So, I am teaching the students how to reuse pre-existing data in SolidWorks. The project is using a Truarc – E-Clip retaining ring. Cool stuff – Toolbox has the Truarc catalog to just drag and drop. Toolbox Pull-down has the groove generator with the intelligence to select the correct groove size/feature for the Truarc E-Clip by having the user just select the shaft surface. Awesome stuff right? That is until you realize that the dimensions, relations and tolerances have to be applied manually. All the information is there so why doesn’t SolidWorks just dump the info in.Here is the best part, up until that point the students think I am God handing out the solution that they could have used the semester previous. “Oh man! We could have used this on 4 project last semester” Then we DEFINE the groove. “Why would I want to use this tool?” That is the outstanding question of the year! Why have an incomplete tool. It ends up being 3 times the work to define the groove than if you just did the revolved cut. No matter if your company is model centric or still uses drawings the size/location dimensions and tolerances still need to be there. Please jump on this bandwagon and complete the enhancement request to finish this tool. In theory it is a huge time saver and could potentially help designers and engineers from making mistakes about o-ring and retaining part numbers, sizes, dimensions and tolerances. –Chris MacCormack
Category: ASME Standards
Dimensioning of Slots in SOLIDWORKS for ASME Y14.5
Ever since the additions of the slot sketch tool for 2009 and the Hole Wizard Slot for 2014, SOLIDWORKS almost seems like a whole new software for the those who design machined parts. Adding these tools were long overdue. Additionally, SOLIDWORKS supports the standard methods for dimensioning slots when they are created by using these tools.
ASME Y14.5M-1994 paragraph 1.8.10 and figure 1-35 provide three methods for the dimensioning of slots, with no stipulation regarding which is preferred for particular scenarios. (Note: all three methods require the insertion of a non-dimensioned “2X R” note pointing at one of the slot’s end radii.)
In one fashion or another, SOLIDWORKS supports all three methods, though it does have a default for both simple slots and arc slots. For brevity, this article will only cover simple slots.
The first slot dimensioning method (a) provides the width and the distance between the end radii center points.
Method (a)
The second method (b) is the easiest and simplest to dimension. Simply state width and overall length, and use an arrow to point to the slot’s object line. Though originally reserved for punching operations, ASME Y14.5M-1994 (and later versions) allows for the use of this method on any simple slot. When using Hole Callout to dimension a slot in SOLIDWORKS 2009 or later, this is the type of dimension that is inserted.
Method (b)
The third method (c) provides the width and overall length of the slot in linear dimensions. This method is preferred if the slot has positional tolerances that use the boundary method (see ASME Y14.5M-1994 figure 5-47).
Method (c)
For all of the above methods, add the “2X R” separately by using Smart Dimension tool.
Side note: of the three choices, the ASME board almost left out (a) and (b). The original release draft of ASME Y14.5M-(1994) only shows method (c) in figure 1-35.
Inch or Metric?
A recent discussion on eng-tips.com has prompted some interesting replies. The discussion revolves around one individual asking for advice to help in the battle to promote metric at his company, despite push-back from their machine shop, and a lack of concern about the issue from higher-ups who have taken a pragmatic cost related approach. I believe that the responses received may have surprized this individual.
There are some who point out that the cost of switching to metric must be justified and explained to management. The problem here is that there IS a cost associated with switching from a shop based on inch tooling to a shop based on metric tooling. Is there savings associated with the switch? The benefits of switching units of measure are likely limited, unless they are dealing with much more complex issues. Once a company has a system in place, it is generally not economical to switch it midstream.
Several made the point that if the company is already standardized to inch, then any individuals at that company should adjust their methods accordingly. This is the same if a person accustomed to inch joins a company that has standardized to metric.
What I personally questioned was the rather strange idea that metric is somehow some sort of default when it comes to making the choice. The universe doesn’t know the difference between an inch and a millimeter. For us in the engineering field, it is easier to think in metric than in inch, but what are the real world advantages of one system or another? Unit of measure is completely arbitrary. One person who responded to the posting even pointed out the advantages of using hardware from both systems at the same time.
“But the rest of the world is using metric!” Umm, really? That, by itself, is an arbitrary point.
A counter arbitrary point, the United States of America has the largest economy on the planet by almost 2-fold. It doesn’t really matter what rest of world does because the U.S. is so big. It’s like saying that the 800lb gorilla in the room should wear jeans just because all the chimps in the room are wearing them. Maybe the gorilla is happy with his corduroys instead.
To this, there was a response about how the world combined outweighed the U.S. economy, and that the US is not 100% inch. My point at that time was simple, “…Americans might be surprized by the number of countries that ARE NOT 100% metric, many of which are in Europe. ”
I was surprized by the responses that comment provoked. There is apparently much less standardization going on around that planet that we’ve been lead to believe by hardcore metric proponents here in the U.S. I know about the imperial gallon, the pint, and oddities like the metric ton. However, I didn’t expect responses from the international community stating that there are significant fields and regions where standardization is in the old traditional imperial system and not metric.
The more I explore this topic, the more I’m convinced that it really just doesn’t matter. Once a choice for a company is made, then they should stick to it. I’m also learning that some strong proponents of metric here in the U.S. have a tendency to assume metric has greater adoption than what is true in reality.
Model Based Definition (MBD)
As we move further into the realm of 3D CAD software, something that is still catching on is the idea of driving all specifications directly from the model file, instead of having a separate drawing. There are various terms for this, but I’ve seen Model Based Definition (MBD) most recently. I personally am not critical of this idea. I am critical of moving 100% to this form of documentation without better support from our 3D CAD packages and ASME/ISO standards.
