Design Cycle - Tutorial

Design Cycle

Right firstly I must admit in reality I didn’t follow this Diagram. I did a sketch knocked it up in CAD did a 2Ddrawing and started machining. Then went back and filled in the gaps for this article. but.. had I not got carried away and played by the rules no doubt the out come would have been better! (also worth mentioning this design cycle misses out some stages that would be present in industry as it’s a one off and I’m the customer.) Anyway its useful to have a bit of a road map as short cuts often lead to dead ends…

Project Planing

SWOT

SWOT (Strength, Weakness, Opportunity, Threat) analysis Looks boring… but I actually find it quite fun to do as it is basically about day dreaming your way though the project. simply use the headings to help prompt a list for each section. Constraint/Criteria It’s important to know your limitations and aspirations, or your end up no being able to make your design or making something that doesn’t do what you wanted. Constraint: Lathe only (no milling), Small selection of cutting tools, Fit stem/steered except standard bolt. Criteria: Look Rad, Light weight, challenge my machining skills. I should probably mention Gantt charts but I’m not going to use one as I have no deadlines! but should I have a bike race in 3 weeks time that I absolutely need a new top cap for it then it might be a good idea… (some info on them here: Gantt chart)

Sketching

Sketching: Rendering, Hand drawing, thumbnails sketch, call it what you want, its one of the fastest ways of getting your idea across to someone else, or helping you to visualize your idea. I’m Far from the best Sketcher/Renderer but I’m good enough to get by, If its something you want to get better at practise make perfect the more you do the better your get and there are lots of good YouTube tutorials that can inspire/help (my advice is everyone can sketch it just takes practise and learning a few tricks, there’s no such thing as cheating with design use rules, guides, underlays, copy paste, and Photoshop it until your happy.) (FYI Render is a posh way of saying colouring and if your in the US Colouring is an English way of saying Coloring So down to business! A top cap is essentially a washer that helps preload your headset and stem to the steer tube on your forks. so basically it doesn’t need to be much more than a flat bit of something with a hole in the middle for a bolt to go though which is ridged enough to not bend when tightening, you could actually remove it once the stem bolts are tighten up, but for safety leave it in, open ended tubes go though the body like a knife though butter in a crash

Material Selection

Material selection Is a very important part of the product design process and has the potential to make or literary break a product. there are lots of things to consider when picking the material/s to work with. In industry its often about balancing cost with performance. its also a point of fashion for example, a headset cap could easily be made from plastic and do the job very well but customers prefer ‘sexy’ materials like carbon Titanium anodized aluminium. Cost is not only the material cost but associated costs how hard it is to machine will effect cycle time and tool wear, specialist handling requirements potential for wastage work with and handle. A carbon fibre frame is a good example, the material its self is relatively cheap but everything else adds up.. raw material needs to be stored in a fridge[equipment energy], made from hundreds of individual cut parts [time to cut challenging to manage], all parts are laid up by hand [labour intensive however low skill], moulds are expensive and different moulds are required for different size frame [not very flexible], needs baking [time and energy], cleaning up/finishing [generally involving manual labour] All this aside its Light, Strong, High performance, Distinguishable and Desirable! Back to the top cap and using my lathe.

3D CAD

3 Dimensional Computer Aided Design. In the design to manufacture setting it’s about producing a dimensionally accurate virtual model of your design. This model can then be used to drive a 2D production drawing and also be saved/converted to a file type that can be used by CNC (Computer Numerically Controlled) machines or 3D printers. There are lots of different 3D CAD Software out there my experience is with Solidworks and CATIA V5. I’ll primarily be using Solidworks. Why use 3D CAD? although at first it may seem that it takes more time to design product in 3D it most definitely saves time in the long run by reducing trial and error, number of prototypes, flagging up problems earlier, work more efficiently, improve quality and can enable design automation. among many other benefits, from experience the more time and effort you put into the CAD design stage the more benefits you will get. So for the top cap the 3D model is made up from a simple profile sketch with a solid body revolve applied to it. (like most parts designed for making on a lathe) I’ll leave it at this for now and not go into too much depth here as this is a big subject, that ill cover it in more depth in future.)

