Control Root Size of Drafted Rib on Curved Surface

*This article makes some inaccurate statements regarding the capability of SolidWorks.  Please see the correction article for details.  Inaccurate statements have been crossed out.  The methodology described in this article should be referenced as an example of bad practice that should only be employed if traditional methods fail.  Edits to this article appear in this color.*
*Additional comment: this article does demonstration a good method for getting a line along a curved surface into a sketch. *

Good mold design means that one must take care to control the root width of a rib.  How does one do this if the rib is based on a curved (non-prismatic) surface? 

SolidWorks has many powerful features for making injection molding parts.  It has both rib and draft features.  Unfortunately, these two features together have one important limitation.  When applying a draft to a rib based on a curved surface, SolidWorks does not allow the user to hold the root width of that rib.  SolidWorks requires a prismatic surface to use as a neutral plane from which to start a draft.  This means in this case, the draft can only be started from the top of the rib, not its root.  If one wishes to hold the rib root constant along a curved surface, one cannot use the rib or the draft features.

SolidWorks does have an arsenal of other features and tools to allow one to build an alternative strategy to workaround this limitation.  

Basic shelled part with curved surface

This first figure shows a fairly simply shelled injection molded part with a complex curved surface.  To make drafted ribs using this method, first create an axis that can be used as an directional guide. You can choose to use features on the part itself for this purpose, instead. I prefer to create a special sketch at the location where I plan to add a boss.  Regardless of the method used, the directional guide should be parallel to the direction planned for the ribs.

 Setup Sketch for Directional Guide

The second step is to start a new sketch above the curved surface.  In that sketch, draw the outline of the rib.

Sketch outline of ribs

If there is a series of ribs needed in one direction, try creating a sketch pattern the other instances.  Make sure to turn sketch entities of the other instances into construction lines.

Project outline using Split Line

Use Split Line to project that outline onto the curved surface.  Split Line will only project one contour per sketch.  This is why it is important to turn all other instances of the rib into construction lines.  Having those other instances pre-drawn will save time when making the other ribs (covered in Part 2 of this article). 

Next, start a 3DSketch.  Use Convert Entitles to bring the Split Line curves into the sketch.  Drag the end points of the curves so they are coincident (on the surface) of the outside surface of the outer walls, or some othe appropriate location.  Then, close the contour by drawing lines to connect the curves at each end. 

Convert split line edges in 3DSketch

Extrude this sketch.  Use the previously drawn axis from the first sketch as the direction.  Use the top surface of the cavity (or whatever is appropriate) as up-to-surface entity.  Turn on Draft and specify the desired angle.  Here’s the funny part.  Be sure to extrude a small amount (smaller than the wall thickness of the part) in the other direction without draft.   If this isn’t done, a zero-point error will pop up preventing the completion of this step.

Use previous setup to set extrude of 3DSketch

The end result will be a drafted rib with a controlled root width.

Final result

Part 2 of this article will detail how to create repeated and crossing ribs using this same technique.  Again, please note this is not a best practice method.  See the correction article for details.

Dual Dimensioning and ASME Y14.5M-1994

This entry is part 2 of 8 in the series Dimensions and Tolerances

Dual dimensioning is the drafting practice of using multiple units of measure in a dimension in the same direction of a feature.  SolidWorks and many other CAD programs support dual dimensioning.  This support is usually a little quirky.  It’s actually not  the fault of the CAD application.  At one point, it was a surprize to me (and often is to others too) that no current drafting standard actually supports dual dimensioning.  In retrospect, this makes perfect sense.

My experience is with ASME Y14.5M-1994.  When invoking ASME Y14.5M-1994 (or even ANSI Y14.5M-1982), one will find that rules regarding dual dimensions do not exist.  ANSI Y14.5M-1982 does mention in its appendix that support for dual dimension no longer exists in the standard.  This is apparently because it was mentioned in a previous version.  That said, dual dimensioning has never really ever been allowed by any incarnation of Y14.5.  This is because of very specific wording under the standard’s Fundamental Rules.  The wording may vary between versions, but carries the same meaning in all versions.  In ASME Y14.5M, that wording is as such in 1.4(d), “Dimensions shall be selected and arranged to suit the function and mating relationship of a part and shall not be subject to more than one interpretation.”  (Support for dual dimensions in pre-1982 versions was a mistake that was likely political in nature.)

