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Which means "Evil Twin". Lets see your projects where you change boring into fun or create the fun from scratch.
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 Post subject: Re: Welding wheels
PostPosted: Fri Feb 15, 2019 4:46 pm 
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I am really not sure how you find time to know all this stuff, but I am glad to know you and learn all this stuff.
I would like to draw all that cool stuff, but I have enough on my plate at this moment.

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 Post subject: Re: Welding wheels
PostPosted: Sat Feb 16, 2019 8:43 am 
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FoaTech wrote:
I am really not sure how you find time to know all this stuff, but I am glad to know you and learn all this stuff.
I would like to draw all that cool stuff, but I have enough on my plate at this moment.


Thanks but I'm just winging this....probably a dangerous way to do design :)

I suck at drawing... projects like this kind of force me to at least learn enough to be able to muddle through...I want to get on to making something.

I realized yesterday that there was probably more reinvention going on than there should.....there have to be standards for best design that I should be following. I'll need to dig those up before I can finalize that part of the design.

Originally I was thinkin double side mold for the bead area.....and I still might but the koniggseg video has me thinking maybe it would be best to leave it 1 sided to be certain the vacuum bag is effective and not worry about molding the bead profile...just make it thick and machine it or spec after, many cut the mounting flanges at the same time and know for certain the wheel will spin true.


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PostPosted: Thu Feb 21, 2019 9:39 am 
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I'm going to try and pull a few posts together and put all the carbon fiber wheel stuff here.


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PostPosted: Thu Feb 21, 2019 11:01 am 
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loopingz wrote:
Hi there,

I love your project mke. I have seen you want to build cf wheels on a budget.
As a pro (aerospace composite engineer) and hobbyist board builder I would like to stress some points here.
Prepare yourself to waste some wheels at least you have to budget it.
What can go wrong.
By conception matting on the screws will be hard. Be monolotic around there. Ply orientation and quantity is vital at least a minimum thickness is vital.
The shape on the 308 is not very carbon fiber friendly. Koenigsegg put some tubic branch and everything is rounded.
By tooling. Vacuum pump go for industrial straight. My 3 free fridge pump + relays and microcontrollers is around 500$ and yet not that good (3 pump is for redundancy here). Oven you will need one and you will need to cook high temp 200C minimum 400C would be better. Mine is "almost free" but reach only 70C. You need to control ramp up and ramp down temperature. Failure to do so = trash.
By building. You can have mass reaction (better to constantly mix resin and never more than half inch high in your bucket), avoid it at all cost. You will have bubble visible outside and hidden inside. How much can you tolerate?. Warping, that is a wheel you need to avoid it a lot. Milling afterward should be limited to a minimum! You can have vacuum failure, oven failure, epoxy too humid... Prepreg can remove some issues. Molding will be key. Infusion is interesting too but it might be trickier for a start. If you want to use some filling material you may want use herex/airex, c70-75 or stronger. Avoid honeycomb too much added pain...
You can have delamination too and a lot more possible issue.
It is doable still with your energy I am sure you can manage. But take your budget and multiply by a factor 2, 3 or 4. There is so much to learn!


A lot of good points here.

Looking at the koenigsegg design and listening to the video I think they used tubular spokes mostly because they had a process to make them and he seems pretty proud they they are hollow.....but I don't see any structural benefit of the shape? They may have varied the wall thickness to make it more optimal though.

I am taking some liberties with the 308 wheel design to make it a bit better for composite. Specifically where the spokes meet the hub and rim have been altered significantly....and I'm still not loving what I've done honestly. I still need to play with that a bit.

A piece the really bothers me is the ribs...aka stress risers. Where my head is right now is I don't see the car with black wheels, I just don't so they will be painted....I was thinking maybe something a little bit translucent but it will probably just be silver paint. If that is true and I'm not trying to get a show quality surface layup then my thought is to make the ribs from fiberglass so they are way less stiff and under way less stress...making them effectively just decorations. With this approach I can have decent radii on the corners of the carbon spokes to reduce stress and make layup easier but still achieve a 308 appearing final wheel.

Thee are currently sections of the design that are hollow. Laying up and molding hollow is hard.....so the plan is to use foam in the "hollow" space. The foam will not serve any function purpose once the wheel is cured so the strength of the foam or potential delamination is not a concern....ideally I would have a hole and dissolve the foam out but it adds so little weight my thought is just ignore it.

In a similar thought as the foam, I'm also pretty certain there will be excess epoxy is certain regions....unneeded weight for sure but I don't think it causes any actual structural concerns? so I'm not sure just how hard to work at minimizing this issue?

My plan is to make a fiberglass wheel or 2 or as many as it takes to get a working layup process sorted out. Then test layup a couple of the more challenging sections in CF.....then attempt a full CF wheel. I'm pretty sure a well designed 8x18 front wheel should be about 11lbs....mine will be a few lbs over that kind of on purpose. I mentioned post machining and allowing for this is part of the extra weight, design thickness/layout would be completely out of the way of any machining....so the hub say will have 2 or 4 extra layers slapped on like a spacer, it serves no structural purpose so mill it flat and to size paint it and call it done. Same on the bead surface....the tire can't go anywhere but it would be nice if it ran true so a few extra layers to know I'm not cutting anything structural and it should be good I'd think.

