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Modeling add-on makes 3-D design easier.

Tahl Inc. designs and builds practically any mechanical device from medical products to mining equipment. The company can fabricate all but the mining equipment in their own tool room.

Experience in 3-D design at Tahl was gained working with AME (Advanced Modeling Extension, Autodesk's solid modeling add-on for AutoCAD R12). Unfortunately a job for a complex mining machine for an Australian firm came before AutoCAD R13 had stabilized with the C4 update. Engineers had received the first release of Mechanical Desktop just two months prior and did not have enough time to learn how to use it for this job.

Purchasing of a high-end workstation-based CAD/CAM system, ranging between $60K and $100K per seat including hardware and software costs, was financially prohibitive. Another problem seen with high-end CAD/CAM systems is a long training process normally required to become adept in their use. This presents a problem for smaller companies that cannot spare their employees for extended periods.

Fortunately, Tahl found and purchased Context CAD's CSG Editor. It restored and improved functions that were familiar to engineers from their AME. The project was completed, and the mining crawler is now in Mexico processing 300 st/hr of gold-bearing ore.

The 40-ft long, 80-st mobile mining crawler machine is mounted on excavator tracks and pulls a mobile processing plant behind it. Dirt is shoveled into the hydraulic grizzly, which removes the large rocks. The dirt then moves via vibratory feeder into a scrubber and then is conveyed to the processing plant. The scrubber was an 8-ft dia x 20-ft long tube, which rotated on truck tires.

The Australian company had worldwide patents on their dry mining process. They had begun designing and building the processing plant,which was to be pulled and fed from the crawler. This work was being done in Tucson for transportation to the mine site in Mexico. The principle designer had just quit the project and left them stranded. Initial design was conducted using AutoCAD R12 in 2-D. Inquires had been made of Tahl Inc. to conduct some 3-D constructions of the 2-D plans to verify some complex spatial forms.

The principal designer at Tahl Inc. is doing almost all of the designing in 3-D solids. The CSG Editor makes it possible to do serious solids modeling in AutoCAD R13 or R14. One of the payoffs for working in solids is the ability to have accurate hidden line drawing views automatically created. Place associative dimensions on your format and you have a good drawing. Mechanical Desktop is also used where parametric solids and assembly modeling are needed. The CSG Editor is a must for starting out in solids modeling.

Using the CSG Editor to create editable Boolean solids can be a much faster solution to a difficult design construction problem than using a fully constrained parametric model. A Boolean subtraction of a cylinder from a plate results in a hole in the plate. When the CSG Editor is present in your drawing session, it is possible to move or resize the hole. It is easy to step through all of the primitives in the solid and edit or copy them. The CSG Editor makes all of the solid commands editable and adds some new ones.

The CSG Editor provides AutoCAD R13 and R14 with essentially the same solid modeling capabilities that were contained in AME under AutoCAD12. This modeling technique makes it possible to build the model in a free-form manner, without worrying about the exact dimensions until the basic concept is honed. That models do not have to be fully constrained makes it possible to generate rough geometry quickly that can be used to evaluate concepts or communicate them to others. It's important to note that the commands of the add-on product match AutoCAD commands perfectly in style and syntax so little training at all is required to use the product.

The key difference from the standard AutoCAD approach is that the CSG Editor is used to refine the geometry. To increase thickness of a block, for example, it would normally be necessary to create a new solid to take up the additional thickness. Instead, using CSG Editor, the engineer simply selects the primitive and changes its dimensions.

Virtually any solid that can be created in AutoCAD can be edited with the add-on product in very little time. The engineer can change dimensions of primitives including length, width, height, and radius; delete, move or copy primitives; select another path or change the taper angle of extrusions; select another profile for extrusions or revolved solids; change the axis or start and stop angles for revolved solids; delete or change the size of chamfers and fillets; and undo or change the cutting planes of solids.

The program operates through a single command: CSGEDIT. This command prompts the user to select a solid and then shows all of the solid's primitives while it offers appropriate editing options. For example, to change the size of a chamfer, you select the solid and the program prompts if you want to edit the primitive or the chamfer. You enter "C" for chamfer and are prompted to choose to delete the chamfer or change the base distance or angle. To change the distance type "D," and enter the new distance.

CSG Editor also makes it possible to define or alter solids by dragging the appropriate boundary of the object. The CYLINDER command, for example, lets you drag a circle to define the radius of a cylinder. Performing the same task in Mechanical Desktop is much more difficult because each dimension must be typed, which means the user must perform many commands to determine all the dimensions in the model.

The ability to create and edit solids easily made it possible for the engineer to create all major components of the dirt processor in rough form to see if they would fit together before he started the time-consuming process of accurately dimensioning the model. This method saved weeks of work because it eliminated time that would have otherwise been wasted dimensioning models that would later be discovered not to fit together.

Two things that were of special interest at Tahl Inc. were the file converter that would convert AutoCAD R12 AME solids into editable R13 or R14 solids and the ability to use all of the solid creation and query commands in AutoLISP, the AutoCAD programming language. Using AutoLISP, the CSG Editor makes it possible to extract a region from the face of a solid. This region is then exploded into lines and arcs for use making tool paths for CNC machines.

If it were not for the fact that the CSG Editor was purchased separately from AutoCAD, one would think that it was part of it.
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Title Annotation:CSG Editor software
Publication:E&MJ - Engineering & Mining Journal
Article Type:Evaluation
Date:Aug 1, 1998
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