General practice in the use of dual dimensions is that they are of equal importance to the primary dimension.  This creates issues in that it allows for more than one interpretation of the dimension.  It is nearly impossible for nominals and tolerance ranges to be identical between units of measure.  This means that the dual dimension tolerance range is usually resized to fit within the tolerance range of the primary unit of measure.  This creates a situation where the dimension has more than one interpretation, which is specifically prohibited by 1.4(d).  The conclusion that can be drawn from this is that dual dimensions are actually not allowed by ASME Y14.5M-1994.  This is the hard argument against the use of dual dimensions.  I could end this article right here.  However, I will also explore the soft arguments against their use.

ASME Y14.100-2004 paragraph 4.32.3 uses soft language to discourage the practice of converting inch to metric and vise verse (“should not be used”).  This is known as soft conversion.  This is not an outright prohibition against dual dimensioning by itself. However, the practice of soft conversion is integral to using dual dimensions.  With this practice discouraged, dual dimensioning is also discouraged.

ASME Y14.5M-1994 defines a reference dimension as such,

“A dimension usually without tolerance, used for information purposes only. A reference dim is a repeat of a dimension or is derived from other values shown on the drawing or on related drawings. It is considered auxiliary information and does not govern production or inspection operations.”

By definition of reference dimensions, dual dimensions must be treated as reference dimensions. However, anyone who uses them knows this is generally not their intent. As generally intended, dual dimensions are disallowed unless they are considered reference only.

The final soft argument is gleamed in the wording of ASME Y14.5M-1994 paragraph 1.5.  This paragraph assumes dual dimensions are not in use.  For example it begins one paragraph as so, “Where some inch dimensions are shown on a millimeter-dimensioned drawing…”.  It never then says “Where many inch dims are used on a metric drawing….” This is not a specific exclusion, but should be noted for its wording. It does allow for the use of both inch and metric units on the same drawing, but not multiple values of dimensions for the same features.

With all of these arguments aside, CAD applications do attempt to accommodate users who feel they need this capability.  However, if used, caution must be exercised.  Handling of dual dimensions by CAD (and common practice) can create confusion on a drawing, particularly if the software assumes values for the dual dimensions and its tolerances.

In the effort to avoid issues and violations of the standards, it is my opinion that if dual dimensions are used, they should be noted as for reference only on the drawing.  This can be accomplished by adding a note similar to “DUAL DIMENSIONS IN BRACKETS ARE FOR REFERENCE ONLY.”  This avoids problems caused by multiple interpretations for dimensions.  Of course, over use of reference dimensions is also discouraged by ASME Y14.5M-1994. But hey, who’s it hurting?

For SolidWorks, dual dimensions on a drawing may be employed by going to Tools>Options>Document Properties>Detailing and checking Dual dimensions display.  Also at that location is the choice to display the dual dimension on top, bottom, left or right of the primary dimension.  These are SolidWorks 2007 instructions (other versions of SolidWorks should be similar).

I did make a sample SolidWorks macro that will turn on dual dimensions for a drawing and automatically set them to display on the bottom (default is top).  This example macro can be downloaded here.  It can be modified to use any settings as default.

For the record, this article was inspired by multiple posts on various SolidWorks related forums over the past few months such as these at SW Forums, eng-tips.com, and Pro/E discussion at eng-tips.com.

Silicon Valley or Solar Valley?

Something is stirring in Silicon Valley again. I drive around and still see a lot of empty commercial lots in the industrial area where I work. Even still, larger new buildings are being built around me. Even weirder, the lunch crowd is becoming larger. I’ve been noticing this slow change over the past 6 months or so. Where lines at the local Togos and Subway used to be easy to get through, they are now extending well out the shop door. More people are starting to work in the area. The job market looks like it’s starting to pick up.

