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Earlier this week, I appeared on MakerBot TV to chat with Annelise about how I use my MakerBot in my work. As a part of my job as a scenic designer, I create scale models of theatre sets.  Are you curious about how you might put a MakerBot to work on your scale project?  Want to hop on the playsets bandwagon? I’ve put together a short blog series about getting started working in scale.

This week, we’ll learn about scale factors and use a bit of miniature math to consider what scale to work in.  Stay tuned for more in coming weeks!

Choose Your Subject

There is a huge variety of scale model and miniature genres in the world.  Seemingly every mode of transportation is represented: spacecraft, trains, cars, ships, and military vehicles.  There are also buildings, houses and structures of all kinds.  Don’t forget scale favorites from the toy and games market: from wargaming to minifig to Barbie, there’s a scale for everything.  I was a little shocked myself at the sheer number of scales on this list at Wikipedia. You might choose to work in a common genre, or dream up a new idea.

The reasons for creating a scale models are varied. For a new 3D enthusiast, modeling common objects is a great way to practice CAD skills.  Hobbyists create models to examine how things work, to experience a different time period, or create a dream world. Various trades use scale models to analyze designs, and show clients a dimensional representation of a finished product.

Thing About Scale Factors

After you’ve chosen a subject, choose a scale to work in. Miniatures have a specific relationship to the real world that is described in a scale factor.  Scale factors are conveyed in a variety of ways:  1:24, 1/24, and 1/2” = 1-0” are all expressions of the same ratio. This ratio states that one unit in your scale model represents 24 units in full scale.

You might already have a scale in mind, as there are standards for a variety of hobby and trade specific model genres.  If you are uninitiated in the miniature world, do some research before you get started. If you choose to work within an existing standard, you will be able to utilize commercially available products, or the work of other Thingiverse users.

Think about your subject matter.  How big is it in full scale?  How small are the smallest details?  The answers are very different if you’ve chosen an airplane instead of a chair.  You want to choose a scale that will allow the right level of detail, but fit on a MakerBot’s build platform, whether in a single piece or many.   We’ll do some miniature math to think about the properties of a 3D print in the context of a given scale.

How Low Can You Go?

Capturing small details of an object is one of the most important  parts of creating a successful scale model.   The accuracy of 3D printing is increasing, but there will always be a limit on precision of a print. Let’s figure out what details can be printed with a MakerBot.

What are we looking at?

For this example I’ll use 1:18, which is the scale of choice for the MakerBot Rocket & Fairytale Castle Playsets seen above.  Most 3D printers software uses millimeters and the metric system, so if your brain already operates in metric, thinking in scale is very straightforward.

1 mm :18 mm
This means that 1mm in your scale model represents 18mm in full scale

Many of us find it difficult to think about the world around us in terms of the metric system, so let’s also convert to inches.  The conversion factor from millimeters to inches is .0394, so multiply our full scale distance by this value.  If you ever need to go the other way, use a conversion factor of 25.4.

1 mm  =  18mm x 0.0394
Therefore,
1 mm : 0.71 inches
This means that 1mm in your scale model represents .71 inches in full scale.

Consider your 3D printer

Two limiting factors for details on a 3D printer are thread width and towering elements.  A single line of plastic from the extruder, or thread width, is a little under 0.5 mm.  Towering elements are skinny vertical columns, and a printer’s ability to reproduce them without failing will vary based on make, model and the operator’s technical prowess.  With my Replicator, I can easily reproduce details between 1-2 mm with minimal deviation from the stock setup.  Older or less precisely calibrated models may only be able to tower 4 mm details.

What does this mean for a 1:18 scale model?  We know our 3D printer can create 0.5mm thread widths, and towering details 1-4mm in diameter. Multiply our previously calculated value by .5 to get the smallest printable detail in a given scale.  Multiply it by 1 to 4, depending on your printers abilities, to understand what size towering elements will be in 1:18 scale.

18 mm x .5 = 9 mm    or    0.71″ x .5 = .355″
18 mm x 4 = 72 mm   or    0.71″ x 4 = 2.84″

In 1:18 scale, the smallest details we can represent
will be approximately 3/8″ to 3″, or 9 mm to 72 mm, in full scale.

Try the same math for a dramatically different scale.  Wikipedia states that Star Trek toys and miniatures are often in 1:3900 scale.  The smallest details a MakerBot can reproduce in 1:3900 would be 12-50 ft.  Try out this exercise for the scale factors you’re considering to get a better idea of the precision you can expect.

How BIG Can It Be?

Thinking about size on the opposite end of the spectrum, there are two things to consider.

How big will your final assembled project be?

HO (1:87) scale train sets are a perfect example. These sets are designed so a track layout fits on a 4

Visit link: Makerbot & Miniatures: Thinking About Scale

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