Re: [CAD_CAM_EDM_DRO] Re: Newbi needs advise on torch table. - now THC

I think that the system that you are using has some
very strong merits for most people. Eventually I will
prbably go that route or something simialiar. I have
two problems with it though.

1. I can't controll a oxy/acetylne torch with
this system. Which probably is not a very big deal,
though I would like the ablity to cut larger pices of
steal then what plasma will pirce. Ideally I would
like to have the ablity to gut some varly thick lumps
of steal up to say six inches. Obvously I will need
to make multible passes no matter what I cut with.


--- caudlet <info@...> wrote:

> --- In CAD_CAM_EDM_DRO@yahoogroups.com,
> "turbulatordude"
> <davemucha@j...> wrote:
> > > MACH2 is cheap, well written, constantly being
> improved and the
> THC
> > > is real and working. I cut for 4 hours today
> using it.
> >
> >
> > Hi Tom, and all,
> >
> > I am not totally clear on the THC problem.
> >
> > it seems that the table requies an X/Y to move the
> head, but the Z
> > can be independant. lower to part, start cutting,
> let it be
> > independant of the rest of the CNC software and
> just keep it's
> > location based on voltage.
> >
> > Then just wing that sucker around the table as
> needed.
> >
> > why is it so critical to have the CNC software
> keep track of the
> > head ?
> >
> > a command up with an end switch prior to any
> non-cutting moves, and
> a
> > start cutting with a resultant 'go' from the
> independant head
> control
> > seems like a simple approach.
> >
> > After all, don't a log of guys just ignore THC all
> together ?
> >
> > My EDM is similar in that the electrode postioning
> in seperate from
> > X/Y and even total feed is not counted as
> electrode wear has a huge
> > effect on distance.
> >
> > I 'home' to home, then re-zero on the first spark,
> then burn to
> depth
> > figuring no electrode wear, then home again, then
> back to the
> > starting zero and then measure the electrode wear.
> From that I can
> > caluclate wear in that part and how much farther I
> need to go.
> > Mind you none if this is critical, I'm still
> setting things up.
> >
> > Dave
> Dave: You are correct. You can run the Z totally
> independent of the
> XY. There are several commercial products ($$$$)
> available to do
> that. In essence they use an external micro chip to
> measure the gap
> voltage and adjust the torch height using DC motors.
> That has been
> the conventional way it has been done for a long
> time.
>
> As an Engineer I started looking for a THC solution
> as I was building
> my table. I could not afford the commercial units
> and the nearest
> thing was a RUTEX kit that was about 500 bucks and
> required a
> bewildering array of sensors that had to be
> constructed and provided
> by the "Builder" (me). Since I had already planned
> on making the Z
> axis a full Step and Direction design so my table
> could also be used
> for other stuff, I felt is was redundant to design
> and build some
> sort of electronic "switchover" so that the motors
> could be
> controlled by the THC rather than the
> computer.....if only I could
> find a piece of software that could do the "logic"
> part as well as
> the XY control then all I had to design was the
> sensing and measuring
> hardware. Art of Master5/MACH1 fame agreed to
> modify his software to
> my specs and I set out to build a real cost
> effective solution.
>
> Once you get out of the manual control or the
> set-it-and-let-it-cut
> approach (both which I tried), then you face several
> issues:
>
> 1. You need to be able to control the pierce cycle.
> You need to be
> able to find the material surface, move the head
> down to a specified
> pierce point, and start the arc.
>
> 2. You need to wait a variable length of time until
> the arc has been
> established, lower the head into the cut then
> release and start the
> XY moves.
>
> 3. Dynamically adjust the head during the cut to
> account for material
> unevenness and warpage.
>
> 4. Do that cycle each time, for each cut, because
> the position of the
> head is not known after it starts adjusting UP and
> Down
>
> The reason the commercial units cost so much is that
> they have to
> provide all of that logic in the unit. My reasoning
> was that if I
> could use the power of the controller PC and the
> software logic then
> I could do several things.
>
> 1. The sensing (surface zero) could be done and
> maintained as
> a "referencing" move in a g-code.
>
> 2. The pierce cycle could be integrated with the
> controller to
> provide XY hold and the sequence could be simple
> g-code and added to
> my CAM post processor.
>
> 3. The controller software would adjust the Z height
> on the fly and
> it would "know" where the absolute position of the
> head was so you
> could skip the re-zero move on every individual cut.
> That would also
> provide a know distance to start the pierce and
> lower the head for
> cutting.
>
> 4. You could set limits in the software to prevent
> the head for over
> compensating (max and Min adjustments).
>
> The cost then becomes just the external sensing
> components.
>
>
> We were able to do all of those things so that now
> cutting material
> is a smooth operation and I trust my machine enough
> to load a piece,
> hit RUN and walk off to work on cleaning up the
> previous piece I just
> unloaded. My CAM software POST puts in all of the
> g-codes so now I
> just draw the design, run it through CAM to define
> the cut vectors
> and lead-ins, and load it on the machine. The whole
> process takes
> minutes.
>
> Can you live without a THC....yep. You can use a
> drag tip and
> floating head and do a lot of stuff but that has
> issues as well.
> If you cut very much material though, you will
> quickly decide it (THC)
> is a neccessity rather than a luxury. Could you use
> a different
> approach? Sure, but you would be giving up some
> features that are
> real nice to have. I find my consummables (tip &
> electrode) costs
> are almost double when I don't do things in the
> right sequence and
> use the THC. If you cut 3 pieces a week then NBD,
> but if you cut 20
> a day like I do sometimes then I go through a LOT of
> tips.
>
> Tom C
>
>
>
>
> Addresses:
> FAQ: http://www.ktmarketing.com/faq.html
> FILES:
> http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
>

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