GOAL:Take detailed measurements of the electronics parts to be inserted into the watch base and create an accurate 3D model that matches its real world counterpart when produced by the intended desktop 3D printer.
The first (often overlooked) stage for the design of a 3D enclosure, model, or bezel: measure your electronics and create a digital "dummy" object that is an accurate match for it's real world counterpart.
The creation of dummy objects is a long-standing tradition from the world of fashion, craft, and industry -- typically used to optimize how multiples of an object will be assembled. This process has added relevance to the digital designer within the wider open source / open hardware culture of today:
- Make use of the efforts of other people who have tackled these components before you.
- Share back digital models to help others print and tune your project for other, novel purposes.
- Why should anyone recreate the wheel when they can make a better functioning, better looking wheel by studying the wheels of others?
Research Available Measurements ("Cheat")Depending on the electronics components you want to enclose or mount, there may already be resources available online to help you speed up this stage. There are benefits to hunting for existing models: you can test and report back whether the model is accurate enough and you can meet designers who are also working with the components you selected -- an opportunity for exchanging models and getting feedback.
Great places to hunt for resources:
- Product datasheets and tech specs.
- Thingiverse and other object repositories.
- Project pages for the PCBs -- including resources such as Fritzing.org where vector models are necessarily accurately scaled.
- Electronics component suppliers.
When you are done with the process of measuring your components and making your dummy part(s) -- you should strongly consider including your dummy object with the community as well as your final model.
Creating Orthographic Projections (The Three Views)One handy time-tested approach to capturing accurate model data is to take measurements and sketch out the top front and right sides of the object as "orthogonal views" (ie eliminate the foreshortening ).
- If it is helpful, do all six views (think in terms of all of the faces of 6-sided dice).
- Isometric projections can be helpful, particularly for recording references for how the elements match up. Performing them accurately is a real skill (or a keypress in expensive CAD software) but might not be necessary.
- Record notes about where parts of these views match up to each other.
- Plan in terms of the software's object snap options.
Plan for Insertion of PartsA cavity for your electronics is no good if you can't place parts in there.
Simplify Geometry to What Is RelevantSimplify geometry to what is significant for fit and mounting. Rendering all of the surface mount components will only increase the complexity of using your dummy as a boolean subtraction tool later -- account for a little bit of wiggle room and group a number of components together into a coarser block.
Plan to Accomodate Mechanical TolerancesThe amount of space between these two parts is known as the "enginneering tolerance" (http://en.wikipedia.org/wiki/Engineering_tolerance) and should be factored by the machine used to fabricate the part. Typically, this difference is determined by the thread width on x-/y- axes or the "resolution" on the z-axis, the factors that determine how accurately that element of the part can be produced.
You Are Making Two (Three) Digital Dummies, Not Just One
- The "first" dummy model is designed such that the machine that produces the model will fabricate a dimensionally accurate match for the electronics. (Keep in mind that most FFF desktop 3D printers produce objects that shrink by 1%-2% as they cool: the dummy model is designed to match its real-world counterpart after cooling/setting/etc.)
- The "second" dummy is a "cutting tool" that has been resized to carve away the cavity required to insert the "first" dummy object.
- It might be helpful to create a "third" dummy -- a virtual dummy positioned precisely between the object and and dummy cavity. Adjustments for this version could be made to suite any type of manufacturing no matter the threadwidth/kerf etc involved with manufacturing it by determining the engineering tolerances forced by the machine being used and creating new first and second dummies by adjusting the third dummy by the tolerance factor. Printing the third dummy wouldn't be helpful as it would tend to be too large to fit into cavities exported by the same design files.
- Print your dummy object and check it with accurate calipers.
- Does it match your model? Adjust until it does.