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0 pointsabakker11y ago0 comments

My $1500 home CNC will give .001" of an inch of accuracy. You'd be amazed how much errors in the .01s of inches stack up into unusable parts (try doing inlays with wood).

You are quite right that the cost of operation is quite a bit higher though. Bits, collets, spindles, etc really add up. Even with wood, all the tooling is made of solid carbide.

subtractive machining has its benefits though. While printing can make some unattainable shapes, subtractive machining gives a nicer variety of materials, and can be faster.

as to the more mature technology now, CNC definitely has 3D printing beaten, at both scale and precision. Hopefully soon, we'll be able to 3D print carbon fiber parts and then we'll have a real 3d printing boom.

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sgnelson11y ago

Don't get me wrong, I'm also a machinist, and I do use subtractive machining quite a bit. And I'm guessing your CNC machine is a router, not so much a mill (to make life easier, I'll classify a mill as having a much larger Z-axis movement, and built to deal with harder to machine materials (steel essentially.)) And in that case, it's much easier to get a router to hold smaller tolerances than something that's designed to handle steel. Now I could be totally wrong, and if so, props to you, you got a deal. But really, even the cheap chinese mills (again, talking about something like the Grizzly g0704, maybe the Sieg X2) I've seen that (sans CNC equipment) start at around $1000. And once you add on ball screws, servos, and all the control hardware, you're pushing $1500 easily. And like you said, then you have to actually buy the tools you need to use it.

But while prices on CNC mills are getting cheaper, I'd argue that they aren't declining in price the way that 3d printers are (my reprap cost me $400, my makerbot clone $550). A mini-mill still costs more than it did 10 years ago, with very little improvements to what it does (better motors, electronics, that's about it.)

But to put it simply, I agree with you. Subtractive machining has it's place for sure, but so does 3d printing. But to say that 3d printing sucks, period, is just silly and ignores all the benefits that 3d printing provides. I believe in using the right tool for the job. Sometimes that's old school machining, some times it's 3d printing.

I'll add two quick, somewhat off topic points. It's now (apparently at least, according to GE) easier for them to additive manufacture turbine blades made out of inconel than it is to subtractive manufacture them. I've never had to machine inconel, but from what I've heard, it's quite the difficult thing to do, and most places that machine it, try to cast the part as close to net as possible to make as little machining as possible to do so. But this is something that truly shows the advantages of 3d printing that (might) be better than the traditional way of machining.

The other anecdote is my own. The other day, I was making a part, and for shits and giggles, I took the blueprints, made the part in CAD, printed it out on my 3d printer, and just the act of holding it in my hand and looking at it really helped me think about how to go about machining it out of steel. Most people think "On, CNC is easy, you just throw the file on the machine and it makes the part." It's not that easy, and I was just doing this part on a manual machine. But having that part in my hand really helped me make better decisions on how to best machine the part itself. I thought that was a neat little aspect of 3d printing that I would have never even thought of using it for.

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