What are fillets?
Fillets are the surfaces which round off the corners of an ICEMSurf Class-A surface model. If you’re surfacing for manufacture then filleting the model is essential. If the ICEMSurf model is to be used in rendering or animation then leaving out the fillets might save some time but the results will be far less satisfactory. Fillets catch the light and give a realistic appearance.
What qualities do ICEMSurf class-A fillets need?
Engineering requirements
The manufacturing process and material selected will determine the minimum radius that can be achieved. For example, it may not be practical to press a fillet tighter than 3mm radius into a 1mm sheet of aluminium whereas an injection moulded part may be made with 0.5mm fillets.
Legislative requirements also determine minimum radii in some areas. On car exteriors there are pedestrian impact zones where the minimum radii are specified. E.g on a front bumper, where a pedestrian’s head could impact, the minimum radius is typically 5mm. On interiors, particularly on the instrument panel, there are defined zones where the minimum radii are specified to reduce the effects of head impact. The exact legislation and definition of zones is a subject in itself. The legislation is constantly moving forward and varies from one country to the next. To find out the relevant requirements you need to consult an expert in this field.
Occasionally, engineering companies or departments will dictate minimum radii that make creating the offset surface (B-surface) easier in their engineering CAD system. This is not really best practice as far as the design is concerned as the ICEMSurf Class-A surface may then being compromised in order to deal with the short-comings of a downstream CAD system.
Aesthetic requirements
The designer will usually specify the size and type of ICEMSurf fillet that they want. Most designers describe their requirements in non-technical language, for example they might want a tight fillet or a large soft fillet whereas an engineer would ask for a fillet of a specific radius.
For small ICEMSurf fillets, say less than 3mm in radius or chord, then an arc-based/constant radius/rolling ball fillet is normally acceptable and is often preferable from the point of view of constructions. However, every company has its’ own ICEMSurf Class-A surfacing standards that must be followed. Some may insist on curvature matched fillets everywhere.
Larger fillets (greater than 3mm radius say) should be curvature matched (G2 continuous) to the block surfaces when aesthetic appearance is important. This is because rolling-ball fillets (G1 continuous) have a very hard appearance at their edges. This is especially noticeable on reflective surfaces where there appears to be a shadow at the fillet edge and a sunken appearance to the block surface in this region.
Where one side of the fillet is to a flange which extends into a gap then tangency only on this side is fine.
To achieve a certain minimum radius at the centre of the fillet section then a curvature-matched fillet will be wider than a rolling-ball fillet of the same radius. Sometimes this can result in too soft a look for the designer and they may ask for a tangent-matched fillet with some lead-in rather than a fully curvature-matched fillet. Lead-in is where the curvature reduces towards the edge of the fillet.
For good aesthetics it is important to control the edges of the fillet and therefore the light lines along the fillet.
Other Considerations
It is sometimes not possible to achieve curvature-matching of the fillet because the resulting wider chord fillet would create a bad condition elsewhere, e.g. where the edge then goes under a wall and therefore gives a wobbly line or where the fillet goes over the edge of another fillet to give a poor condition.
The ICEMSurf fillets must be built to the correct Company standards, if specified. If you’re not sure then to be completely safe, build everything to a position match of 0.001mm with tangency of 4 minutes.
It is important to minimise the complexity of the ICEMSurf Class-A surface model. There are two reasons for this. Firstly, a simpler model is easier to modify and control. Secondly, the database size is minimised. This is very important if the model is ultimately going to form part of a large assembly. Therefore keep the degree of the fillet patches as low as possible and the number of patches low. Time-constraints will limit how long you can spend simplifying the geometry. Mostly I use degree 8 along the patches and 7 across with a tolerance of 0.001mm. Setting a relatively high degree of 8 along the fillet reduces the patch count for a given tolerance. Degree 7 across the fillet means that, in the case of rolling ball fillets, the radius will be accurate. The tolerance of 0.001mm ensures that most of the fillets will match the block surfaces without any more work being required.
The ICEM Surf Filleting Process
The starting point will be to create 2 sets of block surfaces which either meet at a common edge or intersect. The fillet function will create fillets between surface sets which have a small gap between them but this is not good practice as you should always check the quality of the intersect before attempting to fillet. It is tempting to think that a bad intersect condition can be covered up by filleting but this is not the case. The highlights on the fillet will emphasis the bad intersect even more.
