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Comment by digdugdirk | Hacker News Reader

I love your optimism, and would absolutely love to have this capability in a garage. But as someone who designs physical products (and deals with all of the manufacturing techniques you mentioned above on a regular basis) I can't say I agree. There's a huge amount of knowledge and skill required to make machined/cast/extruded metal components, and a very steep learning curve before someone can do so safely.

Gamechanger? Yes. But likely mostly for the ambulance industry.

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> Gamechanger? Yes. But likely mostly for the ambulance industry.

While I laughed, I don't find this to be very true at all for working in metal.

Working on metal seems to have WAY fewer injuries than people who work on wood. Metal working is almost always in a vise and your hands are on levers/cranks--away from the cutting surface.

Whereas, with woodworking, your hands are almost always the motive force and directly next to the cutting envelope.

Simply take a look at the hands of long time machinists vs long time woodworkers. The woodworkers are the ones missing some finger bits.

It really depends on what area of industry you are in and the safety culture of the shops you are around. I hear a lot of stories of really bad safety practices in metalworking. Including the exact inverse of your statement about machinists/woodworkers and missing fingers. I would also argue that accidents with common machine shop tools like lathes and mills may have higher consequences than your average table saw or jointer in a cabinet shop. The "potential energy" is higher so to speak, although I'm not trying to downplay the forces involved in something like a table saw kicking a workpiece back. For example, there's a prominent post on r/machinists now where a poster witnessed their coworker getting sucked into a lathe (fatally). This is not something that is a risk at most cabinet shops, but is a risk at most machine shops. That accident was indirectly caused by disabled safety interlocks on the lathe, an unfortunately common practice in the industry. All anecdotal evidence, of course, but I think machine shops have a different risk profile that isn't necessarily less risky overall.

I don't know, I'd have thought the angle grinder - signature tool of the metalworker - is probably one of the most dangerous tools you'll find in the average DIYer's garage.

I imagine a circular saw with 1 inch teeth will do far more damage to human flesh than a grinding disc

The grinding discs shatter. Wear a full face shield.

Yup. I've seen several stories about such incidents, one of the good things about the internet is the ability to spread info on these things.

Safety specs saved this guy's eye from an exploding angle grinder disc.

https://www.reddit.com/r/pics/comments/4npyfu/safety_specs_s...

Pretty much everyone I watch on YouTube calls them some permutation of “the wheel of death”.

Agreed. I've seen a lot of people coming from 3D printing become interested in CNC and assume the complexity, risk and investment are similar. They hit a wall pretty quickly when they realize all these things are much higher when machining metal. There are a lot of hobby mill companies willing to perpetuate this assumption by selling cheap benchtop mills. But to do produce anything with "industrial" precision, strength and surface finish at a decent rate, the physical size of the equipment alone is more than what most garage shops are willing to accommodate.

I've often considered a CNC Mill though. A huge variety of plastics are readily available from McMaster-Carr of varying machining qualities (Acrylics are best for Laser cutters, but you can get extruded Nylon, Cast Nylon, extruded ABS, etc. etc.). There's also a wide variety of cheap woods available.

This guide focuses on Urethane Casting, which is yet another set of plastics you can work with.

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I've worked with all of these plastic technologies and materials, not necessarily in my lab but in various Makerspaces. Its all easy enough, and "safe enough" to work with.

Obviously, even woodworking equipment can chop off your limbs. So you should go in with a degree of woodworking training and/or study. But there's plenty of woodworking classes available at community colleges everywhere. Take one of those and you _should_ be set for wood/plastic level cutting tools (like a CNC Mill).

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Taking the next step into metalworking... ugggh. I know people who take that step, but it is another level of safety / study above and beyond wood/plastics. I'm happy with my woodworking level of knowledge (and its incredibly practical, especially if you're a homeowner).

The problem is that once you start adding up the cost of the components to make a capable CNC mill, you get really close to the price of existing ones. Ball screws, good linear rails, etc. are no joke. Big heavy castings (cast iron or polymer concrete) are no joke. The most "disruptive" maker-style machine is the Tormach and it's not well liked.

Lots of open source designs that can route steel, like PrintNC [1] and OpenBuilds [2]. If all you need is Aluminium, then you can make do with something like the RS-CNC32 [3] or MultiBot [4].

[1] https://wiki.printnc.info/en/about

[2] https://openbuilds.com/builds/category-list

[3] https://www.makerfr.com/en/cnc/rs-cnc32/

[4] https://hackaday.io/project/176110-multibot-cnc-v2

They don’t hold great tolerances, but if that’s ok then they’re fine.

What do you consider a great tolerance?

Not parent, but I’d consider 0.001” over 10” to be totally acceptable for home and hobby use and 0.00025” over 20” to be acceptable for general production use (“great” isn’t really meaningful, but “makes parts to spec” is good enough).

That's the specification of a measuring instrument. Commercial VMCs don't hold 0.00025” over 20" even without being loaded. A slight temperature change will throw that off.

What you say is correct, except that a hobbyist can source parts from Ebay and the like. Which you could never do for a production machine. That can bring the cost WAY down.

you can also buy an old fadal or some other thing and just run it or retrofit it, and this is pretty cost effective.

I cast aluminum in my backyard frequently. My forge is made from 2 one gallon paint cans, some charcoal, and a hairdryer. It cost me less than ten dollars to build. It's only as complicated as you decide to make it.

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