The Polar Bear – Open-Source, Multipurpose CNC Machine with a Rotary Axis | Hacker News Reader

The Polar Bear – Open-Source, Multipurpose CNC Machine with a Rotary Axis

kadirilkimen.com

448 pointscapitaogirafa150 comments

The cantilevering arm looks as though it wouldn't have any real overall rigidity for carving or for rapid, accurate motion with any kind of resistance... But I really love that this made it to hacker news because I feel like "hacking" doesn't exclude non-software hacks and it's always awesome to see hardware for design and making alongside all the other software news.

The idea of open source robotic assemblies or mechanical assemblies is another cool, separate thing. Another cool project I came across was the AR-1, AR-2, AR-3 series of desktop 6-axis robots. The inventor/designer made all the assembly docs open-sourced and sells kits or specs to make your own.

Yes, this looks like a great learning device! It could also be good for prototyping controls for a more serious tool, and the pen tool and maybe even a light extrusion head might produce some good results.

But cutting anything is, umm questionable.

In general, a cantilevered configuration is inherently wobbly compared to a gantry configuration that rolls on parallel rails/beams at the outside of the workspace. Even a massive Bridgeport-style mill has issues vs a moderate gantry CNC mill (although uses a lot less shop floor space). All the force paths are working to bend the cantilever device, vs all the gantry geometry that works to minimize error.

So, while it looks like a great effort and good for some things, if they want to offer any even slightly serious cutting capability, they'll need real work on the stiffness.

Neat kinematics with a horribly flexible frame that denies any serious usage. That said - it's designed to a low budget that increases the potential audience, and that is something that can only be welcomed. I'm particularly interested in the software as that will be an enabler for future variations that have mechanical rigidity.

Nice website!

Are there similar systems- CNC with multiple heads- that don't have this problem?

I played with a wood router CNC in high school and loved it. I've also played around with 3D printers a bit. The idea of having (and building?) a reasonable system that can do both strong appeals to me.

no. anything that is strong enough to, say, CNC will also be very slow for 3d printing or laser. different processes demand different designs.

Depends on the price class, of course. If you spare no expense, you can employ lots of iron and lots of power to throw around the iron.

https://youtu.be/RcansEmVknA?t=150s

For context, that DMU50 mill is about $275,000 new.

The closest that can do both is probably MPCNC (https://docs.v1engineering.com/mpcnc/intro/).

it is built with that modularity in mind but as other commenters have pointed out building something for rigidity makes it slower and heavier. a cheap 3d printer like an Ender 3 in addition to the MPCNC makes more sense, especially since you can save on the MPCNC by 3D printing the components yourself.

The main benefit to swapping a 3d printer head onto the MPCNC would be the pretty massive XY size you can build the MPCNC out to. If you need to print really large, flat objects it is probably cheaper than a lot of alternatives. But at that point it probably would make more sense just to mill it out of wood anyway.

>with a horribly flexible frame that denies any serious usage

What's the risk from this? That CNC work will be affected by resistance from materials, causing the frame to bend? What kind of scales would that effect be noticeable on?

For any real cutting, you need rigidity or nothing will be accurate.

You will not be doing any real cutting on this machine.

But to what extent will it be inaccurate? It seems unlikely to me that anything used for machining hard materials can be 100% rock-steady. Presumably, industrial machine are simply inaccurate to very small, tolerable degrees.

I have a small mill, it still weight around 1250kg… to be accurate at 0,01. And for that I would need to lock the unused axis and respect the power of the machine. This is not CNC, where the forces are often higher because they can work faster, with curve and some other things I’ll have a hard time doing.

Accuracy and Precision would be problematic with this design, but, lack of rigidity is more insidious. Most of these high speed spindles will use carbide tooling, which is highly susceptible to breakdown under vibration. A flexible horrible frame like this is going to vibrate a lot even in materials like delrin or HDPE.

Also, with a vertical spindle and CNC control, there is no reason to have a vertical rotary axis. The reduced motion doesn't buy any capability upgrade. The 4th axis that is helpful would be angular. (you could put a horizontal spindle on this, I guess, but this machine is not up to the task.

Obviously there is no perfectly accurate machine for any application.

The extent it will be inaccurate depends on a lot of factors, such as tool length, material parameters, feeds/speeds, etc. You can probably cut aluminum somewhat accurately on this if you take extremely slow cuts, with a tiny tool spinning at an extremely high RPM (which keeps cutting forces to a minimum). Surface finish would still be pretty bad simply due to vibration of the arm. Likely going to break a lot of tools too. The majority of metal cutting setups you would do on a mill are simply impossible on this machine.

For a few tiny cuts, it might be handy to have one of these, but it definitely seems more useful as a 3D printer, plotter, etc. Though even most 3D printers are significantly more rigid than this design.

The frame will vibrate resulting in chatter and in turn your cut will have waves and dips.