Models are generally considered basic. All this means is that the tolerance is derived from some “other” specification. This is normally in the form of associated Geometric Tolerances. To fully define a part in MBD, you’ll need a GD&T scheme, often supplemented by traditionally dimensioning and tolerancing where needed. The difference is that if drawings are not used, this has to be done within the model itself and then is somehow communicated to the manufacturer. The task to communicate this information to the manufacturer via the model is harder than it might seem as first glance. This is due to the myriad of 3D CAD formats and versions now available. GD&T information may not translate to other formats, such as STEP and IGES.
Additionally, any information that would’ve appeared on the drawings now has to appear within the model itself. So, shortcutting the drawing step doesn’t mean one gets to ignore the information that would’ve been included on a drawing. It just means all of that now needs to appear in the model.
With that said, ASME Y14.41 supposedly standardizes this effort. In my opinion (and yes I’ve read it and “own” a copy), it is lacking right now.
If considering a MBD program, just make sure everyone understands that the model is now the drawing; and that means it will need to be as accurately detailed as the drawing would’ve been; and since this information is now in the model, a method of communication will have to be established with the manufacturer if they don’t have the ability to use the format where the GD&T information resides.
An alternative is to use the drawing in conjuction with the model, which together provide the complete specification. In this case, the drawing will still be the primary specification (usually for critical-to-function specifications), but it makes use model to complete the specificaiton. The model can either be basic, or used with some traditional tolerance. Where the model is basic, I’ve seen companies place a generic profile feature control frame in the general notes. This FCF is applied to the model for any dimensions that are unspecified on the drawing. If such as system is employed, it is important to clearly state this on the drawing to prevent ambiguities.
SWW09: Focus Groups (Drawings and Sheet Metal)
As previously mentioned, I attended two focus groups (also called roundtable discussions) this year. These are generally held on Sunday before all the major SolidWorks World activities begin on Monday.
Sheet Metal
The first group I attended was for sheet metal functionality. Though attendence was very light, the number of different methodologies and opinions was high. My own interest in the topic is the problem with being forced to use assemblies to fully document sheet metail parts with inserts. This is an issue because if you start a drawing of a part, you cannot later replace that part with an assembly. So, if you create a sheet metal part with no inserts and then you need to add inserts on some later revision, you are forced to recreate the drawing practically from scratch. This is a horid time and resource sink.
Others in the group talked about using K-factors to determine the material used by the sheet metal part (for flat patterning), while others disregarded K-factors in favor of bend reduction techniques.
One request that seemed to get common acceptance is the idea of creating a table of all the bends of a part with their full characteristics, with the ability to highlight each bend by clicking on it within the table. When this table is on a drawing, it was suggested that details be added to a specific layer.
The session also revealed that some used work arounds to use the SolidWorks model to instruct sheet metal tooling to perform certain actions (either via direct or translated input). Some use alternative features which do not match the final design in order to instruct a tool to produce the feature desired in the final design.
One work around solution did come out of this session. Right now, the material mass number changes from bent state to flattened state. Although this difference is minor, over a large quality of parts, the error multiples and can create issues in part handling. Use a non-configuration custom property to link to the the material property (of a specific configuration?). Use this custom property as the source for the mass regardless of the configuration or part state.
Drawings
A large portion of the drawings discussion revolved around printing and saving issues with Drawings. It seems many people are experiencing similar problems. When saving as a PDF, views randomly disappear. When printing as a PDF, text locations get shifted. Also, changes to parts at lower levels of an assembly may cause errors and view changes in higher level assembly drawings; meaning the the company has to open up all levels of a product’s assemblies to make sure that any change did not affect the drawings in unexpected ways. It seems more people are having these kind of issues that I originally thought. Many of the problems are magnified by use of PDM’s.
The meeting also focused on DimXpert and how to handle its dimensions. One comment is that it should place dimensions per current standards within the model. Another comment noted that datums and feature frames should drive the model.
I voiced my other major concern as well. Symbols from the Gtol.sym library file should be stored within a drawing. Right now, I cannot give native drawings to others outside of my organization because they will not be able to see symbols that we employ. When a symbol is used within a drawing, it should be included in that drawing’s file and not require editing of any other user’s Gtol.sym file.
Virtual Sharps
In the past, I’ve settled on using the phrase “TO V.S.” after a dimension which is to a virtual sharp. I’ve seen this type of referencing used elsewhere. Another set of initials I’ve seen used is TSC, which I guess stands for theoretical sharp corner. I think this is likely older wording. I used to like the shorter “VS” myself because it refers to what I would consider a more common term. However, none of this matters too much since the standards say nothing about what is proper. ASME Y14.5-2009 uses the term Point Location, but doesn’t specify any identification symbols or abbreviations for this concept.
SolidWorks graciously offers a multitude of marks to create an identification of a virtual sharp. The main problem I run into with SolidWorks and this function is that I’m working in drawing scales or with radii sizes that frequently make such marker nearly invisible without a magnification glasses. The other problem is that none of the marks are identified in any standards. Heck, a third problem is that fact that the functionality is extremely hidden. You have to know how to make a virtual sharp mark because there’s not button, or icon specifically for it. It’s a short series of steps that would be nearly impossible to guess at.
Those steps being (within a drawing): 1) Select each of the two object lines that intersect in space. 2) Select the Point function. How is anyone to know intuitively to select the Point function? Hmm. Anyway, at least SolidWorks offers some method. That’s more than can be said about the standards.
I guess I should ask what are others doing to identify dimensions that are to virtual sharps?
Here is an updated article about Virtual Sharps.