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Comment by rich_sasha | Hacker News Reader

Meta; as a non-engineer I'm always fascinated by all the seemingly arbitrary, though surely well thought through design choices that go into anything mechanical.

For example, panels can be screwed in, welded, glued, riveted, snugly fitted, attached with some kind of retaining bolt... And so on. When assembling IKEA furniture, someone clearly though some bits require dowels, other screws or nails, other still those weird round spirally things that, when twisted, pull the metal bit in.

I guess car panels obviously (???) need to be removable for repairs, but still. In an alternative universe, I'd love to be an engineer and understand some of those things.

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IKEA is regularly mocked for selling junk made of newspaper clippings and chewing gum; but no one would question their ability to design passable furniture made out of the cheapest materials possible, transportable in an average car, assemble-able by an illiterate, with prices that are below their competitors and often get reduced as they find new efficiencies.

Tesla probably takes a lot of inspiration from IKEA; but consumers expect a lot more from a 80K USD car expected to last hundreds of thousands of miles, than wobbly furniture that will be trashed at the first move.

> other still those weird round spirally things that, when twisted, pull the metal bit in.

Those https://www.ebay.co.uk/itm/284791145273 (sorry can't seem to find them as an official IKEA part)?

They're quite clever. They achieve at least these things:

- assembly happens from the inside rather than the outside, which looks better and may be easier to assemble in place

- the cam pulls the fixing to a particular depth, and no further. Overtightening a screw would be easily done but completely destroys the chipboard from which IKEA products are made

- load spreading in the chipboard. Again a screw into the end of chipboard would be very prone to splitting it

- very resistant to self-loosening

You can order replacement spare parts for free. The US ordering system is https://www.ikea.com/us/en/customer-service/returns-claims/s..., and the cams have spare part number 103114. Obviously this is meant to be used if you break or lose a cam or two during assembly.

Think of different manufacturing techniques as software frameworks - different frameworks (manufacturing techniques) have a niche that they can do well, but they all have their impacts on development (manufacturing/assembly/shipping) and operational costs (long term reliability in the field). Sometimes developers swear by a framework and know it inside and out, but ask them to work in a different framework and they'll be slow to get up to speed and potentially make mistakes that experienced developers wouldn't.

The main breakdown in this analogy is that the differences between manufacturing techniques can be immense, so the range of "good" techniques for any specific application is much narrower. Using one manufacturing technique vs another might result in not being able to ship your product in separate parts, making your shipping costs 20% higher and reducing your profit margin into the "bankruptcy" range.

This seems like a decent analogy. Still, one product might use lots of different processes in different places. It's a bit like mixing many different web frameworks within one web app, for example.

I'd say the better analogy is different libraries rather than frameworks.

They're called cams, the metal part it pulls in is a dowel. Older ones you had to make sure were fitted before you put the dowel in, but the newer ones you can fit afterwards - so if you have a panel that has many dowels to go through many holes you no longer have to swear many times when one falls out and you have to start the process again. Beautiful in their simplicity.

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