I've started by assembling the window. It is a 3mm quartz plate, sealed with two rubber o-rings (that will be later replaced with fluoride rubber ones)
After that I've screwed down the windows part to the chamber body, sealing this joint with another o-ring. To the vacuum flange an vacuum valve was fitted (Leybold full metal manual valve).
So assembly is done, now for testing it we attached the chamber to pumping station consisting of a rough vacuum pump and turbomolecular drag pump. Pumping station is attached via an metal flexible hose. The pump was left for ~1h to evacuate the chamber.
After one hour of pumping we achieved pressure equal to 1,6 *10e-5 mbar. It is quite good result for that pump. On a normal cryostat pumped for an hour we achieve 5,4*10e-5 mbar, so the results are comparable (the cryostat is slightly bigger). The only one thing to test is the vacuum tight sealing. I'll take a look at the chamber after some time to see if it's still under vacuum.