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PostPosted: Fri Oct 17, 2014 12:25 am 
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Joined: Wed Oct 23, 2013 9:55 pm
Posts: 110
I thought people might be interested to see how I designed and built a weight weenie spider for a Specialized S-Works crank. So, I’ve shown some photos and brief descriptions below.

I purchased a used S-Works crankset from this forum. It had the graphics removed and both the carbon arms and the aluminum spider had been painted black. I decided that I preferred to see the carbon weave so I stripped the black paint off the arms and refinished them with a gloss clear coat. I loved the new look, but now the spider looked a little rough so I decided to strip the paint off of it too. Underneath the paint, the spider was a bit scratched. But more importantly, I found the stock spider too heavy (60g) and rather ugly. I’m not a fan of the specialized twisted shapes, and I don’t like the combination of carbon arms and silver spider. So, I decided to design and build a new spider to reduce the weight and improve the looks.

First, I measured the original spider. Then I created a 3D solid model of the spider to establish a baseline for the new design:
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Then, I created a new design based on the original geometry, but changing the style to better match my Extralite chainrings:
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And I created a second design for comparison:
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I refined the two new designs and found that both of their masses were approximately 40g. Next, I compared stress and deflection between the three designs. I used a torsion load due to the chain tension, and a side load due to shifting gears. The design with the open holes had significantly higher stress and deflection. That design would be much easier to machine, and I like the looks of it, but I decided to go with the stiffer design.

Next, I programmed the CNC mill to create the design:
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And machined the part:
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The part after machining:
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I polished everything except inside the pockets:
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Then black anodized:
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Final mass is 38g, compared to 60g for the original (sorry about the fuzzy photo):
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Here it is mounted on the crank and the bike:
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Total mass with bearings, shields, wavy washer, and chainrings is 535g.
I'm very happy with it. I think it looks much better and it's dropped a little weight. I've only just got it on the bike, but so far everything works perfectly.


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PostPosted: Fri Oct 17, 2014 12:45 am 
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Joined: Tue Aug 02, 2011 9:20 pm
Posts: 1626
Location: New Zealand
That is awesome! Brilliant work and only 1 gram heavier than the compact spider that Lightning make for their cranksets of the same design

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2012 BMC SLR 6.02kg http://weightweenies.starbike.com/forum/viewtopic.php?f=10&t=110390


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PostPosted: Fri Oct 17, 2014 1:35 am 
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Joined: Wed Oct 23, 2013 6:58 pm
Posts: 42
Location: Western Pa
Props


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PostPosted: Fri Oct 17, 2014 1:59 am 
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Joined: Wed Oct 08, 2003 4:15 am
Posts: 3301
Location: tucson
Did you do the 3D modeling in solid works?


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PostPosted: Fri Oct 17, 2014 2:13 am 
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Joined: Thu Jun 28, 2012 10:52 pm
Posts: 218
Location: eNZed
BEAUTIFUL!

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PostPosted: Fri Oct 17, 2014 2:29 am 
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Joined: Tue Jun 05, 2012 1:57 am
Posts: 52
Any chance you could make and aero model ? Something that works with praxis rings?


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PostPosted: Fri Oct 17, 2014 3:16 am 
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Joined: Fri Oct 05, 2012 3:52 am
Posts: 590
You should sell these.....

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PostPosted: Fri Oct 17, 2014 3:30 am 
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Joined: Wed Oct 23, 2013 9:55 pm
Posts: 110
The modeling was done in Creo and the FEA was done in SolidWorks.

An aero model would probably be easier to machine overall, but the shape would be a little tricky under the arm - I think it would need a little extra clearance there.


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PostPosted: Fri Oct 17, 2014 4:19 am 
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Joined: Sat Aug 29, 2009 4:30 pm
Posts: 1915
Awesome job!


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PostPosted: Fri Oct 17, 2014 5:00 am 
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Joined: Wed Nov 21, 2012 11:01 am
Posts: 2
Incredible work.


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PostPosted: Fri Oct 17, 2014 5:36 am 
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Joined: Thu Aug 21, 2014 6:24 pm
Posts: 47
Location: Phoenix, AZ
Those are beautiful!

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'14 SW Roubaix / '16 Allez Sprint


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PostPosted: Fri Oct 17, 2014 10:17 am 
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Joined: Thu Jan 12, 2006 5:58 pm
Posts: 571
Location: Surrey, UK
Good effort, that looks great!


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PostPosted: Fri Oct 17, 2014 2:32 pm 
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Joined: Wed Jun 08, 2011 6:08 am
Posts: 565
Every man's dream is to be able to do just this sort of thing in his garage. Very nice.


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PostPosted: Fri Oct 17, 2014 3:35 pm 
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Posts: 222
Location: Bremerton, WA
Lovely work. As F45 said, this is exactly the sort of thing I wish I had more time and money for. Do you own the CNC mill, or do you have access to one at work/school?

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PostPosted: Fri Oct 17, 2014 4:19 pm 
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Location: Stockholm, The Arctic...
Pro!


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