The risk is that you will only be able to mill materials that are very soft; materials that could be cut with a pair of scissors (card, foam). Anything harder will be an exercise in frustration (friction rubbing instead of cutting, frame flexing, motors stalling, terrible tolerance).

You have limited use for subtractive CNC work. Materials it can work on will be like chalk, charcoal, graphite. It might be usable on machine wax but I doubt it.

I would like to see software compensation for frame flexibility.

Either open loop (ie. use mechanical models to predict frame flexing and compensate for them), or closed loop (have sensors to detect realtime head position).

The whole idea of having a frame which is 100% rigid seems like a simplifying assumption that makes everything more expensive, with knock on effects too (eg. making stuff stronger makes them heavier, which in turn means a bigger motor is needed, which uses more power, so a bigger power supply is needed, etc)

I would think it would have to be closed loop. Material density is not always uniform (especially with something like wood) and that has one of the biggest effects on how your tool behaves.

Even then, compensating for sudden release in tension, where the tool tries to spring back, seems perhaps insurmountable.

I expect it would be easy to compensate position (closed loop is already table stakes in the professional tier) and extremely difficult to compensate chatter. What would it take to drive the motors of a 5 axis CNC to responses well into the kHz? You would need that, to compensate chatter. You would also still need to handle the same peak force, whether or not you do it with negligible deflection.

There are some industrial machines that compensate for chatter by slightly varying the spindle speed when chatter is detected. However machines so equipped are fundamentally very rigid and usually experience chatter occurs when pushing end mill performance to its limits. I suspect the adaptive spindle speed strategy would be much less useful on a machine like the Polar Bear.

Right, resonance dodging and deflection compensation aren't going to cut it here, not by a long shot. I still think a sufficiently good 5 axis control loop could damp acoustics: for one, the (fractional) millisecond timescale of the acoustic oscillations are geological by compute standards, and while I'd expect limitations from sensing, actuation, and power electronics, I don't see anything fundamentally prohibitive. I'm pretty sure this is an engineering problem, not a physics problem, and that eventually someone is going to crack this nut. It won't be the Polar Bear.

One way to compensate chatter is to have a small mass (say 50 grams) on an X-Y-Z voice coil on the cutting head.

Then you can use that to apply large brief forces in whatever direction is needed to stop chatter for a few milliseconds with each turn of the cutting tool.

It's the same mechanism used in iphones "taptic engines" to make 'clicks'.

The same mechanism can be used to actuate the head at far higher frequencies, allowing cutting fine detail at high speeds.

It could work to have two towers. The first carries the cutting tool. The second carries a measurement device and is subject to negligible forces. Alternatively some form of photogrammetry, possibly with a structured light field.

The Shaper Origin handheld CNC router makes an impressive attempt at compensating for imperfect frame rigidity, as it's designed to be handheld. The Origin operates in only two axes and uses consumable tape placed on the workpiece as an optical reference, but its progress is noteworthy.

Not pragmatic IMO - flexible usually means resonance and vibration which leads to poor finish and deafening the operator/upsetting the neighbors.

If a lighter frame was the design goal (but low cost wasn't!) then carbon fiber has an interesting stiffness/weight ratio and could have viscoelastic damping elements incorporated too. Realistically though, lightness isn't a prioritized design goal though I certainly see the appeal in marketing for home usage where you wouldn't need a crane to move the machine about.

The problem isn't so much the rigidity for absolute positioning, it's the high-speed vibration/chatter than a rotary cutter will induce. You can't really damp that out in a system like this (remember, you're spinning your cutter at thousands of RPM). This results in additive errors. Think of the washboard pattern that arises on dirt roads in dry areas. It's the equivalent, but your cutter doesn't have shock absorbers. If my limited experience is any guide, you'll eventually start snapping off your cutter, breaking your stock free from the mounting, and/or getting mysterious gouged cuts into the stock that destroy your detail.

Exactly. I can't speak for laser, extruders, knives or such, but for subtractive work (i.e. milling / drilling operations with some form of rotary tool) this design would be an exercise in frustration. Typically, you would have encoders on each axis to tell the machine where things are happening. These encoders are excellent, but any flex/slop in the chassis or moving parts is not caught by the encoder... so the software will not know that the cutter is in the wrong place. Thus, crappy parts. Any reasonably useful CNC design takes rigidity and backlash prevention seriously. Take a look at PocketCNC for a good (and yes, expensive) design.

You could probably use it for ECM or EDM, but yeah, not stiff enough for traditional hogging cuts as a lathe or mill.

could you use strain gauges to measure the deflection and fix it in software?

Great question. Human arms are also very bad in rigidity, repeatability, etc. but we manage to do great work by adjusting. Of course we try to move and rest on things to get out of the error-prone postures (so in effect moving from this to a gantry type of configuration), and need to measure, create jigs and templates, etc. but there is something here to be covered by sw for sure.

