CNC MACHINE COORDIANTES

The CNC Machine Coordinate System is illustrated in Figure below. The control point for the Machine Coordinate System is defined as the center-face of the machine spindle.

The Origin point for the machine coordinate system is called Machine Home. This is the postion of the center-face of the machine spindle when the Z-axis is fully retracted and the table is moved to its limits near the back-left corner.

VMC Machine Coordinate System (At Home Position)

As shown in Figure above, when working with a CNC, always think, work, and write CNC programs in terms of tool motion, not table motion. 

• For example, increasing +X coordinate values move the tool right in relation to the table (though the table actually moves left). 
• Likewise, increasing +Y coordinate values move the tool towards the back of the machine (the table moves towards the operator).
• Increasing +Z commands move the tool up (away from the table). 

CNC Motion Control:

Most CNC machines can position each axis within .0002 inches or less over the entire machining envelope. This accuracy is achieved in part by the use of a closed-loop servo mechanism, illustrated in Figure below. 

The machine control sends a motion signal, via a controller board, to a servomotor attached to each machine axis. This causes the servomotor to rotate a ball screw attached to the table or column, causing it to move. The actual position of the axis is continuously monitored and compared to the commanded position with feedback from a servo transmitter attached to the ball screw.

Ball screws have almost no backlash, so when the servo reverses direction there is almost no lag between a commanded reversing motion and corresponding change in table direction. CNC controls employ electronic compensation to adjust for any minor backlash that may exist. 

CNC Motion Control

Work Coordinate System :

Obviously it would be difficult to write a CNC program in relation to Machine Coordinates. The home position is far away from the table, so values in the CNC program would be large and have no easily recognized relation to the part model. To make programming and setting up the CNC easier, a Work Coordinate System (WCS) is established for each CNC program.

The WCS is a point selected by the CNC programmer on the part, stock or fixture. While the WCS can be the same as the part origin in CAD, it does not have to be. While it can be located anywhere in the machine envelope, its selection requires careful consideration.

The WCS location must be able to be found by mechanical means such as an edge finder, coaxial indicator or part probe.

• It must be located with high precision: typically plus or minus .001 inches or less.
• It must be repeatable: parts must be placed in exactly the same position every time.
• It should take into account how the part will be rotated and moved as different sides of the part are machined.

For example, Figure below shows a part gripped in a vise. The outside dimensions of the part have already been milled to size on a manual machine before being set on the CNC machine.
The CNC is used to make the holes, pockets, and slot in this part. The WCS is located in the upper-left corner of the block. This corner is easily found using an Edge Finder or Probe.

Work Coordinate System

A typical example of WCS is show below with a WorkNC environment.

WCS Shown in WORKNC

Now as we became familiar with the various coordinate systems related to CNC machine we can get started with the WORK NC tutorials.. 

In next post we will learn about  setting a tool and work piece offsets so as to start machining with cam software.

Images Courtesy : CNC Handbook HSMWorks

Before Starting.. Introduction To Machine/Work Co-Ordinate Systems And Machining Units..

Cartesian Coordinate System

CNC motion is based on a 3D Cartesian coordinate system.

Number Line: 

The basis of this system is the number line marked at equal intervals. The axis is labeled (X, Y or Z). One point on the line is designated as the Origin. Numbers on one side of the line are marked as positive and those to the other side marked negative.

X-AXIS Number Line

3D Cartesian Coordinate System:

The Cartesian coordinate system consists of three number lines, labeled X, Y and Z, set at 90 degree angles to each other as shown in Figure below. The origin, or Datum, is where the three axes cross each other. 

The labels, orientations, and directions of the Cartesian coordinate system in Figure below are typical of most Vertical Machining Center (VMC).

3D Cartesian Coordinate System

Quadrants:

Any two axes form a plane. Planes are named by the axes that define them. For example, Figure below shows the XY plane, which is the primary work plane for machining on a VMC. A plane can be divided into four quadrants, labeled I, II, III and IV with axes designations as shown in the illustration below.

Quadrants

Units:

CNC Programs can be written in either Inch or Metric units. The machine can be switched with a single code to accept either. 

In India mostly we use metric units. In the United States, most programming is using inch units because most tooling is in inches and machinists are more familiar with the inch measurement system. Even if the part is designed in metric, it is usually converted to inch units for machining and metric tools are used only when no inch equivalent is available (for example when creating metric tapped holes).

Table below shows the units and maximum precision for inch and metric data used by CNC machines.

