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Old 04-25-2017, 05:25 PM
miniman82's Avatar
miniman82 miniman82 is offline
First Light: 1952-2011
 
Join Date: Jun 2009
Location: Great Mills, MD
Posts: 4,159
EDM possibilities for gun rebuilding

Electrical Discharge Machining (EDM) is a process of spark eroding a conductive material using pulses of high current into a workpiece, in our case the cathode retainers in electron gun assemblies. An electrode moves up and down on a ram, bathed in a dielectric oil, controlling the spark gap to the workpiece until a cut is effected. In the case of our electron guns we're not exactly cutting through a workpiece, merely eroding the cathode retainer to the point where we can remove it from the G1 cup without damaging anything.

The cost of an EDM machine is quite high, I found a very old one on Ebay for around $1,000 and newer computer controlled machines are much more- in the neighborhood of $3-6k for a used one.

While $1,000 is not outside the realm of possibility for something like the Charmilles D1S currently on the bay, I have no idea what the capabilities of it are or whether it would be appropriate for a process like gun rebuilding. That being the case I've done some digging, and apparently a DIY one can be built for a few hundred dollars using common shop tools and electronics.

http://www.homebuiltedmmachines.com/

The site above sells a book and bare PCB to build a pulse type power supply for a homebrew EDM, and the ram control can be implemented by stepper motor controlled by small computer (Arduino or similar). This would allow us to get the cathode retainers out of the guns without risk of breakage to the glass multiforms holding it together, a task that currently is completely manual in nature (hand grinding) and carries risk of gun breakage.

Please discuss, I need input as to how feasible a stepper controlled ram would be. The rest is pretty simple, as far as filtering of the dielectric oil and power supply end of it is concerned. Also if anyone has info on the D1S machine mentioned above, I would be interested to know if it's able to do precision work like this. We are talking thousandths of an inch, not just punching a hole in a piece of sheet metal here.
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