COMPUTER NUMERICAL CONTROL basics
To better be familiar with problems involved to successfully use your Rhino data for a CNC-controlled engineering or cutting type operation, you need to understand the CNC process and how functions. Ideally, this little 1er will help.
1st, a couple of definitions
CNC : Computer Numerical Manage – Taking digitized data, a pc and CAM program is utilized to control, handle, and monitor the movements of a machine. The machine can be considered a milling machine, lathe, router, welder, grinder, laser beam or waterjet cutter machine, sheet metal rubber stamping machine, robot, or many other types of machines. With regard to larger commercial machines, the computer is generally an on-board dedicated controller. Yet for more enthusiast types of machines, or with some retrofits, the computer can be an external PC. The particular CNC controller works together with a number of motors and drive components to move and control the machine axes, performing the programmed movements. On the commercial machines there is usually a advanced feedback system that constantly monitors and adjusts the cutter's speed and position.
Desktop CNC : There are numerous smaller modelmaker-hobbyist style desktop COMPUTER NUMERICAL CONTROL machines. In common these are less heavy, less firm, less precise, reduced, and fewer expensive than their commercial counterparts, but can do well for machining objects away of softer materials such as plastic materials, foam, and polish. Some desktop machines may run a lot like a printer. Others have their own shut command system and maybe even dedicated CAMERA software. A few will also take standard G-code as input. Some commercial standard desktop machines can be found with dedicated remotes for doing exact small work.
CAMERA – Computer Assisted Machining or Production – Refers to the use of various software deals to produce toolpaths and NC code to run a COMPUTER NUMERICAL CONTROL managed machine, dependent on 3D computer model (CAD) data. When the two are utilized together, this is usually referred to as CAD/CAM.
Notice: CAM does not actually run the CNC machine, but just creates program code for this to follow. It is also no automated procedure that imports your CAD model and spits out the correct NC program code. CAM programming, like 3D modeling, requires knowledge and experience in running the program, developing engineering strategies, and knowing what tools and procedures to use in each situation to get the best results. Whilst there are simple programs that for the inexperienced consumer to get going without too much difficulty, more advanced models will take a great investment in time and money to become proficient.
NORTH CAROLINA code – A unique relatively simple computer language that a CNC machine can understand and perform. These languages were initially developed to program parts straight at the equipment key pad without the help of a CAMERA program. They inform the equipment what techniques to execute, one by one, as well as managing other machine functions such as spindle and feed rates of speed, coolant. The most common language is G-code or INTERNATIONALE ORGANISATION FüR STANDARDISIERUNG code, a simple alphanumeric programming vocabulary developed for the earliest CNC machines in the seventies.
Postprocessor - Whilst G-code is definitely the standard, each manufacturer can change certain parts such as auxiliary functions, creating a situation where G-code designed for one machine might not work for another. There are also many machine manufacturers, such as Heidenhain or Mazak, which have developed their own programming languages. Therefore, to translate the CAM software’s in house calculated paths into specific NC program code that the COMPUTER NUMERICAL CONTROL machine can understand, there exists a bridge software piece software called a postprocessor. The particular postprocessor, once set up correctly, outputs the appropriate code for the chosen machine, so that in theory at least, any CAM system can output code for just about any machine. Postprocessors may be free with the CAM system or added cost extras.
Here is a summary of the steps necessary to get a digital model to a CNC milling machine.
CNC managed machines, common
CNC machines might have several responsable of motion, and these movements can be either geradlinig or rotary. Numerous machines have both types. Cutout machines like lasers or waterjets generally have two linear responsable, X and Con. Milling machines normally have at least 3, X, Y, and Z, and might have more rotary responsable. A five axis milling machine is one which has 3 linear axes and two rotary, allowing the cutter to work in a full 180o hemisphere and sometimes more. 5 axis lasers can be found as well. The robot arm might have more than five axes.
