91–100 of 133 posts
Earlier quoted context omitted.
Will you be adding servo support in the future? Steppers are great, but anything big needs a servo, as the steppers get to expensive and too slow very quickly.
can you point to some continuous rotation servos that would replace steppers? I haven't been able to find any that are affordable.
Earlier quoted context omitted.
It's not that easy. You need accurate models of your machine, the tools and the stock material. Your simulation has to be linked to the real machine movements and be ahead of time so you can estop the machine before the crash happens. But that still doesn't help in case of insufficient workholding or breaking tools.
It seems like the machine itself could implement some safety checks, like if a motor is commanded to go outside of its range of motion you trigger a stop with an error code and let the operator sort it out. Or go even more oldschool and have physical safeties on the machine that trip if your cutting tool attempts to exit the work area. I mean these aren't cheap machines, it seems like they could be engineered to be j…
The problem usually comes up by crashing into something that is inside its known workspace. e.g., cutting into a vise instead of the object that's held in the vise, or an incorrect offset causing a crash into the table. The machine may know that it can only travel up or down by 12.500 inches, but it has to hold cutting tools that may be of unknown length and that can cause it to hit things (like its own table).
Earlier quoted context omitted.
can you point to some continuous rotation servos that would replace steppers? I haven't been able to find any that are affordable.
I believe he means servos as "high-speed DC brushless motors with feedback" not the low cost gearmotor servos used in R/C models.
If you're interested in Open-Source CNC you should check out two of my Open-Source projects. https://camotics.org/ a CNC simulator and https://buildbotics.com/ a CNC controller. I'm somewhat surprised neither of these were mentioned.
Is there any reason why CNC machines aren't directly controlled by CAM software, beyond it always having been done that way? I'd think it would be useful to integrate the two, instead of the CAM software just firing-and-forgetting toolpaths.
In some cases, it is.
There are integrated CAM + Machines depending on industry and price point. (see woodwop, etc, which are the interface to the machine)
The motion planning aspects can be taken care of (despite other comments), beckhoff, for example, does real time plc on windows machines by isolating cpus away from windows. i have no problem using it as a plc. They also support CNC control.
Outside of software like that, it's usually being taken care of by an FPGA card and that's a pain in the butt. Assume you can solve this.
You still have the next problem: Actually driving the machine.
First, the low level
Most of the servos in these machines are using pulse train inputs of some sort. That's what the FPGA cards are doing, generating the pulse outputs, etc.
It's only in the past 5 years that things like "drive my servo over ethercat instead" became viable.
They use simple relays, etc to control safety/limit switches/you name it.
Now i could use an ethernet based field-io. So i'd say they are actually now there (in the past 5 years) for the low level. I can run all my field io/spindles/servos off ethercat now, for example. I do, in fact, outside of servos (my cnc software can't drive them over ethercat yet)!
5 years ago i couldn't do this.
Okay, so that's one level up. Now i can at least drive it from the CAM software in some standardized way if i knew what was what. Which is your next problem - knowing what anything does. Which io's are the limit switches. How do you home the machine or execute a tool change? How do i turn on the vacuum? Which drives go with what axes?
There is no standardized way of describing this, such that a piece of CAM software could actually do anything.
We'll get there, mind you, but it'll be a while.
Earlier quoted context omitted.
Is there any reason why CNC machines aren't directly controlled by CAM software, beyond it always having been done that way? I'd think it would be useful to integrate the two, instead of the CAM software just firing-and-forgetting toolpaths.
Wild assed guesses: Damage/safety issues: operating the milling machines incorrectly, or in an untimely manner. Related to latter point: lack of hard real-time processing in the upstream software?
(Both are these are solvable, it's interfacing with the machine in any standardized way that is not)
I've been looking into building my own CNC. Sounds like there are some experienced CNC peoople here. Does anyone know why there are not more polar coordinate based CNC machines? I've been wondering what the pros and cons are.
A gantry-style machine, on the other hand, has the same rigidity anywhere in the X-Y plane. Rigidity is a bit less as Z changes (due to a longer moment arm), but it typically doesn't travel as far.
Earlier quoted context omitted.
There are machines that are "self-aware" in the sense that they run a simulation parallel to the NC control, slightly advanded in time, to catch catastrophic crashes and ESTOP the machine. Cutting into the machine bed can be _very_ expensive.
Which machines are you referring to? How aware? Do they have any vision? Can they "see" or otherwise "know" about the cutters / workholding?
AFAIK the crash guard is a separate component that relies on 3d models of the machine and the tools, it doesn't see anything.
If you workholding is weak and a piece comes loose the crash guard probably won't make a difference.
Earlier quoted context omitted.
It's not that easy. You need accurate models of your machine, the tools and the stock material. Your simulation has to be linked to the real machine movements and be ahead of time so you can estop the machine before the crash happens. But that still doesn't help in case of insufficient workholding or breaking tools.
It seems like the machine itself could implement some safety checks, like if a motor is commanded to go outside of its range of motion you trigger a stop with an error code and let the operator sort it out. Or go even more oldschool and have physical safeties on the machine that trip if your cutting tool attempts to exit the work area. I mean these aren't cheap machines, it seems like they could be engineered to be j…
CNC is programming "for keeps". Any tiny little error in your gcode has a chance to crash the machine. Unlike a computer crash, a CNC crash results in broken metal flying across the room and anywhere from $5- to $5000 in damage. I programmed for a heavy machine shop for a year before I gave up and went back to making websites. Hobby CNC is fun though, it is amazing what you can make out of wood when you can shape it…
Yes. This article is about very low end CNC, just 2D routing. Using a Dremel tool as a CNC router never works very well. The motor isn't constant speed, slows way down under load, and can overheat. The bearings can't take side loads for long, either. It's been tried. A Bosch router from Home Depot works much better. Those can cut wood all day. You can take off the handles, leaving a motor cylinder that can easily be…
I've been looking for a home PCB machine and would appreciate any recommendations on what to look at or what to avoid. I've been told multiple times that it's easier to just have a service print your board which is probably true, but that would take a lot of fun out of the entire process for me.