The Schwinn City Portable Urban Velo is the latest in a long line of high-quality concept bikes from Cycling Sports Group (CSG).
It took just four months for the bike to go from a series of sketches to a fully functional working prototype
With the help of Bristol based Amalgam Modelmaking it took just four months for the project to go from a series of sketches and a loose description to a fully functional working prototype. And in September 2012 it made its debut at the Euro-bike show in Friedrichshafen, Germany.
CSG had a clear idea of the qualities the bike needed to have but turned to Amalgam to incorporate all these points into one functional working prototype.
The brief was for a quick folding city bike targeted towards the female customer with many innovative features including a quickrelease mechanism for shopping basket or child seat, built-in stand and lock, self-centering steering and much more besides.
Starting softly
From the outset it was clear that this would be a major project.
Before producing the fully functional ride-able prototype a ‘soft’ version was mocked up to evaluate and test the various innovative features such as the folding mechanism, built-in stand and lock, plus giving CSG’s design team a chance to see and evaluate the whole package in a physical form.
Much use was made of Fused Desposition Modelling (FDM), CNC machining and good old traditional model making skills, which is still the only sensible way to economically interpret pencil sketches into a working model without a lot of specialist (and costly) computer time.
As this first ‘soft’ model came together the various components were assembled in front of a full-size print of the original artist’s impression allowing everyone to see progress, brainstorm and troubleshoot in real time.
Meanwhile, regular trans-Atlantic communication and a couple of carefully timed visits kept everyone abreast of progress.
Moving into metal
Once completed the initial model was used one last time as the focal point for final decisions before starting into the more durable metal version.
Sketches became proper 3D CAD using SolidWorks, plastic tubes and sections were replaced with aluminium extrusions and machined elements – both three and five axis, plus some more traditionally machined parts.
Alongside the latest technology Amalgam is keen to retain more traditional skill sets and recognises that automation, while playing an ever-increasing role, should not always be the automatic choice.
That said, for the Schwinn City, it was decided to produce the wheels using SLS, supplied by Amalgam Modelmaking’s friends and colleagues at 3T alongside a hand made wicker basket and hand stitched leather handlebar grips and saddle.
Amalgam’s specialists then welded together all the metal elements, assembled the mechanisms and included the very few bought-in parts (drive train and tyres), gave the frame a lustrous high-gloss teal-coloured top coat and applied Schwinn’s logos and pinstripes from computer cut vinyl.
Signed, sealed, delivered
The completed bike was then packed into a lockable, reusable airfreight case custom fitted out with shaped foam packing for its journey to Eurobike 2012 and beyond. 
Amalgam Modelmaking enables Cycling Sports Group to produce a functional bike prototype
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