were painted at CES-Annex building #69

 The east and south end of the 40m emergency exit doors are sealed- tapped off temporarily.  They will be painted on the out side only.  This job will be done by tomorrow noon

 Do not open chamber if you smell the paint !

  12930   Thu Apr 6 15:35:44 2017 SteveUpdatePEM envioirmental noise

Building:         Central Engineering Services

     

Date:             Monday, 04/10/17          

          

Time:             7:00 AM TO 9:00 AM           

 

Notification:     Crane Activity

    

Contact:          Ben Smith, X-4190 Brad Nielsen, X-8751

 

Contractors will be removing the large vaporizer located on the South

side of CES. Vehicle access will be restricted due to crane placement

and operation, but there will be a single traffic lane available. This

work may create minor noise and vibrations.  

  3591   Mon Sep 20 17:10:10 2010 steveConfigurationPSL enclosure beam guides to IFO are installed

The PSL out  2" OD beam guide tube was cut  1.5" shorter to 13.5"

The 10" OD  0.25" wall Al tube was replaced by a  lighter, not anodized and thinner  wall 0.094" tube of 15.5" lenght, that is 0.75" shorter.

The new position of the PSL table made these cuts necessary.

  14294   Wed Nov 14 14:35:38 2018 SteveUpdateALARM emergency calling list for 40m Lab

It is posted at the 40m wiki with Gautam' help. Printed copies posted around doors also.

  9098   Tue Sep 3 14:23:21 2013 SteveUpdatePEM earthquakes

 ~Vancuver, Canada earthquakes: magnitude 6,  5  and more shaking

 

  11932   Thu Jan 14 13:44:05 2016 SteveUpdateSUS earthquake 3.6M

No obvious sign of damage.

 

  11975   Thu Feb 4 10:14:52 2016 SteveUpdateSUS earthquake 3.5M

 

 

  3404   Thu Aug 12 10:56:31 2010 steveUpdateEnvironment dusty floor work in progres

I powered down 1Y1 and 1Y2 instrument racks of MC and RF-systems this morning.

Both racks, SP table, clean tools-parts boxes and MC2 area are also covered with plastics.

Bertin Bros. Construction, Inc is working on the floor preparation. Their head man is Robby Bertin, cell 626. 831.2264

Today's job:

remove tiles, clean off tile glue, drill for ribbed  steel bars, rough clean- surface for good bounding. paint floor with bounding agent

  12656   Fri Dec 2 10:57:08 2016 steveUpdatePEM door seal replaced

The south end door leaky weather seals replaced.

The aim is here to get some overpressure inside / outside so the lab partical count would not depend on outside condition.

 

  12020   Fri Mar 4 11:07:10 2016 SteveUpdatesafety crane inspection completes 2016 safey audit

All 3 cranes inspected by professional and load tested with 450 lbs at max reach.

 

  13630   Mon Feb 12 14:56:00 2018 SteveUpdatesafety crane inspection 2018

Our 3 cranes passed  professional  inspection. Fred Goodbar of Konacrane with 450 lbs load at full extension.

Certificates will be posted in 40m wiki as they arrive.

 

  12868   Mon Mar 6 09:12:59 2017 SteveUpdatesafety crane inspection 2017

All 3 cranes inspected by professional Fred Goodbar of Konecranes and load tested with 450 lbs at max reach on Friday, March 3, 2017

 

 

  5307   Fri Aug 26 10:45:17 2011 steveUpdateGeneral crane at ETMY is fixed

Quote:

The horizontal trolley drive stopped working  at the east end this morning. It is working intermittently. In the worst case we can take the door off with the manual -Genie- lift.

I'm working with Konecrane to solve  the wormgear drive problem.

 New gear box installed and tested by Fred KoneCranes.

  10023   Wed Jun 11 08:57:49 2014 SteveUpdatePEM air cond maintenance tomorrow morning

Quote:

  The 4th week of no wet mopping of the floor  and no wet wiping  the vacuum envelope.

