CNC milling with open source software • Hacker News Board

Re: CNC milling with open source software

#81

Post by jdietrich » Fri, Jan 18, 2019, 10:14 PM UTC

felipemnoa wrote: post #65

opwieurposiu wrote: post #18

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…

>>Any tiny little error in your gcode has a chance to crash the machine. I would assume that an emulator for the machine exists that allows you to test your program before trying it out on the real thing. Was that not the case?

Good CAD/CAM software will detect obvious errors in the toolpath, but there are things that require common sense. A large proportion of machine crashes are caused by a discrepancy between the computer model and the real state of the machine, which the software is obviously unable to detect or prevent. CNC machines generally have no sensing capabilities; they rely on the operator to provide accurate measurements on tool height and work positioning. A transposed digit or a value entered in the wrong field can easily cause an ugly crash.

Workholding is a common issue - a 3D model just floats in abstract space, but a real part needs to be securely held in place. It's quite easy to inadvertently crash a tool or spindle into a clamp or vise, or to apply cutting forces that exceed the clamping force and throw the part.

https://www.youtube.com/watch?v=PsFNeiAu04M

Re: CNC milling with open source software

#82

Post by PascLeRasc » Fri, Jan 18, 2019, 10:19 PM UTC

th0ma5 wrote: post #23

opwieurposiu wrote: post #18

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…

Is there no way to test? Or there is, just not everything?

Some CNC machines, like the Bantam Tools "Othermill", have software that does a "test" and will tell you if you'll crash into the board, and can recommend drill bit sizes. I'd highly recommend this machine btw, excellent support and I've been very happy with the results for both wood and PCBs.

Re: CNC milling with open source software

#83

Post by dekhn » Fri, Jan 18, 2019, 10:19 PM UTC

Hasz wrote: post #41

jcoffland wrote: post #5

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.

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.

Re: CNC milling with open source software

#84

Post by jdietrich » Fri, Jan 18, 2019, 10:19 PM UTC

gangstead wrote: post #51

dylan604 wrote: post #36

Earlier quoted context omitted.

There's a big difference between an additive process vs subtractive process. To me, additive is much easier as it starts at the bottom and build up. Nothing is ever in the way of the next step. Subtractive is much more difficult as you have to figure out how to get to places that needs tooling, how to hold the piece to do the work on it (especially as the piece changes shape in the process). Most projects I work on r…

I've found the work holding on the CNC to be somewhat analogous to bed adhesion on the 3D printer. When milling you have to figure out how to hold this block down and printing you're using glue sticks and tape to try to get the first layer to stick. Both of these require the same trial and error shade tree mechanic skills that I enjoy developing. My sticking point is more in the CAM side of things. First I'll design…

I might be a dreadful old fogey, but I think that everyone should learn manual machining before getting into CAD/CAM. There's a level of mechanical sympathy that can only be learned by turning the handwheels and making chips. CAM is complex because machining is complex - removing the software from the equation makes it far easier to learn the fundamental principles, IMO.

Re: CNC milling with open source software

#85

Post by dekhn » Fri, Jan 18, 2019, 10:20 PM UTC

51lver wrote: post #74

jandrese wrote: post #67

Earlier quoted context omitted.

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…

If an axe could detect your thumb was in the way, it would no longer be useful. There's a balance. Sometimes it really is up to the operator to maintain safety. Sometimes the machine can handle it. IMHO, other than reliably finding zero, everything else is up the the operator. The tool doesn't REALLY know how big it is or how fast it's going (just what it was told), and even if it did know, some operator would screw…

gotta disagree. I don't know anybody who works in a machine shop and doesn't want sawstop enabled, unless they need to disable it for a specific cut (wet wood).

Re: CNC milling with open source software

#86

Post by dekhn » Fri, Jan 18, 2019, 10:23 PM UTC

Animats wrote: post #61

opwieurposiu wrote: post #18

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 have to repeat the points in this comment. I've worked extensively with low-cost CNCs, and they can't really do anything more than light engraving of aluminum and slow cutting of wood. There are some straightforward physical reasons for this (there is no cheap and fast replacement for mass and torque).

Re: CNC milling with open source software

#87

Post by nickpinkston » Fri, Jan 18, 2019, 10:24 PM UTC

rmu09 wrote: post #31

nickpinkston wrote: post #25

Earlier quoted context omitted.

The best shops use simulation tools, but you need the 3D models / configurations of everything to make them work, and then the machinist still needs to load everything correctly. It's very easy to make a mistake. Check out a simulator here: https://www.ncsimul.com/

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?

Re: CNC milling with open source software

#88

Post by nickpinkston » Fri, Jan 18, 2019, 10:24 PM UTC

onmai-xyz wrote: post #56

nickpinkston wrote: post #25

Earlier quoted context omitted.

The best shops use simulation tools, but you need the 3D models / configurations of everything to make them work, and then the machinist still needs to load everything correctly. It's very easy to make a mistake. Check out a simulator here: https://www.ncsimul.com/

>machinist still needs to load everything correctly. It's very easy to make a mistake. Tool configuration is kinda-sorta solved with ISO 13399, this is being supported in more and more CAM systems and tool vendors, but as you say it is very easy to make a mistake. Assuming the mistakes are happening when the tool data is reduced from the comprehensive format that ISO 13399 supports to the barebones and simple TxDxHx…

Not to mention workholding, etc. that might be off.

Re: CNC milling with open source software

#89

Post by rmu09 » Fri, Jan 18, 2019, 10:31 PM UTC

juliangoldsmith wrote: post #80

rmu09 wrote: post #77

Earlier quoted context omitted.

CAM can take a lot of time and need considerable computing resources. Not that much of issue today, but still, why do the same computations over and over again? Also, you will want to inspect the toolpaths before running them on real hardware.

Yeah, you'd still definitely want to look at the toolpaths. As far as recalculating everything, it could still calculate most of it ahead of time. What I'm thinking of is something like a CAM workspace in FreeCAD. That is, something like would let you take your model, generate and inspect a toolpath (or flip through possible toolpaths), and produce a part. The CAM software would get feedback from the controller, so i…

It should not be that hard to export current axis positions and get it into FreeCAD. Look at machinekit, they have remote control and toolpath display. Pause/run/start, override of feed and spindle speeds also is easy.

Detecting chatter is not that easy. Slowing down may be wrong, sometimes it is better to speed up.

Doing on-the-fly adjustments of toolpaths in CAM integrated into a machine control would be a major research project.

Re: CNC milling with open source software

#90

Post by JeremyHerrman » Fri, Jan 18, 2019, 10:33 PM UTC

th0ma5 wrote: post #23

opwieurposiu wrote: post #18

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…

Is there no way to test? Or there is, just not everything?

There's a lot that can go wrong, and it's too much work & tech integration for most shops to make the investment.

Even if you have the 3D models for everything involved: tooling, tool holders, stock material, fixtures, CNC machine, along with the instructions for the movement of all of it, there are still many opportunities for both configuration errors and runtime crashes.

For instance, CAM tools usually simulation axis movements only, before they've been converted to gcode/NC. If there's a bug in your post-processor that generates gcode or if it doesn't perfectly match your machine configuration, you're going to crash.

Even if you use a simulation tool like Vericut or NCSIMUL, which both simulate using the actual gcode, the physical machine settings may be out of sync, or there could be a wrong piece of stock material loaded or some foreign object (a wrench) that causes a crash.

Probing routines and careful selection of Work Coordinate Systems can help verify/eliminate some of these unknowns at runtime, but it's still no guarantee that the part will come out right.

Hardware is hard!