[buran77]

Normally I love this kind of article too because I consider it engineering, not marketing, the product name dropping at the end just reinforces the message. But either I'm missing some details that could have been spelled our more clearly, or the engineers were taking a break when the marketers were writing some parts. I'd love to stand corrected if someone more informed has details.

> advanced polymers such as Sterrox® LCP

> we have implemented a tip clearance of only 0.5mm (120mm models) or 0.7mm (140mm models)

> Achieving such small tip clearances is essentially at the absolute limit of what injection moulding can consistently reproduce.

Typical tolerances for injection moulding are 0.1mm, or 0.03 for high precision, or even better. LEGO was said to be in the 0.01-0.03mm. So on the face of it the last statement is patently false or at least too generic, injection moulding can consistently do much better than 0.5mm. With standard injection moulding precision (0.1mm) the worst case scenario for the two parts (fan and shroud) mating would still stay comfortably below 0.5mm.

So the question to the experts, is Sterrox® LCP that much harder to work with and the marketing team just didn't understand the importance of being clear about this? Is it a decimal point typo and the numbers should be 0.05 and 0.07?

[double0jimb0]

Expert here.

When very precision molds are made, what Noctua talks about in "multiple tuning iterations are required until the geometry, cooling, gating, and moulding parameters are perfectly stabilised" is the standard process for this type of stuff. (Gears, bottle caps, or any molds than make 8, 16, 32, 64, or 128x of the same part in one shot, require that you start with "steel safe" geometry, meaning you mold the first test parts, measure them, and then modify the mold (by cutting material AWAY, it's very hard, usually bad idea, to add steel back to a mold)).

You can do your best to determine what geometry is "steel safe", and all of this is baked upon having very good engineering understanding of what material you are molding (and using very expensive software like MoldFlow to simulate this).

Legos are made from ABS, there are decades of research and data on how ABS behaves in mold, it's relatively safe to use results from Moldflow and be pretty confident in it. Noctua is using LCP. LCP is very niche, and it sounds like they themselves are doing the research on moldability/warp/process effects. And while also being a company that produces things on timelines, the friction/side effect is that sometimes best guesses will fail and they have to start over with new molds (that's a 2 month hit usually) and months of testing. That is what they were trying so say.

I design glass-filled nylon and polycarbonate parts/assemblies with tolerances 1-5x higher than theirs. The 6-month delay they described is something I've lived through many times when we had to "cut new molds" because we couldn't salvage the first mold. (Advanced molds like these are $50k - $200k+). As a company/designer gets more experience with new materials and colorants (like their stuff with LCP), they will probably be able to hit end-goals on first try more often as they collect learnings from their failures.

[CableNinja]

Noob here. If you dont mind ive got some questions for you!

Ive recently started messing with the idea of making my own model car kits as a hobby. I understand a lot of the basics, but have never done anything like this before.

Im obviously not going to make kits in mass, but, i plan on doing injection molding using polystyrene. I do not currently have a cnc, but have been eyeing a SainSmart, though they say "can do metal under certain circumstances", but doesnt cover any of those circumstances. I also was looking at various injection machines and the price for entry is insane to me - $1000 for something that would probably burn your house down.

Anyway, to my questions..

1. Suggestions for a hobby cnc that can work aluminum? Id be willing to go as far as $2kUSD, unless theres something more that you think would serve me significantly better 2. Suggestions for a hobby injection machine that can do ~60-100g shots, that wont try to burn my house down, and doesnt cost a ton? 3. Any tips or thoughts for someone diving in to this? 4. Things i should purchase for QoL with cnc or injection molding? 5. Where does one buy materials (in hobby quantity) like aluminum block stock and polystyrene pellets?

[double0jimb0]

Those are all things I've spend some time in, I'm not sure what to say. Learning curves for each one of those things are pretty dang steep. With AI you can probably speed up learning curves, but I think you will still go on many dead ends.

On the small CNC that will work with aluminum... There is a whole tradespace around how small of a feature you are trying to mill vs spindle speed vs machine stiffness & spindle runout. If you were to get something like a HASS you can sorta do it all, but when you get into the hobby stuff, you need to be very certain about what smaller set of machining limitations you will be dealing with and if they will still get you where you need to go. You need to work backwards from what actual tolerances you need to hold for the downstream thing to be able to work. (For instance, if you are making an aluminum mold, when you machine it, you will most likely be repositioning the work piece... if your machine isn't square enough so that when you flip the part on it's side or upside down, then do your next op, the part may not have been square to begin with, so now you have something that won't match the other thing you are trying to mate to.)

I build a 2'x5' 3 axis with ATC, starting from a CNCdepot concept and did my own control. I probably spend as much money on precision straight edges, levels, 90deg blocks, lapping tools, etc that were required to build a machine that could hold tolerances to 0.001", which is probably where you need to be landing to have molds that work.

I guess I am just trying to say it's a very big and ugly can of worms you are opening up.

