Plasma+THC

[manmardam]

i have worked with mach3 in "MILL" but now i want to learn how to work with that in "PLASMA"
in some videos i saw that nozzle moves to the desired point when it reaches to the destination point it moves down and then up and after that the PLASMA turnes on and it stops for a short time(delay) began to move.

How mach3 do this operations in its program routine
i think that the PLASMA operation is so,but if i make any mistake please describe.

in my country i can't buy any thing using internet .
THC basis is on voltage difference between the nozzle and the plate that it compares with a refrence voltage .the nozzle and plate distance tunes depand on the voltage between nozzle and plate.
is it a complicated project you think or it can be done easily with a microcontroller?

best regard.
amir

[Torchhead]

The moves you are seeing are not "MACH". They are in the software running MACH (g-code). You need a CAM program that is for Plasma cutting.

microcontrollers are like a paintbrush. They are capable of many things. It's up to the artist/programmer to make it do the many things.

[Larken]

Does bumping the torch against the work to find zero not damage the tip at all.?

Is this the way most THC in mach sense the material or are there other methods ?

[jimcolt]

There are quite a few methods of finding the surface of the plate...here are some:

-Stall force sensing...indexing toward plate until collision....increase in motor torque/current or stall sensed....then retract known distance to pierce height

-Mechancal switch activation when plate contacted

-non contact proximity switch activation

-ohmic contact (electrical conductivity) between the copper torch shield and the plate


Jim

[Larken]

is it a complicated project you think or it can be done easily with a microcontroller?

The problem with using a microcontroller is isolating it from the severe electrical noise and high voltage so it doesn't crash and lock up all the time.
Thats why Torch heads controller has 2 boards, one in the plasma unit and the other a distance away.

Jim, how dangerous is it getting a shock from a hand held plasma ? Seems pretty nasty, is it worse than a Tig welder ?

larry K

[jimcolt]

A hand plasma torch should be considered far safer than a tig torch from a shock perspective.....with tig, the electrode is exposed on the front of the torch......if your finger touches the electrode and another part of your body touches work ground.....you will get open circuit DC voltage.....you also can get zapped with the high frequency quite easily if you are using HF start on a tig torch.

With plasma.....the electrode is inside the torch....to access it you would have to carefully stick a fine wire up inside the shield and nozzle orifice on the front of the torch....then pull the trigger on the torch. I'm not real sure if you would actually feel the shock....because the resulting plasma arc would burn the hell out of your fingers holding this piece of wire! Most hand plasma systems today do not use high frequency start....so that is out of the question as well.

The major brand plasma systems today are very safe. I cannot say that for all of the low cost imports......I see exposed full potential DC on many of the torch connections for these units....and many use high frequency start. They totally ignore most safety precautions.

Jim Colt

"Jim, how dangerous is it getting a shock from a hand held plasma ? Seems pretty nasty, is it worse than a Tig welder ?

larry K"

[Torchhead]

How to get a nasty shock from a plasma cutter:

Turn on the plasma
Clip the workclamp to the work
Do not ground the table or workpiece
Fire the torch and touch the work AND a chassis or object that IS earth grounded.


Plasma workclamp is NOT ground. It's + arc volts. With no reference to a safety ground you can become the conductor. All tables should have good earth ground.

I think TIG voltages are a lot lower than plasma. Anything below 48VDC is not enough to break normal (dry) skin resistance. You can get a tingle from arc welders where the work is not grounded but unless you first wet your fingers (or use your tongue as a connector) and stand bare-footed, a real shock would be hard to acheive. I know MIG operates down below 35VDC but high current.

Useless bit of trivia: Dialectic strength (arc-over point) of air is approx 10,000 volts per inch at 35% RH and sea level pressure.

TOM Caudle
www.CandCNC.com

[Larken]

Exactly,
Lets say you were working outside on a car with a hand held plasma, and you forgot to put the work clamp on the frame. You are leaning against the car with one hand and start cutting. You become the path to ground !
Will it kill you ?

On my Tig (miller Synrowave 180) it can shoot an spark high voltage about 1/2" then i start welding aluminum, just like a spark plug wire on a car. A tig is hasty compared to a mig.

Larry k

[jimcolt]

Tom,

I agree that the plasma work clamp is not ground....however in a properly designed plasma or welder..it is referenced to earth ground through a resistance back in the power supply....for safety reasons. I have hand cut in thousands of different positions....including underwater (in a dry suit) with a plasma torch in my hand....never felt a tingle. I have also unloaded many cutting tables over the years while as many as 4 plasma torches were cutting...often standing in puddles.....never a tingle from that either.

The plasma voltage is generally higher than tig, however the highest potential (electrode) is harder to get to in a plasma torch as compared to a tig torch. Pretty safe process....however it pays to be careful and properly install and ground your equipment.

Jim

[jimcolt]

Larry, I cannot count the number of times that I have been laying on my back under a car....often in the dirt....with a plasma torch in my hand......and tried cutting then realized the work clamp was laying on the ground next to me. Maybe I'm a little lucky....but I have not been zapped by it. I have actually finished cutting a few bolts off with the pilot arc....which is a path from electrode to nozzle....which finds its way back to the power supply via the + cable in the torch leads.....I suspect there still is some voltage on the car when this happens....but must be low enough so you cannot feel it.

Jim

[Torchhead]

As long as you and the workclamp are at the same potential then no current flow. Both laying on the ground is the same spot. Workclamp to the frame and you laying on the ground with no shirt on and there is a possibility of current flow through you body if you had a bare hand on the car frame AND good contact to the ground around you. The most dangerous time would be if you fired the torch in the air and the current is looking for a place to go. While cutting the lower impedance of the car frame to the electrode would cause most of the current to travel in that direction.

To shock yourself with a plasma is not as easy as just doing one thing wrong. Like most accidents the cause is often doing multiple things wrong at the same time (e.g. not wearing gloves + not wearing a shirt + having the workclamp on the frame and firing the torch in the air) All industrial equipment have elements of danger. The CNC table can hurt you bad. Saws and routers take off body parts as easily as wood or metal. Flying objects can damage eyes. In one rare case a friend of mine was almost killed when cutting with a table saw and a carbide tooth from the blade penetrated him in the chest and hit his heart. He almost bled to death before he crawled to a phone a dialed 911. When they got him to the ER his blood pressure was so low they thought he was dead.

I once watched a guy cut off the end of his finger while using a manual paper cutter. This was in 1970 and before the manual cutters had guards. Sometimes dumbass has it's own punishment (:-)

TOM Caudle
www.CandCNC.com