Guerrilla guide to CNC machining, mold making, and resin casting (2015)

https://lcamtuf.coredump.cx/gcnc/

by Tomte • 5 years ago

251 74 5 years ago

lcamtuf.coredump.cx

Wow, really short section on gears. But there is so much to cover I can't blame it.

If you've ever dabbled in robotics, you've probably found it is an enormous step function from kits like Actobotix [1] to custom parts. It is infinitely easier to use kits or frameworks that have already taken a LOT of the guesswork out of gears, linkages, motors, compatibility, etc. Especially gears, they are an enormous pain in the ass to source online, and even when you find the right gears, you still need hubs and axles, and then you hit min volume issues, non retail sales, overseas... I even have access to a phenomenal machine shop, but what I don't have is a machinist. (There are a few that mill around (pun intended) but they are mostly introverted decent guys that don't really want to help a noob.)

[1] https://www.servocity.com/actobotics/

paulgerhardt• 5 years ago

Having spent a million dollars making gears, my ultimate conclusion is it’s the sort of thing you machine from brass gear stock unless you want to spend a million dollars.

SavantIdiot2• 5 years ago

For what 99.99% of makers are doing, Actobotix is fine. But if you want to make your own fancy differential or a hypercycloid linear translator, yeah, you're gonna have to do it yourself.

failwhaleshark2• 5 years ago

What dimensional scales, materials, turn-around, volume, and/or processing?

Breaking tools and getting G-code just right seem like the perpetual headaches of modern machinists. Other than occasionally being bitten by a bitchy blade-like chip begging to fillet your grizzled knuckles one last time before banishment from the bench to the backyard becycling bile of betal bits.

If electricity were cheap (or the electric meter rewindable), would multiple beam concurrent FDM be a consideration if the materials and metallurgical characteristics allowed it? I think at some point, it's easier to print complex shapes additively than machine them subtractively, and that needs to be part of structured cost decision-analysis for manufacturing.

chrisseaton• 5 years ago

What is 'brass gear stock' as opposed to normal brass?

jalgos_eminator• 5 years ago

In case anyone wanted an approachable introduction to machining your own gears, there's a This Old Tony video about it: https://www.youtube.com/watch?v=Q-XOM4E4RZQ

mikewarot• 5 years ago

I spent 5 years making gears in a job shop.

I did a cursory look through the section on gears, it seemed adequate for someone who is doing a hobby project.

I'll watch this thread and answer any questions you might have.

Scene_Cast2• 5 years ago

Would you know what type of approaches and machinery is needed for relatively loose tolerance / low load helical gears? If going the CNC route, do I need full 5 axis and specialized end mills?

Even with regular involute straight gears, there's a bunch of ways one could manufacture one, and I'm out of my depth here.

ganzuul6• 5 years ago

The industrial strength version: https://m.youtube.com/watch?v=EefFxEGVbWo

I made sprockets with an endmill and a simple macro on a C-axis lathe. Worked just fine since the tolerance on those is very forgiving.

In principle you could make a helical gear as a multi-start thread. I'll have to test it once I have the machine free an afternoon.

jjk1662• 5 years ago

It's way easier to start with components you can readily source and design your system to use them than to make custom components. If your robot isn't going to space, the benefits of custom components will not be worth it.

dls20162• 5 years ago

Timely… spent the day machining a mould for a foam windscreen.

mod• 5 years ago

Can you elaborate? I'm having a hard time imagining what a foam windscreen is, or what its purpose is.

Is it just like a motorcycle windscreen that you don't need to see through?

dugditches2• 5 years ago

I think they're referring to a microphone 'windscreen'.

tmaly• 5 years ago

I would like to try resin casting to make some wall on-lays. Has anyone on HN tried making molds for detailed castings?

dugditches2• 5 years ago

Might be better with just 3D printing, body filler and spray paint.

ArtDev• 5 years ago

I bought a similar kit from Smooth-On to make casting of Warhammer 40k miniatures. It was amazed at the detail and accuracy of what I created! The secret was using a back massager to vibrate the table to get out the bubbles!

This is the kit I originally bought: https://www.smooth-on.com/products/pourable-silicone-starter...

haram_masala• 5 years ago

I’ve done it for making fake ancient coins - like another responder, I used a Smooth-On kit and it couldn’t have been easier. Though I was casting bismuth alloy rather than resin. One tip, be sure to dust the mold with talc to allow air to escape. Also the vibration table tip sounds good.

grae_QED• 5 years ago

Artisan Alliance made a couple of very good videos on high detail resin casting with silicone molds [1]. They focus on mechanical keyboard keycaps, but the same ideas apply to many other things.