A few limitations of PC NUMERICAL CONTROL managed machines
Based on their age and elegance, CNC machines can be limited to the abilities of their control and drive systems. The majority of CNC controllers only understand straight collection movements and round arcs. In several machines, the arcs are restricted to the main XYZ planes as well. Rotary axis movements can be considered like geradlinig movements, just levels rather than distance. In order to create arc motions or linear motions that are at an angle to the main axes, two or more responsable must interpolate (move precisely in a synchronized manner) with each other. Linear and rotary axes can also interpolate simultaneously. When it comes to five axis machines, all five must be completely coordinated – no easy task.
The velocity where the machine controller can get and process the incoming data, transfer commands to the drive system, and monitor the machine’s speed and position is critical. Old and less expensive machines are certainly less capable in this, much in the same way that the old computer works less well and much more gradually (if at all) on demanding jobs than a more recent one.
Interpret your 3D and spline data first
An average problem is how to setup your documents is to do your CAM development so that the machine executing your parts works efficiently and effectively with the data. Given that most CNC regulates only understand couronne and lines, any form that is not describable using these entities needs to be converted into something usable. Common things that require transforming are splines, i. e. general NURBS curves which are not arcs or lines, and THREE DIMENSIONAL surfaces. Some desktop computer machine systems are not able to understand circular couronne either, so everything must be transformed into polylines.
Splines can be damaged up into a number of line segments, a number of tangent arcs, or a mixture of both. You can imagine the very first option as a number of chords on your spline, touching the spline on each finish and having a certain deviation in the middle. Yet another way is to convert your spline into a polyline. The particular fewer segments you use, the coarser the approximation will be, and the more faceted the end result. Going finer boosts the smoothness of the approximation, but also significantly increases the number of sections. You can think about that a number of arcs might be able to estimated your spline within tolerance with less, longer pieces. This really is the primary reason for preferring arc transformation over simple polyline conversion, particularly if you work with old machines. With more recent ones, there is less of a problem.
Imagine areas since the same kind of spline estimation, just multiplied many times in the across direction with a space between (usually called the stepover). In common, surfaces are executed using all line sections, but there are situations where couronne or a mixture of lines and arcs may also be used.
The size and number of sections are determined by the accuracy required and the technique chosen, and will straight influence the performance. Too many brief segments will choke some older machines, and too few will make a faceted part. The particular CAM system is usually where this approximation is done. With a skilled operator who understands the actual user needs and the machine can handle, it is almost always no problem. Yet some CAM systems might not handle splines or certain types of surfaces, so you might need for converting the entities in the CAD software first (Rhino) prior to going into CAM. The interpretation process from CAD to CAM (via a neutral format such as IGES, DXF, and so forth ) may also occasionally cause problems, based on the quality of the import/export functions of the programs.
Common exhibitions used in explaining CNC procedures
Your own project can be:
2 Axis if all the trimming takes place in the same aircraft. In this situation, the cutter will not have any capacity of movement in the Z (vertical) plane. In common the X and Y axes can interpolate together concurrently to create curved lines and round arcs.
2. 5 Axis if all the cutting happens completely in aeroplanes parallel to the main plane but not necessarily exact same elevation or depth. Within this case, the cutter can move in the Z . (vertical) plane to change levels, however, not simultaneously with the X, Y motions. An exception might be that the cutter can interpolate helically, that is, perform a circle in X, Y while moving simultaneously in Z to form a helix (for example in line milling).
A subsection, subdivision, subgroup, subcategory, subclass of the above would be that the machine can interpolate any 2 axes together concurrently, however, not 3. This particular does create a restricted number of THREE DIMENSIONAL objects possible, by cutting in the XZ or YZ planes, for example, but is a lot more restricted than full 3 axis interpolation.
3 Axis if your cutting requires coexisting managed movement of the X, Con, Z axes, which most free-form areas require.
4 axis if this includes the above +1 rotary axis movement. Presently there are two options: 4 axis coexisting interpolation (also known as true fourth axis). Or just 4th axis placement, in which the 4th axis can reposition the part between 3 axis operations, but does not actually move during the machining.
5 axis if this includes the above plus 2 rotary axis motions. Besides true 5 axis machining (5 axes moving concurrently while machining), you also often have 3 plus 2 or 3 axis machining + 2 separate axes placement only, as well as in scarcer cases 4 plus one or continuous 4 axis machining & a single fifth axis positioning only. Complicated, isn't it…