Comparing human arms to CNC "arms" makes about as much sense to me as comparing a sparrow to an F16.

Yeah both humans and multiaxis cnc machines can articulate their arm to apply a tool to a work piece and both a sparrow and an F16 can fly through the air.

I like your analogy, but just to clarify, which is the human being in your comparison: the sparrow or the F16?

A sparrow can take off and land on a branch, and it regularly weaves through thick foliage no wider than its wingspan. So, I assume the human is the sparrow?

Yeah I was thinking of the human as the sparrow.

I don't know if there's any strain gauges designed for this application. I'd be worried about nonlinearity, creep and how you would calibrate it in the field. (If it requires a dial indicator and a surface plate, you'd probably be way better off getting a regular CNC mill)

Optical tracking might be easier.

I'm not sure how much deflection you could actually tolerate before deforming the joints in the arm. Even with deflection tracking you might end up taking very, very shallow cuts. A 3D printer that runs for 16 hours in your apartment is annoying, a CNC mill running for 16 hours will be genuinely intolerable.

>could you use strain gauges to measure the deflection and fix it in software?

No. There's no substitute for rigidity in fixturing and of the machine itself. There will also be vibration motions that have unpredictable nodes, frequencies, and amplitudes.

Consider that a 2 flute mill at 20,000 rpm will induce vibrations with a fundamental frequency of about 670 hz. This would require a servo system with a bandwidth of about 2 khz to correct, a sampling rate of 8khz would be a bare minimum.

Next, what to do if the tool digs in, and shoves the part? You have to have backlash sufficiently damped, and rigidity enough to keep the tool or part from being snapped off.

There's a good reason machine tools are as heavy and rigid as they are, and why they must be on a thick foundation, and leveled precisely before use.

If you're going high precision, you'll also have everything in a temperature controlled environment, and allow the materials to soak at a day to achieve the proper temperature. Cooling is very important when you get into fractions of a millimeter, or "tenths" (1/10,000 inch) tolerances.

The best machine tools are old American cast iron machines from about 1940 to 1960, rebuilt with modern control systems.

The rotary axis is controlled by a stepper motor. This is not a usual turning lathe. The rotary axis can be made as slow as necessary and the only relevant analysis is a quasi-static one. Answering to parent comments: there are usually no encoders on these machines. The controller firmware just counts the motor steps. If a motor misses a step, everything will be off from then. For the cantilever design: it is already used by Prusa 3D printers which are well regarded (in the field of amateur 3D printing) so I do not think this is an issue for the targeted accuracy which is typically 10 to 50 micrometers.

The only issue I have with this design is that the accuracy decreases with the distance from the rotary axis, hence it is not uniform over the building volume.

It is 0.025mm on the outer edge of the table.

>For the cantilever design: it is already used by Prusa 3D printers which are well regarded (in the field of amateur 3D printing) so I do not think this is an issue for the targeted accuracy which is typically 10 to 50 micrometers.

3d printers don't have forces pushing back on the print head, nor the vibration from a cutting tool to deal with.

This design might work ok for 3d printing, or laser cutting, or anything else where no contact between the working head and the material occurs.

As far as accuracy and repeatability, it's going to be about as good as the average 3d printer design. It's a nifty idea for a system, but it's only a decent machine for cutting if it's scaled up massively and built of cast iron or similar materials.

Depends on what you cut. It cuts wood pretty nice. I couldn't documented the wood cutting performance on prototyping. I will demonstrate it's wood cutting capacity in v1 release. It's a 3d printable desktop machine and never intended to cut precise metal parts. May be I can design a full metal body version with professional components like rail guides instead of plastic v-slot wheels.

Whats the definition of "serious" here? Is there a standard measure of tolerance or material compatability that it can be rated against to see if it would work for a specific need?

CNC (and mfg in general) will have different tolerance needs. And the flex on this machine will depend on the material and work speed.

I'd probably argue that anything worse than 0.5mm (~20 thou) will start giving you headaches if your making parts that are supposed to interact with each other. That said, if you're making basically oneoffs and are willing to handfit, that tolerance is probably tolerable (ha!).

Serious = harder (hence more useful) materials. As it stands I would say only materials that could be cut with a pair of scissors (card, foam) could be used on this safely without frustration.

It's not hard to make a mill that can cut shapes into a block of styrofoam. If I stretch I can maybe imagine some industrial uses for a styrofoam-only CNC mill. (Moldmaking?) But what would a regular consumer use it for?

"Serious" just means the ability to cut more useful materials, like wood or steel.

This could be greatly simplified (at higher cost) by using linear motors for the cross-slides.

It may even be more rigid than what is there now (though nowhere near rigid enough to do anything real)

The design is actually not unique at all - you can buy much better versions of it (at higher cost, obviously).