[1] https://www.youtube.com/watch?v=5cnLJm0kMdg

s53003• 5 years ago

I really think that every well rounded person/STEM academic should at one point in their life (hopefully sooner rather than later) expose themselves to some hands on machining... like, even just a few hours on an old decrepit mill/lathe.

I feel like the foundations of the industrial revolution (speaking within the US) are... very much forgotten/taken for granted given the fact the near entirety of our modern life and comforts exist because of it.

There's fortunately a ton of great, readily available content on YouTube/elsewhere that's sprung up in the past 10 or so years you could just watch, but actually machining is such a cathartic experience... at least when you're in a position to do so that isn't in a grimy ass factory/warehouse with somebody yelling at you to push out more operations than is humanly possible, haha.

prpl• 5 years ago

Most working undergrads (RAs) in the physics department at my university had been trained in the Physics department machine shop at some point in time, so it was common for them. Probably the only program outside ME where that was true

R0b0t13• 5 years ago

Not sure this is normal. Have heard stories of physics department needing to contract to the engineer's union, and people getting in trouble for screwing together a wooden box.

azalemeth• 5 years ago

Me too -- I had a 30 hour course in the workshop as a graduate student in physics. We covered both manual and CNC milling and turning, with Bridgeport mills and Colchester lathes.

Completely opened my mind. Made me a better experimentalist. I spent about 99% of the time utterly terrified and wanting to check everything about ten times to make sure that I didn't wreck either the job or myself.

mmaunder2• 5 years ago

CAM is also humbling and then exhilarating. And agreed, everyone should do it at least once.

ganzuul6• 5 years ago

expose themselves to some hands on machining... like, even just a few hours on an old decrepit mill/lathe.

Excuse me but as a pro in this field I have to raise an objection. There are aptitude tests just for the education because some people who are otherwise brilliant are absolute terrors, a dangers to themselves and others when presented with machine tools. Trial and error works very differently when you focus enough pressure into carbide to cut steel like it was butter. You should watch the horriffic videos of people being turned into bloody messes on machine tools and THEN decide if this is something you want to try. Nobody knows in advance if they belong in the danger-category but school instructors are quick to spot them and talk them out of the field.

If you are adamant on going at it on your own, stick to tools which don't output more than 1000W. In a panic you can produce that much power and you might only lose a finger instead of your life. ALWAYS pause and think about what you are going to do the very next moment and what you expect will happen.

I'm sorry if it sounds like gatekeeping. Those videos are very convincing that the gate is there for a reason.

quartesixte3• 5 years ago

I’m pretty sure a few hours on a Haas VF3 or ST20 running a simple part under supervision will be safe enough.

I don’t think anyone in their right mind will be handing over the keys to a roomsized VTL any time soon...hopefully...

Manual machines on the other hand—absolute death traps.

pasabagi4• 5 years ago

Are they really so dangerous? I've generally worked with the rule of thumb: glasses, no dangly bits, don't touch anything, don't use your hand as a machine vice, and so far, no injuries.

My feeling was that since metalworking machines are usually relatively slow and not that grabby, they were safer than, for example, a circular saw.

I mean, that's not a high bar, but nobody is saying that people shouldn't do hobby woodwork.

s53003• 5 years ago

You raise some good points, but I think they're a bit too overreaching.

I started working with manual machine shop machines (mills/lathes/presses/all types of saws/water jets/lasers) over a decade ago, and I'm only in my early 20's now.

There are aptitude tests just for the education because some people who are otherwise brilliant are absolute terrors, a dangers to themselves and others

This is true. Working as a student shop instructor in Uni, I've had to remove a fair amount of people/literally leave & shut down shop from stress/frustration after people repeatedly nearly lost fingers/limbs doing what they were told not to do multiple times - mainly on table saws. As to why these people are they way they are... I do not know.

Trial and error works very differently when you focus enough pressure into carbide to cut steel like it was butter.

No instructor/supervisor should be letting newbies work with steel to begin with, except possibly very mild steel... we have things like 6061 T6 Al and even polymers for demonstration/early learning. It was a good bit until I was allowed to work with stainless steel on mills/lathes.

You should watch the horriffic videos of people being turned into bloody messes on machine tools and THEN decide if this is something you want to try.

I grew up doing this, still do, and always recommend it to anybody who's about to start working with machine tools. I have yet to meet an instructor/shop supervisor who doesn't make it very, very clear how easily and instantly everything can maim and kill you. In the 21st century, if there are those who don't do this... that's just unfortunate.

