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Archive for July, 2008

While searching for a SolidWorks model of a presser foot for a sewing machine, I ran across the site of a place called the TechShop. I must have been living under a rock all this time, because I had never heard of anything like this before.  This place is a public access workshop, like a Kinko’s, only full of all kinds of equipment that can be used to work on almost any kind of project you can possibly imagine: milling machines, sheet metal working equipment, welding stations, plasma cutters, tubing and metal bending equipment, lathes, equipment for working on plastics, and even a Dimension BST 3D printer. All kinds of neat stuff, all under one roof, and available for anyone that needs to get some project done or simply wishes to learn how to use the equipment, since they also offer classes and assistance from instructors. There’s one of these in Menlo Park, not so far away from my place, so I’m thinking about going on a little “field trip” one of these weekends and tour their facility (yes, that 3D printer is making me insanely curious).  So, I’m wondering, have you ever tried a place like this? If so, did you become a member or just visit every now and then? Is it really as good as it sounds? Is it worth the cost?

This is a little tip that those who are seasoned SolidWorks users probably already know, but that can be very useful for those who are not so experienced in “the art” of top-down assembly modeling (I’m not extremely experienced but I learned this one by hitting my head against a wall a few times). It’s also a very simple tip, because all you need to do is remember one thing:  the infamous in-place mate. 

Every time you create a new part in the context of an assembly, a special mate is added that will define the position of the new part in the assembly: an in-place mate.  This is true regardless of where you choose to place the new part’s base sketch: a plane in the assembly, or a plane or face of another component in the assembly. The following image shows the in-place mate between the part Rod Support and the part Rod, which was created in-context.

On one hand, this is a good thing because you don’t have to worry about mating the new component to keep it from floating around; it’s already been done for you. The tricky part, though, is that the in-place mate means the new component is fully defined, completely fixed, it can’t move or rotate at all.

This is important to keep in mind if you are adding other components to the assembly that would require this one component to move or rotate in order to mate correctly.  If this is the case, you are likely to see errors displayed here and there in the feature manager, you will get warnings about how adding this or that one mate will over define the assembly, and other mates will fail as well, but it’s not likely that you will see an error message or warning next to the in-place mate. Nevertheless, always keep in mind: in-place mate means fully defined, no movement whatsoever. So, if you really need that component to move, you are going to have to get rid of that in-place mate, otherwise it just won’t happen.

Once you decide to delete the in-place mate, you’ll get the following message.

What does this mean? Well, if you answer “yes”, not only the in-place mate will be removed, but also all the external references to geometry of other components in the assembly will be broken, as well.  In this case, you will have to proceed to dimension sketches in the component, then add mates in order to define its position relative to other components in the assembly.  Remember, once you break the external references, you can’t undo it and your component won’t automatically update when changes are made to the other components in the assembly that it used to reference to. Also, you can’t add an in-place mate yourself. This is a special kind of mate that is automatically applied to parts created in-context. On the other hand, if you answer “no”, then you get rid of the in-place mate, but you get to keep all the external references. You still have to add mates in order to place the component correctly in the assembly, but you can rest assured that your component will update when changes are made to the geometry of those other components it references to. Neat, huh? Now, keep it in mind. Not that your life depends on it, but it may come in handy one of these days.

ME!!!! Just a few minutes ago, I finished taking my CSWP test and… I passed!!!! Thank you, Jesus!!! And thank you to my wonderful husband for supporting my crazy dreams!! I feel soooo tired, and sooooo happy! I’m crying, but these are tears of happiness! I still can’t believe it! I passed!!!

And now to sleep for a month… If I can…

Learning how to use the different tools for drawing and detailing in SolidWorks is not precisely the most fun I’ve had with the software so far. I’d much rather work with the solid model!   Maybe that’s why I had been putting it up for later, and why I get sidetracked so often.  Anyway, after beating myself up for not being more diligent, I’ve spent most of this week studying and practicing with the different tools available for adding dimensions and annotations to drawings.  It’s not as bad as I thought it would be. In fact, it’s kind of fun… sometimes. It’s a bit confusing at times, because the books and manuals I have are based on SW2007 and I’m finding that a few things have changed in SW2008, if only in the user interface and the way to access some of the options. It’s no big deal because I’ve found everything so far, it’s just confusing. However, I must admit that I got stuck when it came to all the different tolerance and precision options.  More in particularly, I got stuck with the different options for fit tolerances.

Perhaps, it’s because I never really used such tolerances in the past that now they seemed so confusing. The SolidWorks help file explains how to use the functionality, but it didn’t help me much to understand what  they were all about, so I searched around in a few books here and there, and I think I finally got it. This kind of tolerance refers to the fit between mating parts, more typically holes and shafts. There are four classifications you can choose from in SolidWorks: user defined, clearance, press and transitional.

