[IgorPartola]

Aside but one interesting consequence of using plastic in certain kinds of products is that it can be a sacrificial part. If you don’t design a point of failure into your system one will be assigned to it. I recently had this realization after installing a new garage door opener. The motor on it is much stronger than my old one but some parts are far flimsier. Then it dawned on me that I’d rather have a cheap plastic gear break if something goes wrong than have it burn up the unit or swing a high tension belt around.

Longevity doesn’t always mean making everything out of cast iron and stainless steel. It can mean making the thing repairable using cheap and available parts.

[thegrim33]

3D printing options aside, there's no possibility of me replacing random plastic components that break. I'm dependent on some industrial manufacturer producing the random plastic broken part for me, and getting it to me. If something metallic fails, it's much simpler in comparison to fashion a replacement / repair the failure myself. I can work with metal. I can't work with plastic.

[jjav]

> I can work with metal. I can't work with plastic.

You're right that metal (and wood) are much more amenable to work with in a home workshop.

However:

> 3D printing options aside

I wouldn't put 3d printing aside. The main limitation is the size of what you can print, but if the part is small enough (depending what printers you have access to), it is a game changer. We don't have a 3d printer but my child has access to them at school and watching him fix all kinds of gadgets by 3d printing replacement parts has been very cool.

[mythhabit]

If you have the tools to work with metal, you can use those tools with few, if any, modifications and do the same thing with nylon.

[CraigJPerry]

Even for larger items I’ve often found printing sub-assemblies and gluing together to be a useful technique.

E.g. I needed to replace a shaped plastic cover for a handle mechanism on a motorhome/RV. Breaking the design into two parts and making it so they clip together (rather than permanently gluing in that particular case) meant I could print a complex design without supports.

[picture]

Have you used polycaprolactone/PCL aka "InstaMorph" for hobby/projects? It's a very tough plastic that can be melted by putting it in hot water, then formed by hand. I think something like a linkage made out of this material could be a fantastic intentional failure point for certain mechanical systems, as long as the temperature requirement is not much higher than human conditions. Also, if you have a hot air blower, you can repair it in-situ.

I'm honestly not sure why we don't see more of this plastic used for consumer stuff. Something that you can melt down and fix stuff or make little ornaments sounds like a great marketing gimmick. It's also generally a pretty bio-safe plastic.

[eropple]

In industry, it's because it's so low-temperature. The benefits of using it aren't outweighed by the potential failure risks in it in pieces not designed to be repaired.

Also, just kinda--it's not well known! You can't even find it as a 3D printer filament without a lot of effort, even though those "3D pens" often use it, because the output is so unimpressive to most people. That's not that it is unimpressive, it's because they don't know much about it, much like how people act like there's a "leveling up" by switching from PLA to PETG to ABS.

[skjoldr]

ABS is a level up because it curls like mad off the print bed because of internal stresses, and this will cause prints to fail if you do not have a heated chamber, which is a bit of a challenge to set up over Ender 3 like printers. PETG meanwhile likes to be dehumidified under heat first to avoid excessive stringing, which requires a separate doodad, and it likes all metal hotends that do not include the usual internal PTFE tube, which off-gasses nasty stuff if heated above roughly 250°C. PLA has none of these problems. "Level up" is about printability, not material characteristics of the end product.

[eropple]

> "Level up" is about printability, not material characteristics of the end product.

You think that. The people in forums who go "I never print in PLA" despite it having advantageous material properties for some use cases (it's very stiff, for example! sure, it snaps hard, but it's strong until then) do not.

Printability and usefulness aren't on the same axis, but when it comes to FDM materials, a lot of people do.

[esyir]

While from a materials standpoint, its more of a "what fits the needs", from a printing point of view it's definitely a level up going from PLA to PETG / ABS. Both in terms of skill (PETG can be annoying to dial in) and machine reqs (Hot End, ventilation, etc)

[nmcfarl]

If you need heat resistance and can give up reforming and strength sugru is a moldable silicone that I’ve used for a quite a number of repairs. A knife handle I repaired in 2014 is still going strong.

(InstaMorph is new to me - but will certainly get used in the future)

[ElevenLathe]

Can it be injection molded? If not, I would assume it would be much much more expensive to mass-produce than an ordinary injection molded part.

