Hi all,
I'm still new to all this, but like many of you I'm extremely interested in plasma fusion. So I'm having trouble creating the grid for my fusor. I'm following Daniel Spangler's instructions from Make Magazine.
The grid is to be fabricated from .032" diam, soft temper, 302/304 stainless steel wire. I have a standard soldering pen, flux, and solder. Everytime I try to join one of the rings of the grid, the solder just rolls off.
What metals do you guys use in your grids and how do you fabricate them? Would brass or copper work in a fusor?
Great Thanks!!
- Arya Afshari
creating the grid
-
Arya Afshari
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Carl Willis
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- Joined: Thu Jul 26, 2001 7:33 pm
- Real name: Carl Willis
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Re: creating the grid
Arya,
You would be well-served by browsing archived discussions about successful projects to get a good idea of what materials and techniques have been used to fabricate grids. The recent Make Magazine article doesn't necessarily reflect the known best practices emerging from more than a decade of refinement by the hobby fusion community; it only shows you what one individual (not a known contributor in our forums) did to construct a fairly basic, low-power demonstration fusor.
The grid gets too hot for solder in fusors operating at anything but the very lowest power levels. Soldering is therefore not recommended. Silver brazing is a better alternative, but still inferior to the tried-and-true spot welding that many members use. There are also straightforward ways to make grids that involve NO joining techniques; my own favored method was pioneered by Jon Rosenstiel and has been discussed frequently. If you feel the need to try soldering anyway, you will need an acid flux to break down the oxide layer on stainless steel alloys. I use LA-CO N-3 for stainless soldering. It is highly corrosive and will need to be thoroughly removed from any joints. A quick-and-dirty alternative flux is made by dissolving a sub-equivalent quantity of zinc metal in dilute (2-5M) hydrochloric acid.
Tungsten is the typical metal of choice for the grid. Stainless steel has been used effectively, but lacks the high-temperature performance of tungsten. Copper is low on the list of preferences for this application because it is easily softened (annealed) or melted by the heat. Brass is a poor choice since its zinc content has a high vapor pressure and will contaminate the vacuum environment when the grid heats up.
-Carl
You would be well-served by browsing archived discussions about successful projects to get a good idea of what materials and techniques have been used to fabricate grids. The recent Make Magazine article doesn't necessarily reflect the known best practices emerging from more than a decade of refinement by the hobby fusion community; it only shows you what one individual (not a known contributor in our forums) did to construct a fairly basic, low-power demonstration fusor.
The grid gets too hot for solder in fusors operating at anything but the very lowest power levels. Soldering is therefore not recommended. Silver brazing is a better alternative, but still inferior to the tried-and-true spot welding that many members use. There are also straightforward ways to make grids that involve NO joining techniques; my own favored method was pioneered by Jon Rosenstiel and has been discussed frequently. If you feel the need to try soldering anyway, you will need an acid flux to break down the oxide layer on stainless steel alloys. I use LA-CO N-3 for stainless soldering. It is highly corrosive and will need to be thoroughly removed from any joints. A quick-and-dirty alternative flux is made by dissolving a sub-equivalent quantity of zinc metal in dilute (2-5M) hydrochloric acid.
Tungsten is the typical metal of choice for the grid. Stainless steel has been used effectively, but lacks the high-temperature performance of tungsten. Copper is low on the list of preferences for this application because it is easily softened (annealed) or melted by the heat. Brass is a poor choice since its zinc content has a high vapor pressure and will contaminate the vacuum environment when the grid heats up.
-Carl