SEM Buildblog

The SEM welds have been leak tested and verified to be good to at least 10^-3 Torr! Click below to read on and see some vacuum porn!

The original idea was to use the O-ring present within the face of the lid to “suck” down onto a polished stainless steel plate with the vacuum hose attached to one of the KF-25 flanges with a gauge on the other KF-25 flange and a cap on the KF-40 flange. But first, a KF25 to KF40 and a KF25 to KF16 adapter had to be machined in order to allow these connections. I turned these on the heatsync labs mini lathe out of 6061 aluminum and then bathed them with brake degreaser to remove the cutting oils.

And here shown stacked up on the lid with a gauge on top for no other reason than a good vieing of vacuum hardware porn.

The method of sealing the plate proved to not hold a vacuum. The O-ring deformation was such that the aluminum plate itself made a rather nice fit to the steel plate and the flow rate was too low to get a readable vacuum on the gauge.

The second approach was to mate the vacuum hose to the welded flange and seal the gauge to the hole on the back side of the lid using a KF centering ring. This worked quite well using a KF-25 centering ring for the KF-40 flange and a KF-16 centering ring for the KF-25 flanges. The gauge was drawn until the max value of 10mV (10^-3 Torr) and then spritzed with water and then isopropyl alcohol. The vacuum level never crashed following the spritz (as we observed during the earlier hairline cracking of the original brass fixtures present before machining) and thus it can be concluded that no major leaks are present. Any micro-leaks which manifest at a greater vacuum level can be traced using a healium leak detector and sealed using commercial high vacuum epoxies.

And now its time to weld the rest of the chamber!