[s1artibartfast]

> I can't work with plastic.

Why not? If you can machine it from metal, it is easier to machine it from plastic. I fabricate plastic replacements often with a drill, files, and saw.

[skjoldr]

It's because plastic injection molding has different constraints and trade-offs in parts design compared to metal machining. E.g. injection molding, after the mold is done, doesn't really care about machine time, complexity, or the availability of specific cutters and drills. So sometimes the geometry and tolerances of an injection molded part is a pain in the arse to replicate manually -- it's just not made to do it, unlike metal machining, which at scale is still a rough approximation of the manual process.

[s1artibartfast]

I get the manufacturing Tradeoffs. What I was responding to was not an issue with part complexity, but part material.

They said "I can work with metal. I can't work with plastic."

Sure, nobody is going to machine a plastic replacement complex injection molded housing. You probably werent going to re-create a complex press-formed metal part either.

IT seems like it is more of a design complaint than a material issue.

[ElevenLathe]

How often do you encounter mass-produced consumer goods that include parts made of machined engineering plastics?

[s1artibartfast]

That's not what Im saying. Machined plastics are rarely encountered, but many molded plastic products can be trivially machined.

Im saying that the fabrication difficult is driven by design, not material.

almost nobody is going to home fabricate a spline gear at home, and it doesnt matter if it is metal or plastic. If something is like a plate or flange, it is trivial to fabricate and doesnt matter if it is metal or plastic.

For any given design, I think refabrication is the same or easier for plastic.

[MeImCounting]

I have a pocket knife in my pocket (perhaps not quite as mass produced as what you were imagining) whose handles are made of G10 which is a composite material made partly of epoxy. It has been 3d machined into its current shape.

[TeMPOraL]

It's an... unusual skill to have, I'd say. Maybe it's the issue of education or culture, but I'm with GP here: in my mind, metal parts can often be repaired by hand, or an improvised replacement can be made; plastics break too easily, and you can't make new ones without a 3D printer or something.

[Freak_NL]

Yup. Same with wood and fabric. Those kind of parts or components I can replace and work with. Plastic? That's a whole different ball game due to the potentially low tolerances in terms of dimensions and the nature of the type of plastic used. With wood, metal, and fabric it is much easier to gauge the correct replacement material.

[kbenson]

I'd say education and culture might be right on the money. I'm not sure it's occurred to me to take a small block of some type of plastic and cut it to shape using knives, planes, chisels and files like someone could with wood, but now that I'm thinking about it, it seems like it might be considerable easier to work with than wood in some cases, especially with how easy it is to join two parts afterwards with some epoxy or maybe even through heat.

Additionally, it looks like you can possibly re-melt the shavings into another block (I'm not sure if specific plastic types are required).[1] That's like woodworking but being able to easily gather and compress your bits and ends and sawdust into more wood.

1: https://www.youtube.com/watch?v=34wPmcgDRmg

[throwanem]

Yeah, I was gonna say. Not that I'd necessarily want to cut a gear with hand tools even in nylon, considering how exacting the profile would be to get right, but it's doable.

[s1artibartfast]

I'd rather hand cut a gear in nylon than one in steel. If you arent doing it by hand, who cares what it is made of.

[userbinator]

Plastic welding is a thing, and has been used ever since the discovery of thermoplastics. Solvent glues also work well for some types of plastic.

The only reason why it's not more common is usually due to cost of repair vs replacement.

Thanks to YouTube, you can now find plenty of information on this.

I can work with metal. I can't work with plastic.

How about pot metal, which is what has been replaced by plastic in many applications?

[alanbernstein]

Are you a machinist? I don't understand why you'd dismiss 3d printing and say metal is more feasible to work with. 3d printing is much more accessible to the average DIY-minded person.

[nmcfarl]

I think this is cultural or location based – I know at least a dozen people who can weld and no one who has a 3-D printer, but I live /way/ out and rural America. The Internet would suggest that urban America is the reverse.

[alanbernstein]

Sure, but if we're talking about replacing machine parts, I'm not sure how far welding will get you. You need to be able to machine custom metal parts, for parity with basic 3d printing capability.

