Troubleshooting. Differing performance of Autocad releases & using alternative methods.

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Troubleshooting. Differing performance of Autocad releases & using alternative methods.

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Many events that could be perceived as software errors may be nothing more sinister than differing performance between the various releases. Furthermore, in a given release, the A and B revisions may also differ. If a situation occurs that doesn't give the desired result on screen there is usually an alternative method to achieve the same result. Aim to achieve what's described in the text even if it means introducing commands that aren't scheduled in the text. The need for unscheduled commands shouldn't occur often. If it does occur please email 3D Cadcea for technical support using the email address at the bottom of this page.

Projection errors.

When setting up projections for detailing, care must be taken to ensure projection consistency. Since the views are defined, scaled, and aligned manually it is possible, through human error, to define inappropriate projections. These situations are easily rectified as highlighted in task 39.

Hidden lines and surfaces

Situations may arise with complex 3D objects, where features on the blind face of a projection are being plotted as solid lines. This suggests to the person reading the drawing that the entities are on the forward face. Such objects may require surfaces to be added either by assigning lines with a " Chprop - thickness" to create a surface as in tasks 4, 26&36, or creating a surface by using the " 3D face" command. Both methods will have the effect of masking the entities that shouldn't appear. The 3D face command is discussed later in the appendices, and Section G " Efficient modelling" is also useful regarding surface usage.

If objects are constructed as wireframe only, that no lines have been assigned thicknesses, then this situation will be a regular occurrence because wireframe objects are transparent. The " Hide" command will have no effect. All entities will plot as solid lines unless masked by surfaces.

There shouldn't be a need for hidden detail lines with 3D because views can be defined quickly enough to show all the objects' faces fully. If hidden lines are necessary, put them on the " HL" (Hidden Line) layer in Tilemode - 0 paper space. Don't use hidden lines in the model space environment because the hidden line format will be displayed in all views, not just the view it's required in.

Disappearing entities

Occasionally circles can be masked by a surface if they are behind it. This can also happen when the circle is ON the surface but not always. If a circle / hole on a surface disappears after a " hide" or " hide - plot" , it will need to be moved proud of the surface by a minuscule amount. Move it 0.01 mm away from the surface.

UCS's and line thicknesses

When assigning Chprop thickness to a wire entity, it will extend only in the Z direction of the Ucs plane it was created in. Put another way, if a line is created in the Wcs, its thickness behaviour is always in relation to the Wcs NOT the active Ucs. It is also worth remembering that " Thickness" applies itself ONLY IN THE Z DIRECTION. If a line is drawn in the Z direction (such as 0,0,50) the effect of applying a Chprop thickness to it will be to extend its length.

A similar phenomenon occurs with blocks. Have you ever inserted a block expecting it to be upright only to find it came in lying on its side? Blocks are inserted relative to the Ucs that was active when they were created. Remember to create blocks and Wblocks in the Wcs, not in a Ucs.

Different xp viewport scales and DIMLFAC.

This is touched on in task 46 and is applicable mainly to older versions of software. If one drawing has several Viewports and their " Zoom xp" values are different, it is important to set the Dimlfac each time dimensioning work is done on a window with a different XP viewscale. If Viewport dimension values seem too large or too small, they will need to be confirmed using " list" or " distance." Use the " Mspace" command to highlight the suspect window as active, and then use " list" or " distance" to obtain details of the model space entity in question.

Unwanted entities

Unwanted entities occur most commonly in shaft and cylinder applications. When drawing projections are created, a solid line is often situated where a Centerline is expected so the unwanted solid line(s) needs to be removed. This same situation occurred in task 41 and the solutions are as follows:-

Stretch the Pspace Viewport to obscure the shaft in the offending view. Create the shaft as 2D entities the same way a shaft would be created using orthodox AutoCAD 2D methods. IE. Draw 2D entities in Tilemode - 0 Pspace to represent the end of the shaft. Leave the Tilemode - 1 model as a shaft. Do not change its construction in any way.

There are pitfalls to be aware of if this method is undertaken. Assume that some months later, the design needs to be modified and the shaft is to be longer. When the model is changed to reflect the new length, the change will only be seen in the un-obscured Pspace Viewports. The obscured Viewport will mask the new length. The 2D entities drawn in Pspace to represent the shaft will not update with the model. Whenever a design is modified, check ALL detail drawings carefully that dimensions still apply. Most releases of AutoCAD do not have associative dimensions in Pspace.

Choose the desired views carefully. If the part can be defined for detailing using as few views as possible without being ambiguous, try and avoid using a plan as well as an elevation. Use one or the other. In these circumstances, the 3D model needs to be modified so that the shaft is modelled as two flat disks and only two Quadrant entities. (In terms of pictorial model visualisation, four Quadrant entities is the norm.)

If cylinders make up a large part of a design, consider creating shafts as Solid Models, using the solids commands that accompany the later releases of AutoCAD. Experiment with solid shafts and drawing projections to see if the results are satisfactory. If they are not, it might be worth investigating the use of other software packages.

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