Most positioning actuators you can buy are literally built to be attached to each other in a cross-slide configuration, and to have a rotary table attached to it. They also directly sell pre-built cross-slide actuators.

If you just google "cross-slide stepper" or "cross-slide servo", you can see this (servo/stepper just gets rid of the manual ones, which also exist).

The normal reason the configuration is not used is because it has no meaningful rigidity.

Well said.

Are you talking about products like this? https://www.amazon.com/Electric-Sliding-Ballscrew-SFU1605-Wo...

I'm not sure what you mean by "linear motor", I think these cross-slides typically use steppers or steppers with feedback.

A linear motor is essentially a stepper motor that has been unrolled. The Stator and rotor are flat. Kern uses them in really high end VMCs and the result is better position control and better rigidity.

do you have a pointer to a reasonably accessible device I can buy? I work with CNC and 3D printers and other motion stuff a lot and always want to find better products than the cheap steppers I'm using.

What is your budget?

I'd like to build this: https://www.thorlabs.com/thorproduct.cfm?partnumber=PT3-Z8 but for about $500 or less. I don't think those Z8s are linear motors, though. They mean "linear translation", but using DC servos.

It doesn't need to be nearly as precise,

Here you go:

https://www.kollmorgen.com/en-us/products/motors/direct-driv...

and their page on success in CNC seems fairly impressive.

https://www.kollmorgen.com/en-us/service-and-support/knowled...

Edit: I'm not sure how accessible these are, but they have a life sales rep chat, so they seem to want to get them to you quickly...

Generally, if a product requires talking to a sales rep, it's not marketed towards my interests (hobbyist automated microscopy and astronomy), and the product will be too expensive.

Ah yes, at that level, you've probably found lots of reasonable linear actuators - rotary motors paired with a screw drive - but I don't recall seeing any low-cost ones either. Maybe eBay is the best bet, but it's hit or miss. It does seem there would be a market for some low-cost options.

I used to work at Kollmorgen — they really are top-notch for this kind of work, but there is a relatively large used market available on eBay. No need to buy direct from them, unless you want brand new stuff at a markup.

My uncle uses Kollmorgen drives and servos on his homemade CNC, all sourced from second-hand machines and people, so it's totally possible to do!

I recommend that you use Clearpath servos. It is a step up in budget, but the motion is much smoother and there is no vibrations which are somewhat inherent in steppers.

Linear motors are great, but are overkill unless you are concerned with the lost motion inherent in any screw, r&p, or belt. servos and double nut ball screws are adequate for almost everyone (including Mazak, DMG, HAAS, etc).

Here's a video on it: https://www.youtube.com/watch?v=FYIBTIHOMxI

Although a tip to the creators: just pay someone to voice-over this. The robot voice is... terrible :D

I kind of like the robot voice. Very soothing.

Today quality of text to speech is amazing. They could have used a better service. Take a look at these samples https://wellsaidlabs.com/

i could not bare it after few seconds and muted it and read the auto-generated subtitles instead. it sounds really terribly annoying to me. its weird because otherwise this video appears quite well laid out and all but listening to it was destroying the overall experience of it for me.

Less annoying than the tiktok voice somehow.

I agree, the voice detracts from the experience -- but perhaps this was the best they could do under the circumstances. We don't know how good their command of the English language is, maybe they can't even tell how bad it is. Or maybe they're just of the Tik Tok generation and this jarring awfulness seems normal :)

I'm not sure which is worse, the robot-voice videos or the no-voice-waving-hands-music ones.

How does one navigate this website with a keyboard? The mouse wheel switches between the slides. The cursor key, page up/down, spacebar, don't work to navigate and the slide selectors at the right side can't be accessed using Tab as well.

Also by tabbing to some of the links you break the page as the scroll is out of sync.

>How does one navigate this website with a keyboard?

One doesn't.

Nor with a trackpad apparently.

I didn't have a problem navigating the page with a trackpad. I agree that it is bad that you can't use arrow key and page keys do switch between slides, but I don't see the problem a trackpad would pose.

Even with a mouse it's bad. If you have a free spinning scroll wheel scrolling a little can cause huge jump, but once you start scrolling faster the page will do opposite and not scroll at all (probably some kind of mechanism trying to prevent skipping over multiple pages). The fake scrollbar can't be used either and menu bar is useless because because who knows what each two letter pair means.

Load it without JavaScript, and with a `.swiper-container { overflow: unset; } .swiper-wrapper { display: unset; }` user stylesheet, and it’s perfect except for the contact form which they’ve implemented badly (the fields don’t belong to a form, and they’ve just put a click handler on the submit button, which basically turns into a form submission, just done AJAXily), but you couldn’t read the form field labels anyway so maybe that doesn’t matter.

The website is a disaster. Browser scrollbars don't work, page up/down keys don't work. There's some kind of barely contrasting menu of two-letter codes on the right-hand edge of the page.

