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Archive for July 20th, 2009

If you are one of the few that visits at least every week and you are wondering where I’ve been, well, let me just remind you that it’s summertime here in California, and right now I’m home with a sick dog and eight kids. No, I’m not Octomom.  I only gave birth to two of them, but the other six are friends and neighbors that come to play or get “casually” dropped off by their mothers when they need to go shopping or visit the doctor. It never fails! Almost every day I’ll hear the doorbell ring and a boy will be standing there… “Hello, Mrs. Ethan’s mom, um, my mom has to go shopping/to the doctor/to the dentist/to visit a friend, so she said I could stay here with you.”  And how can I say no when the mom is already driving away like a madwoman in a high speed chase?  Sigh…  In all fairness, sometimes my boys go to visit them, but I never drive away (too fast), just in case they want to come back.

Anyway, I’ve also been spending some time exploring SolidWorks 2010 Beta,  preparing for my presentation at my local user group (although I just learned it’s been changed for September), getting ready for a couple of trips (travelling with dogs is complicated), and answering old and new email that has been accumulating.  One of those emails inspired this post.

A reader had a problem trying to create something like a spring. I know, you can make that easily with a helix and/or a sweep, right? Yes, but the tricky part was that he needed the ends of the spring to bend towards the axis of the spring.  I wasn’t quite sure at first what he wanted to do, so I referred him to a couple of tutorials from Matt Lombard’s SolidWorks 2007 Bible that I remembered going through a while ago. In one of them a spring with a little hook attached to one of its ends is modeled using projected and composite curves. The other one is a helical sweep where the profile appears to grow larger as it travels along the helix. Just as I was getting proud of myself for saving those old files “just in case”, he wrote me back saying the tutorials were good, but he still couldn’t find the way to do what he needed to do. He sent me a picture (that I won’t publish here) and the practice part he was working on, and my first thought was to start fixing the sketches for the projected curve he needed, but after taking a closer look to those pictures, it occurred to me that what he was really trying to do could actually be accomplished in a much simpler way, just by taking better advantage of what splines and 3DSketches have to offer.

See, you start with a circle centered on the origin and a simple helix, not tapered and constant pitch. I only needed one revolution or so for this one, but that’s not really important.

Next, you are going to open a 3DSketch, select the helix and convert it into the 3DSketch by using Convert Entities. See, unlike what happens when you convert a helix into a sketch, where you end up with a projection of the helix on the sketch plane, when you convert a helix into a 3Dsketch, you end up with a sketch entity that is just like the helix you had before, all 3D and no flat, it’s actually a spline, and you can drag the ends and add other entities and relations inside the same 3DSketch, as well.

My reader needed the ends of the helix to go back to the center.  Imagine a wire that runs vertically along the axis of the helix, then bends around to form the spring and comes back to the center to continue running vertically along the axis. That’s what he needed.  In order to do that, and still inside the same 3DSketch, change to a Front view and sketch a vertical line along the Y axis. You should see the relation AlongY added to this line, if you don’t have it, add it through Display/Delete Relations, Add Relation.  Also add a coincident relation between this line and the origin.

Still inside the same 3DSketch, change to an isometric view, or at least rotate the view a bit so you can see better what’s going on, and sketch a two point spline joining one of the ends of the helix with one of the vertical lines. At first, the spline will look like it’s just a line, but you can make it look curvy by dragging the handles.  Select the spline and the helix and add a relation (Display/Delete Relations, Add Relations). This relation can be tangent or equal curvature, whichever works better for your purposes.

Now, in order to smooth out the transition from the spline to the vertical line, select both the spline and the vertical line and use Tools, Spline Tools, Fit spline, to fit both entities into one single spline.  Make sure the option to close the spline is unchecked.

Notice that you can still adjust the transition even more by dragging the spline handle, like in this image.

Then you simply use this 3DSketch as the path for the sweep and that’s it. No need for complicated ways for this one, just to remember what can be done with the tools we have.