 

We cleaned the intakes of the south arm IFO air condition. The bottom duct have quite a bit accumulation Atm1

See wet wiped contrast on Atm2

We found 3 holes around pipes ( coming from CES ) on the east wall that has to be sealed.

After closer examination of these holes, they are sealed off well.

 Air condition maintenance will be finished by 11:30am tomorrow.

 

Yesterday, Kelvin mopped with chemicals the whole floor area of the  lab. This was triggered by some  visiting  ants at our PSL last week. It was 6 months since we had the last fully wet mopped IFO floor.

The cleaning- mopping water became   very dirty at the end.

  12572   Wed Oct 19 17:02:34 2016 ranaUpdateGeneral Viewports & coating of 2016

These old specs are not so bad. But we now want to get replacements for the TRX and TRY and PSL viewports that are R <0.1% at 532 and 1064 nm.

I don't know of any issues with keeping BK-7 as the substrate.

  12570   Wed Oct 19 14:43:15 2016 SteveUpdateGeneral Viewports & coating of 2001

Tilted viewports installed in horizontal position. Atm2

  14106   Thu Jul 26 15:11:18 2018 SteveUpdateGeneral Viewports & coating of 2001

New optical quality BK-7 windows in 2001 [4 substrates ] AR coated R<0.75 % for 630-1064nm " Azury BLue" broadband : TRX, TRY, ITMY-Oplev &  ITMX-Oplev viewports.

The BS-Oplev and PRM-Oplev 10" CF with 5.38" diameter view was coated the same way. The window here is Corning 7056 Borosilicate

5 more BK-7 substrates were coated R <0.1% of 1064 nm "Golden Orange" Their location: IMC-IN, IFO-REF and OMC   The next vent we have to confirm optical quality window locations.

All other conflat flange viewports are 7056 Kovar sealed .

Technical notes of 2001 40m upgrade can be seen at LIGO-T010115- 00- R  ....page 14

  12848   Thu Feb 23 14:50:26 2017 SteveUpdateGeneral USB microscope returned

The microscope shipped back to the vendor for credit yesterday.

Quote:

http://www.amscope.com/3-5x-180x-boom-stand-trinocular-zoom-stereo-microscope-with-144-led-ring-light-and-10mp-camera.html will be ordered today.

The actual unit we are getting has lockable zoom for better repeatability after calibration: SM-3NTPZZ-144

Quote: CWQ6-020817

 

 

 

  12813   Thu Feb 9 08:03:08 2017 SteveUpdateGeneral USB microscope ordered

http://www.amscope.com/3-5x-180x-boom-stand-trinocular-zoom-stereo-microscope-with-144-led-ring-light-and-10mp-camera.html will be ordered today.

The actual unit we are getting has lockable zoom for better repeatability after calibration: SM-3NTPZZ-144

Quote: CWQ6-020817

 

 

  12788   Thu Feb 2 12:17:48 2017 SteveUpdateGeneral USB microscope

This AmScope microscope would have 3.5x-180x magnification, calibratable measurement function, 5MP picture and good working distance to work on printed circuit boards.

 

  8432   Tue Apr 9 21:27:48 2013 JenneUpdate40m Upgrading TRY temporarily in place

Quote:

I've used a Y1 mirror to steer the Y transmission to an R98% BS. The reflected beam falls on PDA520 and the transmitted beam is steered to the camera. The earlier normalization of TRY is no more valid as the power distribution at the PD has changed.

 To take this into account, last night, I reduced the TRY gain by a factor of 2.  This is not exactly correct - when the layout is finalized we need to figure out what the pickoff situation used to be (we think, based on the Xend, that it could have been 0.5*0.9), and do the correct normalization.

  12952   Thu Apr 27 16:41:13 2017 Eric GustafsonUpdateLSC Status of the 40 m PD Frequency Response Fiber System
There two reports in the DCC describing the state of the system as of October 2014 including: (1)  Alex Cole’s “T1300618 Automated photodiode Frequency Response Measurement System” and a Wiki  created by Alex Cole where there are some instructions on the Master Script at https://wiki.ligo.caltech.edu/ajw?AlexanderCole    

And (2)  P140021 “Final Report: Automated Photodiode Frequency Response Measurement System for 40m Lab” by Nichin Sreekantaswamy and also as part of Nichin’s report by there is an archive of data at   https://wiki-40m.ligo.caltech.edu/Electronics/PDFR%20system   

I made a visual inspection of the system and saw that the following fibers collimators are still mounted in alignment mounts and the fiber is attached and pointed at a photodetector but possibly not aligned. 

