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Hobby CAD, CNC machining, and resin casting (2015)

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71–80 of 111 posts

Re: Hobby CAD, CNC machining, and resin casting (2015)

#71

Former MechE for a decade and I owned personal CNC routers and on my 6th 3D printer. The biggest issue with CNC is the cost for consumables and accessories. Need a special bit? $$$ Need stock to cut? $$$ Want a nice ER11 or R2 collet set? $$$. A nice vise? $$$ Cut something wrong with a carbide bit? Shrapnel explosion. 3D printing has a bunch of limitations but is a way better machine for hobbyist. But I have been ey…

Any time I see a guide like this, everyone will go on and on about the types of cutters, toolpaths, speeds & feeds, etc. but will always gloss over work holding. For every action, there is an equal and opposite reaction. Without reaction forces, the best cutter in the world is useless. A sizeable chunk of your tooling will just be clamps and indexing tools needed to align and secure the thing you're CNCing, while also trying to keep them out of the work area. 80% of the end mills I've ever broken have been by crashing them into a clamp or vice by accident. This is another thing you tend not to see in 3D printing or laser cutting, or plasma cutting for that matter.

Re: Hobby CAD, CNC machining, and resin casting (2015)

#72
I followed that guide (it is excellent, if a little outdated) to get really good results. I should really write up and share my experiences, there is so much to learn.

In brief:

* It's an excellent method of producing very precise parts with fantastic mechanical properties (the next step up is aluminum, but you don't need it in most cases).

* It is much more difficult than just throwing something at a 3d printer.

* It is not comparable with 3d printing at all. I use both methods: FDM printing for most stuff, resin casting for parts that need to be strong, dimensionally precise, or nice.

* Yes, you can use your resin printer to produce originals or master molds, but you will have two problems: 1) precision, 2) silicone cure inhibition.

* Tips for those in the EU: Sika Biresin F50 is fantastic, Rencast 5146 is slightly worse (higher viscosity), but works very well, too. Both are relatively easily available. For silicones, BLUESIL RTV 3450 is unbeatable.

* For desktop CNC machines, there are good options now: Makera Carvera (either the full model or the "Air" scaled down version) are really nice and precise machines. Software is crappy, but hopefully will get better. I had a Nomad 3, but switched to Carvera.

* Don't buy a cheap CNC. There is simply no way to produce a desktop CNC with good precision for less than, say USD $2000. You will be disappointed. Perhaps if one day a Bambu Lab arrives with experienced engineers and a lot of money, they could mass-produce something cheaper, but right now this is roughly the cutoff.

* Autodesk Fusion, much as I hate it and the company behind it, is pretty much the only game in town if you want integrated CAD+CAM. Again, I hate the software with a passion, but there is simply nothing else that is as well integrated, works well, and is reasonably priced.

* Achievable precision: ±20μm is doable with a little care, things get difficult below that. This is roughly 10x better than what you can get from FDM 3d printing. Note also that this is the limit of what most people can measure: your calipers have an error of ±20μm if they are good. I also noticed that the 3d-printing crowd often has no idea what precision means, so you'll see crazy numbers thrown around.

* Mechanical properties of produced parts are way better than what you can get from FDM printing. I laugh at those "strong filament with carbon fiber" youtube videos.

Re: Hobby CAD, CNC machining, and resin casting (2015)

#73
post #11

Earlier quoted context omitted.

It is definitely more expensive than 3d printing in terms of consumables but china/aliexpress has really good hobby-quality equipment now - if you don't mind the country of origin. Many of their coated end-mills are decent and Maybe not stuff you would want to run professionally but it works quite well in a hobbyist setting and a mistake won't cost you $50. I also looked into the Millenium Milo, only downside for me…

Have you seen the Carvera Air? Not gonna lie, I'm equally tempted but that price point is tough to swallow. Its about $7-800 more than the Milo but has a bunch of things built in that you would probably would enjoy like touch probe leveling and camera zeroing. Its the "Bambulab" of the CNC world.

