MicroMimesis

Micro + Mimesis
From Wikipedia – “Mimesis (Ancient Greek: μίμησις (mīmēsis), from μιμεῖσθαι (mīmeisthai), “to imitate,” from μῖμος (mimos), “imitator, actor”) is a critical and philosophical term that carries a wide range of meanings, which include imitation, representation, mimicry, imitatio, receptivity, nonsensuous similarity, the act of resembling, the act of expression, and the presentation of the self.[1]”

Micro is a word that comes from the Greek μικρός (mikrós), meaning “small”. It can be used to indicate a smaller than average scale (microscopic scale), as opposed to prefixes mega and macro, which can be used to indicate a larger than average scale.

Combining the two gives (shrugging here) – Greek: μικρός μίμησις (mikrós mīmēsis) which I translate (tongue in cheek) as “small mimicry”.

1. ^ Gebauer and Wulf (1992, 1).

MicroMimesis
MicroMimesis then is the name I chose for my website I will use to sell small mimicries.

I was updating a .stl file earlier and realized that I had forgotten what scale I was working in .. and the reasons behind some of the design work. This is much like when you go back to look at some code your wrote six months ago and have to work your way though it step-by-step to see what the heck you did! In the programming world this is where you are told .. “Comment .. Comment .. Comment” .. and “Comment”.

So. This is going to be my “Comments” on my various projects – a place I can refer back to.

Measurement Systems
Sketchup Modeling Info Screen

Sketchup Modeling Info Screen

When working in Sketchup you have wide choice of what system of measurement to work in.

You can choose Architectural, Decimal, Engineering and Fractional. Normally I work in Decimal Inches since this what i am used to. I can’t “think” in metric. (funny thing about that – estimating distances I think in meters. I learned that as a Gunner on an Abrams tank. I’m sure that says something about my mind .. probably not very complimentary)

Most of the time the unit of measurement doesn’t matter that much. If I am working on a building it makes sense to use Architectural since that just ‘works’ with buildings. Otherwise I normally use Decimal Inches. The problem comes when working with small objects such as O scale items.

Drawing small radii
Minimum Radius: Sketchup refuses to draw a radius smaller then 0.018″/0.455mm. The problem is that I am working in O scale. A 0.018″ radius in O scale (1:48) is .865 inches. That means that I can only make a circle that is 1.728 inches in diameter or larger.

A reasonable person might ask why I wanted to do this anyway. If for example I want to draw a 3/4″ nut why not draw it full-size? Well .. if the need is just to draw that 3/4″ nut then sure, I would draw it full size. If the intent is to create that nut in 3D and attach it to a surface of an object so it can be 3D printed .. then I have a problem as Sketchup will not draw a radius that small. What to do?

Scaling: The answer is to make the object larger then scale when finished. Sketchup doesn’t have a problem scaling down. Example: Let’s take that 3/4″ nut as an example. That 3/4″ measurement is taken across the flats. This is strictly speaking a 1/2″ bolt that a 3/4″ wrench fits .. but that’s beside the point. The measurement across the corners is 0.866″. This is the important dimension since when Sketchup is drawing a Hex – it is simply a circle with six sides and a radius of 0.433″. If we divide 0.433 by 48 (O scale) we get 0.009″ .. which is below the smallest radius that Sketchup will draw. Oh woe!

Side Note: When designing for 3D printing you also have to keep in mind the minimum size printable. Shapeway’s FUD (Frosted Ultra Detail) has a minimum detail of 0.1mm/0.0039″. It doesn’t make much sense to design something that can’t be printed (although I suppose designing for the future when it CAN be printed might make some sense)

Larger then Smaller: One way then would be to draw the bolt 10x larger – so the radius would be 4.33″. Now, the bolt would have a 7.5″ measurement across the flats. When finished you could simply scale the bolt so that 7.5″ is now .75″. That works. The problem is that I constantly have to move the decimal point. Not THAT big a deal but still there. There are other considerations such that Sketchup exports in inches .. no matter what system of measurement you are working in. Depending on the system of measurement and what file type is exported can cause problems.

Pmm
My solution I am going to call PmmPseudo-MilliMeters ….

  • I model in Sketchup in Decimal Inches – but use MilliMeters to measure the object I am modeling
  • Let’s use that 3/4″ nut as an example. I need to draw a hexagon (circle with six sides). Convert that 0.433″ radius to MilliMeters – 0.433″ x 25.4mm = 11mm.
  • Remember, I am using Decimal Inches in Sketchup. I draw the nut with a 11″ radius. No problem of course.
  • Here’s the reason behind the madness. When I export a 3D mesh to upload to Shapeways to print, I end up with a .stl file. STL (file format) is also known as Standard Tessellation Language. This file format is supported by many other software packages; it is widely used for rapid prototyping and computer-aided manufacturing.
  • This format does not contain what unit of measurement was used. It only uses .. units. Our 3/4″ nut would be represented within the .STL file by the X/Y/Z coordinates of each vertex of a triangle. What this means for uploading to Shapeways is that this nut is 22 UNITS across the flat. Not inches, feet, miles, meters, millimeters .. but units (of measure).
  • When you upload a file to Shapeways they ask you .. “What unit of measure is this?”. I simply say .. “MilliMeters”. That 22 ‘units’ within the .STL file are then assigned by Shapeway’s 3D software as MilliMeters .. and everything works fine.
  • This works for me – and is the system I will be using in these ‘notes’

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