Designing a Diesel Shell? Print Sill/Walkway Separately!

[C855B]

Justin @MRLX1020 and I were chatting this evening about my upcoming Briggs Models RS-27 kits. He voiced a concern I also had with the "aftermarket" conversion kits emerging with the proliferation of 3D printing - diesel shells printed as a single piece.

This makes painting very difficult, especially schemes where the color breaks between the hood and the walkway or sill. F'rinstance, I destroyed a Shapeways shell beyond recovery trying to paint a very complicated walkway transition from the body. The otherwise working chassis has been on the bench for over a year now, awaiting the courage to finish painting the replacement shell. And there are two more to go. 

Anyway... our advice to our intrepid 3D model designers: with hood units, follow the design style of the major manufacturers - body, and walkways and sills need to be separate castings (i.e., prints). Use alignment tabs. It's not important whether they're a snap, friction or glue fit, just give us the opportunity to paint complex color breaks before assembly. And, generally, bear in mind that inclusion of certain bits integrated into the main assembly such as railings or grabs may work against a quality finish.

[Iain]

This and this and this again.

[JMaurer1]

There just might be a reason that the major manufacturers do it this way...just a thought.

[peteski]

There just might be a reason that the major manufacturers do it this way...just a thought.

And they didn't do it that way originally. One that sticks out in my mind is Bachmann SD40-2. The Arnold Geeps too. One-piece shell and walkaways.  I'm sure there were many other examples.  But they have later figured out that it is better to separate those two items.

[narrowminded]

There just might be a reason that the major manufacturers do it this way...just a thought.

There is.   At least two big reasons.  Machining the molds is one and then getting the parts out of the mold is another. 

3D printing can do one piece because it doesn't need a clear access to machine the molds or a clear exit to release the part BUT it often has support issues and then access to remove those supports that are somewhat captured and then, if all else works, clear access to clean up those places.  But 3D also has the option of breaking the assembly into as many pieces as you want and where it makes the finish work easier there's little reason not to.  That's kinda' the point of this thread, yes?

When doing the drawing virtually all of the details can be saved as components or groups and as such, when it's time to prepare the file for the printer (slice it) those pieces can be inserted in the file or left out and can also be selected to make individual files (sliced) for individual printing.  Bottom line, there's little reason that I can think of from a printing standpoint not to break the print down any time that it makes life convenient at the later steps.  

IF a part is crazy tiny there can be reason to try to leave it attached just from an individual print support standpoint but that's about the only thing I can think of.