I have the Carvera (not Air) and it's a very good machine mechanically, the software leaves a lot to be desired.

It isn't even close to being the Bambu Lab of the CNC world, unfortunately, but I'd say only because of the software. If they open-source their controller, things might improve quickly.

Re: Hobby CAD, CNC machining, and resin casting (2015)

#75

I'm not too excited by the idea of making little plastic precision gearboxes for robots, so when PLA printing isn't good enough, I mostly want to machine metal. Not car parts or firearms but flashlight bodies, knife blades, small tools, that sort of thing. Nothing wrong with robotics but there are other interesting areas too. I think the article skips over that a little too easily. That said, it's a good article.

Flashlight body would probably want a lathe, but one of the newer flat ones would be easy in two halves.

For an example of a knife blade:

https://www.youtube.com/watch?v=G5TYla5x-Nk

small tool:

https://community.carbide3d.com/t/nomad-made-custom-titanium...

Re: Hobby CAD, CNC machining, and resin casting (2015)

#76

Former MechE for a decade and I owned personal CNC routers and on my 6th 3D printer. The biggest issue with CNC is the cost for consumables and accessories. Need a special bit? $$$ Need stock to cut? $$$ Want a nice ER11 or R2 collet set? $$$. A nice vise? $$$ Cut something wrong with a carbide bit? Shrapnel explosion. 3D printing has a bunch of limitations but is a way better machine for hobbyist. But I have been ey…

Have you tried metal 3D printing? Is that a thing for home hobbyists?

Compared to plastic 3D printers, metal 3D printing ones are at minimum 100x more expensive, if not 1000x or 10000x.

Re: Hobby CAD, CNC machining, and resin casting (2015)

#77
post #58

To the machinist/s here: For nearly a year, I've been contacting local machinists for a small[*] project which involves 1) an accurate cut on both ends of a 17" billet of T6061, 2) two crescent cuts, 3) up to 8 threaded holes, but probably, 4) a wee bit o end shaping. All the aesthetic contours, shaping and weight reduction I'd do manually - I hand machine bronze, aluminum and wood archer's thumb-rings, so can wangle…

Have you looked at Shapeways or sendcutsend or xometry or 100k Garages?

That said, I have an especial interest in archery and multiple machines.

Contact me at: https://community.carbide3d.com/u/willadams and we can at least work out doing a couple of prototypes.

Re: Hobby CAD, CNC machining, and resin casting (2015)

#78
post #72

I followed that guide (it is excellent, if a little outdated) to get really good results. I should really write up and share my experiences, there is so much to learn. In brief: * It's an excellent method of producing very precise parts with fantastic mechanical properties (the next step up is aluminum, but you don't need it in most cases). * It is much more difficult than just throwing something at a 3d printer. * I…

> It is not comparable with 3d printing at all.

Not just not comparable, but totally opposite. Subtractive vs Additive. CNC is like chiseling the David out of single block of stone by removing bits. 3d printing is starting with nothing and adding material.

Re: Hobby CAD, CNC machining, and resin casting (2015)

#79

Earlier quoted context omitted.

>Having a CNC Router table in a non-industrial zoned area will not work for most people. Lolwut? Throw it inside where the narcs can't see it (you'll want it inside or at least in an out building anyway). They're not loud. The venting you'll want isn't loud either. Source: I do this stuff in my house.

Are you using a full sized "router" on steel plate, or a mini-engraver made from a hobby-motor on balsa? Even a compressor fed Plasma-cutter rig is usually far quieter by comparison, as cheap import engravers often just make a mess of the surfaces. Best of luck, =3

My router itself is a 2x2 with the Vevor 3hp spindle (not a repurposed handheld wood router). The router, regardless of material it's being used on, is quieter than just about any woodworking tool with a circular blade. When it's indoors nobody cares. I mostly use mine for making wood mockups of parts before I make them in steel. I have more traditional tools for steel fabrication. The router makes basically no noise compared to the "loud" ones of those.

