Page 1 of 1

FAQ - Repurposing an insulator

Posted: Sun Jul 09, 2017 8:33 pm
by Richard Hull
Recently a poster mentioned passing by a naval bulkhead insulator at a flea market/hamfest. This FAQ is how I purchased and repurposed a U.S. navy Antenna bulhead insulator from a hamfest back in 2001.

It turns out that around the year 2000, a huge cash of these insulators entered the surplus market and soon showed up at hamfests all over the East Coast. "I can see at sight." I saw that a good bit of effort would have these lovely items in their original naval boxes and packing work out perfectly as a fusor high voltage terminal. They did!!

I noted that the sellers generally wanted $20 each for these. I approached one seller at Raleigh's RAR fest in 2001 and offered to purchase all 16 that he had for $10 each. He took the deal. At subsequent hamfests from Maryland to North Carolina. I bought up every one I saw. In the end, I had about 25 of these beauties. Over the years at HEAS and on line, I sold all but the one spare I now have remaining.

Now for the effort involved in turning this insulator into a fusor insulator that I have used in fusor IV since 2004 up to 43,000 volts. (The limit of my current supply)

Refer to the images attached below.

The insulator is of pure Beryllium Oxide, ( a fabulous and weather resistant material). You will note in the images, the warning label related to the insulator material, something I ignore.
The base and HV terminal are of naval brass with a very tough, thick and tenacious chrome plating. (hard impact sea salt resistant)

The base, as is, is probably rather easily adapatable to a custom made SS flange, hand done by an accomplished amateur machinist. However, I chose to adapt it for attachment to a common 2.75" conflat flange on my fusor.

I mounted the base in my lathe and turned off the thick, oddball, heavy flange at the base of the conical "skirt". I then took a through-hole 2.75" blank and bored a hole a bit larger than the tubular pass-thru insulator in the center of the blank CF flange. On the top of the flange, (outside part), I turned an inleted ring about .2 inches deep from the center hole to slightly larger than the base of the skirt remaining on the insulator. I, next, removed all traces of chrome plating from the bottom .2 inches of the flange skirt. I, then, braze-tinned this skirt base carefully.

The final act in this trauma/drama was to place the skirted insulator in the well of the prepared CF flange. After applying some jeweler's 60% silver brazing paste in quantity all around the skirt base packed into the well, I oxy-acetylene heated only the Conflat fitting to near red heat until the paste braze disappeared and flowed all around the skirt base leaving only the white borax flux visible. I immediately removed all heat and let the flange cool as I used a tiny squeeze bottle of water cool only the very edge of the conflat. (do not quick quench)

The resultant conflat flanged insulator has served continuously since 2004 on fusor IV.

Note... I did add a large chromed sleeve over the threaded top of the insulator and a chrome ball that will accept a bannana plug on the end of the HV silicone HV wire. This helps remove all sharp, exposed edges. (field control) Later I found that the isulator would arc in air at around 40kv to its base. I added the 1/4" thick HDPE insulation pad at the base of the insulator seen in the image below. It has never arced since. I am sure this was not needed if the insulator is wiped down with an absolute alcohol soaked towel just prior to a run. This pre-run action removes all moisture and dust that has accumulated during periods of non-use. However long run times will, via electrostatic action, atract and attach dust to the terminal, (electrostatic percipitator), and arcing might occur. The HDPE shield helps avoid this. Both this shield and and the insulator are both now wiped down before every operation of fusor IV with the alcohol towel and dried with a lint-free cloth.

The upshot is keep a lookout for these types of insulators online and at hamfests. I occasionally see many useful, "adapatable" insulators at hamfests.

I will post this in the construction forum FAQs as well.

As always, click on image to enlarge.

Richard Hull