ASP Table

Photodetector Label                             Fiber Label

REFL11                                              REFL55 Fiber on mount        

REFL33                                              REFL33 Fiber on mount

REFL55                                              REFL11 Fiber on mount

REFL165                                            No Fiber

AS55                                                   AS55 Fiber on mount

MCREFPD                                         MCREFPD Fiber on mount

No PD                                                 Loose unlabeled Fiber No mount

 

ITMX Optics Table

Photodetector Label                             Fiber Label

POX11                                                POX11 on mount

Unlabeled PD                                      POP22/POP110 on mount

NO PD                                                 POP55 loose fiber No mount

 

The RF switch seems to be hooked up and there is a fiber running from the Diode Laser module to the fiber splitter module. So REFL 11 and REFL545 seem to be illuminated by the wrong fiber. I’ll try and run the software on Monday and check to see if I need to move the fibers or just relabel them.

  12043   Wed Mar 23 11:55:47 2016 SteveUpdateGeneral Smart UPS 2200 Battery Replaced

Batteries replaced in control room UPS after 3 years from replaceUPSbattery.com

 

 

  8686   Thu Jun 6 15:46:10 2013 Max HortonSummaryGeneral Smart UPS 2200 Batteries Replaced

Replaced the batteries successfully in the control room.  We just had to switch the clips from the old batteries to the new one, which we didn't know was possible until now.

  352   Mon Mar 3 13:58:10 2008 steveUpdateComputers RFM Network are down
The CODAQ_RFNETWORK are down, except C1SUSVME & AWG
  353   Mon Mar 3 19:34:40 2008 ranaUpdateComputers RFM Network are down

Quote:
The CODAQ_RFNETWORK are down, except C1SUSVME & AWG

All of the FE machines were found to be down this afternoon. I called Alex and he suggested several
things which didn't work (restart EPICS tasks, power cycle RFM switch, etc.).

Then he suggested that I go around and power cycle every crate!!! And that sometimes the order of this
matters!!! I think he was just recording this conversation so that he could have a laugh by playing it on Youtube.

However, power cycling all of the FE crates seemed to work. Alex's theory is that 'something goes bad in the
RFM cards sometimes'.

Its all green now.
  7566   Wed Oct 17 08:30:49 2012 SteveUpdateSUS PTICH damping needed

Quote:

Quote:

  [Koji, Steve, Den]

TT alignment is fine, yaw damping is satisfactory, pitch damping is slow. We might want to add magnets to the mirror and attach blades to the frame for pitch edge current damping.

We are moving towards electronics testing.

Atm1,  TT 1.5" high adaptor base will be back from the shop in 10 days.

Atm2,  There is no PITCH damping, YAW edie current damping works well at 0.5 mm gap

Atm3,  Adjustable Al -disc that contains a small magnet is purely designed.

We have to come up with a solution to have damping in PITCH

 Pitch damping solution needed! It should be in the machine shop already.

  13538   Fri Jan 12 10:26:24 2018 SteveUpdatePSL PSL shelf work schedule

Measurements for good fit were made. The new shelf will be installed on next Tuesday at 2pm

The reference cavity ion pump is in the way  so the cavity will be moved 5" westward. The shelf height space will be 10"  Under shelf working height 18" to optical table.

Quote:

I have just received the scheduling of the PSL self work for tomorrow. Gautam and I agreed that if it is needed I will shut the laser off and cover the hole table with plastic.

 

  13549   Tue Jan 16 11:05:51 2018 gautamUpdatePSL PSL shelf - AOM power connection interrupted

While moving the RefCav to facilitate the PSL shelf install, I bumped the power cable to the AOM driver. I will re-solder it in the evening after the shelf installation. PMC and IMC have been re-locked. Judging by the PMC refl camera image, I may also have bumped the camera as the REFL spot is now a little shifted. The fact that the IMC re-locked readily suggests that the input pointing can't have changed significantly because of the RefCav move.