FEA

“Finite element analysis (FEA) is a computerized method for predicting how a product reacts to real-world forces, vibration, heat, fluid flow, and other physical effects”- I’m not an expert in anyway with this but intend on learning more. as its a powerful tool. what I do know is the quality of results you get from FEA is completely dependant on the quality of information you put in. I didn’t spend much time with the FEA on the top cap for a few reasons, [1] I was confident it would work, [2] I don’t know much about it. [3] The real world forces involved with a top cap are actually quite variable due to the friction between the bolt and the cap.

3D Rendering

One of the advantages of 3D Cad is the ability to produce photorealistic images based on the model. there are lots of different rendering software that can do this. some 3D CAD software will have a render built in. Some software uses a graphics card/s to do the calculations that create the images (GPU) and some that use your computers processor (CPU) I’ll be using Keyshot its a separate stand alone CPU based software, from my experience it is fast to setup and pretty quick to render (its weakness is more when it comes to complex animation) This render including setup took about 5mins: Import assembly, assigned materials, add texture bump to cap, select a spherical HDRI environment, Set environment to light source only, Set ray bonces & Hit Render!

Production Drawings

Production drawings, engineering drawings or orthographic projections, there a 2 dimensional way of showing a 3D object. No doubt Wikipedia will be better explaining this than me! so read this. There are 2 different ways of arranging the 2d projections called 1st and 3rd there both correct and the only important thing to remember is to put on the drawing and if reading a drawing check which method has been used. here in the UK we are the stepping stone between the US and Europe so it pays to be flexible. first angle.(Europe (UK)) 3rd angle (USA Canada (UK)) I will be (mostly…) drawing to the BS8888 standard (3rd angle). – but as you have to pay for a copy of the full standard (which is ridiculous IMO) I’ll no doubt make mistakes. The process of producing a drawing from a 3D part in Solidworks is simple and linked (i.e. the changes you make in the 3d will update in the drawing.) that said from my experience producing ‘high quality’ production drawing can take more time than the 3d work, even with all the productivity advancements within Solidworks. but its time well spent. I’ll cover the process of producing drawings in more detail in the future.

Manufacturing/Machining

Manufacturing and machining is at the heart of this website and is the area I will try and focus most on in the future, it’s also what I have the most to learn about myself. so I wont say much here. Prototyping is key stage in the design cycle that I have missed out, this is because essentially anything I will be make is more of a prototype than a production component. For the top cap I first faced off the raw bar and then drilled the hole for the top cap bolt. Then I used a boring bar tool to machine out the recessed pocket for the cap head to sit in. After this I machined the upper surface of the top cap angling the ‘top slide’ to give the correct angles. I then machined the lower surfaces of the top cap in a similar way and ‘parted off’ the top cap from the stock de burred & fitted to bike!

Testing

Time to reap the rewards of the hard work. To be honest if you made it yourself chances are it can be pretty lousy and your still love it! I have been using the top cap on my bike for over a month now and it’s worked faultlessly and it’s great to look down at it on a hard climb and think 'I made that!'

Evalulation

Well on the whole I’m really happy with how the cap turned out but if I had to be critical I would have preferred to have achieved a tighter tolerance on the pocket for the cap head bolt (but my boring bar was a bit big.) and the tool chattered a little bit at the deepest point of the top surface. From a design point of view it fulfilled my requirements but it’s not suitable for multiple production as created lots of waste, took quite a while to machine and it’s more complex and heavy than required.
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Well there you go, and well done if you read down this far… I’ll go into greater depth in some of the more interesting areas in future components. Sorry if this article was a bit dull in places but I thought it important to cover as much as possible.