My day is too short to figure this out. Moving on....

Works fine with Vim Vixen add on

If the software was compatible with proprietary vinyl cutters, there would be a slew of stay at home moms who would love to use it. Popular manufacturers have completely destroyed their customers' faith - I recommend this excellent write-up in r/hobbydrama:

https://www.reddit.com/r/HobbyDrama/comments/mmmcy7/home_cra...

I interviewed a guy for a dev job a while back who had written software for a consumer embroidery machine just because he had one and wanted it to work better, that had turned into a pretty good side business and it sounded like he had the same customer base, and it was a very profitable niche. A small but devoted group of users who weren't well served by the manufacturers and didn't have the technical skills to develop a solution for themselves.

One of those bad ideas that crops up again and again and again. Any multipurpose machine will be bad at all things. You're far better off getting a separate CNC mill, 3D printer, laser cutter, etc. Even if this costs a bit more and takes up more space, you'll have some useful machines.

Space and cost saving multi-purpose designs are ubiquitous in the professional space. At a home-gamer level "just buy all the separate machines!" is a ridiculous argument.

Not in professional machine shops or manufacturing of any kind.

At first, yes, I agree. But folks could say the same thing about phones, cameras, GPS, etc. years ago (now all in one device). Or multi function printer/copier/scanner/fax. Over time, things improve. Who knows if that will happen here, but it seems likely to me.

So many critical comments, with albeit legitimate critiques, that are missing the point. This is an open source hobby project that is designed to be built with a 3d printer and a few inexpensive off the shelf parts. I have yet to see another rotary table based cnc project like this. does it have some inherent design compromises and short comings? yes, but this is a starting point. The initial reprap project was (an ancestor of this project, no doubt) was also very flawed. This is the starting point of a pretty novel take on desktop cnc and if it gains some traction, will also evolve and iteratively improve.

I think we simply rejected the point. There are many newcomers thinking they can disrupt the space with terrible designs. Open source shouldn't mean terrible design. There are many better open source CNC already.

Machining without rigidity is a Hard Problem. If someone expects to just iterate past it or trade away a bit of performance and ignore it, they are in for serious disappointment.

This isn't necessarily obvious to people without CNC experience: just look at the number of people in this thread who think deflection compensation can solve rigidity problems. There's no shame in being new to CNC and not really understanding or believing the hype about rigidity, but the Polar Bear company has a financial interest in pushing people towards learning these lessons in an expensive & time consuming manner. That's exactly what they're doing. The people with CNC experience have seen this show before, have seen the burned customers, and are just trying to make sure that expectations stay in the ballpark of reality.

Cantilever design will be fine for small machines. One of the bigger problems of the design would be keeping one's work piece attached to the table.

For controller software I would recommend customizing klipper[1] that runs on RPi/most controllers for custom kinematics. It's written in python and C and it's well documented.

https://github.com/KevinOConnor/klipper

Thanks. It was on my scope.

This reminds me of the Dual-Disc Polar Printer: https://hackaday.io/project/177633-dual-disc-polar-printer

What a nice project. How I missed that :)

Ok, I'll bite. Can this machine be used to 3D print a part and then switch to a sanding/engraving tool to achieve a nice surface finish? The machine is too "floppy" to do any serious milling but it is good enough for some cosmetic surface operations and depending on your target audience, cosmetics might matter a lot.

Maybe? Not all plastic plays nice with machining, but E3D demoed mixing additive and subtractive manufacturing with their tool changer setup, which is a much more rigid Cartesian system.

I'm pretty sure this is addressed in both the video and the website. There's a whole section where it shows swapping out various tools at different angles for different functionality, including 3d printing and CNC milling.

But if you looked at their CNC example, the result was pretty dang coarse. Painting on something like XTC-3D from Smooth-On is one way to get a better finish while avoiding tedious sanding.

Hi, I am the developer of the Machine. It is a bad machining. But not because the machine. I don't have a good 4 axis paid cam software. So, I developed a software myself to generate 4 axis milling. Obviously it has a bug and it wasn't possible to generate a finish work.

After I release mechanical design v1, I will work on the codes and hopefully will be able to demonstrate a clean finish work.

It wouldn't be easy to secure a printed part, especially without adding slop. Also, is there any overlap between materials you can 3d print with in this thing, and ones you can mill (or even polish) without shattering the part?

Very cool project. I guess actual subtractive manufacturing can only performed on very soft materials like foams - I have an eShapeoko which is stiffer than this construction and the frame starts flexing quite easily.

What do you mean? Lathes have been used to do subtractive manufacturing with metal for thousands of years. Modern Lathes are CNC types and can build a lot of stuff.

https://en.wikipedia.org/wiki/Lathe

Lathes are kind'a more rigidly built though and I think that is what GP tries to point out.

This thing is not very rigid and the interconnections are made of plastic. There is a lot of flex and anything other than soft materials can not be milled with any precision.

