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Learning how to build Lotus Seven replicas...together!
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PostPosted: January 26, 2020, 8:14 pm 
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I’ve done a couple of small scale CF projects and like the rigidity and incredible lightness of the finished product and been thinking how to make a complete chassis using CF. The first thing that jumps out would be the myriad of shapes and bends making it impossible to do it from one or two moulds.

So I thought why not for instance, build two side rails extending from the front to the rear suspension points, then a floor with all the various brackets and a centre tunnel, then a front bulkhead and a rear bulkhead and bracing. There are great adhesives to bond the parts but I’m not too keen on putting all the forces into shear and wondered, why not build the parts so they have male and female joints ala, LEGO blocks putting the joined forces into tension and compression.


Your thoughts please?


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PostPosted: January 26, 2020, 11:39 pm 
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My first thought is that you will have more time and effort into the several molds than building the car.

CF strands do not 'Flow" well into complex shapes, they resist corners, pulling away from the mold.
Strand orientation and avoiding voids are very important to final strength characteristics.

I want to do a CF chassis for one of my projects, but co$t dictate that if I do a monocoque it's going to end up being plywood.

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PostPosted: January 27, 2020, 11:55 am 
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RichardSIA wrote:
CF strands do not 'Flow" well into complex shapes, they resist corners, pulling away from the mold.
Strand orientation and avoiding voids are very important to final strength characteristics.

As part of that, CF really gets its great strength specifically from the individual strands that are in tension. Every bend in a fiber is a reduction of strength. I don't see how you would make the male/female features themselves without adding complexity to the strand path. So while the joint design may be a bit stronger, it may be making the joint features substantially weaker.

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PostPosted: January 28, 2020, 7:40 pm 
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Thanks, great inputs. This what I’m hoping to do. The LEGO idea was a method for joining but may be over complicating things. Page 41
http://www.mate.tue.nl/mate/pdfs/10019.pdf


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PostPosted: April 24, 2020, 9:39 pm 
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see this lego go kart
https://www.youtube.com/watch?v=Ae7XLg3RFWY

https://www.youtube.com/watch?v=9af8c2zHGqw


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PostPosted: April 27, 2020, 7:45 pm 
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Going back to the first post, why are you reluctant to put glued joints in shear? I haven't chased down the numbers but a quick reference to Gougeon Brothers (WEST System epoxies) publications indicates that shear loading is their preferred orientation for glued joints. Joint configuration is typically designed to maximize shear area for glue, not minimize it, and to avoid peeling loads.

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PostPosted: June 25, 2020, 5:49 am 
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I would probably do something like this -> https://www.slideshare.net/ThomasAyres/ ... eport-2010


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PostPosted: June 26, 2020, 9:37 am 
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I'd probably first want to see or personally do testing beyond what that Formula SAE paper described. The strength of the material was well established, but strength of the construction technique was not. Perhaps there's other established info on the strength of the folded joints?

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