Quote:
Originally Posted by pipsqueaker
Thanks for the replies everybody! People have been saying that the laser cutter's out of budget so let's throw that away, i knew it was a luxury anyways.
On the other hand, I'm interested in why you guys recommend the lathe so strongly? My understanding of lathes is that they're good for making shafts and things, but why does that give more utility than a 3-axis mill? I might not have mentioned this but we want to manufacture custom parts with these new machines, and it seems like a 3 axis mill would be much more useful/versatile than a lathe, which seems sort of limited in what it can do
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To put it simply, a lathe gives you freedom, moreso than a mill. It singlehandedly took our team away from being held at the mercy of what's available COTs, and gave us the ability to make custom parts and mechanisms tailored to our robots. Sometimes it's things that we flat out couldn't have done before, other times it lets us to something in a cheaper, or faster, or more space or weight efficient manner, which pays dividends elsewhere on the robot. Some specific examples:
-Spacers, standoffs, etc. We make every single spacer we use on our lathe out of raw delrin (occasionally aluminum). We can make them to any length, diameter, and center bore that we want, and save tons of money over COTs spacers like the vexpro hex ones. Our students can hold tolerances within a few thousandths of an inch on our small machine, a more rigid one will give you .001" or better. Being able to make a precision spacer any length we want allow other shaft parts to dictate the exact length of the spacer, and makes designing custom gearboxes, drivetrains, and other mechanisms much easier. The spacers tend to end up ugly lengths, but that's okay, you only have to make them once. And the precision really helps solidify our robots, and allows us to use axial-sensitive parts that we wouldn't have attempted in custom systems before, like small pitch chain and belting. It doesn't seem like that big a deal until you've done it, this alone has dramatically improved our robot quality.
-Custom shafting. The lathe made widespread use of hex shafting practical for us, a huge improvement over poorly retained keys causing failures at the worst possible times. Turn down each end of a half inch hex to half inch round, save a few bucks on hex bearings (which REALLY add up, and are a pain to align), and get foolproof axle retention in the process. Like spacers, you can get it cut to precision length on the lathe, and allow other components to dictate shaft length rather than trying to design around a COTs part. We can also add a 1/4" round to the end of any shaft for encoder mounting, and cut our own retaining ring grooves, which save tons of weight and space over shaft collars. Even for dead axles, it's helpful. We ordered about 30 feet of 3/8" aluminum round for dead axle applications, all of which turned out to be a few thousandths oversize and too big to fit our bearings. We shaved it all down on the lathe, rather than giving it to some poor freshman with a file. We've also made oversized shafts for some extremely high stress applications, in sizes you typically just can't get from andymark and the like.
-Custom boring. Need a bearing bore in a gear that doesn't have it? Chuck it in the lathe and bore it out! We've also pocketed out nearly the entire body of a few gears on the lathe, sometimes for weight savings, other times to nest the mounting of an adjacent part in in space critical spots.
-Custom pulleys. 1687's winch based catapult last year would not have been possible to fit in the robot the way it did without the ability to turn a custom winch and two pulley wheels on the lathe. We've also done polycord grooves cut right into ABS or PVC for conveyors.
-Stepped diameter shafting, allowing what would previously have been a pile of loosely connected parts to become one rigid piece.
-Knurled inserts. Before VexPro, we made press-fit inserts for Colson wheels.
And so on. Being able to carve anything roughly round out to precision measurements just changes the way you think about robot design, it opens up so many doors. I strongly recommend that all teams get one as their very first "serious" equipment purchase beyond the very basics.
A few other specific examples of parts made for this year's robot, which I couldn't imagine doing without a lathe:
- Dozens of spacers and hex shafts cut to precision lengths
- Custom standoffs which allowed us to nest elevator bearings inside of slots in our box frame lift system
- A hexagonal sleeve coupler, which enabled super-quick removal and replacement of our drive gearbox.
- A hex/round hybrid shaft which enabled a reverted gearing system for our elevator tilt mechanism, a HUGE space saver.
- A stepped pin used to lock up our elevator.
- Shaving down the outer diameter of dozens of bolts in our elevator ever so slightly, allowing them to press into bearings.
A lot of these systems incorporated milled parts as well, but we could have done a whole lot better at reproducing these without the mill. We couldn't have come close to these turned parts without our lathe. In addition, we've found that parts for these custom systems which absolutely demand a mill are generally few in number, very complex, form the big "obvious" parts of an assembly, and as a result, tend to be very well planned out. The turned parts, by comparison, quickly add up in a huge backlog, are generally individually pretty simple despite the precision demanded, and are occasionally forgotten until assembly time. The former lends itself very well to being produced by a manufacturing sponsor, the latter demands an inhouse machine.
I would also argue that a pretty minimalist lathe would adequately serve for most of the jobs above, whereas with a mill, you need a pretty signifigant chunk of machinery to make many of the parts you likely have in mind with a high level of precision. For three years now, nearly every one of our turned parts has been made on an old Atlas Craftsman 618 benchtop lathe, which has performed like a champ for us.