Soldering Troubles with Cavity

I made a bit of progress over the past few weeks:

  • I finalized a purchase ($175US shipped, eBay) of another, and hopefully final, port for the vacuum chamber through which the microwave signal will be injected.  I have lots of the little ports in the large batch of microwave parts I bought previously and some of those are blanks I hope to retrofit with an N-to-N connector.
  • I also got the vertical seams for the cone and straight section soldered by first fitting the cone and straight section into the plastic mold, marking the seam with a Sharpie, then taking the copper out and holding it in place with metal clamps (On my makeshift work bench in the basement during the cold weather).  Once solidly held in place, I then hand sanded off the sharpie mark and the two edges down, applied flux and brazed it with satisfactory results.
  • I also attempted to solder the circular seam around the bottom of the cone but ran into difficulties with the copper warping.  The result was open seams:

    I tried soldering the seam two ways, first by just using clamps to hold it in position, but when the copper got hot, the seams I had just closed would open up again.  I then stuck both parts into an extra plastic mold that Motive sent and that worked the best.  The plastic did melt/burn and it took considerable pushing and twisting to get the copper back out once cooled, but the plastic held up surprisingly well.

    I am going to try closing the seam by putting an aluminum strap around it, which won’t solder, but can take the heat.