Most fillets between 2 sets of surfaces are created using the Surface-Fillet function. If aesthetics are not important then this will give a good result in one hit. However, if you want a full class-A result then, as with all class-A surfaces, you must inspect and, if necessary, modify the fillets to achieve the best result. In some cases, for example when the angle between the block surfaces is very small, you may have to build the fillet manually.
Checklist for filleting:
• Does it meet design intent?
• Minimum radii OK?
• Fillet rails (edges) are smooth?
• Does it meet tolerance standards?
• Minimum degree
• Minimum number of patches
Fillets are the surfaces which round off the corners of an ICEMSurf Class-A surface model. If you’re surfacing for manufacture then filleting the model is essential. If the ICEMSurf model is to be used in rendering or animation then leaving out the fillets might save some time but the results will be far less satisfactory. Fillets catch the light and give a realistic appearance.
What qualities do ICEMSurf class-A fillets need?
Engineering requirements
The manufacturing process and material selected will determine the minimum radius that can be achieved. For example, it may not be practical to press a fillet tighter than 3mm radius into a 1mm sheet of aluminium whereas an injection moulded part may be made with 0.5mm fillets.
Legislative requirements also determine minimum radii in some areas. On car exteriors there are pedestrian impact zones where the minimum radii are specified. E.g on a front bumper, where a pedestrian’s head could impact, the minimum radius is typically 5mm. On interiors, particularly on the instrument panel, there are defined zones where the minimum radii are specified to reduce the effects of head impact. The exact legislation and definition of zones is a subject in itself. The legislation is constantly moving forward and varies from one country to the next. To find out the relevant requirements you need to consult an expert in this field.
Occasionally, engineering companies or departments will dictate minimum radii that make creating the offset surface (B-surface) easier in their engineering CAD system. This is not really best practice as far as the design is concerned as the ICEMSurf Class-A surface may then being compromised in order to deal with the short-comings of a downstream CAD system.
Aesthetic requirements
The designer will usually specify the size and type of ICEMSurf fillet that they want. Most designers describe their requirements in non-technical language, for example they might want a tight fillet or a large soft fillet whereas an engineer would ask for a fillet of a specific radius.
For small ICEMSurf fillets, say less than 3mm in radius or chord, then an arc-based/constant radius/rolling ball fillet is normally acceptable and is often preferable from the point of view of constructions. However, every company has its’ own ICEMSurf Class-A surfacing standards that must be followed. Some may insist on curvature matched fillets everywhere.
Larger fillets (greater than 3mm radius say) should be curvature matched (G2 continuous) to the block surfaces when aesthetic appearance is important. This is because rolling-ball fillets (G1 continuous) have a very hard appearance at their edges. This is especially noticeable on reflective surfaces where there appears to be a shadow at the fillet edge and a sunken appearance to the block surface in this region.
Where one side of the fillet is to a flange which extends into a gap then tangency only on this side is fine.
To achieve a certain minimum radius at the centre of the fillet section then a curvature-matched fillet will be wider than a rolling-ball fillet of the same radius. Sometimes this can result in too soft a look for the designer and they may ask for a tangent-matched fillet with some lead-in rather than a fully curvature-matched fillet. Lead-in is where the curvature reduces towards the edge of the fillet.
For good aesthetics it is important to control the edges of the fillet and therefore the light lines along the fillet.
Other Considerations
It is sometimes not possible to achieve curvature-matching of the fillet because the resulting wider chord fillet would create a bad condition elsewhere, e.g. where the edge then goes under a wall and therefore gives a wobbly line or where the fillet goes over the edge of another fillet to give a poor condition.
The ICEMSurf fillets must be built to the correct Company standards, if specified. If you’re not sure then to be completely safe, build everything to a position match of 0.001mm with tangency of 4 minutes.
It is important to minimise the complexity of the ICEMSurf Class-A surface model. There are two reasons for this. Firstly, a simpler model is easier to modify and control. Secondly, the database size is minimised. This is very important if the model is ultimately going to form part of a large assembly. Therefore keep the degree of the fillet patches as low as possible and the number of patches low. Time-constraints will limit how long you can spend simplifying the geometry. Mostly I use degree 8 along the patches and 7 across with a tolerance of 0.001mm. Setting a relatively high degree of 8 along the fillet reduces the patch count for a given tolerance. Degree 7 across the fillet means that, in the case of rolling ball fillets, the radius will be accurate. The tolerance of 0.001mm ensures that most of the fillets will match the block surfaces without any more work being required.