One main reason professional 5 axis CNC machines are so expensive is because they are very rigid yet can move quickly and precisely.

And they were built using solid cast iron. Meanwhile this machine consists of one big aluminum extrusion and a thin extrusion. It's clearly built for speed not rigidity.

> Meanwhile this machine consists of one big aluminum extrusion and a thin extrusion.

With long cantilevers (i.e., supported at only one end) on both, to boot. Long cantilever, thin material = slop.

Even a small bench top lathe has hundreds of pounds of cast iron in the bed and ways, as you said.

That aside, a lot of the jobs they show in the video (pen-plotting, wood-burning, 3d printing, etc.) don't really demand a huge amount of rigidity. I wouldn't want to try any serious milling or turning with this machine, for sure, but for those jobs it looks like a totally reasonable design.

And I do like the fact that it's designed to be 3D printed itself (other than the extrusions and stepper motors, etc.), so well done on that.

Rigidity of the frame is key for accurate and safe subtractive manufacturing.

You do not want your frame to flex while a spindle is cutting aluminium at 20kRPM. See Marco Reps and Kris Temmerman on youtube, they built formidable high precision CNC mills out of steel and concrete. For machines that rely on frames made out of extruded aluminium, flexing has always been an issue, even with much sturdier designs such as the Avid CNC machines.

Also, FYI, in a lathe the workpiece spins, and in a mill the tool spins.

That cantilever design is known for having rigidity problems for 3D printers and isn't used at all for subtractive manufacturing. Compare it to a MaxNC 10[0] or a Taig[1] micro mill and you'll be able to see how much more robust their construction is.

[0]http://millingaccessories.biz/2015/04/07/maxnc-10-cnc-millin... [1]https://lh3.googleusercontent.com/-TkXnpUUXqLg/T4Qj3qVU9JI/A...

Hi, I made some carving on wood while developing the prototype. But didn't documented it. It is possible to cut wood. But not metal of course. You can get good results with the wood.

I machined plaster and wood on this machine. Both works well. I had only one 775 motor without speed controller while developing the machine. So, if you have a configurable rpm spindle with low vibration, you can get very good results on wood.

It's a 3d printable cnc machine. Of course it is not rock solid rigid and can't machine hard parts precisely.

It is pointless to compare this machine with a high end high precision machine. You can't get that rigidity and precision from a 3d printed part.

But, may be someone wants to build it from metal. Then you may consider to get better results.But this requires more modification because you can't expect high precision while using v-slot wheels.

Highly recommend watching the explainer video. Very versatile tool!

They should embed the video in the front page, glad I went back to watch it!

Don't understand why they used a robot voice for an otherwise well thought out and high quality video tho.

Maybe the author speaks English with a strong accent so he decided to use a voice robot...

Hi, Thanks! I am the only one who works on the project. I didn't like my sound on the record and decided to use robot voice.

That's right. I would embed the video on the front page. I will do it as soon as possible.

If you need open source control, use LinuxCNC. If you need open source designs a) why? b) download any of the many designs on the internet constructed out of 8020. If you need to budget less than 8020, use maker slide.

I've build multiple BIG cnc routers. One with 8020, one out of steel. The industrial design of the frames are not that hard, its more cable management, PLC stuff, sensor placement, and calibration that get you. Linear rails (e.g Hiwin rails) offer excellent linear motion and rigidity. Rolled ball screws also work great.

I've also converted some older manual mills to CNC, most recently a Bridgeport that is running a Masso G3 controller.

The reality is that the need for open source in this space is limited because most of the hardware that is available for Mach3, Mach 4, UCCNC, is highly versatile, and the "closed source" software still allows scripting, etc to modify buttons and routines to suit you. And again, if you really want to control everything, LinuxCNC works.

If you are new to this space, I recommend buying or building a gantry router. It gives you 3 axes of motion with a vertical spindle, and depending on the level of weight and rigidity you add will influence the hardness of the materials you can cut.

What are your thoughts on ballscrews vs r&p? Is whip an issue with higher ipm on a long machine (4x8)?

ball screws are better, more expensive, and more rigid. to get them longer than ~50 inches you probably want to either get ones with a very high lead angle, or use ones with a driven ball nut design.

R&P works totally fine for wood and aluminum, and is significantly cheaper and easier to implement.

Once consideration is that in driven ball nuts and R&P the motor must traverse with the moving axis. In standard ballscrew config the motor can be static which makes cables and packaging easier.

I should add - rotational inertia becomes a detractor with big ballscrews, too. An 8ft ballscrew weighs a lot, and that can make positional overshoot a problem with steppers or servos.

Also, most ballscrews that hobbyists buy are rolled screws, and I've never encountered one of those that was super straight. it doesn't matter much for accuracy if they are a bit warped if the bearing support is done right, but it sure can make the whip a problem.

