Increasing the efficiency reduces the Step over variation permitted in the spiral, which makes the side steps in all directions more equal and accordingly producing a rounder spiral, looking more like a circle. The remaining areas are cleared with trochoidal-like cuts.

When opening 2013 and earlier CAM-Parts in SolidCAM 2021, if the Finish floors option was enabled in the Offsets section of an operation, then a Floor offset of 0 is automatically specified for that operation.

Only the iRough + iFinish and iFinish technologies enable you to define the Wall finish quality. All iMachining 2D technologies enable you to define the Floor finish quality only when the Floor option is selected. When not selected, the Floor (Ra) parameter is inactive.

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What Is dimensional tolerance

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Roller coasters must operate and withstand outdoor conditions for long periods of time, which is why a range of factors go into designing and producing the final products. One of the factors is manufacturing tolerance. Depending on the intended application of the parts, this could include natural phenomena like corrosion.

In July 2017, a rollercoaster ride in Ohio failed dramatically, killing one person and injuring seven others. The cause of the accident? Corrosion.

All morphing spirals approach the stock material from air, whether it is from the outside of an open pocket in the case of a converging spiral or from the inside of a closed pocket (using a pre-drill or helical entry) in the case of a diverging spiral.

The specified Ra values affect the finish feed rates automatically calculated for the tool, which are shown on the Data tab of the Tool page. Increasing the Floor (Ra) value produces a higher Finish feed floor value. Increasing the Wall (Ra) value produces a higher Finish feed XY value. Decreasing the Wall or Floor surface roughness produces correspondingly slower feed rates.

All technologies support the Floor option, which enables you to define the finishing of the pocket floor. When selected, a finishing cut is executed to remove the Floor offset. A Floor offset value greater than 0 must be specified in order to use this option.

Manufacturingtolerance standards

Instead of one-way (trochoidal-like) tool paths, you can choose to perform Climb or Conventional cutting with a Zigzag tool path to connect the cuts. When machining narrow passages, separating channels and tight corners, the cutting direction changes from cut to cut containing both climb and conventional movements.

As a result, the average side step is smaller than the maximum side step, which makes the average Material Removal Rate (MRR) less than the maximum MRR possible. This means that a morphing spiral is potentially less efficient than a regular round spiral.

In the instance of a completely open pocket, where there are no walls or islands, an iRough operation alone can be defined to perform the rough and finish machining of the pocket floor.

Unlike other SolidCAM operations, the cutting direction calculations in iMachining are unaffected by the operation geometry chains.

The third reason is to extend tool life to the maximum possible; because of this, a low Efficiency level is used since it is proven that a continuous spiral cut causes less wear on the tool than repeated short trochoidal-like cuts.

Preview – clicking this button displays a projection of the current geometry directly on the solid model. Depending on the Offset modification, one of the following icons will be displayed next to the Preview button:

The iMachining technology automatically calculates most of the technological parameters according to many factors. You can modify the defaults as well as define tool path parameters and options that are specific to the iMachining 2D or iMachining 3D Technology types.

In iMachining 3D, the parameters used for calculation of the Step-up tool path passes will appear in this section of the Operation dialog box according to the specified Technology type:

This option adds a semi-finishing cut to the operation. The Offset parameter defines the machining allowance that will remain on the pocket walls/islands before executing the finish pass.

The iMachining 3D tool path is calculated by first taking into account the tool plus Wall offset and then by offsetting the tool along the tool axis by the distance equal to the Floor offset.

Floor offset – this parameter defines the machining allowance that will remain on the pocket floor after the operation, unless the Floor option is enabled in the Finish section. For iRest and iFinish, the Floor offset value is inherited from the Previous floor offset of the Parent operation with no available override.

Design is all about tradeoffs and high precision comes with a high price tag. Unless your design absolutely requires tight tolerances, looser tolerances can lower your manufacturing costs.

The second reason is to gain a higher global efficiency for the whole pocket or part; because of this, the iMachining technology is willing to sacrifice a little in the local efficiency of a specific spiral by using a default Efficiency level of 6.

When you hover the mouse pointer over the Offset modification icons, a screen tip displays up to the first ten modified chains and their specified offsets.

When the Semi-finish option is enabled, the default Offset value is automatically calculated and dynamically updated according to half the Wall/island offset to minimize your operation entries.

In most cases, only positive values should be used. The offset can then be removed by further finishing operations (using the HSM module).

