The inside story at Nevis Labs, Conclusion.

Todd, the Assembly Engineer, had invented an adequate process for building the optics. It was labor intensive and held together with duct tape and baling wire in places, but it was effective. There was one critical assembly component, however, that was poorly designed - the strongbacks, which held the epoxied spacers on the glass until the epoxy had cured.

Each strongback was constructed of several components. The base was designed to apply even pressure along the length of the spacer. The parts that actually held the spacers were called shoes, and they are where the design was weak. The shoes were built from two or three pieces screwed together. There was a groove in the top for the spacer, under which was a Buna o-ring, at first, and then later replaced with Tygon tubing, a superior solution.

To hold a spacer in a shoe, a strip of Teflon tape was applied over the groove, and then the spacer was inserted. The problem with the shoes was that the width of the grooves was inconsistent, which resulted in some spacers being held inadequately. Sometimes the epoxied spacers would fall out when being attached to the glass, which resulted in a bit of a mess. The problem was limited to the double shoes, which were used where glass segments met. That was because the doubles were constructed of more parts.

Sometime in the fall Tom came up with a useful solution. If he discovered a double shoe in which the spacers were inadequately held, he marked it with a felt pen. When I saw that mark, I used two strips of Teflon tape on that shoe. It was a minority of the strongbacks that had the mark - two strips of tape on an unmarked shoe would result in the spacers being held too tightly.

Sometime after the first of the year there was a problem with the accuracy of the grinds. When Todd returned to Nevis, he embarked on a project to rebuild each shoe. That's when the o-rings were replaced with Tygon. Todd spent several very long days modifying the shoes.

I was happy about the modifications, because I thought I would no longer have to apply double tape to the marked shoes. I did pay attention, though, and if I noticed that Tom had added a layer of tape the previous day or if I thought a spacer was loose, I marked the strongback myself and subsequently applied two layers of tape. That sort of worked, except that in one or two cases where two layers of tape fixed one slot in a double shoe, it made the other slot too tight. Tom pointed those shoes out to me, and eventually only a few of the doubles were marked. None of the singles had been marked before, and none was marked now.

It was a few weeks before Tom mentioned to me that spacers in a few of the unmarked double shoes were loose. I asked him to mark them, as he had previously, but he said he was too busy to do it. (Both Tom and Iliya had an idle hour or more when the glass and spacers were being automatically scanned.) He wanted me to determine the shoes that needed double tape. I used the standard test, which was to shake the strongbacks upside down to see if a spacer fell out. I thought I had identified the loose shoes, but I hadn't gotten them all. Tom had a lot of experience in evaluating the shoes, but he had become annoyed and was not willing to help. Ken pushed Tom to mark the shoes as he had before, and Tom relented, but he did not mark any shoes. He was making one of his infamous stands.

Finally Tom and I got together to discuss what could be done. That's when he told me that the modifications that Todd had made didn't affect the width of the slots, so I should be double taping the same shoes as previously. It would have been good to know that a couple of weeks earlier, but no-one had told me, even though it was obvious to them that some of the marked shoes weren't double taped. After I told Tom I'd double tape all the marked shoes, he said, "The single shoes are okay. [pause] No, the tape on them has to be changed more frequently."

Then, mysteriously, spacers started falling out of single shoes, even though the grooves were the same width, the tape was the same, and no spacers had escaped from single shoes in the past (except for my mis-inserted 1.6 mm x 1.5 mm spacers).

The normal procedure was to replace the tape if it was torn or if it had been pulled loose when the spacer was removed. During my training, Iliya told me that he had changed tape on all of the shoes every week, regardless of condition. I was doing twice as many shoes as Iliya had ever done, but I worked out a system to change the tape on the spacers on each tray (there were six trays of strongbacks) on a specified day each week. Now Tom was complaining about loose spacers, so I modified my routine to change the tape a minimum of two times a week. Tom said that was inadequate. Since no spacers had fallen out previously, even with only a weekly change, I was aware that Tom was having another emotional reaction, and I wasn't sure how to handle it. I asked Tom to mark any single shoes in which a spacer was loose so I could double tape it, but he refused.

I asked Tom why the spacers had started falling out, and he decided that some of the spacers were curved, so that the ends were up too high in the shoes. Why that caused them to fall out, I don't know. More important is that I could see no evidence that any spacers at all were curved. Some had slight curves along the 1.2 mm axis, but they were uniformly straight along the 1.5 mm axis.

The evening of March 2 Todd sent me an email:

>> Kurt,
>>
>> We are still on L132 on FM1. We had a spacer not bond correctly because it partially fell out of a shoe and bonded crooked on the glass. There is only one strongback on FM1 and half the guidewheels. I've set up the grinds for rough and finish grind.
>>
>> If you have another hic-cup like we did this morning, just leave the machine as is so I can try and diagnose it in the state where the error happened. I think this mornings issue was with Windows and not Delta Tau but I can't be for sure. Also, don't change any of the grind parameters without first consulting Ken or I. Since I had to completely power down FM1 machine, all of the parameters that I've updated revert to the settings as built by Dan at layer 1. This means that the machine now thinks it is grinding layer 1 which would be disastrous.
>>
>> FM2 will advance to layer 126 and take two grinds as usual.
>>
>> Thanks,
>> Todd

I responded:

> Todd,
>
> Okay.
>
> I haven't changed the grind settings in months, except for the time a couple of days ago when I did a regrind. The last time I touched FM1 was when I was adjusting for the previous day, as you told me to. I'll stay away from them.
>
> I really don't know why spacers are falling out of single shoes all of a sudden, when they were fine for so long. I'm replacing more frequently than Iliya did. A couple of weeks ago I was in the lab with Tom and Ken and Tom was talking about the doubles, and he said, "The singles are fine. Well, no, you should change the tape every couple of days." I don't know what's going on, but I told Tom to mark any shoes he things are loose so I'll double tape them. He doesn't want to do that.
>
> Kurt

That seemed like a normal exchange.

The next morning I arrived at the lab and checked my email from the gowning room. That was my normal procedure, because Todd often sent email instructions in the evening after I'd gone to bed. Todd had responded to my reply with one sentence: "What time do you estimate you'll start the second grind on fm1?" The meaning of that was clear to me: Todd wanted to come to the lab to discuss the spacer issue.

It was March 3 and my last day at the lab was scheduled to be March 11. FM1 would be complete after one more layer, and I'd already been told that I could go home when only one optic was being built because the guys could easily handle what I'd been doing. I knew that it was inevitable that if Todd came in, he would side with Tom regardless of the circumstances.

After several minutes, I made a decision. I took my keys and left them on a table in the lab, then went home. Iliya, Tom, and Todd had all quit previously, and now it was my turn. The difference was, I had no intention to return.