This is called an "all in one" tool. There are others. The Snapmaker [1] is very similar to this. There are even some with turntables.

[1] https://us.snapmaker.com/collections/snapmaker-original/prod...

Given that the parts for this are meant to be 3D printed and thus the people who have this presumably already have a regular 3D printer, it probably makes more sense just to make a rotary table for your cartesian 3D printer.

Also given that objects on the rotary table can not overhang without causing interference with the vertical axis column, there's really no harm in adding another column and spanning the horizontal axis across, instead of cantilevering it. This will provide a substantial improvement in rigidity.

This is totally doable and there is no harm to do it.

It would be another project and I hope someone develop something like that.

All these things can change widely by choises. We can't claim that this is better or that is better. All have their own pros and cons.

I designed the PolarBear this way because I was hoping that machining 4axis like would inspire a lot of people to do different things on cnc machines.

I love 3d printers and this is a refreshing take on it.

Also looks super cheap to build which is good news.

Being from a country where 3d printers have a 100% tarif this is great, because the BOM is simple and one can just buy the parts and assemble it without too much of a hassle like a cantilever style (this looks even simpler than that), doesn't look complex to assemble like i3 Prusa or Core XY designs.

> The PolarBear CNC machine needed special CAM software to use the full potential of the PolarBear. So I decided to start an open source Cam software project.

> It's kind of necessary. Because there is no powerful and complete open source CAM software that is useful and easy for everyone.

That helps me understand where this falls on the plausibility scale

Not to mention the github repo for the CAM software is currently empty except for a readme and license.[1]

I would love to see a functional open source CAM software that would compete with basic tiers of Mastercam/Fusion360/etc. I think it would be of huge benefit to the manufacturing industry, education and hobbyists. There are a lot of machinists/CNC programmers very worried about Autodesk's dominance over the field and the consequences of further consolidation and crapification. Many machinists are currently learning hard lessons about SaaS.

Unfortunately in my observations (as a user and CAM software purchaser, not a CAM dev) writing toolpathing engines seems to be a Hard Problem with most of the expertise concentrated within entrenched companies. There are a few smaller companies developing CAM software but most seem to build either on one of a couple licensed CAM engines or very old legacy software from back before the big players dominated the field. Lots of the functional requirements for a CAM system have been stable for years (decades even), so a casual observer would think it is ripe for an open source alternative. However I haven't yet seen an open source alternative that could plausibly compete or even achieve feature parity with any of the commercial CAM software I use.

Best of luck to the PolarCam dev. I don't have high expectations given the magnitude of the task and the hobbyist nature of the associated hardware, but I'd love to be proven wrong.

[1] https://github.com/kadirilkimen/PolarCam

Hi, of course I am not saying that I will develop a complete software package. I am a single guy who loves to work on these stuff. The repository is empty, Because I have no work on it yet. I developed several 2d and 3d toolpath generators for specific purposes for private companies. Always suffered from cam softwares and since I have enough background on the toolpath generating, I decided to work on it. We'll see in time. Most of strong open source projects started as individual initiatives. Someone failed but another one got inspired and started a better project that succeeded. So it could be me or someone else.The key is to have a powerful open source CAM software.

I appreciate the reply. How did you get a background in toolpath generation? I am curious because I have a background in both software dev and machining, but haven't combined them much. Was this something you became familiar with in school or only when working at those companies? Any resources you would recommend?

How did I get a background in toolpath generation. I don't like talking about myself in public. You have my website. If you really want to know more about these, please contact me. I happily answer your questions.

About recommendation; Toolpath generation is based on 2d and 3d geometry math. Simply dive into 2D and 3D geometry and try to understand some libraries. This is a very good one: http://www.angusj.com/delphi/clipper.php

Most 2d and 3d calculations are based on triangle calculations. There are also solved algorithms like finding the closest point on a curve. Once you start playing with triangles, I'm sure with some software development and machining background you can easily begin to understand how toolpath generation works. It's easier to create toolpaths from stl files. Because stl models only consist of triangles. Thanks to the gaming industry, triangle-based math isn't a cutting-edge science these days, and there are many open source libraries.

You also need tons of coffee and tons of dedicated time.

Very cool project. I read the GitHub notes and agree on the need for more (and better) open source CAM software!

Donated.

I guess the limits of this are the tools & attachments available. Do they have to be specially prepared for use with this? And does the controller s/w need to be adjusted depending on what tool you are using?

Hi. Thanks! So far, there is no a specific controller. I will eventually start to develop a specific controller. But currently we have to work with available ones. So, if you want to use a specific purpose toolhead, you must look for ways to adapt it to the controller too.

Once I develop the basic controller, It will be possible to adap a new toolhead easier.

This is just a Prusa i3 clone assembled the most wrong way possible

I'd like to see one of these with aluminum or steel framing.