Ra (Roughness average) is the most widely used one-dimensional roughness parameter that measures the microscopic peaks and valleys of a surface, describing its arithmetical mean deviation. Expressed in micrometers (microinches), the default Ra values are 0.8 µm (32 µin) for the Floor and 0.05 µm (2 µin) for the Wall. A larger number specifies a rougher surface with more deviation. A smaller number specifies a smoother surface with less deviation.

Tolerances define the upper and  lower limits. This range is called the tolerance band. For example, if an ideal part is to be 0.5 mm +/- 0.1mm, any resulting product between the range of 0.4 to 0.6 mm will be acceptable; the rest will be rejected.

The Efficiency slider enables you to control the efficiency of the morphing spiral tool path. The examples below illustrate the effect of using this slider.

Why tolerance is importantinengineering

When the Wizard is in the Operation dialog box, the Step down is shown with a icon because it needs to be synchronized with the selected set of Cutting conditions. If you want to manually enter a preferred value, the Wizard can be turned to open the field for editing.

The Conventional option enables you to perform a similar style tool path as the aforementioned but in the opposite direction.

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Tolerancein manufacturingexamples

iMachining 3D analyzes the Target model and then recognizes all its features and depths automatically. A single iMachining 3D operation removes all the volumes of material that can be removed using the selected tool. The iMachining 3D tool path consists of both Step down (roughing) and Step-up (rest roughing) passes.

Manufacturingtolerance chart

In iMachining 3D, the parameters specified for the tool and the operation are used to calculate the single steps of the tool on the mathematical model, which results in a PCode file that is given the *.pj file extension. It later serves as input to the generation of the GCode file.

There are three reasons why the iMachining technology permits control over the efficiency of the morphing spiral tool path:

The Step down defines the axial depth of cut for the operation. The value displayed in the locked text field corresponds to the largest Step down (if there are multiple steps with different depths) shown in the output grid on the Technology Wizard page.

The flip side of over-tolerancing is that designers often err on the side of caution and add tighter tolerance factors than needed. Manufacturing parts with precise tolerances can be challenging and requires specialized equipment and labor. It also causes more rejected parts and could get expensive.

Priorities and cost structure (relative cost per part of machine time, tooling and labor) are the determining factors for what level is best. Although it will increase the cycle time, a lower level is usually best when regularly using expensive tools.

Manufacturing tolerance is necessary when operating conditions can be unpredictable and extreme, or if a part is expected to perform for decades on end without much degradation. The physical parts themselves might change shape naturally. Railroad tracks, for example, have thermal expansion due to high summer temperatures factored into their design.

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Production processes use  International Tolerance grades (IT grades) which help engineers determine the tolerance needed for a given part. For example, injection molding might be an economical way of mass-producing parts, but its assigned IT grade might be too high, persuading designers to use a different process if it cannot deliver the kind of tight tolerances they’re looking for.

In manufacturing, controlling your tolerances means controlling your prices. Finding the balance will allow for mass-scale economical delivery of parts that still meet the required quality.

According to a definition from an industry standard, ASME Y14.5M, tolerance is “the total amount a specific dimension is permitted to vary. The tolerance is the difference between the maximum and the minimum limits.”

When opening 2015 and earlier CAM-Parts in SolidCAM 2021, the Wall/island offset and Floor offset values will be kept in existing iMachining 2D operations.

When using the iMachining technology, it is highly recommended to leave the Wizard On and utilize the optimal step downs that are provided. The Wizard automatically calculates these values and manages synchronization across step down, step over, spindle speed and feed rate.

By default, the iMachining technology performs Climb cutting with one-way (trochoidal-like) tool paths to machine narrow passages, separating channels and tight corners.

When using the iMachining technology, it is highly recommended to leave the Wizard On and utilize the optimal cutting angle and step over ranges that are provided. The Wizard automatically calculates these values and manages synchronization across step down, step over, spindle speed and feed rate.

Wall/island offset – this parameter defines the machining allowance that will remain on the pocket walls/islands after a roughing (iRough) or rest machining (iRest) operation. For iRough + iFinish and iFinish, the finishing is executed in the same operation to remove the allowance. For iRest and iFinish, the Wall/island offset value is inherited from the Previous wall offset of the Parent operation with an available override.

If you override the defaults, changing the tool or its diameter will have no effect on your user-defined values.

For iRough and iRest, the specified Wall/island offset will remain on their respective contours after the floor finishing.

In iMachining 2D, the specified Technology type determines what tool path options will appear in this section of the Operation dialog box.

This parameter enables you to modify the tool diameter. The tool is moved away from the machining surface by the defined value, leaving the offset unmachined on vertical and sloped surfaces.

