Friday, January 23, 2015

CNC Plasma cutting for noobs.


CNC plasma cutting is the use of a CNC machine to cut metal.

It is not as accurate as laser, or water jet.  This is because of how the plasma torch works. 

It will be accurate for things like auto parts, structural steel fabrication, farm equipment etc.

However it is not accurate enough for firearms, or electronics parts requiring high levels of precision.

If you are looking for a side business or even a small cash business you can run from your garage, CNC plasma can fit the bill. Of course your individual situation will vary. You need to do careful study and all the usual business was stuff.

CNC plasma is 2D cutting, much like water jet or laser.  There are 3D plasma machines, but they are well above 100k USD and beyond the scope of this article.

First things you need some basic skills in CAD, drafting, metal fabrication, and ability to read blueprints.

Second you need a machine.  

My experience has been that you need at least 4x8 foot working area and preferably 5x10 feet.

This is because steel comes in 4x8 sheets.  Smaller machines will result in lost work, and extra headaches.  I learned this the hard way.

You need a separate plasma torch with what is called a machine torch.  For money making you really only have one choice, and that is the Hypertherm Powermax series.

This is because of the consumable parts. There are China machines and Thermal Dynamics which are cheaper initially but over the course of even a few months, the consumables cost of the cheaper machines will save you more than what the price difference was.  

You need at minimum a Powermax45 or Powermax65 with the machine torch, NOT the hand torch. 

This is for the next part of the machine you need which is the automatic height control.

Steel will flex when cutting and the torch will either crash into the steel or get too far away to make proper co tact and the flame will go out. Manual height control machines seem like a great deal but they are a 2 man operation and you need to take all sorts of extra precautions with eye wear etc.

Save yourself the headache and get it.  

You need a good air compressor.  Something big like 5hp. I used 2 smalller 1hp compressors running at the same time.  It did work.  Along with that you need a air dryer.  Some guys get obsessed about it. An ordinary harbor freight dryer for paint sprayers works ok, just run the air thru a large 1-2inch steel pipe that will act like a radiator before the water separator to let the air cool down and the water will condense easier.  Water will kill your torch tips.

You also need a water table.  The machine sits on top of the water table.  When the torch cuts it produces sparks and smoke.  The water will catch the sparks, smoke, and cool the metal reducing distortion.

Consumable parts are expensive. A typical set of tips will get you an hour of cutti g with a Hypertherm. Mostly it depends on the pierces the torch makes.  Each time it fires there is a little bit of an electrode inside made from hafnium that gets consumed. A set of torch tips for a Hypertherm will get you 3x the amount of pierces that a Thermal Dynamics torch will give you and cost the same amount for a set. A Chinese torch will cost half per set of tips and get you 1/4 the amount of pierces as a the thermal dynamics.

I have cut over 1/4 mile of 6mm steel plate with one Hypertherm tip, and I have cut 1/4 sheet of 12mm steel and consumed a tip.  But generally the Hypertherm was consuming 5-6 sets of tips per month in my shop on average.  

Electric service.

You need good electric.  As in 20kva.  If you plan on running a generator get 30kva. The surge in power draw will wreak havoc on lower rated generators.  Or get a Miller brand all in one gen set for welders. They are rated for this type of duty cycle.

Most households in the US will have enough power to handle a CNC plasma.  Basically you need around 50-60 amps service which means you need anywhere from 4-6ga wire depending on how far you run the wire.

You also need a angle grinder.  Something good not cheap.  Cheap angle grinders vibrate.  Vibration will ruin your hands fast.  Plasma leaves slag on the back corner of the cut.  It needs to be removed with a hammer and angle grinder with a flap disc or a grinding wheel.  You will use both.

Angle grinding is a often overlooked art and skill that you will have to master.  

