Heavy Metal! Part Deux - The Carbon Copy

[dedyplay]

The last build is the stuff of legends!

[Jonny042]

Originally Posted by dedyplay

The last build is the stuff of legends!

Thanks! I've got lots of interesting plans for this next one, I'm hoping to speed the development of the carbon parts a bit so I can share something that's of more interest, especially if pondering the minutia of resin shrinkage isn't as fascinating as watching paint dry or grass growing!

Back to the minutia: Like I mentioned I took quite a while to come to terms with this and even did some testing. I made a mold of a steel ruler to see what would happen:



And sure enough, once the ruler "popped" from the mold, it would no longer go back in the mold:



This mold was made under the ideal conditions for low shrinkage, with a relatively slow cure under a tightly controlled 20 deg C temperature. The shrinkage isn't massive, but it also isn't nothing. Over the 12" ruler it's somewhere in the neighborhood of .5mm. Still enough to allow the dimension of the decklid mold to end up with a dimension 1.5mm "off" of the pattern part.

I have not yet tested the shrinkage of the composite carbon/resin matrix when cured, but I suspect it will be very slight (if again nearly undetectable).

With all that, I decided to very slightly increase the size of the pattern part. More on that soon!

[dedyplay]

Yeah right.

[Jonny042]

So, to recap - if you take a mold from a part and the mold shrinks as it cures, the mold will be smaller than the pattern part (the one you're trying to copy).

If the resin you make the part from shrinks, the part you make from the already smaller mold will be even smaller.

Both of these factors are very, very, very small, but if you're trying to build a car and want to maintain tight, even, parallel gaps, even a single mm is going to wreak havoc.

So I decided it would be easier for me to add a small amount to the pattern part, rather than having to add dimensionally to the carbon part which isn't really easy to do. Then the parts can be fit to the car.

Singer does this (at least with their "classic" model) - the carbon body panels are made with intentionally small gaps which are then fit by hand to the individual chassis.

I did a bit of testing and figured out a way to add a 1mm strip to the edge of the decklid on three sides:



And went through the surface coat spraying and block sanding process again, and again, until it was perfect...again!





And finally made a mold, again!

[Focker]

Looking great, Jon!!

[chrisbalich]

IDK what's in the water up there, but I could use some.
Jonny, your determination and attention to detail is unmatched.

[Jonny042]

Originally Posted by chrisbalich

IDK what's in the water up there, but I could use some.
Jonny, your determination and attention to detail is unmatched.

It probably has something to do with the fact that most of the world needs to make ice.

For much of the year, we need to make water.

As always, thanks for the compliment! I sure hope this mold lives up to the promise!

[Jonny042]

I was (a few years ago?) truckin' along with the motor build, most of which involves rounding up the necessary parts and cleaning. I don't care for cleaning parts but I do enjoy looking for parts... as I get back into the project I'm hoping to be able to share something other than me pulling my hair out trying to make carbon parts!

These showed up from the other side of the Atlantic (if it's even still called that) a few days ago.

Originally Posted by Jonny042

Just closing the loop one these - I never did hear back from Rosepassion who could not get an answer from their supplier as to how their alu sprockets are made, or from what. Not really a very comforting feeling. Certainly they don't even look to be anodized.

I ended purchasing a full set of 6 sprockets and 2 drive hubs from a different source in the EU (they are made in a different part of the EU) and was able to get commitment from the manufacturer that they are 7075, with hard anodizing.

They showed up yesterday, and are darn pretty. And pretty light! From my measurements they will save a little over a kg (2.2 pounds).

Not only that, they are pretty hard. Brinell hardness of the anodized surface averaged 144, a small portion with the anodizing removed showed 138. This corelates to the hardness you should see with heat treated 7075.

The original steel sprockets (one from a 3.0, another from 2.7) measured today with the same hardness tester a value of 81 Brinell. I can't even find an example of a steel that would have such a low hardness. Even mild steel should be 120 or so.

A newer set of "OEM" sprockets that I previously tested had a hardness of 119 (going from memory on that one).





Cheers!

I've only been able to gather opinion on the longevity of these. The lone factual data point is from Grady Clay who worked on a motor that had them for 40,000mi but it's unknown the material construction of those. Possibly they were factory 935 parts that by the looks of it weren't hard anodized, although they could have been heat treated post machining but the amount of scratching on these makes me think they are a bit soft. Some 935 for sale in the classifieds in 2006:



As you can see I've done my homework, but homework was never my strong point... still, I'm going to follow the science and run these with confidence.

Many thanks to Brookieslayer for the help with the hardness testing!

[Focker]

I can't help but admire the attention to detail. simply amazing

[chrisbalich]

OOOOOHHHHHHH.
I like that.

[AG81]

Very very nice stuff.

[Jonny042]

Messing around when I should be working. What good is a prototype if you aren't testing it?





Of course there's a video. What my methods lack in sophistication, they make up for in relatability(I hope!):

https://www.youtube.com/shorts/he94OwHGVIc

[LJ851]

That’s impressive, Jonny !!
Nice work.

[Jonny042]

Sorry to bore with more sunroof stuff, but it's all I've got today! This one goes out to Cali tomorrow or the next day.

I've been trimming reinforcement from the layup in some places and adding it back in to where it can be used to strengthen and stiffen the part. I've managed to keep the weight down as I do this. I would like to trim an ounce off, though!



I'm also trying to get better and faster at the construction but the sunroof involves a lot of cutting, trimming to fit the factory hardware, and making of holes in various shapes and sizes:





I'm really pumped about the quality of the latest (hopefully the last!) mold. The surface of it it great. It's not so much the surface finish it's the lack of waves or ripples in the surface. This is bare carbon straight from the mold, no sanding, no clear coat!





Proudly made in The Great White North and comes with all necessary hardware. The graffiti is just silver sharpie and washes right off with wax and grease remover.

[Billiam 911 2.8]

Simply beautiful.

[AG81]

I would sign that stuff too.... well done Jon.

[Uwon]

Jonny, that is truly outstanding work. Beautiful result.
BTW, today I’m installing your carbon mini duck to Alberto.
Cheers,
Johan

[Jonny042]

Well that went well...



I'm continuing to strive to make parts that are incredible in every measure: beautiful, light, strong, and most importantly, something that I would put on my own car. I don't mind saying that this decklid is all of those things. I literally laughed out loud when I popped it out of the mold and I saw how great it looked and how light, stiff, and strong it is.



This is a rough weighing of both pieces without hardware and adhesive. I do have a target weight that is a tiny bit lower than this, but I'm confident I will get the necessary grams shaved off in time. It's possible that I overshot the "strength" goalpost... (keep reading )



Did I mention strong?

It passes the jackass test





The test setup. You can see the marks on the inside of the decklid skin where the blocks bore my fairly considerable downforce:

[Focker]

so awesome!!

[Uwon]

Beyond impressive, Jon.
Cheers,
Johan