 

  13551   Tue Jan 16 21:46:02 2018 gautamUpdatePSL PSL shelf - AOM power connection interrupted

Johannes informed me that he touched up the PMC REFL camera alignment. I am holding off on re-soldering the AOM driver power as I could use another pair of hands getting the power cable disentangled and removed from the 1X2 rack rails, so that I can bring it out to the lab and solder it back on.

Is anyone aware of a more robust connector solution for the type of power pins we have on the AOM driver?

Quote:

While moving the RefCav to facilitate the PSL shelf install, I bumped the power cable to the AOM driver. I will re-solder it in the evening after the shelf installation. PMC and IMC have been re-locked. Judging by the PMC refl camera image, I may also have bumped the camera as the REFL spot is now a little shifted. The fact that the IMC re-locked readily suggests that the input pointing can't have changed significantly because of the RefCav move.

 

 

  12844   Wed Feb 22 08:54:17 2017 steveUpdatePEM PSL enclousure particle count

ETMX sus damping recovered.  PSL enclousure is dusty at 20V rotation speed. Rainy days as outside condition.

Quote:

The MET#1 particle counter was moved from CES wall at ITMX to PSL enclousure south west corner at 11am.

The HEPA filter speed at the Variac was turned down to 20V from 40

This counter pumps air for 1 minute in every 20 minutes. Soft foam in bags used to minimize this shaking as it is clamped.

 

 

  7568   Wed Oct 17 11:15:05 2012 DenUpdateSUS PITCH damping needed

Quote:

 

 Pitch damping solution needed! It should be in the machine shop already.

I think we can put ø2mm × 10mm long magnetic material inside 4 holes with actuation magnets. Then magnetic field on the other side of the mirror will be close to one produced by actuation magnet. Magnetic cylinder center of inertia will be in the vertical plane where mirror's center of inertia is. So this should not change alignment significantly. Eddy current dumping will be applied to the end of the magnetic cylinder opposite to the magnet using aluminium disks, we have them in the clean room.

pitch_damping.png

  7571   Thu Oct 18 02:42:38 2012 DenUpdateSUS PITCH damping needed

Quote:

 

I think we can put ø2mm × 10mm long magnetic material inside 4 holes with actuation magnets. Then magnetic field on the other side of the mirror will be close to one produced by actuation magnet. Magnetic cylinder center of inertia will be in the vertical plane where mirror's center of inertia is. So this should not change alignment significantly. Eddy current dumping will be applied to the end of the magnetic cylinder opposite to the magnet using aluminium disks, we have them in the clean room.

 I've tested this approach. As we do not have required cylinders with high magnetic permittivity, I replaced them with magnets simular to actuator magnets ø2mm × 3mm long. Using them and aluminium disks from other TT I've made a "pitch dumping" construction.

DSC_4759.JPG

Pitch Q reduced but not that much as I could expect. I did a ringdown test. 

Plots:

yaw ringdown using original construction     |  yaw ringdown with added pitch damping

------------------------------------------------------------------------------------------------------------------------

pitch ringdown using original construction   |  pitch ringdown with added pitch damping

    yaw_nodamp_20.JPG   yaw_damped_13.JPG

pitch_nodamp_30.JPG     pitch_damped_10.JPG

 

 From this data I've estimated Q factor for yaw (135 vs 88) and pitch (192 vs 77) (original vs added pitch damping). Thess results diverges with the ones obtained by designes. They measured Q~40-50 for original construction. Pitch and yaw have 2 close resonances so this time domain method can not be very precise. I've measured the same with SR785.

yaw.pngpitch.png

In these comparison plots excitation was not the same as coils are not plugged in yet, but resonance Q factors can be compared.

 

  7583   Fri Oct 19 18:30:07 2012 DenUpdateSUS PITCH damping needed

CQuote:

 

 From this data I've estimated Q factor for yaw (135 vs 88) and pitch (192 vs 77) (original vs added pitch damping).

