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cadjunkie member Andrew Ward posted a head-scratcher on the discussion board. We gave it some thought, and this was the best method we could find. What do you think? Is there a better way?
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Adam O'Hern is an industrial design consultant specializing in visual brand languages, and has designed products ranging from laptops to power tools, classroom toys to bathroom fixtures, and robots to lint rollers. He has published with 3DWorld Magazine, CGTuts+, and Luxology, and works with Josh Mings of SolidSmack.com on EngineerVsDesigner.com. |
It’s the Cadjunkie “Nations with troubled economies” world tour! From the US (the people who brought you this down turn), to Greece and beyond. OK, I have no constructive input but to offer that those sprockets were probably forgings, so no feature is going to have straight lines. The only machined feature I’ll bet were the bolt holes done on a gang hydraulic drill press.
??????????? ?????? Solidworks ????????.
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Would the original positive for the forging not have been machined in some way?
Yes, but in 1942 (the year the Sherman was introduced) the forging dies were made mostly by hand. Manual machining of that day was capable of being precise but it was slow and why be precise if you don’t need it. I’m not too familiar with forging processes from that era, but I think they would hand finish a casting then heat treat it to make the forging die. The casting would likely have been a sand casting done from a hand carved pattern so who knows. The contour of the teeth of the sprocket may have been post machined with a tracer mill from a very accurate pattern but I doubt any of the other features would have mattered enough to warrant that kind of work.
PS. How’s the food?
µ
I love this stuff! Great info, I love learning about this kind of thing!
The 2 euro gyro is my new best friend :)
It works, thanks!
Hi Adam,
Wow, I didn’t realize the procedure could be all THAT complicated! :-)
I went about it a different way for various reasons – chief among these was that I created the geometry from a 1/35th plastic scale model, not just from a photograph. I’m also building the entire track assembly, so to ensure that all the parts would fit together perfectly in the assembly file, I used the cross-section of one of the tread blocks as a template to cut the slots in the outer part of the sprocket. The result looks a lot like your finished part, though it’s not exactly alike. Anyway, when I was contemplating how to create those funky angled cuts, it occurred to me that I might as well create them the way they were made at the factory, namely, by using an angled extruded cut as my ‘drill bit’. Selecting the proper radius and angle of the drill bit took a bit of trial and error, but the final result looked good enough for my purpose, which was to create a realistic looking model to render in Modo 501. Now, a SW purist will probably want to object that this method is a sloppy one, because it relies on a bit of eyeballing to achieve a realistic effect. While I’m generally sympathetic to this point of view, I would point out that even your method makes use of a good deal of eyeballing to get the right result. Not having the actual sprocket to obtain measurements from, it would be impossible to determine whether the angles of the scalloped cuts matches that of the actual sprocket, or to accurately gauge the thickness of the material in various places, the draft angle, the radiuses, etc. But since we’re not trying to create something from which we can machine a duplicate of the original, that level of exactitude isn’t required. Some time ago, Mike McCrorey gave me this simple bit of advice for creating models whose only purpose is to look convincing in a rendering: ‘If it looks right, it IS right’. I have to admit that it’s been a struggle to follow his advice at times. I’ve spent decades creating highly accurate measured drawings and 3D models, and the idea of ‘faking’ anything just rubs me the wrong way! LOL
CAD for product design is very different from hobby-CAD for model-making, so feel free to use whatever method works best for you. Glad you worked something out!
Sorry Andrew, I was flying low when I responded last, and obviously ignored my mother’s sage advice: think before speaking.
On further reflection I realize that the term “hobby-CAD” might be construed as condescending, and I certainly didn’t mean it that way! Your work is truly inspiring, and I hope you didn’t take me to mean otherwise.
My intent was not to demean the difficulty or importance of your work, but rather to simply point out that there are fundamentally different ways of thinking about CAD tools. When I’m building a model that’s for viz-only, then I 100% agree that “if it looks right, it IS right!” However, when I’m modeling for industrial design, the rules are a bit different.
Cheers!
Adam
It’s working for me now. Thanks!
Hey Adam, some how the video is not available… ;)
Hi Jorge, Andrew! Thanks for letting me know. I think it should be fixed, but let me know if you still have issues.
Adam
Hmmm. All I see are two horizontal yellow lines. Where’s the video?