Custom Center Caps for Porsche Wheel [from CAD, prototyping to finish]
 

So let’s make something together!

Some of you already know that I am a bit of a wheel gaga and often looking for ways to make my wheels look kool’er. Keeping them surgically clean in & out is obviously not enough, installing LEDs on the valve stem is not-an-option, and modifying/compromising the structure of the wheel in any ways is somehow less than smart.

Therefore, this leaves me with no other options than the center of rotation, the hollow area; The Great Center Cap!!!

Many will have seen the center cap I’ve designed and published here 3 years ago. They are Carrera GT Center Lock “Style” wheel caps (replicas, pic below). They were initially meant at replacing the boring and style-less plastic center caps my (at the time) expansive wheels came with.

Long story short; they came out pretty good and served (to the eye) just perfectly! Almost so good (loll) that today, those same CGT style CC are being copied by a-lot of our fellow Chinese aftermarket car parts mfg. Country-wide (no affiliations in any ways). They became quite popular and being sold by the dozen each week. That’s right - I regularly keep an eye on these folks’ Alibaba, eBay and Taobao stores to track how they are doing. I always order the stuff I do from those guys just to see how they manufacture them cheaper (Chinese are Masters at this!), final product quality, etc, etc. A hobby I have with all the parts that I’ve done in the past which are still being copied by the thousands today (e.g. adjustable race clip-ons, adj rearsets, adj/foldable levers, few others… mostly race bike parts). We’ve done quite good dosh with this work in the pass ;)

So why am I saying all this, well, mainly because we are bored of the One & Only style available and need another one I guess. Almost urgent; Club friends locally here have been asking for this since quite a while now so I’ll finally deliver what I’ve promised in the past. They’ll still remain for Porsche wheels only, but looking slightly different. And perhaps, who knows, we’ll come up with a new GT Series (design variations).

Inspired from other DIY I’ve done in the pass, I’ll share with you the whole process; touching CAD/CAE/CAM, validations and other PLM involved for getting a product designed, prototyped, manufactured and hopefully, packaged.

Hope you’ll all enjoy as much as I do :)

F.

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[Original CGT Style Center Cap ]

For now, I need to come up with a cap that reassemble the GT3 center lock (most wanted/requested for), does not protrude as much out of the wheel (for those with non-concave wheels), and it has to be far much easier to install than the previous one - which needed the wheel to be taken off, etc.

All very challenging but I think we can pull this off. I'll update as I progress with sketches and proto visuals.

If I am boring you to death, please do not change channel as this may only become more interesting in the future. Certainly not interesting during the initial phase and I apologize in advance ;)

ps: I promise we'll eventually do performance parts in the future; links, suspension, adj arms, intake improvements for the "Two-point-Fivers" loll stuff like that.

Yes Fred we need intake improvements for the 2.5 for sure. Glad to see you are getting back into the swing of things :D

GT3 center caps first!
 

Ah, yes, the turbo-kit v2.50 ;) We surely need that eventually having been let down completely during the last 20 years. However and for now, the GT3 Center Caps that every one is asking me for are far more important. Need to get this done... and besides, cool-lookin center caps offers far more horsepower (using the bling-dyno of course).

Funny you mention though, because you'll be pleased to hear I've actually did the prototype model already. Was playing with the idea a few weeks ago only. Regardless, we have the CFD ready for the crop of engineers here to see and contribute to the proof of concept. We'll be able to cancel stalls, adjust geometry based of optimized velocities in various air densities, temperatures and pressures.

Technically speaking; we'll be making the stock plenum in our Super 2.5 liter flat kick car comparable to the PVC pipe found in hardware stores today :D Stay tuned (exclusive to 2.5 only, sorry )

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ps: Hey back to you Tommy! good to see you around again bud

I've learned to love this sort of stuff, I work with the universities Formula SAE team on the business side of things. It's fantastic to see people creating useful components from an idea to an integral part of our car!

