Finishing Cavity Soldering

I put some rubber on the tarmac this past week and made good progress:

  • I fixed all the open seams along the bottom:

    (Thanks to Randy for the suggestion about using a wet cloth to keep the heat from remelting the previously finished sides)
  • I then got help from my father to solder the top on (I am applying flux):

    There were two tricks, the first was to use a fairly thick but long rectangular piece of aluminum and wind it up inside where it pushed on the edges of both the top and bottom pieces to keep them round and line up the seams.  That aluminum piece won’t take solder and it is what is holding the top on in the picture above where, because of warping, my father is holding the seam closed.  The seam around the middle where I expected to have the most trouble is where I had the least, due to experience gained from the bottom.  Another trick was to use very little flux versus solder, such that I could tack the solder across the seam and then apply just enough heat to make it flatten out, then immediately blow to harden it in place.  The piece is held such that gravity pulls the solder down and around the seam.  Here is a shot from the raw footage after I have pulled out the aluminum ring:
  • I still have a couple hours of sanding to get all the rough edges smooth, both inside for smooth current flow and outside so it fits into the plastic enclosure.

    I bought really fine sand paper and the last sanding will be to buff and shine the inside to make sure no copper oxide is left over.

After sanding, the copper liner will be done and can be fitted into the plastic enclosure. (which from a few test fits, it is going to be nice and tight)

The list of things left to do is now a great deal shorter:

  • Get the tuning plate waterjet cut
  • Mount the probes
  • Mount the tuning mechanism
  • Bolt everything together

Then I will be going to the university to test the Q, hopefully somewhere close to the calculated maximum of 61K!  If there is a sufficiently high Q, then we can apply power and see if it moves (or melts, or does nothing).

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.

Soldering Copper Cavity

Happy Holidays!

Before Christmas, I ordered four N-type and four SMA connectors from Digikey and they arrived in short order:

(It is an optical illusion, as both of the dielectrics are the same length)

I have also started to document the method used to build the cavity on the wiki.

Kevin , Adrian, Lin and Lukasz came over for Christmas dinner and we took a stab at soldering the cavity.

Under pressure from the hot copper, the plastic bulged a bit.

I have been thinking up a refined method of soldering in the copper liner, which I will attempt this week.

Unfortunately, this time of year is typically a busy one for TOF, but I hope to be back up to the university with the finished cavity soon.