Tricks of the Trade for Tolerance AnalsysisSEE WHAT YOU’RE MISSING U2U ConferenceU2U Conference Tricks of the Trade for Tolerance Analysis Jonathan Pietkiewicz Sigmetrix . SEE WHAT

SEE WHAT YOU’RE MISSING U2U Conference SEE WHAT YOU’RE MISSING U2U Conference

Tricks of the Trade for Tolerance Analysis

Jonathan Pietkiewicz

Sigmetrix

SEE WHAT YOU’RE MISSING U2U Conference

Introduction

What I’ve been working on (and how long)

– Lots of configurations and measurements

– Long term assignment

– Higher level of efficiency and organization


New SSC Articles

Fillet tangency and tangent edges

Dimensioning dovetails

Customizing analyzer layouts

Mate vs. Align

Slot feature float (along major dimension)


Tricks of the Trade for Tolerance Analysis

General

Modeling

Validation

Reporting


General

Use the CXM file

Boilerplate language

Release/Backup Strategy


General: Use the CXM file

Save to CXM often (Save to File As…)

Use a naming scheme and keep multiple versions – 20131022-1546_81322-asm_C142-to-C156-WIP.cxm

Mapping similar parts to one another

– Same-function parts in product family


General: Use the CXM file (continued)

Import newer part data (i.e. dimensions) into older assembly analysis – Export part data from newer analysis into CXM – Import older top level cxm into top level assembly – Save – Switch to part and import new part data from cxm – Save – Switch to asm – Read from CAD – Fix any issues – Re-run – Export CXM


General: Boilerplate language

Use boilerplate language in descriptions to standardize descriptions

Keep a file of boilerplate open in a text editor with spell check (i.e. Notepad++)

Make edits in editor and copy them into CETOL Example: The clearance between the xxxPartxxx xxxfeaturexxx and the yyyPartyyy yyyfeatureyyy. A result less than zero indicates interference. Other limit is arbitrary. The green limits shown represent 3.5 sigma.


General: Release/Backup Strategy

Whenever a report is released: – In a single directory:

• Backup CAD to zip file (or note version of each CAD file in text document)

• Export the CXM

• Copy the report directory

• Copy the images for the report

– Zip the entire directory


Modeling

Standardize configuration and measurement numbers

Object names and notes

Insert>Advanced Measurement/Joint

CAD reference geometry

Gage Size and Remove Draft

Invariant dimensions need notes too

Measuring to points? Dimension surfaces


Modeling: Standardize numbering

Use zero-prefixed sequential numbering for Measurements and Configurations – M001, M002, M003, … – C001, C002, C003, …

Reset numbers by major project (or never?) Why:

– Easier to name and reference screenshots for reporting

– Easier to lookup and replace a picture if it needs to be updated (sorting by name)

– Easier to reference and catalog in a project spreadsheet


Modeling: Names and notes

Use descriptive names for ALL: – Parts

• “Guide Left” vs. “8678-9008”

– Features • “Pivot pin hole” vs. “Feature61”

– Configurations • “C037: Slider Up and Left to Guides” vs. “Config17”

– Measurements • “M023: Slider underside clearance to Frame” vs.

“Measurement1”

– Configuration joints • “Slider pushed UP to Guide Left” vs. “Slider;01 to Guide; 01” • “Slider;01 to Guide; 01” vs. “5541-1428;1 to 8678-9008;1”


Modeling: Names and notes (continued)

Add descriptive notes to ALL Configurations

Why? Clearly defines model state The more time you spend writing a note for a configuration, the less time you spend trying to figure out what all the joints mean in a month Will appear in the enhanced report



Add descriptive notes to ALL Measurements

Why? Clearly defines objective The more time you spend documenting the objective in the model, the less time you’ll need to explain it individually Will appear in enhanced report



Add drawing number, revisions, zone, sheet, and view details to dimension’s notes to document where the tolerance information came from

Additionally, include information about differences from part variation rule

Why? Identify dimension missing from drawing/assumptions/corrections related thereto This information will show up in the enhanced report Documenting the source of a tolerance assumption early in the design phase is critical to avoiding mistakes when the model must be revisited/updated