Sketch & features for the main cap
 

Well, ladies and gentlemen, congratulations on your new president! Looked pretty cool from the News clipping angle :cheers:

Without wasting time, and more importantly than all forms of world-politics (combined), is the Great Center Cap! I did try a lot of different revolving curves & shapes and came up with this. Not 100% final but there, we’ll start with this. So far I've only shown it to my neighbor(loll) and a friend who, actually, deserve the credit for the GT3 style center cap idea, and surprisingly, he confirmed that we are going in the right direction.

So it all appears to be good geometry and a good starting point to base the remaining of the assembly onto (e.g. planed adapter, center with crest, etc).

http://986forum.com/forums/uploads02...1484899739.jpg

^ The most frequent request I had during the years was “less protruding out of the wheel”. To comply with this, I’ve come down from the 42mm (CGT style) down to 13mm (GT3 Style). For those guys with non-concave hub wheels, this will be a better option (visually).


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^ Here you are looking at the base sketch for the revolving feature of the main cap along with the distance between the outer edge of the wheel hub and end side of the cap.


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^ Once revolved, the geometry look pretty prismatic in nature. What we are looking at here is the stock that will require turn machining operations (material AL6061).


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^ Then goes the main cap feature to give it the look & feel. Although not an exact replica of the official GT3 center lock in terms of lock/tool features, it is pretty close and (to me) quite attractive. Simple! We are trying hard to get in features in a as-simple-as-possible way to avoid the ‘too busy’ effect, but also to make it easy later in rendering to achieve a good curve continuity and lighting reflections. After all, it is a cosmetic part more than a functional one so we might as well put energy in the bling area instead!


http://986forum.com/forums/uploads02...1484900110.jpg

^ Those features; simple revolution of extrusions with a radius of 1mm (highlighted in orange) at the floor end. Again, all useful geometry for rendering purposes, and also very machine-able with a dedicated bullnose carbide cutter. The hollow center is obviously to accommodate a separate part having the crest or club logo stamped dead center. This part is separated from the main cap mainly because it will be in a totally different color than the rest of the assembly (most likely silver).

I’ll do this part later. Again, all subject for changes but so far this is what I am aiming for.

Under (basic) lighting conditions in neutral tones. Meaningless to you guys I know but you'll soon see where I'm going with all this.

I'll update as soon as I'm done with the Center. Hopefully by tomorrow this should all start looking like a center cap loll

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Subscribed, Fred; thanks!!

I like where this is going!

The Center's Center ;)
 

Thanks guys!

Right. Here goes the most complex car part known to man kind loll

So... Center is done. This will snap right in the center of the cap and accommodate a P shield that I am already familiar with. I'll assemble all this together tomorrow if all goes as planed (e.g wife going shopping) and get this to render.

Next is the wheel hub adapter. I already had the concept in mind since a few days already but until I have a proof of concept to see for myself, I won't publish. Might actually need a few days for this part alone :/

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Just love your projects Fred

Same here :cheers:

Ah some old friend :cheers:

Hey Captain. Hmm must feel different from seeing all the 'advanced' aerospace parts you get to see all week/flights long. Very flattering comment from you Sir, if you are being serious:D

Very serious:D Let's see, I have your headlights and your wind deflector! Keep feeling better Fred!

Fred I'm in for a pre order of a set in silver. Um throw me in for a super upgrade plenum as well :)

Assembly and weight
 

Well, success RE the wife going shopping ;) I have fresh and imported Cheddar Cheese to put on my toasts tonight and the dogs have their weekly cow-bones to finally get busy with. Hmm sharing with you what a typical Saturday night looks like here in Shanghai (loll we're getting old).

Not so much success on the rendering of the parts however. Not sure what's happening but the rendering PC I use here is blowing its life out of the cooling fan each and every time I switch it ON. Fear the CPU will melt if I use it - Hopefully I'll be able to fix that later myself :/

In a meantime, I have those which I think is sufficient for now. Surely gives a good idea of where this is going. Another good news is the kit only weight 77grams. Ultra-Light if you ask me.

