Re: CAD library

Dave Nelson

I’ve been doing 3D Cad for rail sims for almost 10 years now, starting from complete ignorance to being quite proficient in Sketchup.   I have a library of components that I often reach for so I think I might have something useful to contribute to this discussion:


First, You do need to know about manufacturing tolerances but don’t get hung up on how the components in the library will become physical objects in your hands.  Shapeways is here today but tomorrow there might be three other superior service companies, each of whom do things differently.   Given that, my recommendation is the 3D models should be done 12 inches to the foot and cataloged in your library as such.  When somebody wants a model, they get a copy and make any and all adjustments for scale and manufacturability then.  If that modified model goes back into the library it should do so as having been scaled and/or modified for manufacturability by XYZ Company.


Second, experience will show only a few things can be reused w/o further adjustments.  Consider your basic Z bar used on STMFC: It’s a standard profile but not a standard length.  Actual length and where the holes get drilled for those standard sized carriage bolts will vary from car to car and so it’s better for the master model to be a very short Z Bar and expect all individual modelers to stretch it out to and apply those bolts to be correct for the one car.  Really now, what’s the use of cataloging a 9ft, 10.5” Z bar w/ bolts when what you want is 9.25 inches shorter?  The same thing is true for car ends – you need the corner done right, the transition from the corner to the standard corrugation done right… but the length of the standard corrugation is specific to the width of the car, right?  So the end user should do that last step.  Ditto for door corrugations.  The same issue applies to car roofs only it is the slope that needs to be set by the final modeler as slope depends on the width of the car.


With that in mind you’ll find that having a library of period shape standards per the specs of various US Steel firms to be very useful – C channels, Z bars and so on.  Get a 10” C channel section and pull it out to the correct length for you side sill, and so on.


Crossbearers etc., are a tiny bit more problematic as you need to move more points to pull the length out to fit your car but that’s an issue to understand w/ your CAD tool and not an inherent problem with a library.


That said, there is still a great need for custom work… maybe not so much w/ STMFC but if things branch out into architectural models it’s a whole ‘nuther set of issues and components.


Castings almost always turn out to be a one-of tho I suppose you can fake it w/o great loss… one Miner Door Lock from the 40’s looks like most.  Striker castings are, in my experience, a royal PITA but again it might be that having one is good enough for everyone.


Pipes and bars are trivial to create so there really is little need to catalog those in a library.  OTOH an assembly of such items would be useful so grab irons, ladder steps and styles, and any number of side sill steps should go into a library.  Ditto for typical brake equipment.


Hope this is of some use.


Dave Nelson


From: STMFC@... [mailto:STMFC@...]
Sent: Wednesday, August 20, 2014 9:38 PM
To: STMFC@...
Subject: RE: [STMFC] Re: CAD library


Most useful to the modeler would be to have a library of shareware solid models in one of the common CAD interchange formats; DXF, IGES, or STEP. Most CAD software will import at least one of these formats, and the solid models become available for unlimited modification, with a new STL file exported only for printing. This could allow good parts to get better; multiple variations could become available because only the work to do the modification need be invested, rather than modeling the entire part all over again. On the other hand, good parts may become corrupted, as people make changes without checking their data, and of course, everyone who contributes would feel that the commercial guys were using their work without compensation, whether that was true or not.
This could get interesting.
Dennis Storzek


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