 I've made a more precise measurement of pitch damping using spectrum analyzer.

damp.png   pitch.png

Measurements confirm that damping using small actuation magnets reduces pitch Q by a factor of 4 and is not enough.

  7585   Sat Oct 20 01:23:56 2012 DenUpdateSUS PITCH damping needed

Quote:

Measurements confirm that damping using small actuation magnets reduces pitch Q by a factor of 4 and is not enough.

 I've tested the idea to use coils as eddy current dampers. I terminated them with a wire and measured Q factor during the ringdown test. Sadly, I did not see any significant damping and Q was ~150. We need stronger magnets if we want eddy current dumping down to Q~1.

P1010059.jpg      P1010060.jpg    P1010058.jpg

  7586   Sat Oct 20 20:37:55 2012 DenUpdateSUS PITCH damping needed

Quote:

 

 We need stronger magnets if we want eddy current dumping down to Q~1.

 I've inserted 10mm * 10mm magnets to the 4 corner holes on the front side of the mirror frame according to actuation magnets polarity. I realigned TT and measured Q factor for pitch and yaw, it was 5-10.

DSC_4778.JPG     pitch.JPG   yaw.JPG

 

I was able to do it for 1 TT only, because others have smaller (~0.1 mm) hole diameter and magnets can't go inside. I tried to warm holes up to 850 F but still was not able to insert a magnet.

DSC_4776.JPG

  7588   Mon Oct 22 11:26:12 2012 ranaUpdateSUS PITCH damping needed

 

Too bad - I thought it would at least give a little damping. Since we want the viscous-like energy loss to be ~49x larger, we need to have the field modulation in the damper (not dumper) increase by ~7.

  7593   Tue Oct 23 01:46:53 2012 DenUpdateSUS PITCH damping needed

Quote:

 

Too bad - I thought it would at least give a little damping. Since we want the viscous-like energy loss to be ~49x larger, we need to have the field modulation in the damper (not dumper) increase by ~7.

 I've made SolidWorks models of damping bracket and eddy current disk. They will me manufactured and used instead of old ones. New bracket will be mounted in exactly the same place where the old one was. Drawings might not be complete but all dimensions are in the models so we can fix drawing tomorrow before going to machine shop.

I think we can use ring magnets for passive damping. Then we won't have the vent problem. I've found some at K&J Magnetics, we can get them any time. Magnets are Ni-Cu-Ni (fine for vacuum?) Diameter is 3/8'' with advertised tolerence 0.004'', so they should fit the holes.

  7598   Tue Oct 23 17:12:30 2012 DenUpdateSUS PITCH damping needed

 Koji and Steve pointed out that previous design  of a damping bracket was a bit complicated to manufacture. So I made it simpler and also added a tap hole for original yaw damping. We'll give drawing to Mike in the machine shop tomorrow morning.

I've purchased K&J magnets for eddy current damping, they should be here in 2 days. 

  7602   Tue Oct 23 18:18:29 2012 JenneUpdateSUS PITCH damping needed

Quote:

Quote:

 

Too bad - I thought it would at least give a little damping. Since we want the viscous-like energy loss to be ~49x larger, we need to have the field modulation in the damper (not dumper) increase by ~7.

 I've made SolidWorks models of damping bracket and eddy current disk. They will me manufactured and used instead of old ones. New bracket will be mounted in exactly the same place where the old one was. Drawings might not be complete but all dimensions are in the models so we can fix drawing tomorrow before going to machine shop.

I think we can use ring magnets for passive damping. Then we won't have the vent problem. I've found some at K&J Magnetics, we can get them any time. Magnets are Ni-Cu-Ni (fine for vacuum?) Diameter is 3/8'' with advertised tolerence 0.004'', so they should fit the holes.

 Den mentioned that the disks will have threaded holes, and that he has made a note to that effect on the paper copy of the drawing that he will bring to Mike at the shop.  Also, all threaded holes in the new plate are marked on the paper copy.

ELOG V3.1.3-