The old days of semi-conductor giants springing up over night are gone.  The dot-com boom-bust is long over.  The new industries of the valley are Biotech and Solar. Solar is starting to take off so fast that a new nickname for the valley might end up being Solar Valley. Biotech is growing rapidly too. It’s contribution is a little more dispersed thoughout the San Francisco Bay Area. Either way, you cannot throw a rock without hitting someone that is currently working in either of those fields.  That said, semi-conductor is still King.  You can’t pick up a rock to throw without bumping into someone working in the semi-conductor industry.

Another thing I’ve noticed is that the business casual guys are back. These are the slightly older guys that wear slacks and shirts that make them look like they just stepped out of a Leave It To Beaver episode.  They are filling the lunch lines with their open discussions of confidential information about their new jobs.

Speaking of confidential conversations in public, late last year I overhead this one group of younger guys.  They were dressed up a bit in the way that younger guys dress up (all name brand clothes, but not well coordinated). Anyway, they were going in to very exact detail about the technology of their start-up Biotech company. Let’s just say I understood what they were talking about. I heard so much that the only thing I needed to make their information useful was to know their company name. I tried and failed to catch a glimpse of their door badges (which foolishly had their company logo printed on them).   I think they figured out I was eavesdropping at that point, so they smartened up. They really shouldn’t have been talking about the proprietary matters in line at a sandwich shop in the first place.

The lull in the crowds and traffic was nice while it lasted. It looks like we have another boom cycle getting ready to take off as soon as the economy turns more favorable.

SolidWorks Functionality that we take for granted…

Some of the students here at my school recently attended the Minnesota PTC user group.  Here they unveiled the Wildfire 4.0 release.  Many were very impressed by some of the new functionality Pro-E had to offer.  Let me give you a couple of items to ponder.  I will add more later this week:

New functionality in Pro-E Wildfire 4.0 –

1. They can now import Word and Excel into their files.

2. Their sketchers automatically selects your reference geometry for you in an attempt to reduce the number of clicks you use to define your sketch.  (Wait a second, no I have to delete that reference geometry and add the correct geometry.)

3. One of my students asked, why can’t I add more than 1 hole in the hole command?  Response :was that would be very complicated programming as it would be a feature in a feature.  The student replied he can do it in the SolidWorks Hole Wizard!” (These statements were not exact quotations but what the attendees had told me.

Anyhow, these are functionalities whether you like them or not that have been available in the software for many years.  Do not take these for granted.

Workaround to edit Macros that are locked on network drive

Question:  I have macros on a network drive and need to edit them.  Unfortunately, someone has them locked (open).  How do I unlock them without going to that computer to manually unload the macros?

Answer: There is a live workaround.  While you cannot edit the files while locked, you can change their folder name! This allows for a sneaky little trick that doesn’t require going to the offending computer.

Simply rename the folder on the network drive where the macros are located. Then copy that folder (files and all) to the same drive. Rename the new folder to be the same name as before the original folder was renamed.

The macros in the old folder with the changed name will still be locked out, but the macros in the new folder with the original name will be free to edit!

In a day or so, the files in the old folder will be unlocked again.  Simply delete the old folder at that time.

Addendum: It should be noted that this method will not always work.  However, it is worth a try before taking any other action.

That Kindling in my Heart

I must confess.  Up until just very recently, I considered Amazon’s Kindle to be a bit of a joke.  Think about it. Who wants to get a device whose only purpose is to read books?!  Well, I may have been wrong about this little gadget.

This is a feature packed tool that looks to be a serious attempt at moving books into the electronic realm without strapping the reader in front of a computer screen.  That said, I’ll reserve further comment about this gadget until I’ve actually tried one  Of course, this is where the first problem arises.  It’s a $400 gadget.  So the decision to buy it may be delayed by my willingness to pay that kind of price for a book reader.  However, even at that price, I am now tempted.

Why am I talking about the Kindle on a SolidWorks related blog?  Well, I recently came up with the idea (jokingly) to put the SolidWorks manual on the Kindle device in a sarcastic comment criticizing SolidWorks’ lack of printed manuals.  However, after looking into the gadget, and reading Matt Lombard’s insightful insider comments regarding this matter, I’m changing my consideration.  I seriously think it is a good idea, at least in principle.

If I do get this device, I will post a review.