The ICEM Surf Filleting Process
The starting point will be to create 2 sets of block surfaces which either meet at a common edge or intersect. The fillet function will create fillets between surface sets which have a small gap between them but this is not good practice as you should always check the quality of the intersect before attempting to fillet. It is tempting to think that a bad intersect condition can be covered up by filleting but this is not the case. The highlights on the fillet will emphasis the bad intersect even more.
Most fillets between 2 sets of surfaces are created using the Surface-Fillet function. If aesthetics are not important then this will give a good result in one hit. However, if you want a full class-A result then, as with all class-A surfaces, you must inspect and, if necessary, modify the fillets to achieve the best result. In some cases, for example when the angle between the block surfaces is very small, you may have to build the fillet manually.
Checklist for filleting:
• Does it meet design intent?
• Minimum radii OK?
• Fillet rails (edges) are smooth?
• Does it meet tolerance standards?
• Minimum degree
• Minimum number of patches
CreateSurface-Fillet Menu
Surface1 is the first set of patches and faces chosen.
Surface2 is the second set of patches and faces.
Surface3 is the third set of patches and faces but is only required if you’re creating a 3 fillet corner.
Surface1 is the first set of patches and faces chosen.
Surface2 is the second set of patches and faces.
Surface3 is the third set of patches and faces but is only required if you’re creating a 3 fillet corner.
Each set must be contiguous i.e. they must join in position and tangency within tolerances specified in the CreateSurface-Fillet-Parameter menu (ICEMSurf will work with very loose tolerances if you want which is great for roughing in surfaces quickly when you’re concept modelling).
Creating a Rolling-ball Fillet
In these ICEMSurf tutorials I tend to use the term “rolling-ball” fillet to describe fillets of constant radius i.e. that have a circular arc cross-section. I think it helps visualise the resulting fillet clearly.
As we discussed before, rolling-ball fillets are used in many places even in class-A surfacing when the fillets are small (less than 3mm for example).
Assuming that you have two sets of intersecting or touching surfaces, then set Radius to a suitable value depending on the size of the block surfaces that you have. The edges of the fillet must lie on the surfaces. Tick Arc to give you a rolling-ball fillet. Extended and matching should be off for now.
Make sure that Quality is set to Standard.
Now click on the Parameter tab. This is where we can control the accuracy and complexity of the surfaces.
Creating a Rolling-ball Fillet
In these ICEMSurf tutorials I tend to use the term “rolling-ball” fillet to describe fillets of constant radius i.e. that have a circular arc cross-section. I think it helps visualise the resulting fillet clearly.
As we discussed before, rolling-ball fillets are used in many places even in class-A surfacing when the fillets are small (less than 3mm for example).
Assuming that you have two sets of intersecting or touching surfaces, then set Radius to a suitable value depending on the size of the block surfaces that you have. The edges of the fillet must lie on the surfaces. Tick Arc to give you a rolling-ball fillet. Extended and matching should be off for now.
Make sure that Quality is set to Standard.
Now click on the Parameter tab. This is where we can control the accuracy and complexity of the surfaces.
Make Deviation=0.001 for accurate results, set the order of the Fillet=8 (this is the number of control points along each Bezier patch), and Arc=7 (this is the number of control points across the fillet. Order 7 ensures an accurate radius). Leave all other settings at their default values.
Return to the main Fillet tab.
Return to the main Fillet tab.
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Pick Select. This will prompt you for the two sets of surfaces. You now pick the surfaces in the graphics window for the first set of surfaces. Once you have selected these then click the middle mouse button to OK the selection. You will now be prompted for the second set of surfaces. Click the middle mouse button to OK this selection. You will find that the Select, Surface1 and Surface2 buttons are all highlighted, verifying that the surfaces have been picked.
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Before we create the fillet, we must check that the normals (the green arrows) are pointing towards the centre of where the fillet will be. If not, click on the white dots to turn the normals around. Now we can OK the fillet menu. Hopefully you will now have generated a fillet.
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