Grid Update

22 04 2009

I sent in the STL of the grid shown previously to Prometal for a quote. Unfortunately it can’t be made as designed:

We feel that you could expect warping up to about 1/8.”  We also think that we may have some breakage as well.  Unfortunately, this part is not a good fit for our process.

Going to go with TeslaBoys design. He sent me the DWG files for the lasercut inner grid. However, the current design needs some tweeking:

The problem with the design is that the rings intersect at angles so the grooves need to be cut at an angle, but you cannot do that with a (2) axis laser so you have to grind or machine the angles into the grooves.

The improvement is to make the grooves wider based on the angles that the other rings intercept it.  I have not sat down and worked out the geometry, but it is worth it because machining the angles into the narrow grooves was very time consuming and tedious.

I’m also going to attempt to make a cruder version out of welding wire.




6 responses

22 04 2009
Vik Olliver

See if Bathsheba Grossman can make you one :)

Vik :v)

22 04 2009

He uses the same company (Prometal) I just got the NO CAN DO from.

I’m guessing I could use their process with thicker grid wires.

22 04 2009
A. McEvoy

The cruder (and cheaper!) the better, I say. Fusors are very forgiving in terms of tolerance for grid warping, since radial ion convergence isn’t really that critical at ~mTorr. Unless aesthetics is one of your main concerns, there is no need to spend $100(s) getting a pretty, symmetric grid.

23 04 2009

A. McEvoy: I’m looking in to welding wire for the grid. Which type is best?

I’m guessing ER 308L— Solid— For welding Types 301, 302, 303, 304, 304L, 308, 308L, 312, and 347 stainless steel. Resistant to corrosion, impact, and abrasion.

23 04 2009

Actually I need a TIG rod:

23 04 2009
A. McEvoy

So long as the grid material is a relatively good conductor it shouldn’t matter what you use. In fusor mode, ion collisions will liberate electrons from the grid, requiring a supply of current. The work function of the material you choose will have some impact on how much current you will need to supply, but I don’t think you need to concern yourself with that too much. I would just try something cheap and workable.

In Polywell mode you will have to worry about drawing the current off, as you will have a higher (hopefully!) population of electrons. In this case, secondary electron emission can be a serious factor in terms of efficiency and so you might care a bit more when it comes to this part.

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