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cnc milling

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oldschoolace:
Sounds like you know your stuff Peter, i may have to pick your brains at some point  :daumenhoch: The stem idea i have is pretty straighforward apart from one piece so machining would be minimal hopefully. I did wonder about materials but from what little i do know about metals there are more grades than you can shake a stick at.
Would a plastic stem be madness? - in one of the harder plastics like tufnol

Peter J:
Short answer is NO




Medium length answer is:

Although composites have, in some instances better liner strength than traditional materials you need to factor in “Product Life Cycle” this covers such aspects as stresses both cycled (pull/push) and twisting. Also these materials have a limited life....the first time its stressed it will retain 100% of its strength the next time it might me 95% etc etc until SNAP !!!

Products are designed with in parameters for example certain F1 parts are designed to last a race because weight/performance is a more important design factor than longevity and therefore engineered/designed accordingly.

 I’m not too good on composites but I would think that they would not react that well to this type of application because of the non standard loads this type of part would experience over its life span............not to mention crashed/bumps/scrapes etc etc

I know you can get MTB stems/bars made of carbon fibre but there are use/weight limitations

I have a 3D CAD package (Solidworks) with an FEA package (Solidworks Simulation) and I/we used to design some really cool stuff and it’s amazing how a little tweak here and there (not to mention material changes which then can impact on the design) and can make such a difference and to “Joe public” they would never notice a design change

http://en.wikipedia.org/wiki/Finite_element_method

oldschoolace:
Dude do you stil work in this field? if not thats some wasted talent right there!  :coolsmiley:

How about 3d printing a prototype then casting? I have just found an ace place literaly next door to my workshop that does laser cutting and 3d printing FOR FREE!!  :shocked:

Peter J:
On I sold up a few years back but I still have a play with designing stuff plus I sometimes help out with the machining/assembly processes

Once you’ve made your 3D prototype then you could get it cast.....however the for a stem this would be a longer more expensive process:

Make 3D Model

Get a Foundry to modify Model with feeder necks/run offs

The model would have to be cast using sand/resin to make the mold (a die would cost £1000’s)

They would probably use LM25 as this has the best machining properties and is a good “general” alloy to die cast with

The part would then need to go though the machining process discussed before

The best option would be to machine a stem from “bar stock” because with gravity casting the crystals of the aluminium are not aligned as well as say extruded alloy

I’m not going to bore you with crystal alignment or mechanical properties of aluminium

One of the clients we had was a non-ferrous foundry in Sheffield and I did 100’s of designs/produce analysis for them

Designs are normally a trade off between cost/function

Example: Rolex Watches are function/feature over cost Casio Watches are cost over function/feature

Peter J:
Oh and with any design/product you have to consider material/design harmonics  :smitten:


Classic example of bad design harmonics would be the Millennium Bridge (London)  :idiot2:
 

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