Most modern manufacturing processes and equipment can’t produce parts exactly according to specifications. There is always a variance between the intended dimensions and the actual delivered parts. These complex parts then require complex processes before their concept becomes reality. But manufacturing these precise parts is not always so precise and for this reason, the idea of an “ideal” part is just that...an idea. The leeway permitted between the design and the actual product is called manufacturing tolerance, essentially giving some wiggle room in final product production.

Engineering Tolerance Chart

The Entry rate slider enables you to control the rate at which the morphing spiral tool path first enters the material. The rate of entry is automatically set by the Technology Wizard in accordance with the Material Properties. The examples below illustrate the effect of using this slider.

This section defines the Angle and Step over ranges for the operation. The values displayed in the locked text fields correspond to the Output Cutting Data shown on the Technology Wizard page.

Standard drawingtolerances

This offset is applied to the tool and has the effect of lifting (positive value) the tool along the tool axis. As a result, this offset has its greatest effect on horizontal surfaces and no effect on vertical surfaces. By default, the Floor offset value is made equal to Wall offset value.

When the Wizard is in the Operation dialog box, the Cutting angles are shown with a icon because they need to be synchronized with the selected set of Cutting conditions. If you want to manually enter preferred values for the locked parameters, the Wizard can be turned to open the fields for editing.

This option enables you to machine all semi-open and open pocket areas with one iMachining 3D operation using your high performance end mill. For the closed pocket areas that require a helical entry, you can define a separate operation using a standard end mill.

If you have a preferred value for semi-finishing, it can be manually entered after selecting the Offset override check box.

Similarly, systems with complicated geometries and interlocking curved parts need tight enough manufacturing tolerances to ensure that they will continue to work as intended even with all of their individual part variances adding up. The same holds true for systems subject to high pressure or temperatures, or parts made from composite materials with different processing techniques such as metal sheet stamping or injection molding, which may vary by different amounts. If manufacturers don’t closely follow the required tolerance bands, products may have costly failures when put into production.

Given that parts can have varying tolerances, they should ideally be tested under a wide range of operating conditions (extreme heat, cold, corrosion etc.) before being produced on a mass scale.

The iMachining technology generates morphing spirals to clear a completely open or completely closed pocket area that does not have the shape of a circle. This means that it generates tool paths with different side steps in different directions.

Since the Technology Wizard adjusts the feed rate at every point along the tool path in order to maintain a constant cutting force on the tool, the actual loss in the average MRR is negligibly small or even zero. This greatly depends on the maximum feed rate the machine can achieve. With very slow machines, the Wizard cannot fully compensate for some of the very small side steps indicated by the morphing action, because the maximum feed rate of the machine is not high enough. In such cases, if your first priority is high average MRR, and long tool life is less of an issue, you can then limit the extent of the morphing action by selecting a higher level of spiral efficiency.

For hard materials, it is better to enter the material more gradually than to directly lead in to the initial radial depth determined by the side step that is appropriate for the specific shape of a morphing spiral.

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The International Organization for Standardization (ISO) or the American Society of Mechanical Engineers (ASME) set standards for manufacturing tolerance. Geometric dimensioning and tolerancing (GD&T), which account for the geometry of interlocking parts, is also an important technique. This prevents the problem of over-tolerancing. Sometimes designers might add a standard tolerance factor to each part, but once you take into account a series of interlocking parts, the net tolerance accumulates (“tolerance stack”), making the effective tolerances too large.

A smaller value will result in less deviation from the mathematical model, but the calculation time will be proportionately longer.

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Based on the diameter of the tool, iMachining provides initial default values for the Wall/island offset and Floor offset parameters to minimize your operation entries. In addition, those values are dynamically updated when the tool diameter is changed or a new tool (with a different diameter) is selected for the operation.

Engineering tolerance

This section enables you to specify the Offsets for the operation relative to the iMachining 2D or iMachining 3D geometry selection.

The Tool path parameter defines the accuracy of the tool path generation by affecting the number of single steps in the tool path. By default, this value is automatically calculated based on the current tool diameter.

Decreasing the efficiency permits more use of the Step over range specified by the Technology Wizard. By managing to morph itself into narrower parts of the pocket, the spiral produced looks less like a circle and covers a greater part of the total area.

Geometry – clicking this button opens the Modify Geometry dialog box that enables you to offset any one or more chains in the defined geometry.

When this option is enabled, iMachining 3D eliminates the roughing and rest roughing tool path passes contained in closed pocket areas (e.g., cavity features of a mold core), leaving only those volumes unmachined.

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