I hope I don't bore you with this, but here it goes. This is for a vehicle oil re-routing (external filter, etc.). I tig welded aluminum without issue, but this housing, I couldn't do it without leak, even after I preheat the aluminum and heat again with propane torch. It wasn't working, yet I had no problem with other aluminum welding at all. The pressure is expected to be much lower than 50 PSI, but I would test it for 80 PSI or even 100 PSI.
So after the failed tig weld attempt, I tried to use brazing. I used low temperature 730 degree rods (harbor freight, and elsewhere), and it melted easily. But it still leaked. I have brazed HVAC without problem with silver solder (using micron gauge to check for leak and also pressure check with nitrogen).
The braze rods above doesn't flow into gap. It's just the way it is. Even clean up shiny and using acetone to clean it up more. That's not good. I tried to test it somewhere else, with flux and it worked. But when I did it with the real thing, somehow with the flux, it didn't melt the rod, but the oil housing melted, even I moved my hand all the time to keep the heat evenly. Really frustrated. So I decided to change the design a little, and decided to use gasket maker to seal it. So think of it as an aluminum cylinder and I put a round aluminum disc inside and brazed it up, and it leaks around the perimeter. So on the other side (the outside), I cut another piece of aluminum, brazed in/out oil ports to it and bolt it down on top of the bottom round one I brazed in before. I also put gasket maker around the perimeter to seal it up and tested with pressure air and soap bubble. The RTV would not have much direct contact with oil.
The perimeter no longer leaks. But to my great surprise, the upper piece (where the hoses are connected) has some leaks, which never happen before (I did this before, but that older piece wasn't round, wasn't meant to seal the perimeter). This time, I cut it round to seal around the perimeter. So I was very disappointed. I knew I can fix that with brazing, but this brazing method doesn't flow into the gap, and only very thin material keeps the bung attached to the metal hoses (round aluminum disc has 2 holes, each brazed with aluminum tubing then to a bung for connecting to hydraulic hose). So vibration may break it or cause leak again. I decided to use flux on it, and filler metal flown into gaps good. But it caused some distortion and just plain ugly, and I wasn't happy at all. Somehow the flux cause the rod to melt at a very high temperature.
I decided that I am going to change the upper piece to be steel/stainless steel and all connectors to be stainless, because I did welded it with it before and no leak whatsover, not like aluminum, easy like walk in a park.
But I decided to change the gasket maker to use gasket instead because I wanted to be able to take it out just in case there is a leak in the future. If I put a large glob of RTV in there, I may not be able to pry it up again.
On the drilling part, I used a drill on the lathe. The cut is much more beautiful than using the drill press, no smoke and just nice. But I can definitely see it's not super smooth.