Before buying anything, you might just want to try using firstcut/protolabs. They will machine the aluminum molds and mold the parts for you. Price per part is not going to be pretty, but it's going to be way less than spending thousands on machines that will never get you to where you want to go.

As for "desktop" molding, there is some startup now pushing their kludged together machine, maybe that is the one you are referencing. I'd stay far away from that thing. I think they were charging a couple $k for it, I feel like you need to be at 5x-10x that for anything reasonable. But at that point, the amount of power and infrastructure you need is well outside anything you'd want to put in your house or even garage. Don't really have a good answer for you here.

One thing to look at, if you are doing those model kits where like 20 parts are all in one flat sheet and you twist them to remove them, people are starting to make these on FDM 3D printers, which might be worth looking at. Now you can prototype and do production on the same machine, which at your stage, is the right place to be.

[buran77]

Thanks for the expert point of view. It was between "difficult polymer" and "marketing blurb". Glad it's the first and I hope anyone from Noctua reads HN and adds this small clarification.

I knew the technology itself can have tight enough tolerances that are not a concern from an engineering perspective when talking about a 0.5-0.7mm clearance, but no details about the challenges of this LCP.

[NorwegianDude]

Noctua wants their fans to last for many years, spinning at 2K rpm, with heat.

Being able to produce something with lower tolerance is one thing. Making it work long term at ~10 m/s and ~200G is another thing. Have you ever been in a car that brakes really hard? You'll move. Now, multiply that force by 100 and you'll get around what the fans must sustain over time.

[buran77]

But that's literally not what the article says. You are talking about the design - Noctua puts 0.5mm because any more and airflow is affected and performance drops. They also use a super duper polymer that mitigates everything you mentioned. The article talks about manufacturing tolerances.

> Their influence on the dimensional precision and stability of the fan blade may be minute, but if the tolerance is only a few tenths of a millimetre, being off by a tenth or two suddenly becomes a problem.

> Achieving such small tip clearances is essentially at the absolute limit of what injection moulding can consistently reproduce.

I'm not questioning their engineering but the wording of whoever wrote this article. For anything with a clearance in the tenths of a millimeter, injection moulding doesn't even sweat, let alone be at the limit. Anything better than bog standard injection moulds get you better precision than "a tenth or two" millimeters.

Let me put it another way, if achieving a 0.7mm gap is "at the absolute limit of what injection moulding can consistently reproduce", what would you say consistently achieving 2-10um (microns) gap is? Magic? Fairy tale? Because LEGO as I said earlier is said to have 2um tolerances [1] over their decades of producing the bricks. Even a more conventional 10-20um (order of magnitude higher) still works.

[1] https://news.ycombinator.com/item?id=47335237

[overfeed]

> The article talks about manufacturing tolerances.

As shown by your quotes, the article clearly mentions tip clearance, and not manufacturing tolerances, which you are infering. The article doesn't characterize the thermal expansion the "super polymer" is expected to undergo under normal operating conditions[1]: something Lego doesn't contend with.

All this to say: Lego's manufacturing tolerances alone can't falsify Noctua's claims because they ultimately are different metrics.

1. I imagine the expansion rate of the fan blade radius doesn't correlate linearly with that of the shroud, so the tip clearance changes with temperature. With this constraint, not even Lego could make its manufacturing tolerances equal the fan clearance, which has to be larger if you want the fan to predictably work without jamming over a 40-degree temperature range.

[thinkloop]

I interpreted it as: with the nature of fans and the associated vibration/movement, some gap is necessary and this is the limit given the precision of injection molding.

Phrased differently: a 0.5mm gap is the minimum possible to also be able to account for the 0.1mm (or whatever) variation in injection molding.

You're right to question the wording.

[buran77]

> a 0.5mm gap is the minimum possible to also be able to account for the 0.1mm (or whatever) variation in injection molding.

The Noctua engineers definitely designed the clearances to perfection and accounted for the variation in the manufacturing process, I don't doubt that.

The article says "being off by a tenth or two suddenly becomes a problem", the 0.1mm you also thought of. But that's the point of contention, 0.1mm is the tolerance from bog standard, cheap injection moulding. The limit of consistent precision is in the single digit microns. Noctua doesn't need anything near that.

Unless working with that polymer is difficult and comes with higher tolerances, this is probably just a case of the article's author trying to pump up stats. To bring it more to the techie world, it's something along the lines of "130nm transistors are at the absolute limit of what EUV lithography can consistently achieve".

[Numerlor]

Because it's spinning blades among manufacturing tolerances you also have to account for the blades expanding when rotating at high speed, and possibly working with 40-50 °C air from the components

[buran77]

I don't think that's it. You're referring to tolerances specified in the design. The article talks about the tolerances the manufacturing technique allows, and this process is an order of magnitude better than this article says. The material used and the design of the part influence how much it deforms in practice far more than the injection moulding process itself.

In their own description of Sterrox® LCP they say it has "extreme tensile strength, exceptionally low thermal expansion coefficient, high environmental inertia and excellent dimensional stability". With such an advanced polymer any deformation in operation has to be a rounding error compared to the manufacturing tolerances.