I think we've done an amazing job so far. More to come on the wheel hub adapter in a few days. Cheese Toasts first :p

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This thread is fantastic! Not often you get to see the inner workings of a master artist at work. Guess a Cheese Toast will have to do... :cheers:

I definitely like the lower profile, they are looking great Fred! My Saturday nights are not so exciting either :cheers:

Bring the Task Manager up and check if the Windows Antimalware Executable is hogging the CPU. If it is, google on how to prevent it from doing that. I had exactly the same issue and had to take care of it.

Damn you Fred! I'll take four.

:-)

Cheers!
-Troy

Do not get hypnotized by these modern and expansive software/tools man. The "true" masters are those who fabricate with their hands, and using tools that everybody has. If you want to know my version of true (genuine) ingenuity!

But thanks for the compliment, well received!

Sorted. It would have been a tad more helpful for me if the main-board would have beep'ed letting me know what it was. My neighbor's son disconnected the E drive and all came back to normal. The HDD was an old style WD and basically died. Not sure why this HDD was left in there anyway, been using SSD since a few years already. Thanks for trying to help bud, too kind :cheers:

haha Troy! ah for you its local pickup only. Always good to hear from you brother :)

Wheel Hub Adapter (start)
 

The part below will be the wheel hub adapter.

It threads & secure itself inside of the cap and meant to clamp the whole cap assembly onto the hub geometry of the wheel. As you can see I am using the traditional clamping style that, well, Porsche and many other automakers are using already. I’m guessing there is a reason for this widely used concept so no point going all creative RE hooks, clips, or new ways to get this to clamp. Let’s stay focus lolll

I won’t lie, I’ve already tough up this part quite a while ago. Often I’ve heard complains about how difficult it was to install the previous CGT style caps and many said “it got to be a better way”. So there, I’ll finally comply with this and provide in the best of my capacity.

The material we’ll be using for this part alone is Acetal (Polyoxymethylene, or Delrin if you prefer). Acetal is possibly ranking Top 1 in its group of engineering plastics and for many reasons (you can read about it). Not exactly cheap, in fact The Most Expansive in its class, but at least we’ll be 100% sure that the part will last for minimum half a century and perform in literally any environments. E.g. whether you roll my cap in Alaska at below 40deg Celsius or Texas at above 40, The Great Center Cap is going to stay on your wheel and perform its task without any complains.

I personally love Acetal because it is magical to machine. If you are familiar with its thermal expansion behavior, you can achieve tolerances of 1~5micron on this thing without much efforts (not joking). Something I’ll need to do for the matting of the threads with those of the cap, you’ll see why later.

I’ll soon explain the method I’ll be using to “thread lock” Acetal with the aluminum cap using its thermal expansion properties. That’s right; thermal expansion is occasionally an “advantage” for engineers, not all negative!

Nuff blah, it’s all about visuals (and Cheese Toasts in between)!


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And off to the part validation (CAE). Lot of work there :/ The ring in front of the adapter represent the exact same geometry of the Porsche wheel hub. Same shape, size and tolerance (0.05mm) and used for non-linear clamping analysis.

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CAE and part validation
 

Acetal is “snappy”.

Here I’ll share with you validation procedures that the part will undergo. In general terms, we need to ensure a few things for this to work. 1) Ensuring that the part does not exceed (in any ways) the Ultimate Tensile Strength(110Mpa) anywhere in the clamping process i.e the ultimate TS is when the part shatters in little pieces, or the moment when you get mad at me loll. We also need to ensure that it stays below its Yield Strength (64 Mpa) when in operation. We don’t want the part to be living under excessive stress during all of its life. Within the range is perfectly fine, but not above!

Lastly, it need to provide a good clamping pressure so when the wheel rotate and X and Z velocities changes, the cap remain where it should. Keeping a pressure above 100Mpa is the target here so watch your fingers when you snap them into place, it’s going to hurt-a-little if you get your skin trapped between the wheel and the cap ;) Although, for a light 77grams cap, I think that 50 would be more than sufficient – but let’s not take any chances!