Units And Precision

So this was basic introduction to co-ordinate systems used by the CNC Machines. In the next post we will discuss CNC co-ordinate systems and work co-ordinate systems..

Introduction To WorkNC V21..

Hello Again..

Lets start with the introduction of WorkNC. Lets see what we can do by utilizing WorkNC software. Basically it is CAM software. 

WorkNC can be used by any CNC operated machines such as VMC(VERTICAL MACHINING CENTRE), HMC (HORIZONTAL MACHINING CENTRE), CNC Routers etc. I am currently using this software for programming of HARTFORD VMC 1600.

We can do following type of machining by using this software.

WorkNC CAM main functions include:

• Automatic geometry and machining zone detection and management
• Specific fluid and progressive toolpaths designed for High Speed Machining
• Full user stock definition (block, CAD, STL)
• Dynamic 3 and 3+2 stock Management (Real time toolpath updated)
• Complete tool and holder collision check with automatic stock update
• Powerful toolpath editor
• Virtual 3D machine representation and machining simulation (dynamic editing of points and vectors)
• Powerful tool and holder library (holder components managed)
• Automatic HTML workshop documentation.
• Fore-casted calculation and machining times can be exported to WorkPLAN, the ERP software from Sescoi
• User predefined machining sequences for automatic machining
• Machining from STL files and point clouds
• Batch mode calculations
• Comprehensive postprocessor generator (NURBS, cycles, circular interpolation...)

Roughing Toolpaths :

• Global Roughing and Re-roughing toolpath designed and optimized for HSM (high speed machining)
• A range of specific toolpaths with trochoidal, spiral or plunging movement, including HVR (high volume roughing)
• Roughing strategies use the Tool and Holder collision check with an automatic update of the stock
• Automatic calculation and machining of rest areas based on dynamic stock
• Re-machining toolpaths enable automatic rest material machining with increasingly smaller tools

Finishing Toolpaths :

• A wide range of Finishing toolpaths optimized for HSM machining
• Z Level finishing, Planar finishing, Flat surface finishing, Contour finishing, Edge finishing
• Automatic Rest-material finishing with a sequence of progressively smaller tools
• 3D Display of rest-material areas
• Automatic 5 Axis conversion possible

2 and 2.5 Axis Toolpaths :

• Pocketing, Contouring, Curve machining, Engraving, Rib machining, Facing, Drilling, Tapping ...
• Automatic Drilling Module
• Automatic feature detection and recognition, Pre-defined drilling sequence selection, Automatically generated drilling operations, Deep hole and intersecting hole drilling management
• Customized Postprocessor

5 Axis Toolpaths :

• Automatic 3 to 5-axis conversion with WorkNC Auto 5 
• Wide range of Simultaneous 4 and 5 Axis toolpaths
• 5 Axis Rolling, Planar finishing, Spiral Blade, Impeller, Tube, Laser ...
• Collisions detection and machine limits management.

Courtesy: Sescoi India.

  

WorkNC V21 Tutorials..

Hello Everyone,

I am going to publish the first software tutorials on my blog which is for a CAM software WorkNC V21.

This blog is for students as well as the professional engineers who work with the Work-NC environment. I am working with this software for one year now. I guess most of the college students never heard about this software because they it is not introduced in syllabus of our universities. 

Suggestion and problem discussions are allowed here.. So please give your feedback in reply section..

I am starting my tutorials with this software because there are very few resources for learning WorkNC over the internet. So keep checking for update we will proceed from very beginning.

What Is WorkNC??

WorkNC is a Computer aided manufacturing (CAM) software developed by Sescoi for 2, 2.5, 3, 3+2 and 5-axis machining.  WorkNC is used by more than 25% of companies in countries such as Japan and is known for having always focused on automation and ease of use since its first release in 1988. 

WorkNC-CAD was introduced in 2002, making WorkNC a complete CAD/CAM product, one of the leaders in its field. The typical users of WorkNC belong to the following industries: automotive, aerospace and defense, engineering, medical & dental, tooling, mold and die manufacturing. WorkNC is supported from Sescoi offices in the USA, UK, France, Germany, Spain, Japan, India, China and Korea, and more than 50 distributors around the world.

                                                                                                         

WorkNC can read the following CAD file formats: DXF, STEP, IGES, CATIA V4 & V5, Unigraphics, SolidWorks, SolidEdge, Pro/E, Parasolid, STL, etc.

Shown below is a typical roughing toolthpath generated in WorkNC..

Roughing Toolpath IN WorkNC

 Keep visiting this blog for complete tutorials and updates on CAD..