Many fabrication shops spend a lot of time and money reworking parts that were cut on the plasma machine to remove dross or correct dimensional inaccuracies. Some of these cut quality problems are caused by mechanical and electrical problems of an old or poorly maintained cutting machine; others are related to the plasma process itself. With so many variables in the cut quality equation, how does a plasma torch operator begin to troubleshoot a cut quality problem? Here we discuss the critical process variables that affect dimensional accuracy of a plasma cut piece. By carefully controlling these variables, the operator can minimize or eliminate dimensional problems and the associated costs of secondary operations or scrap parts.
Kerf is the void created by the plasma cutting process, or the amount of metal removed by the plasma arc. The plasma arc is dynamic (it changes in size and shape depending on amperage, voltage, gas flow and velocity of the moving torch) and so as the plasma arc column changes so does the kerf. Nozzle size also has a direct affect on kerf width since the nozzle orifice constricts the plasma gas jet to a particular diameter. (Nozzles are sized according to amperage rating: the bigger the hole the more power it can handle.) A good rule of thumb for estimating the kerf width is to multiply the nozzle orifice size by a factor of 1.5. For example a 200 amp air nozzle with an orifice of .086', will have a kerf width of approximately .129'.
The PlasmaCAM system includes an instruction manual with some video sections that help you get your plasma cutting up and running quickly.
The Plasmacam DHC2 is designed and manufactured in the USA and is the World’s leading CNC robotic plasma cutting machine of its kind complete with a 3 YEAR WARRANTY. The compact Plasmacam DHC2 CNC plasma cutting machine is ideal for restricted floor space.
The PlasmaCAM Instruction Manual is exceptionally clear and well-illustrated. It covers the following areas in detail: How to quickly set up the cutting table when you receive it. How to use the cutting table. How to use the software, including a tutorial with several example projects you can work through to learn the system.
See why people prefer PlasmaCAM's affordable CNC Plasma Cutting Table. This is the best plasma cutting machine for creating metal art, custom auto parts, or any other metal shape you may need!
Baileigh PT-22 CNC Plasma Cutting Table with 5' Casters, 110V, 3/4' Mild Steel Capacity, 31' Length x 29' Width.
CNC controls for plasma arc cutting have an adjustable parameter called kerf compensation. The operator or programmer enters a value for kerf compensation that is usually equal to the kerf width, (some controls use _ the kerf width). The CNC then automatically calculates to compensate for the width of the cut, keeping the kerf on the waste side of the part. To find the proper kerf compensation value, operators often use a trial and error method. They first estimate the kerf using the rule of thumb or physically measure it to get an initial value. They then cut test pieces, measure them, adjust the kerf compensation up or down, and repeat the process until the part measures correctly.
Kerf too wide (part too small)
This problem can be caused by a worn nozzle, high torch standoff (arc voltage), excessive amperage, inadequate gas flow, or low speed. Each of these variables will cause the arc column to grow, widening the kerf. An incorrect (small) kerf compensation value will also cause an undersized part. Kerf too narrow (part too big). This problem can be caused by low torch standoff (arc voltage), inadequate amperage, excessive gas flow, or high speed. These variables cause the arc column to shrink, narrowing the kerf. An incorrect (large) kerf compensation value will also cause an oversized part.
Bevel angle is the angle of the cut edge
A cut with 0° bevel is a straight cut, perpendicular to the plane of the material. Most plasma torches use a clockwise swirling flow of plasma gas, which produces a straighter cut on the right hand side of the kerf with respect to forward torch motion. Typical bevel angles for conventional plasma torches range from 1-3 degrees on the 'good' side of the cut and 3-8 degrees on the 'bad' side of the cut. High tolerance plasma cutting systems can achieve even lower bevel angles. Although some bevel is inherent in the plasma process due to the shape of the gas jet as it exits the torch nozzle, it is possible to minimize it. Bevel angle greater than 5 degrees may indicate a problem with PAC machine parameters.
(Excessive) Positive bevel
Positive bevel - top of part smaller than bottom
This problem may be caused by a worn nozzle, high torch standoff (arc voltage), inadequate amperage, or excessive speed. All of these variables cause the arc to lag which causes more energy to contact the top of the kerf than the bottom. As a result, the kerf is wide at the top and narrow at the bottom. Improper cut direction around the part may also cause excessive positive bevel angle. A part with excessive positive bevel all around it may also have a hard bead of high-speed dross at its bottom edge.
Plasmacam User Manual Instructions
Negative bevel
Negative bevel - bottom of part smaller than top, undercutting
Plasmacam User Manual Template
This problem can be caused by low torch standoff (arc voltage), excessive amperage, or low speed. These parameters cause the arc to remove more material at the bottom of the plate. Usually a consistent negative bevel around the part is accompanied by low speed dross.
Irregular bevel
Positive cut surface - positive and negative bevel on the same piece
This problem usually indicates that the nozzle has failed, the torch is out of square or the electrode and nozzle are misaligned. These variables cause the arc to deviate from a straight path through the material. Often one side of a square part will have a positive bevel and the opposing side a negative. The cross section of the part looks like a parallelogram rather than a rectangle. Sometimes the cut surface may not be flat, but rather concave on one side and convex on the other. These are all signs of severely worn or misaligned parts.
If you own a PlasmaCAM/Samson/GoTorch product and are trying to make the most of your purchase, this is the place for you!
3 Day Workshop
The first 2 days of our workshops focus on Design Edge software specifically as it is used in plasma cutting. Attendees will start with settings; we will develop a full understanding of what each individual choice does, how it applies to your work, and when you might want to change it. We will spend time with each of the drawing and edit tools and the coordinate system so you can hone your skill to produce great cuts in metal whether it be for art or dimensioned parts.
A portion of the second day will be spent learning about the wiring and mechanics of the table itself which will come in handy should you need to troubleshoot problems with your machine! Then instruction will shift to an in-depth look at the powerful CAD capabilities in Design Edge and how to use them in your drawings to produce a top quality file that will give you better cuts and a top notch finished product. We will work on projects together to go from a picture to a cut ready file.
On the final day until lunch, we will build on the information we’ve covered and learn how tools can be used in combination, reference points can be established, and how to get the most out of your Advanced Design software. If you want to Make Money in Metal Art or Draw Dimensioned Parts Fast then this workshop is for you! After lunch on Saturday I will continue to help any that want to stay and practice or try new things but there won’t be any new material presented other than what comes up in discussion so if you need to go or are ready to call it a day, that will be at your leisure.
Our mission is to deliver skills and knowledge that significantly increase our course participants’ ability to set up, operate, and troubleshoot their PlasmaCAM equipment and software, thereby equipping them with the knowledge to successfully design and cut with their machine for hobby or business.
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