A journal following the history, design, construction and operation of Bernard Kempinski's O Scale model railroad depicting the U. S. Military Railroad (USMRR) Aquia-Falmouth line in 1863, and other model railroad projects.
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January 27, 2021

Is 3D Printing Scratch Building?

This question has come up on some modeling forums in which I participate.  The immediate follow up question is, "who cares?" Well, some people do, especially when it comes to contests for model builders.  The NMRA is not alone in hosting modeling contests. In fact my impression is that plastic scale model builders and figure painters are even more focused on contests and awards than the NMRA.

A similar question arose when digital photography became available. At first the film advocates argued against digital photography in contests. Now, 15 years later, film is dead and no one thinks twice about digital photography. I suspect the same will happen in model building.

The NMRA has addressed the subject of 3D printing in its requirements for Achievement Program judging.  From the NMRA website

The term "scratchbuilt" carries the implication that the builder alone has accomplished all of the necessary layout and fabrication which establish the final dimensions, appearance, and operating qualities of the scale model.  This definition does not prevent the use of any tools or jigs as long as the builder alone has done the work necessary for the tool to make the part.  This would include drawings or computer files to control CNC, automatic lathes, laser cutting machines, 3-D printers, and other tools.  If a third party changes the builder's inputs, then the parts are not considered to be scratch built. 

Meanwhile, other modeling contests have taken a different approach. For example, The rules for the  Bandai Hobby Open, a modeling contest for models made using parts from Bandai kits, says, "a part which is made by 3D printer or 3rd party resin will be not judged." Now this may be because they are trying to promote the use of their own kits, though they will allow, "scratch built parts." So clearly they lump 3D printing in  the non-scratch built category.

If you frequent modeling forums you will see a split opinion on whether 3D printed parts can considered be scratch built. For example, one fellow made an interesting point that it is much easier to make a perfectly symmetrical part when 3D drafting and printing, so called additive machining, than by traditional subtractive machining. OK, that might be true. So what. Use the right tool for the job I say.

I view 3D printers, laser cutters, CNC milling machines, computer controlled paper cutters simply as additional tools in the model building arsenal. If you start with raw materials, you do the design work,  and it becomes a part, then it's scratch built. If you buy a 3D printed part, or you download a stl file to print on a 3D printer, then that is not scratch building any more than buying a commercial injection molded or cast part would be.  That pretty much is in line with the NMRA guidelines.  

I suppose one gray area might involve a person that designs a part, but has a commercial house, such as Shapeways, do the printing. That might not meet the NMRA guidelines.  I know from my own experience that printing the parts on your own machine can take a fair amount of experience and skill. 

3D scanner in action
I am not sure how 3D scanners fit in this category, as those seem to be more like a copying process. But, I suspect there is a lot of art and skill involved in making a useful 3D scan that can become a 3D printed part, so I will remain open minded on that. I read that the new iPhones can do 3D scans, so the technology is becoming more and more available.

Kit bashing is a gray area that lies between scratch building and not.   The NMRA allocates a variable number of points for scratch built content in contest or judged models, so they recognize there is a continuum is this area. Furthermore, the NMRA did adapt their AP requirements to allow super-detailing, especially diesel models, as an acceptable way for a model to gain points in their scoring system.  

In conclusion, this is not an question that I get too worked up about. I do find it an interesting subject and thought it worth some discussion.  I am not a big advocate of model contests in general due to the great amount of subjectivity it involves. I think the NMRA merit system is actually a pretty  good approach. 


  1. I think the issue at hand is "What happens when technology disrupts our notion of skill?" 3D modeling requires a completely different skill set than the traditional, time-honored cutting, shaping and gluing.

    The immediate bias is that the new method is in some way "cheating". I think that's because most people have experienced the time-honored methods and understand how much effort those take while the amount of effort to design a 3D model isn't as well understood. Both require measuring, planning and techniques to generate the shapes involved. The opportunity cost with the time-honored methods is much higher...make a mistake there and you either have to start over or employ a different technique to cover your mistake. With 3D modeling, hitting "Ctrl+Z" will usually get you back to a good spot.

    Eventually, as with digital photography, I don't think this distinction will matter. But that will likely be because the new technology has displaced the old methods to the point that we don't judge the old methods so much anymore. And you've already identified (correctly, I think) 3D scanning as the next disruptive technology to our notion of skill.

    Great post!!

  2. I think also with Bandai; it's the commercial possibility of the part, even if you've only printed the one yourself, it could be seen to have the potential to become a 'rival' product, which is a fair shout in a manufacturer-specific competition? On scanning; a mate and I spend days trying to scan a 54mm figure back in 2012 with no luck at all, a vague cloud of points was obtained momentarily, but nothing usable!