The View Up Here

Random scribblings about kites, photography, machining, and anything else

More Camera Work

Posted by Tom Benedict on 10/11/2012

The new parts for the cameras worked perfectly. In the process I also figured out why the holes on the first set were the wrong size. To make a long story short, I left some stock on the parts for a finish pass of the cutting tool, but didn’t actually include a finish pass in the toolpath. So the holes were precisely 0.0118″x2 too small. (I left 0.0118″ for finishing.) Sometimes the software is too smart for the operator…

But the new parts work great!

CFHT Sitelle Camera Assembly

I got most of the anodized bits assembled earlier in the week. From left to right are the anti-vibration towers for the cryo coolers, the preamplifier enclosures, the cryo cooler hose supports (hiding behind my coffee cup), the vacuum flange clamps for the valve and vacuum gauge, and finally the support rods for the anti-vibration towers for when the camera is off vacuum.

But the real work this week is in the foreground. On the left side are the getter bodies and their caps. On the right are the partially assembled “three ring circuses” that provide the thermal isolation necessary to cool the detector down to -100C while the outside of the camera is still a relatively toasty 0C. Those parts I had to re-make? Those light colored tabs in the three ring circuses are the new parts. They fit perfectly.

But not everything went so smoothly. The three ring circus sitting right in the middle is fitted out with a dummy detector PCB, but it’s not actually attached to the rest of the parts. Why? Because when I placed the nut and bolt order from hell for these cameras, I left out the screws that hold the detector onto the cold part of the camera. I sent out a new nut and bolt order as soon as I realized that, but now it’s a game of hurry up and wait.

In the meantime, though, there’s plenty more to do. So today I built out one of the getters and stuck it into a test cryostat we have sitting in the lab. It’s pumping down now, and should be ready to turn on Tuesday morning. The test for this thing is about as brute-force as you can get: With our PCC cooler loaded with PT-14 gas, our previous getter design would pull the vacuum on the test cryostat down to the high 10x-7 torr range. If this one can’t beat that performance, I have to change the design. It’s that simple. My back of the envelope calculations say it should be able to pull about 1.6x harder than our previous getters, and have a much higher overall capacity. So it shouldn’t be a subtle effect. If it is, it’s back to the drawing board.

There are only a handful of parts left to make for these cameras. Providing the getter testing goes well and the new screws let me finish assembling the camera’s innards, I may be back to serious kite flying in the next couple of weeks. I can’t wait.

– Tom

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