In a clearance fit, the shaft will always fit inside the hole and there will always be a space or clearance between the parts.  In the press or interference fit, the shaft is slightly larger than the hole and there is always an actual interference of material. The mating parts must be pressed together. A transitional fit may result in a clearance or an interference condition. Whenever one of these classifications is chosen, SolidWorks will filter the kind of tolerances available that, according to standards, correspond to that classification. Once the tolerance is chosen for the hole or shaft, the list for the other type is filtered once again to show only corresponding tolerances for the mating part. This can be tricky, sometimes, it may tell you that there are absolutely no matches for the kind of fit you chose, so it’s always useful to remember to select the type of fit depending on the use or service required from the equipment. Most of the time, choosing for the hole first is the way to go, but there may be times when it’s advantageous to choose a fit and tolerance for the shaft first, like if you have several parts, each with different fits, that are required to be assembled on a single shaft.

ANSI has issued preferred limits and fits for cylindrical parts in the shape of tables that recommend standard sizes, allowances, tolerances and fits.  These tables prescribe the fit for any given size or type, and they also prescribe standard limits for the mating part(s) that will produce the desired fit. Letter symbols identify five types of fits as follows:

            RC       Running or Sliding Clearance Fits

            LC       Locational Clearance Fits

            LT        Transition Clearance or Interference Fits

            LN       Locational Interference Fit

            FN       Force or Shrink Fits

These symbols, plus a number that is used to indicate the class of fit within each type, are used to specify a complete fit.  However, the choices you have to select the type of fit tolerance for holes and shafts in SolidWorks aren’t these ones, but the corresponding ISO symbols. At least, that’s all I see. According to the ISO system, limits and fits are divided into three different categories:  clearance fits, transition fits and interference fits.  So, for instance, according to this classification, the clearance fit would include those that were known in the ANSI standard described previously as Running, Sliding, and Locational Clearance fits. The Transition Fit would include those that were known as Locational Transition, and the Interference Fit would include those known as Locational Interference, and Force in the ANSI standard. The tolerance symbols include the basic size for the hole or shaft, followed by a letter that indicates the fundamental deviation (uppercase for holes and lowercase for shafts), and a number that indicates the IT grade. So, as an example if you specify the fit tolerance for a shaft as:  25 f7, it means that the basic size of the shaft is 25 mm, with a close running fit, and the dimension limits for this shaft would be Ø24.98-24.959 mm.

Sounds a bit confusing? Well, at first, but it really isn’t so bad once you look it up on tables, which are available, for example, in the Machinery’s Handbook or even in some drafting books. I actually want to learn more about tolerancing and dimensioning standards after this. It’s quite interesting!

One advantage you have here is that, unless you choose to do it yourself, SolidWorks automatically calculates the bilateral tolerances for you, according to the kind of fit you specify, so if the size of the part ever changes, they will be updated as well. And by the way, you can choose between three different ways to display the fit tolerances:  If you choose Fit from the Dimension Property Manager, under Tolerance/Precision, it will display as the basic size of the hole or shaft plus the tolerance code.

If you choose fit with tolerance, it will display the basic size, the tolerance code and the value of the bilateral tolerances.

You can also exclude the code altogether and display only the basic size and tolerances by choosing Fit (tolerance only).

There’s also the choice of including the type of fit for the mating part in the same annotation, if you wish to do so. This option only works for Fit and Fit with tolerance because they display the tolerance code. Note that the bilateral tolerances won’t be displayed in this case, only the codes. 

As I had mentioned in my previous post, while looking for a SolidWorks Routing Manual, I came across the website of another SolidWorks user who created his own manual and was offering it for sale. Unfortunately, right at that moment he was out of town and not taking any orders, but today I’m glad to announce to all of you who may be interested that he’s back, his site is up and he’s taking orders again. In fact, I just ordered my own manual a few minutes ago. The author’s name is Wes Mosier and he’s Sr. Designer / Detailing Manager for Lortz Manufacturing in Bakersfield, California. He’s also a CSWP with over 18 years of experience in 3D design and solid modeling (among many, many other related areas), and president of the Bakersfield area user group.  He wrote the Piping and Tubing Design Guide for SolidWorks Routing, a very complete manual (perhaps the only one of its kind), with over 250 pages full of colorful illustrations and detailed instructions (just look at the sample pages in the tip and tricks section on his site), and that is offered through his website in pdf form.  The price of the manual is only 50 dollars, which is a really great deal, considering that for that same price you get access to a whole year of updates that may be made to it due to new releases or service packs coming out. You are also authorized to share your copy (ONLY) with those working with you in your same company. It seems amazing to me that not many people know about the existence of this manual. But now you know!  If you are interested, pay Wes Mosier a visit and get your Routing Manual today!