Where to get a valid 3d model
Hi everyone,
I am currently attending an exam at the university about the Catia V5 software.
In order to pass the exam I need to model a mechanical assembly, made of at least 20 parts (shaped by me, excluding the catalogue parts in Catia) .
The parts should be designed, joined in one assembly and then animated through Catia.
Valid models presented by the professor are attached.
Since I don't really know what piece to design,It's tough for me to get a real piece, with the correct measurements of each parts, the way they interact with each other. The measurements of the pieces that I can find here on GrabCad are generally incorrect or approximated.
Do you know if on the internet I can obtain a more detailed description of the full assembly, with the measurements, 2d and 3d of each components?
Thanks in advance for your reply.
Accepted answer
Since it's university task, do it yourself. As for what to model, being at least 20 parts, choose an assembly.
Like a tool of some sort, disassemble it, grab some calipers and make the parts the same dimension.
Example of simple assembly: Vices of all sorts, bench vice, leg vice, woodworking vice, drill press vice, etc, or fixtures for lathes, or a bike hub (the ones with single gear and rear drum brake are complicated enough internally, but not too much), bike rim brake caliper, etc. Gearboxes, clutches, compressors, pumps, vice grips, cranes (engine hoists), car lift, car jack, ratchet wrenches (a torque ratcheting wrench has more parts), engines, valvetrain (valves, spring, cam, tappets, lockrings, guides, seat, etc),
Depends really what you have on hand. Do you have a bike? tool shop (lathe, mill, drill press, table saw, metal shear, ring roller, brake press, bandsaw, ? any tools?, car parts? Even electric tools?
Disassemble it fully and measure all parts in their critical dimensions with some calipers and an angle finder, ruler, etc.
I don't know how exact the parts must be to real, but i'm sure the concept is needed as modeling the features of parts and less about the actual size. You just round any dimensions with some calipers to nearest mm or half a mm if you know otherwise.
Depending of your skill level, try to stay away from plastic housings and injection molding plastics (like electric tools plastic housing), from sand cast items with cores and milling afterwards (like engine blocks, head blocks), cast items have lots of drafts everywhere.
The most simple parts to model are those made by cutting tools like lathe/mill. Example - diesel injection pumps have all parts made with cutting tools apart from the simple housing that is cast.
Now, if you know GSD and curvy pieces don't intimidate you can choose plastics, if you know draft angles and the separation plane is simple for a cast part then cast items are doable as well.
I teach CATIA as well and for such tasks I'm interested in how the student sees the features and finds a good approximation in catia. Also to ensure a good fit i suggest modeling directly in assembly design in context. The exact size is not relevant, the clean model is more appreciated. (don't try do design actual size of part with tolerances, do them nominal value, and loose fit or press fit is just annotated), also i appreciate if some students approach either a complex kinematic, or complex parts (with drafts, GSD elements, multi-section solids/surfaces), or a nice parametrization with formulas, etc.
In general, if you know something, show that you can by choosing a complex enough part that you can manage.
As for looking at ready made models, there are plenty in library. Look for those that look realistic. most of the times the assembly is good fit, and clean nominal values. Like this: Clamp Range 0 MM - 75 MM
5 Other answers
7 Cylinder Radial Engine - with Dimensions
Here I have a PDF. but not all dimensions are complete. It is extensive enough to be a project and sometimes challenging enough to find the dimensions on your own.
You don't really need the 'correct measurements' for each part. It's nice, but not necessary for what you've been asked to do. Just eyeball that #.
You can enter to https://www.mcmaster.com/ and download components in stp format. Design a mechanism, chose components and create your assembly.
Also you can develop something like attached picture.
For any one wishing to have a career in engineering being able to come up with an assembly as per this exam task, should not be that difficult. Get out a pencil and paper and make a list of simple machines and mechanisms that you understand how they work. Make a quick sketch of this and work out for yourself dimensions needed to fit parts together and to function correctly. If you can't do this yourself, engineering is not for you, change to an arts course, so you can drift along. party up more. and prepare yourself for a career in a fast food restaurant. Maybe if you have little of the imagination, creativity and work ethic required for engineering, a political science degree may be for you especially if you can talk for hours about nothing, lie easily, blame your failures on others and have a big self interest in power. Please, if you can't work this all out for yourself, get out of engineering as the profession does not need anymore engineers who don't understand how to make machines and mechanisms work