Side note: for anyone familiar with CAE, I am solving this with SOL 601,106 Advanced Nonlinear Statics (using a 0.2 as coefficient of friction, 2D CQUAD4 mesh and a RBE2 connector for the enforced displacement). Nastran 11 Solvers, what else better ;)


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^ Not 100% completed but going into the right direction! Nasty work I tell ya but still fun to do. Sometimes I think my fellow Chinese friends have the right way of doing things = "looks good, then its okay lolll"

CAE and upcoming Multiphysics Simulation
 

Decided to become a VJ for one day loll

Did this vid to show the ‘behind the scene’ of CAE and how design (or feature) changes are validated. In this video we’ll be lowering the height of the clip and wall by -0.5mm. We’ll then clone the solution and see how stresses compare to the design changes.

When I say ‘nasty job (but fun)’ I really meant that. It can take quite a bit of time to come up with a proven concept – weeks sometime.

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Next: I'll be showing how to balance a part assembly using Multiphysics Simulation tools and sensors. Think some of you will love that episode. I'll try to vid those over youtube for you guys to see.

I'll test the prototypes in red!

The Red are too fast, you'll need titanium lug bolts.

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Yikes. Beautiful!! Fred, your work is amazing.

Jeez Fredric ......did you make them integrate a CAD station in your hostpital bed��.

I will take Five bro...

Looks great as always, bud! :cool:

Dude I think its what they put in the cheese these days :/

Already at balancing this assembly Jay. Doing the 1800RPM(223km/hr) currently. Hopefully be done with counter-weighting the center/badge by tomorrow so I can (finally) send this to CAM. I'm actually really eager to see them myself.

Secret: good tools man... makes for an easy job. Prototypes are always spot on ;)

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Holy crap I want these!!!

A touch of red on my seal gray car with silver wheels will look nice I think!

Caps
 

Holy Cow!!! Just caught this thread. Two questions, when will they be ready and how much? Oh heck, forget how much just when will they be ready? Great work, absolutely wonderful...

Nice work - Fred - love seeing your techniques!

Fred congrats on getting better keep healing and moving forward ! I may have missed it but how are you adding color to the parts ? Does the raw material already contain the color ? Or are they going to be painted ? And what colors will be available ? I think " the beast " needs a set of these but I'll have to figure out the color . Thanks for what you add to the forum and community . :cheers:

Kevin, too kind brother :cheers:

Me too, I think lolll Very humble piece of kit from the wheel/cap visuals that came out yesterday.

Same here. Boxster have the blue CGT caps on since 3 years, time for red I think

Thanks bud! Not done, far from it actually. Subscribe if you haven't done so because there is so much more coming. I'll soon be starting the CAM work, fixtures, sourcing the correct materials for prototyping, we'll machine this using the High Speed machining center (Siemens controllers), We'll also laser-mark this cap with something sexy, etc etc. Planing to hit the shop floor in a week! Plenty of fun to come, stay tuned ;)

Too bad folks doesn't do the DYI section of the forum as much as the General one. No price yet, let's machine all this together, get quotes on materials and that will eventually define the end price. So far we are looking at a pretty cheap-to-manufacture part... I'll try my best to keep it that.

Not hidding anything, everything is real here so what I pay for my caps is pretty much what you'll also pay for yours ;)

Thanks Rick, yup getting better by the week. If I don't get hit by a lightning (i.e my type of luck recently) I should be back to 99% same in less than 12 months. Wish me luck man lolll The main cap will be 6061 aluminum and anodized in the color of your choice (gun metal, red, blue, black, etc). The center where the P shield is should ideally remain silver (clear anodized). Fully custom mate, so if the beast needs something unique I'll be 100% able to provide that for you bud :)

Multiphysics Simulation - Assembly Balancing
 

Just a few visuals on the assembly balancing and a video showing my highly guarded & secret Newton's Cradle below. Run the vid half way to see the motion of the center cap. Just quick visuals for you guys, sorry, not the full thing (man, this is all time consuming this pic/vid/encoding thing loll).