Modeling: (CETOL>)Insert>Advanced…

Use Insert>Advanced measurement and Insert>Advanced Joint when it’s easier to find the feature in the tree than it is to select the feature from the CAD. – Control click the two features

in tree, Insert> Advanced…

Expert: Can also do this offline from CAD


Modeling: CAD Reference geometry

If you need helper geometry in CAD (Planes, Axes, Points, Copy Surfaces, etc.) prepend the feature name with “CETOL_”

Put CETOL helper geometry into a “CETOL_REFERENCE_GEOMETRY” group

Why: • Prevents re-use of features for

non-CETOL purposes • Prevents features being deleted by

others


Modeling: CAD Reference geometry (continued)

Where possible in CAD, use constraints to define relationships for helper geometry to actual CAD features

Why:

– Updates to CAD will require less or no re-work to update the CETOL model


Modeling: Gage size and Remove Draft

Fastened interfaces between drafted features require careful gage size selection

Use a cross section at contact location to assist in determining the gage size of each feature to the size at the cross section


Modeling: Gage Size and Remove Draft

Unequal drafts

Chamfer

Landing pads



Create cross section at plane where contact will occur



Measure size of curves at cross section



Remove draft and set gage size in CETOL

Don’t forget to convert from radius to diameter if necessary (multiply by 2)



Check location of feature origins (do they line up?)


Modeling: Gage size and Remove Draft

Can now apply float/bias with draft removed


Modeling: Invariant dimensions need notes too

When setting a dimension to invariant include a note why – i.e. “Tangent”, “One half of width feature”, “BASIC” ,

etc.

Set the tolerance to Zero

Why? – Documents the reasoning behind what could have

been an inadvertent deletion of variable

– If a ± 0.000 dimension (or one with a description as above) shows up in the report, it could be an indicator that you forgot to set the dimension to invariant


Modeling: Measuring to points

When measuring to a point, users are often tempted to add variant dimensions/GD&T directly to the point feature

What if the surface is added afterward and dimensioned independently?

Since the point is on the surface, it is considered best practice to make zero-valued invariant dimension constraints to the surfaces that the point is on, and dimension those surfaces back to their parent features


Modeling: Measures to points (continued)

Best practice


Validation

Movie screen captures of visualize sensitivity

Customize analyzer layouts


Validation: Movies for visualize sensitivity

When one encounters a variable that has an unexpected, but justifiable sensitivity, it is usually easier to use a movie of visualize sensitivity to explain the situation


Validation: Custom Analyzer layouts

Use filtering to reduce the amount of information displayed in the Analyzer – Results List and Tree

• Filter measurements

• Filter tolerances below a contribution threshold

– Results Tree • Filter features below a contribution threshold

Use “Disable Layout Filter(s)” button to toggle filters on and off

New: Write-up on SSC in Knowledgebase


Validation: Custom Analyzer Layouts (continued)

VS

Filtering out dimensions below contribution threshold


Validation: Custom Analyzer Layouts (continued)

VS

Filtering out features with contribution below threshold


Reporting

Enhanced reporting

Fixed-region screen capture for pictures

Custom report filtering

Boilerplate

Use html editor to keep report html clean


Reporting: Enhanced Reporting

Use the enhanced reporting stylesheet and template to include screenshots in report

See the SSC Knowledgebase article for more information


Reporting: Fixed region screen shots

Use a tool with fixed-region screen capture

– SnagIt ($50, slow > 2 monitors, great editor and other features, only images)

– FastStone Capture (~$20 lifetime license, fast with any number of monitors, fair editing capabilities, video)

Measurements and Parts: 400px by 400px

Configurations, Top Level ASM: 600px by x 600px

Why: Crop as you take the picture


Reporting: Fixed region screen shots

Expert: Use Windows 7+ Search feature in explorer “*.png date:today” will show you PNGs created today


Reporting: Custom report filters

Use a custom report template to filter sensitivities and contributions below a certain level

Also used to select different stylesheets


Reporting: Boilerplate language

Use boilerplate language for reporting Measurement results

Use boilerplate for report background section

Example 1: At 3.5 sigma it is predicted that there will be XXXX" minimum clearance. Example 2: At 3.5 sigma it is predicted that there will be up to XXXX" interference with an as-is sigma of XXXX.


Reporting: HTML editor

MS Word complicates html of report

Use WYSIWYG html editor alternative – i.e. Kompozer


Questions and Comments

Q&A