Re: Hobby CAD, CNC machining, and resin casting (2015)

#80

Earlier quoted context omitted.

It depends on the accuracy you are trying to achieve, and with what technology. If you mean FDM, it's absolutely true. If you mean SLA/MSLA these days, i think you could get there. On the first - i have an entirely ballscrew + linear rails driven FDM printer with closed loop servos and proper absolute encoders - I got bored and do lots of CNC retrofits/etc, so had lots of parts around. Think of it as insane version o…

This sounds fun, have you written anything up about this project? I’ve been considering switching to ball screws and closed loop servos on my next project. I’d be especially curious for component recommendations for hobbyists, as it seems like ball screws and servos are often super expensive or suspiciously cheap.

I haven't written it up.

For hobbyists, i think components are tricky. You have two basic options:

1. Linear motors - these are ideal (because it's a high acceleration, low intertia application. the extruders basically weigh nothing), but harder to find. Peopoly has a kit but my experience has not been the best there. They do seem to be coming down in price, but i haven't yet seen the equivalent of what teknic did with the clearpath steppers, but for linear motors.

2. For closed-loop steppers, you'd be best off with something close to the pantheon - closed loop teknic steppers.

They have a good history at this point (well known in the CNC community), and are now even commonly used in mid-grade CNC machines these days. I've heard nothing but good things about them.

As for real servos, if you want real servos, the problem you hit (relative to the current requirements of the average 3d printer) is not just cost, but the space requirement. You need real servo controllers, and they are all basically built to be in cabinets. So having 6 servo drives is not an insignificant amount of space + power. It is also severe overkill in some sense. Servos are meant to bring more efficient power usage to bear on the problem of generating torque (for the most part). But you don't need that much torque to drive a 3d printing axis, it weighs basically nothing and the mechanisms used rarely have any meaningful inertia or friction. So while I haven't tried it, i suspect you would be a lot better off with steppers + absolute encoders to ensure positioning (absolute so you don't have to home, and because incremental vs absolute cost is a complete wash at this point). The servo drives are just basically PID controllers + rotary encoders on the motors anyway. If you instead used steppers, linear absolute encoders, and controlled them by pid, i would bet you could do very well (assuming you can dynamically increase the step resolution as you approach position).

The ball screws and linear rails are easy - you can get cheap c5 ballscrews (which, over this distance, are fine), and pretty much any linear rail will do (a 25mm linear rail can easily work on a 1000lb gantry).

Don't overdo the ballscrews.

The thing about ballscrews that people miss is that while the grades tell you the rough positioning error (which is caused by deviation in the ball track), they have little affect on repeatability, which is still very high. So even C7/rolled/whatever ballscrews are very very repeatable. The ball tracks just aren't ground as precisely, so the deviation from expected distance is higher.

What this means is that if you just map the position error, once, even on a low grade ballscrew, you can correct for it very easily, because it doesn't really change. (this isn't perfectly true, but is true enough for this purpose).

This is commonly done to get better accuracy out of lower grade ballscrews.

If you do use linear encoders, you don't have to worry about any of this - they will be much more accurate than the ballscrew, especially over this small a distance (ie 300-400mm) and you use their position as the source of truth. In that case, you could easily use c7 or rolled ballscrews.

The thing you won't be able to fix in the end without changing how we think about these printers is the mass. Wood/Metal CNC use mass to reduce vibration because it's very effective. While input shaping is great, in the end, you will hit the limit of the acceleration/movement speed you can practically achieve unless you are willing to add like 1000 pounds to your printer to absorb vibration. This is not fixable. you can't make the vibration 0 and the energy has to go somewhere. You can see this on linear motor based printers. Even without belts and lots of moving parts, they still can't do more than about 300mm/s print speed without vibrating too much.

I would bet with better isolation/etc we'll get towards 500mm/s, but we will hit a limit that will require increasing mass in practice (IE whether you bolt the printer to the floor or built a concrete base or whatever)

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