On Sunday 11 March 2018 05:54:08 Andy Pugh wrote:

> > On 11 Mar 2018, at 06:03, a k <pccncmach...@gmail.com> wrote:
> >
> > i want reverse tool path.
> No, you don’t.
> A reversed tool path will still put the tool outside the part
> material.
> Just use a 3D printer slicer and configure your machine with a dummy
> extruder axis that does nothing.

That to me, still doesn't quite get the job done. He needs to hook up the 
extruders wire feed to the plastic feed, and some way to turn off the 
fire when jumping across an opening in the pattern, and restarting the 
fire when its moved across the empty opening. The fact that the machine 
can lay down a much thicker line of metal in one pass than the 3d 
printer can should just be a matter of programming the slicer for a 
thicker slice. In fact it may be worthwhile in reduced "finishing" work 
to design a new smaller "extruder like" mechanism to handle say .015" 
diameter wire, as that would reduce the final pass to size to a single 
pass, possibly with EDM if its a thin walled and easily distorted item..

It might even be helpfull to replace the drive motor on the "extruder" 
with a reverseable motor so that the wire can be withdrawn far enough to 
extinguish the arc. The rest of this I see as a hal file composition 
exercise, hooking up SSR's to control the arc, and some sort of a THC 
like arc starter. In fact, let the THC output control the x/y feed speed 
as a way of laying down a consistent thickness of metal.

It would also be a good idea to have the workspace flooded with the near 
inert CO2/Argon atmosphere. The CO2 adds carbon to the puddle, making 
the resultant metal layer much harder than straight argon by itself 
would. It wouldn't matter if it leaked, as long as the working envelope 
was flooded to keep slag at bay because that would make the arc restart 
simply a matter of fireing the SSR and extending the wire until contact 
was made again, letting a feedhold hold the starting position until the 
arc was started, long enough to make sure the metal was being 
transferred. The flooding gas would ensure a clean, oxide free 
interface, making the arc so much easier to restart you'd wonder why you 
ever bothered trying w/o it. The initial startup might need a delay 
after gas turnon to assure its well flooded else the weld would slag 
over once the head had moved on, at least long enough for the weld to 

Or perhaps I don't fully understand the problem.  Its certainly something 
LinuxCNC can do once the slicer has created the laydown paths from the 
3d model.

Aram hasn't given us any hint at how big the working envelope of the 3d 
metal printer might have to be as that will determine the gas economics. 
In the size bottles I use, a big box can get expen$ive to flood.

Cheers, Gene Heskett
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>

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