To all

The correct pierce height is the height which results in no spatter on
the tip, nozzle or shield. Thin material is less and heavy plate is
much more - maybe even 1/2". Too high is not good either because
electronic torch height control circuits are generally locked out when
making holes and corners. That means the torch stays at the pierce
height during the cutting of the hole. Which means slag on the bottom
of the cut and a very beveled cut face.

Pierce time must also be set correctly for each material thickness.
Time is approximately equal to the decimal equivalent thickness, i.e.
..100" thick @ .1 sec and 3/8" @ .4 sec etc etc. The machine motion
must not begin prior to the plasma arc penetrating all the way through
the plate.

Cut height is specified in the torch manual from the manufacturer. The
show cutting height as well as voltage. Voltage is listed as a
measurement because it happens to be proportional to distance the
electrode in the torch is from the plate. Also voltage is easy to
measure during the cut - distance is a bit more difficult.

Too close it not good. Too far away is also not good. Think of the
plasma arc as a magnifying glass. Remember as kids, the glass had to
be at just the right height above the leaf to get it to start burning
quickly. Same thing. The plasma arc has a focal length. So follow the
suggestions in the manual. Voltage is only as relative measure of the
correct height, so the right voltage is the one that produces the
correct distance. Not the other way around.

Use less current for slower speeds, less smoke and squarer cuts.
However, you need enough power to penetrate the plate quickly so the
spatter does not ruin the front end of the torch. Also you need
enough power to produce a clean cut

The right power will pierce the metal with no spatter back on the
torch, produce a dross free cut at speeds the cutting machine can stay
on path and then also make you money. If any of the above are not
true, you need more power. Either turn up your machine or buy a larger
plasma system.

Plasma manufacturer go to great pains to design the torch to operate
correctly with the pressure they specify.

It is important to note that increasing pressure will increase flow
which will cool off the plasma arc. The flow of gas is higher and a
bit more dense but the arc is actually colder. Also higher pressure
will make it harder for the pilot arc to start. Very high pressure
may result in the torch not starting at all. Also high pressure
accelerates electrode insert erosion and reduces electrode life.

Reducing the pressure reduces the flow and makes the arc a bit hotter.
It also will make the torch head get hotter as well. Again, stay with
what the manual suggests

If you get top dross it is usually because you are traveling too slow
and or the cutting height is too high.

When you cutting an intricate shape with some long straight cut edges,
the long straight cuts will generally be dross free but the corners
and curves will be very drossy. This is normal because the speed was
correct during the long straight cuts portion of the part, but the CNC
slows down for corners and the THC is locked out the cuts become
drossy. Potentially the wrong cutting height and too much power for
the speed of travel.

The moral of the story is, intricate cuts on thin gage will be best
cut at low power because the corner slow down speed of the CNC and
correct speed for the long straight portions of the shape are closer
to being the same. Also try using the unshielded style tip/nozzle. It
wil produce a much finer cut at low power.

Al




Gunner wrote in message . ..
Cross posted to rec.crafts.metalworking for Ernie etc

On Wed, 21 Jul 2004 12:34:19 GMT, I AM WHO I AM
wrote:


Has anyone used or heard anything about the Plasmacam machine. plasmacam.com
I am installing one in a machine shop in Ontario Canada.

I was called in when the owners could not get it running properly. I have a
recent computer background and a past mechanical background but no welding or
machine shop experience. The owner of the shop here ran a large CNC system
for Caterpillar until they took off for Mexico. The other guy is a real good
beer drinker.

The main problem right now is trying to get good clean cuts. Even though
their website does not list it and in fact suggests avoiding it, the phone
support person says the Thermaldynamic Cut Master 75 which we are using is
one of the most popular models in use and will do the job (this I find very
strange). We get slag build up on the bottom of the cuts and on top. I have
experimented with different currents on the plasma cutter and different air
pressures and different cut heights and different pierce heights and it's
still not great. Does anyone get nice clean cuts like their video shows?

I am working with 1/8 inch sheets of steel. I have done the setup of the
perice height adjustment (z shift) and the cut height (Arc voltage shift),
about 40 times. Every time it comes out slightly different every time. Next I
would like to do the X and Y location adjustment but the 1 inch square I cut
for it is just too rough to measure properly, to do this accurately. I am
just now thinking that maybe I should make it a 2 or 3 inch square and try
that?

Can someone give me some general ideas on Plasma cutting so I can try to get
this torch cutting properly?

Lets say for 1/8 steel,

What is generally the best pierce height above the sheet? I have tried .1 to
.4 and spots in between. The Plasmacam guy suggested twice the material
thickness, in this case .250.

What is the best cut height? Is it very close to the material say .02 above?

What current should I use. 40 amps and below does not seem to pierce the
material, but maybe I have to increase the pierce time?? Does too high a
current create the slag?

What about air pressure? I have tried from around 65 to 100 lbS with no
difference that I can see.

What is the best size of torch tip for 1/8 material?

Plasmacams support is not 24 hour like they say and it takes them 24 hours to
call back after you finally get a hold of someone (maybe that is what they
mean). Thermaldynamic is not interested in helping unles we buy a machine
torch instead of the hand held. Any help I can get here would be very much
appreciated. I will check back tonight.

Thanks Johnnie


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