Home Built 4x8ft CNC Plasma Metal Cutting System

What is a CNC Plasma Cutting System? These are computer controlled machines that can cut through any electrically conductive material (steel / stainless / aluminum / copper). The machine takes a 2D computer generated sketch and translates it to a computer numerical control (CNC) system that is coupled with a Plasma Cutter. The Plasma Cutter uses an electrical arc and compressed air to cut through the conductive material.

I designed and built this system in my personal shop utilizing several off-the-shelf components along with some custom fabricated assemblies.

Check out the following steps for a detailed overview of my custom CNC Plasma build!

Planning

Before beginning, I had to answer a couple key questions:

• How large of a CNC table do I want to make?
• What is the max thickness of material that I need to cut?

These two questions will drive the rest of your project. For me, I decided to build a table that can accommodate a 4x8ft sheet of material (4x8ft is one of the most common sizes for raw steel plate). Based on what I typically fabricate, I wanted the ability to cut through 1/4in thick steel at a minimum.

I also included a few unique aspects into the design:

• Drop down casters for easy mobility
• Down draft system for drawing out dust and smoke
• Nozzle point suction system and water trap for drawing out fine particles near the cutting tip
• Removable cutting surface - allows me to lift off the cutting surface and insert a water pan for an alternate method of smoke and dust control

Components involved

Below is a general list of the main components of a CNC plasma cutting system:

• Plasma cutter - I elected to purchase a Hypertherm Powermax 65 plasma cutter for this build. This machine is capable of cutting 1in thick steel.
• Air compressor - Plasma cutters require an air supply to operate and cut through materials. I chose an Ingersoll 80 gallon air compressor which should have no issues keeping up with the air supply demands from the system.
• CNC Motor Control Package - These are the drivers and motors that control the movement of the Plasma Cutting torch. I purchased my system from a company called CandCNC. This system included all 4 stepper motors and motor drivers in one complete package.
• Table Base - I custom fabricated my table base using raw materials. The main frame is built from 2in x 11ga square tubing.
• Gantry Assembly - this includes all of the bearings, gears, gear tracks, and structural components that make up the moving gantry on top of the table. You can source these parts individually or purchase a full gantry kit. I elected to purchase my gantry from Precision Plasma.
• Software - a few different types of software are required:
  • CAD Design Software - Computer Aided Design software allows you to sketch and design your parts before cutting them out. AutoCad or Fusion 360 are great options for CAD design programs.
  • Plasma CAM Software - Computer Aided Manufacturing software will convert your CAD sketch into a coding language (typically 'G-Code') that the CNC plasma system can read and interpret. I run SheetCAM on my system.
  • CNC Control Software - this software reads G-Code and sends it to the motors on the CNC table. My system uses Mach3 CNC control software
• Computer - a basic computer is required to run your CNC Control Software and hook up to your motor control box

I began by building the main frame using 2x2x11ga square tubing and 2x3x11ga rectangular tubing. I included drop down casters that pin in place for easy mobility. I also extended my gantry rails such that the gantry will roll completely off the 4x8ft area to allow for easy loading of steel sheets. The dimensions of the gantry drove the width of the table base.

I designed the cutting surface as a removable assembly. This allows me to lift the surface up and insert a water pan as an option for dust and smoke control. This cutting surface uses 2x1/8in sacrificial slats and was built using the following materials:

• 2x3x11ga rect. tube
• 2x2x11ga square tube
• 1x1x14ga square tube
• 2x.25in flat bar

The cutting surface drops into place on the table base. A set of 3in wide by 3/8in thick cold rolled flat bars serve as the rails for the gantry. Cold rolled materials maintain a higher dimensional tolerance than hot rolled. These rails bolt to the top of the main frame.

Before attaching your motors and wiring, it is prudent to bench test the system. This will ensure all your motors and connections are fully operational and pre-programmed to turn in the correct directions. The instructions included with my CandCNC motor control kit helped make this a straightforward process.