[buildsjets]

I 3D print jigs to hold things together for welding. Mind, blown.

[TeMPOraL]

You can bend small metal pieces with your bare hands, or with pliers, or you can beat it into shape with hammer (or any stiff object). Plastics get damaged and break when you try that.

[pests]

Then just replace the plastic parts with metal, problem solved.

[fragmede]

> 3D printing options aside

Aside from the solution, there's no solution?

If you don't want to get into 3d printing then fine, but don't act like that's not on you. you can work with plastic, you're choosing not to.

[KineticLensman]

On the subject of sacrificial parts, approx. 25 years ago I bought a lawnmower from a well established UK brand (Atco). The original design included a clutch-like mechanism that would decouple the drive from the drum blades if they encountered a serious obstruction and jammed. In the model that I bought, however, the mechanism had been replaced with a sacrificial plastic cog that would simply break if the blades jammed. Even though I was careful, on average, it would break every two to three years. This was before easy 3D printing was available, and I had no choice but to order an OEM replacement. If Atco had sold packs of the cog I wouldn't have minded, but instead you had to buy an entire repair kit with several other parts that weren't needed. After the fourth time it died, I replaced the entire lawn mower with a non-Atco alternative.

I've come across sacrificial parts in other contexts where they make perfect sense (e.g. holding car body parts in place) but I really don't like them being used as an opportunity for manufacturers to increase their lifetime profit from a long-lived product.

[jimbobthrowawy]

Ideally that plastic gear would be a standard size and shape that you could find described in a parts list somewhere in the manual. I'd much rather be able to buy one out of a giant surplus bin somewhere in mainland china than trying to measure it and find/make a bespoke replacement.

Replaceable fuses make great failure points for things like motors that can draw silly amounts of current when stalled.

[ajsnigrutin]

This really depends on many factors.

Will you be able to get those parts, how fast and how cheap, and how easy/hard is it to replace them? Garage door, maybe... it's an expensive thing... you'll investa lot of time/effort to get it fixed... buta battery powered drill? No way to get the parts. Someone mentione 3d printing... can you imagine some average drill owner designing a part for 3d printing, buying a 3d printer, going through the learning curve to get a usable part.. for a $50 drill? No way. Just having someone open it up to replace it is more expensive than the drill itself. On the other hand, you could pay 20 cents more when buying and got a long-lastin metal part.

If you want a part to fail to not cause greater damage, add some kinf of a standardized fuse to it, or detect the overload and stop it, before it fails. Yeah, sure, something is going to fail at some time (nothing lasts forever), but treating plastic gears that break (instead fo $1 more expensive metal ones) as a good thing,.. i have to disagree with that.

[jkestner]

Underrated is ordering SLS parts from a printer, like on CraftCloud. You can get small functional nylon parts made for $2 + shipping.

Modeling things has always been the biggest friction point. Not easy to make CAD interfaces easier. Part files from the manufacturer would be nice.

[ajsnigrutin]

Sure, but you still have to either open the device yourself, or pay someone to do it, find the broken part, find the part design, order it, ship it, replace it, and reassemble the device. If you don't do it yourself, it's not worth it at all financially, and if you do, it's quite a long process, usually not worth it for a $50 drill, where the company wanted to save a few cents with a plastic part.

[jkestner]

Oh yeah, overall, I don't think 3D printers are useful for this in the real world, not at this point. Just playing to the crowd, for those HNers determined to make use of 3D printing.

Nothing beats simply designing to repair, or at least YouTube how-to videos, and available replacement parts. I've kept a stupid $100 microwave going for 15 years with two $4 repairs, mostly for the principle of it.

[btbuildem]

One could find the part design in a library, and print it at a coop hackerspace or order it online off some pay-per-print shop. It doesn't have to be as complicated as you put it.

[ajsnigrutin]

But it's a $50 dollar drill, that failed due to a cheap part.

I don't know where you live, but just a diagnosis by a repair technician is more expensive than that. Even if you open it up yourself, find the broken part, find that part someone, get someone to print it,get the part delivered, and replace it, it'll be more than $50 of associated costs... and just because a company wanted to save 50 cents on a plastic gear.