Simple you may think but incurably powerful. Pure physics; 60+ years old solvers (NASA(nastran), Recurdyn, Adams, etc). Its all about the quality of the solvers really.

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^ Here you can see the assembly I use for balancing rotary parts. It’s a base having a shaft rotating in the X axis. Not specific to the center cap I am doing now, I’ve actually used this for quite a few other parts successfully (custom spacers, CNC tool holders, custom rotary chucks soft jaws, center caps, etc etc).


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^ The shaft uses a driver (motor) set at 2,400RPM for this test. You can however set this to pretty much anything between 0 ~ 999,999,999rev/sec. Here we are testing vibration on a Porsche wheel with a diameter of 660MM (26"), or a circumference of 2073mm (660*PI). In velocity, and if spun at 2,400RPM, this gives us 82,938mm/sec (or 298km/h). So the target here is to rate the Great Center Cap for speed of 300Km/h without any sort of vibration.


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^ First thing first, calibrating the shaft coupled with the Porsche wheel hub (translucent part; right end side). We should be getting a flat line e.g. no changes in force magnitude anywhere = zero vibration.


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^ With all the parts of the assembly inserted into the wheel hub, we are getting a vibration in the Z axis (i.e. up/down). So by deactivating each part of the assembly, it is easy to figure out which part is causing the wiggle. In the case of this assembly, the Center holding the P badge is the culprit.


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^ To make things a bit easier visually, we slow down the motion solver to 1 (one) rotation only so we can clearly see the vibration curve. Still rotating @2,400RPM (40rev/sec) however the time steps drops from 1 sec down to 0.025sec (e.g 1sec / 40rev per sec). So 1 full revolution only here. Easier to see than the above graph!


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^ Now having found the culprit, you need to go back to the drawing board and counter-weight the part. In this case material had to be removed (orange). Once the center of mass gets back to zero, you re-import the part and re-solve the motion.


And BINGO!

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^ As you can see, we are now getting 100% flat line per revolution (still at 2,400RPM). The badge is set to 50% transparent so you can see where the little pocket is located.

At the manufacturing stage, a very small pocket will need to be machined inside the area where the P badge goes and all will go back in perfect balance!

And that is how we design rotating parts and balance them using Multiphysics Motion Simulation ladies and gent. Fairly elementary and simple lollll


VIDEO

You'll see my Newton's Cradle in there (not a toy!). Again; incredibly powerful. CAE allows us to export Flexible Bodies (e.g. response dynamics) and import those inside Motion Sim. That is how we get table field of data for various materials used for creating parts (forces, damping, etc). This data is then used down the line for crash/impact analysis, fatigue analysis, stuff like that. Could be wrong but I think every engineers have a Newton's Cradle modeled (can't be found anywhere, you got to make your own and mine's not for sale loll)

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F'in amazing

Fred is back!

I love that look.

Now that's very counter-intuitive to me that on a perfectly symmetric looking object, that the lightening relief would be positioned off the line of symmetry. Any explanation as to why, Fred?

Also, I find it interesting that you've modeled a balancing apparatus. Wouldn't it be just as easy to assume the piece is sitting there in space and rotating by some strictly defined (assumed unmoveable) axis? I suppose with your method, you could model flexibility and oscillations of the testing jig, but I'm not sure why that would be useful, unless you were doing real-world testing on the same exact jig and wanted to somehow model very similar predicted results. At some point, the model needs to assume things are fixed. Would this simulation assume the base feet of the testing jig are fixed?

I remember getting some unversity mechanical engineering grad student to help do some FEA simulation work on designing a lightened version of wheel centers for an autocross race car I was running. This was at least 10 years ago, so the tools were a bit more rudimentary to what you seem to have access to. I don't remember using using any solvers, but rather, just manually iterated the design a few times until we were happy. The machined weight of those wheel center came out just as predicted! Very cool and memorable experience for me. So thanks for sharing your fascinating techniques.