At this stage, I also wired up my Hypertherm Plasma cutter so it will auto-start using a signal from the CandCNC control box. The CancCNC instructions walked me through this connection process.

After fabricating the table base and cutting surface, the next step was to assemble and fit check the gantry. My gantry system from Precision Plasma was built with extruded aluminum.

This gantry incorporates a Z-axis allowing for torch height control (THC). Torch height control is a highly desirable feature on CNC plasma tables. This allows for active and automatic control of the distance between the torch tip and the material being cut. A voltage feedback system automatically maintains a specified distance even if the material being cut begins to warp. Without THC, you run the risk of your torch running into the work piece. A THC system also prolongs the life of the plasma cutter consumables (electrode / tip / nozzle).

I also opted to use belt reduction drive assemblies for each motor. This helped to smooth out the operation and movement of the gantry.

I fabricated a desk out of 1.5in square tube to house my computer and monitor. Some folks mount their computers directly to the CNC base. I opted to keep this as a separate assembly. My computer is kept underneath the desk top. I subsequently added some sheet metal around the desk to protect the computer from dust.

An efficient means to draw out fumes and dust while running a CNC plasma system is highly necessary. There are two common methods for this: a water table or a down draft. Each has its own set of advantages and disadvantages

Water Table - this type involves a reservoir of water (often times treated with a corrosion and bacteria inhibitor) that sits just under the material being cut. The water traps a large majority of the cutting dust and helps to keep the material cool. However, water often times splashes around while cutting and will require constant maintenance to keep your gantry system dry and clean

Downdraft - this type uses mechanically driven air flow to suck the dust and fumes down into the table and out to a desired location. With the right fans and enough air flow, this method works very well. However, it does not provide the material cooling capabilities that a water pan does. Keeping the material cool is beneficial to reduce warping especially when cutting thin materials.

I opted to incorporate a downdraft onto my table but left the option open for a water table through the use of a removable cutting surface. I started by enclosing the table base using aluminum sheet metal. I plumbed in qty 4 suction points using 10in HVAC duct work. Each suction point has a slider window that allows me to direct maximum amounts of suction to certain quadrants of the table. To power my downdraft, I used two commercial grade kitchen exhaust fans. These fans are typically mounted on a roof or wall and expel air radially in all directions. I modified the fans to expel air in a single direction using some custom built duct work. My fans blow all dust and fumes to the outside of my shop. Tip: find yourself a local HVAC wholesale company to purchase your downdraft ductwork - this will be significantly cheaper than the local big box home improvement stores.

I subsequently also added a nozzle point suction system. I used 1.5in sump pump drain hose and routed it from the cutting tip, through my gantry cable tracks, and down to a 5 gallon bucket which is also connected to a shop vac. By partially filling the 5 gal bucket with water, I created a makeshift water trap that helps to capture fine dust and particles.

This is a critical step to ensure your system produces accurate and true cuts. By physically measuring the movements of the gantry and making slight adjustments in the control system, you can dial in your table ensuring a perfect 90 degrees between the X-axis and Y-axis. I ran my gantry up and down the table to ensure it remains even and true throughout it's full range of motion. The 'limits' for the table are controlled by microswitches. My CandCNC control system user manual walked me through the integration of the switches.

After squaring up the system and completing all set-up steps from the CancCNC user manual, I was ready for some test cuts. I followed the instructions from my control system manual and got to cutting. This system was ready to work right from the get go. The first cuts were crisp and clean.

This table has changed the way I fabricate. Projects that would typically take days or weeks were cut down to a matter of hours. Anytime I tackle something new, I first consider how I can utilize the CNC table to build it quickly and efficiently.

Here are a few projects I completed for myself and a few of my friends using this table.

See the next step for a video of the table in action.

Thanks for checking out my build and please feel free to ask questions in the comments section!