Friday, September 07, 2012
Mounting the square UKIRT 20um filter
Here's some pictures of the holder for the UKIRT 20um filter, which will be installed in the lens wheel for CD014. The black rings are made from delrin, adapted from the stock rings with threaded outer diameter. I milled out the inside of one ring to hold the filter. The white rings are 0.01" teflon sheets with 0.875" holes punched out. The filter is 0.06" thick; the delrin slot is 0.0815" deep. One teflon ring fits into the slot. The other has the same ID, but will be sandwiched between the two delrin pieces. (so the total material in the slot is just 0.06"+0.01" --> i.e. no compression on the filter).
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2 comments:
The filter is called the UKIRT filter, since that is where we got it. I think is it more for around 17 to about 20, but we'll see.
The filter drops in easily at room temperature. But I'd like to be sure I left enough room for diff. expansion in slot width, but I'm not sure I have all the material properties I need.
Delrin has a high room-temperature coefficient of thermal expansion:
7 x 10^-5 cm/cm/K.
Glass is pretty different --
5 x 10^-7 cm/cm/K to 7 x 10^-7 cm/cm/K, for fused silica and BK7 (i don't know what the filter is).
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