Right now I'm leaning toward a room temp epoxy.....it saves a ton of money both material and equipment. My fear is working time. So small batches as you say (I've already make the big batch mistake once) but I'm thinking of going 1 or maybe 2 steps further. I want to see how thick the stuff gets in the fridge as starting with 40-50F resin should turn 2hour pot life into 3-4hour. If that path isn't enough then working in a cold room might be the go.....a few 2x4s, plastic sheet and a window AC unit should give me a 60F work space which should turn the 2 hours time to 4 hours, then flip on the space heaters and make it an 80F space for the cure time.

If I can't make good looking sample parts on this path it will be time to re-think the effort as the prepreg path would be a lot more investment and doesn't leave me with the same flexibility for future projects.....I've been planning a composite rear decklid for example and the autoclave for something like that would be an insane investment.


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PostPosted: Fri Feb 22, 2019 10:34 am 
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As for the hollow shape it is the holy grail of light weight rigidity.
3/4 inch spoke would be super stiff too. The hard part are the links to the hub and the drum. Koenigsegg manage good continuity by working with hundred of small patches.
There are lots of way to Work slowly. Choosing the right hardener is one key. It depends on your working temp a lot. Some can last hours before drying. Starting at too low temp might be catastrophic sometime: mixture will never harden. Working properly with vacuum will lower your working time as you need your resin fluid when you vacuum. Without vacuum you can add layers on hardened ones no issue. Prepare 200g/half pound at a time. Some resin come with a push pump for super easy refill. I am used to scale but sometimes it is more pressure while working. If it is working one hour fine, you can work n*1hour, it is just that the lower layers will be already drying...
Something fun about the Koenigsegg videos. We are various here at work who have seen them and we are agree that they kick ass. They master a lot of stuff. We usually go simpler on aircraft stuff.
Do not put too much hollow at start and not near the hub. Closed cell pvc like airex / herex is easy to work with. I see that more as optimisation for a later design. Excess epoxy when external is OK. Internal if there is significant volume to fill you need to charge/load/mix/fill (not sure what is the right English word here) your resin with some kind of microballoons. There are various. Resin alone is fragile. Vacuum with correct method will dry your excess resin.
Great idea experimenting with fiber glass. More than enough to validate your work.
Painting is totally fine. You can use color gel coat on mold face too.
Tg or glass temperature is directly linked to your curing temp. Working at room temperature is OK for surf boards. I do my kite boards at 40 to 60C so then it is bulletproof but also stiffer and stronger and higher Tg. You don't want it to warp under the sun. Pushed tires usually go up to 80 - 90C. Just the car sitting in the sun can get to 50 or 60C (sorry not fluent at F but I do read them Ok). Room temp is OK for winter testing only. I would not build a wheel with a Tg under 100C. No idea how much the brakes can add to that.
You can build a small oven on budget. Mine is mainly would space blanket and old school 60W lamps. Much more time invested than money.


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PostPosted: Fri Feb 22, 2019 11:44 am 
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hmmm...I hadn't given enough thought to Tg in this plan. Not a show stopper but for sure something I need to spend a bit more time looking into......the first one I saw doesn't really list a Tg but does say it really won't cure in thin sections below 120-130F (50-55C) even though they call it room temp. More digging required....this will also be pretty important for the engine deck lid I want to make so any heating solution will need to be on that scale.

My current thinking on the spoke end joints is to let the layup overlap into the hollow area and say its fine that it adds weight. that's the main thing I was thinking I'll need to play with in the test layups...spoke goes into the hub, hub into spoke, repeat kind of thing....and/or use the large fillet areas in a similar way. This would need some practice.


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PostPosted: Fri Feb 22, 2019 12:20 pm 
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This one implies the Tg is above 300F (150C) but doesn't say it.

It can be used and cured at room temp then popped out to the tooling and post cured to get the high Tg....at least that's what they imply.

https://s3.amazonaws.com/cdn.fibreglast ... /00408.pdf


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PostPosted: Fri Feb 22, 2019 1:13 pm 
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Here is a wheel I did for a Boxer Restomod, 17 inch.


Attachments:
20150321_130319.jpg
20150321_130319.jpg [ 951.92 KiB | Viewed 8031 times ]

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PostPosted: Fri Feb 22, 2019 1:30 pm 
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looks a lot like the hre 505
https://www.hrewheels.com/wheels/vintage-series/505

Attachment:
13670144480bf2a08af95046059cac061faf586a28.png
13670144480bf2a08af95046059cac061faf586a28.png [ 674.16 KiB | Viewed 8030 times ]


...STARTING at $2000 per wheel.

or the cast version starting at only $1900

Attachment:
14392248048ad4e69af4f828c3604f98852f8c0c4a.png
14392248048ad4e69af4f828c3604f98852f8c0c4a.png [ 657.59 KiB | Viewed 8030 times ]


If I use the .025" thick CF cloth I think there is under $500/wheel of material (cloth, resin, foam) in a wheel so about the price of image wheels I was looking at. Honestly I probably could order the image wheels with drilled center or request they rotate the patter 36 degrees to center the holes in the spoke then a little custom machining and it would look about right......if only the sales manager hadn't decide to tell me how he felt about brexit making it crystal clear he's completely detached from reality leaving me no confidence in his ability to accept facts should anything go wrong with the order or make fact based choices while producing the wheels.


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PostPosted: Tue Feb 26, 2019 3:40 pm 
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Here's where the design stands, this is a rear. Its 15.4lb but I want to add a bit more material in the hub and inserts for the bolts.


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CF 3 rear section.JPG
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CF 3 rear.JPG
CF 3 rear.JPG [ 100.58 KiB | Viewed 7994 times ]
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