Metals and how they react to CNC plasma

Steel, steel cuts the best.  Does not matter if it is tool steel, armor plate, or mild steel, it all cuts the same and the settings will be in the manufacturers handbook.  Armor steel and tool steel HAVE to be cut on a water table with the water touching the bottom of the sheet of steel.  If not you will ruin the steels tempering or in the case of untempered tool steel you will flame harden it which makes it hard to impossible to machine.

Stainless steel depending on your setup can leave some really nasty slag. I have cut a lot of it, it is not fun to clean up.

Aluminum makes a funny type of slag, it can be almost removed with a hand file or a gloved hand for the most part. Sme people are paranoid about aluminum cutting and hydrogen gas buildup.  A regular open water table will not make enough gas to worry about.  It will however give you nice hot thermite sparks in the water if you are cutting both aluminum and steel into the water. The sparks are not a lot, but they will glow bright and briefly in the water.

Brass leaves slag that can be cleaned up with a file or very gentle flap disc work.

The sludge in the bottom of a water table is black iron oxide.  It has it's uses too. It can be made into thermite,  or my favorite, I used it as plant food for iron poor soil. Never made thermite with it.

Now you ask what machine to get.

It all depends on your budget and expertise.

I seriously would not buy a PlasmaCam brand.  It is made from thin sheet metal and will wear out fast, not to mention that it is not strong enough to throw heavy steel on to it for any amount of time.

Torchmate brand is good, especially if you are a noob. Great customer service.  You are going to pay for it. Torchmate occupies that market space at the bottom to middle of the CNC plasma market.  Better than China machines and strong enough to run all day every day, and they work every time you turn them on.  The same can not be said about China machines. Expect to pay around 8-10 grand for everything you need.

DiY route. You can go with the eBay kits but you really need to know your CNC. When I started out I probably would have had a disaster with one, now days, I could build a CNC plasma from scratch.

You can go for the super DIY route by buying steel, and a $350 dollar electronics/motor/power supply kit from China and drive it with motorcycle chain, hardware store bearings, and a $1000 auto height controller from that guy in Eastern Europe that sells on eBay.  It all depends on how handy you are.

CNC plasma has many uses to make money. Most noobs start off making decorative stuff with it and do the flea market thing.  

However you could make a better living by making tool parts, car parts, bead locks, knife blanks, and the like with it. 

Farm equipment is a good market as well as up armor kits.

The salesman for Torchmate told me years ago that they sold a lot of their machines to Mexican companies for vehicle up armor kits.

You can also build boats with a CNC plasma table.

Download the files online, convert to blueprints and cutting files.  Those little 2 plywood sheet boats can be made with sheet metal just as easily.  Of course you gotta know how to weld and the rest.

Billing for services.

CNC plasma typically bills $1.50 to $2 per minute for cutting.  Seems a lot, but often times you get these little 20 min jobs that take you an hour or 3 to set up.

Software.  

Torchmate CAD is a private label version of Signlab.  It is $350 for the light version.

You will need at least the lite version to prepare files for cutting.

For serious design work, it will work, but you need very good imagination and mechanical reasoning skills to draw something in 2D that will be assembled in 3D

Not to mention that  CAD does not do layouts very well. Yes you can do them, but they are a pain in the rear to draw and time waster.  

For that I prefer Sketchup Pro or DesignSpark Mechanical, both of which I have written about before.

If you are asking what a layout is, then you are probably not ready to jump into CNC plasma woot some serious study time first.









Above:

Rice mill parts, structural steel, decorative metal, and a gasifier cook stove.

I'll do an article about wood gasifiers in a future article.




26 comments:

Anonymous said...

What resources (web, books, etc) would you suggest for a noob to get started learning CAD/CAM?

coachloria said...

Really appreciate the information you sharing.

Anonymous said...

Lincoln Electric (owner of Torchmate brand) sells a college class textbook for Plasma Cutting on it's website. It takes some looking, but it is a complete course: CAD design, to G-code, to plasma operation and theory.
http://www.lincolnelectric.com/en-us/equipment/Pages/product.aspx?product=K4143-1%28LincolnElectric%29

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