Hi, I am the developer of the PolarBear. Currently I am improving the 3d printable version and preparing the v1 release. Once I finish it, I will start to work on a scalable lasercut sheet metal body one with block rails. I think you are talking about this kind of machine.

Cool, have fun!

Maybe a trivial way to support the project would be to sell pre-assembled kit to build the Polar Bear itself?

Or just affiliate with some shop that sell the parts?

Unrelated question: I heard that over the last 20 years or so machining has become considerably more precise. By how much?

Go watch some videos of Kern machines. Their demonstrations of drilling through human hairs with a VMC are pretty compelling.

it might be better to say that machine components and coordinate measuring systems have become cheaper, so that high accuracy is more attainable.

Good machines 50 years ago could hold .001" tolerances with care. Most machines nowadays can do that without that much care. Some machines nowadays can hold .0001" tolerances with care, and some can do even better.

terms like thousandths of an inch are thrown around like it's nothing in machine shops, so I'd say pretty damn precise.

That kind of precision was commonplace 40 years ago, not just today.

They have, but they're also still quite expensive.

As precise as you are willing to pay, usually micron resolution is the limit:

https://www.youtube.com/watch?v=2dsrLD52Mv0

This is a DIY EDM(Electrical discharge machine). Proffesional machines are much better (and more expensive too).

What is good about EDM is that it doesn't care about the hardness of the material you work with , only about its conductivity. You can shape diamond or the strongest steel without problems.

it depends on how much you're willing to spend, and in some areas, whether your company is allow to import specific devices which are highly precise.

Many of the most challenging precision and accuracy problems were well understood and documented quite some time ago (books like Moore's Foundations of Mechanical Accuracy). Even today with DIY devices, people are getting impressive results, but often it's hard to say for sure just how accurate something is without expensive calibration tools and custom built environments. For example, if you're working with high precision machining, the temperature of the room matters (since the work will expand or contract) so you will probably need a climate controlled room inside a climate controlled room, etc. Machine needs to be rigid, feedback control, sophisticated optical sensing for position, all makes this very expensive.

I think the folks who make large glass mirrors do well under 0.5 micron accuracy.

If you don't limit the way of machining, you can count microchip manufacturing as machining. So, we can easily talk about nanometers.

If you consider machining only physically removing the material by friction of two different materials, then I think it is practically about 0.001mm. Even this dimension is not always possible. because in this level of precision requires to consider even ambient temperature. If you machine the material with a cold coolant and wait for 10 mins to measure the result. You would end up a bigger part. If you machine it under a warm coolant, then you would end up a smaller part.

One challenge is that the machine has non-uniform resolution. Now, how to turn that challenge into an advantage? :)

Hi, I don't see it as a challenge. Current machine have 0.025mm resolution at the outer edge of the table(260mm diameter). I think it is possible to build a 400mm diameter table with stepper motor. Any bigger table would require a slow operation or a high speed servo motor to get enough precision and speed. It is still not impossible. With a good servo motor you can have 2000mm diameter and good enough rpm.

This would be so cool for cake decorations!

Exactly! I actually was thinking to develop an extruder for this kind of projects. But I had to eliminate it for now. May be in future me or you can have time to develop an extruder or adapt an existing one.

I was hoping it would be able to drill the PCB in the video, too.

btw, "softwares" sounds so incorrect.

Hi, I am the developer of the project. I am improving the prototype and preparing v1. I will publish more videos when I finish V1 and will demonstrate a complete pcb work. printing, etching, masking etc...

Ah, I need more English practice I think.

the rest of your english on that page is fine.

I wonder if this would be good at PCB traces

Why not. It is the point having a replaceable tool head.

I am waiting for assembly instructions...

oh man, this'll be amazing if it becomes a reality

It looks like it's already reality... you just have to print and assemble yourself.

this is amazing

Cool project, I think it's probably doable to print a cube, cut acrylic and laser some cardboard on this machine. Sadly It's not going to excellent at any of these things. I wish the project success, but really it doesn't look like a tool, more a concept of super tool changing toy

Reminds me of this: https://www.opensourceecology.org/gvcs/

I wonder whatever became of it?

While the project itself is interesting, the styling of the website is quite enchanting as well!

It looks really nice but it's a usability nightmare in my opinion. Swiping back with the touchpad doesn't work. Pinch to zoom doesn't work. Page up/down and home/end don't work. Most clickable elements are not focusable I'm not trying to shit on the devs here. I just wish more developers were more mindful of usability/accessibility. Bonus: Press tab a couple times to break the scrolling.

Oh yeah, I see what you mean and I agree with you!

Hi, I am the developer of the PolarBear. Thanks for your feedback. I agree with you and tried to add some shortcuts. But I am not a website developer. I can do website. But It is not my profession. I tried to do a nice website in a short time and I used a library named swiper.js I hope soon I can find more time and improve the website or have more funds and hire someone.

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