Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

Hi Roger,

--- In Homebrew_PCBs@yahoogroups.com, roger lucas <ralucas4277@...> wrote:
>
> Hi Curt,
>
> Good to hear from you again.
>
>
> I am in the middle of designing an electrode feed
> system similar to yours. I have not heard of the NASA
> circuit, is it some sort of servo drive?

It's the circuit used in the Garden of EDM -- I'll be glad to e mail a
PDF of the original NASA Tech brief to you if you like.


>
> If I understand this right you are initiating the
> spark by advancing the electrode and retreating it at
> each point. How does this keep up with your scanning
> speed of approx 20 inches/sec? Or have I totally
> misunderstood the operation of the servo?

You've got it exactly right.

It's not a problem -- the pinch roller that feeds the wire through the
insulating sleeve is driven on the same principal as a voice coil
drive in a hard drive and doesn't need to move the electrode very much
at all.


>
> My early experiments included a solenoid armature
> oscillating an electrode at 50 Hz, amplitude about
> 1mm. This worked very well since the spark always
> initiated at the dielectric breakdown point. However,
> at the moment I can see no way of integrating the
> electrode feed with the solenoid arrangement. If I
> could it would answer a lot of problems.

There are two ways to implement the servo. One is to use a stepper to
control the pinch roller whichs feeds the brass wire through the guide
the other is to use a worm drive and dc motor.

Your vibrating electrode is the same approach Ben Flemming used in his
Ramah Tap Burner design and should work well for PCBs which are
∗FLAT∗. It would simplify the overall design a ton. Well Done!!




> My boards are all 4 x 3 inches, but the attraction of
> EDM is it is the cheapest way to go, and it can be
> left on its one to process with virtually no board
> preparation, and no ink or etchant costs.
>
> Roger


Yep!! And if you incorperate a drill head on the back of your gantry
you'll be able to drill the boards in water and save on dust collection.

Roger, I'm not saying the PCB EDM is a dead end -- just my system is
stonewalled! Since my major efforts in the spring and summer are
working on various Willys Jeep and Truck restoration projects and I
won't be much help in developing the PCB EDM until fall.

Good Luck to you Roger and feel free to ask me questions, I'll try to
be helpfull.

Curt Richards