torch tips ( was Re: Build CNC Plasma cutting Table

The local sheet metal shop has a large steel head that surrounds the
torch tip. it has full clearnace, and rides on the parts.

it looks like a large arrow with the tip cut off so there is roughly
a 2-3 inch dia touching the metal with a 6 inch flange that starts at
the contact and rises up at an angle of about 45 degrees.

the weight of the head keeps the metal flat when cutting and also all
but eleminates any arc from blinding the operator and also allows
evacuation of the fumes.

just an idea.

Dave

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Ross" <rrcarl@n...> wrote:
> I know what you're talking about by the 4 slots. That is not a
true drag cut torch. My Hypertherm is designed so the torch tip is
in contact with the material. Because the tip is in contact there is
no slag on top of the material at all.
>
> On thin material, up to 14ga or so, I can pierce anywhere on the
sheet with no slag on top of the cut. On thicker material, I do get
a little slag at arc start if I start in the middle. This is not
really a big deal because the lead-in contour takes the arc start.
By the time the machine ramps into the actual cut line, the torch is
lit, pierced and running at 1 - 2" per second, depending on material
thickness and type. It will cut thin aluminum at 3" per second.
>
> I've been drag cutting with this Hypertherm machine for a couple of
years now and I change tips maybe once a month.
>
> The machine I had prior to this had a cup with 4 slots. The cup is
designed to hold the tip away from the surface a specific distance.
By holding the torch off the surface, you will get slag on top of the
material, particularly when the arc starts and you will probably have
problems where the cup wants to hang up on previously cut areas.
>
> With a drag cut torch, there is so little surface area in contact,
hanging up is not a problem. If you got close enough to a cut edge
to hang up, you would probably be running off the edge. A 2 axis
machine might have a problem, but on a a three axis machine, you
retract the Z axis before making any rapid travel moves. When you
arive at the approach lead-in for the next part, you drop the Z axis
back to zero, light the torch, pause 2 seconds and cut the part.
>
> You should go to your local welding shop and try out a nice drag
cut machine. Once you do you'll never go back.
>
> Ross