In the end - mills, and especially lathes, are honestly highly predictable machines. It's quite hard for things to go wrong with them aside from tool crash/breaking, which you won't really be in a position to be hurt by. There are some machine tools that are inherently more dangerous - but - nothing comes close to how fucking dangerous a tablesaw is. I consider a tablesaw to be the most dangerous and unpredictable tool I use, as does the person I learned from who's been an industry/custom fab machinist for over 40 years. And tablesaws can be found everywhere, typically without much restriction, if any, to begin using.

The sawstop is cool, but I really fucking hate them for not releasing the patent to it for all to use.

71a54xd• 5 years ago

Fun fact, all CNC machines sold in the United States with more than 5 axes of travel have to be registered with the ATF and have a permanently attached GPS tracking unit. This is even true if you have zero intention of using your CNC to manufacture anything reminiscent of a firearm or firearm component. This is why it's common to see 4.5 axis CNC machines or a plethora of "upgrades" that grant 5 axis capability post purchase.

r3trohack3r• 5 years ago

Fascinating. I searched “ATF register 5 axis cnc” and came up dry. Do you have a reference?

ff--• 5 years ago

That's not true. Machines with enough axes to be used in firearm or aerospace machining are subject to export controls, though.

GravitasFailure• 5 years ago

I believe you're thinking of the GPS/Gyro locks that certain high end Japanese CNC machines have, and the ITAR compliance issues many CNC machines are subject to for export. The locks were implemented because somehow Iran got their hands on some Mitutoyo machines despite sanctions. Either way, it's the State Department and Department of Commerce that get involved and the ATF has nothing to do with individual machines.

jrockway2• 5 years ago

I was thinking about the Mitutoyo incident, but I think those were coordinate measuring machines, not mills. (5-axis implies milling, but Mitutoyo doesn't make mills. CNC is a generic term that really applies to any sort of machine controlled by a computer -- we have CNC sewing machines at the local makerspace ;)

As for geo locks on mills, I have heard about those. My understanding is that they're a software licensing thing -- sell the machine, move it to a new shop, the software stops working. That ensures you can't get your money for the machine on the secondary market, and that new customer has to buy a brand new one directly from the manufacturer. Just your standard DRM scheme to improve corporate profits. Also good to have that equipment on board so that you can switch to a subscription plan if the economy gets bad.

I don't know if all 5 axis machines require registration with the government. I have looked at these before: https://pocketnc.com/ and they don't say anything about it. Could be too tiny for anyone to care about, though.

Grakel• 5 years ago

It's perfectly legal to manufacture firearms, although you must have a license to sell them if you have manufactured them for that purpose.

mnouquet• 5 years ago

If you need more than a good bridgeport mill to make a firearm, you don't deserve to be in a shop... All you really need to make an AR lower is a drill and some aluminium plates. Heck, pakistanies are making a plethora of firearm with nothing but files...

CNCisDenied• 5 years ago

I was considering last week to pick up CNC machining but now I've lost all interest. It sounds very primitive and intersectional. dang, you have trolls.

imtringued• 5 years ago

There is nothing more primitive than a robot that doesn't even know its own position and only follows a program with the hope that it works. (assuming a hobby CNC machine without servos).

contingencies• 5 years ago

You just described most motor vehicles: mobile death traps.

axegon_5• 5 years ago

One thing to note when it comes to resin casting and cnc is the 3d printing evolution since 2015. The amount of detail you can get from an inexpensive 3d printer these days is astonishing and it seems like less far less messy than a cnc. Not that long ago I got a resin-based 3d printer and I was blown away by the prescision. That said, for me at least, there is a big problem in that entire field - the third point - "Mastering CAD and CAM". To put it lightly I really suck at it. I am using Blender(100% linux user) and having to switch between layout modeling and sculpting(etc.) often puts me in a Hulk mode rage. I can't find a pattern in the menus or modes and everything I try to do ends up being 2 hours of googling and youtube tutorials. Which I reckon is me being too used to cli-tools and hardly ever going outside the cli world(if it weren't for browsers and the modern web which cannot work without js, I'd have probably removed my desktop environment altogether).

mmaunder2• 5 years ago

I understand you use open source, but Fusion 360 really is a game changer. The CAD to CAM workflows are easy and intuitive once you learn the basics. Blender is designed to be a lot of things to a lot of people and I can see how that would be extremely frustrating. Yes Fusion isn’t cheap, but it’s very worthwhile IMO.

ganzuul6• 5 years ago

Autodesk is unfortunately doing exactly what one can expect Autodesk to do. As soon as Fusion 360 meets a milestone they add new ways to monetize their users. TBH I can't recommend it for anyone outside US jurisdiction because of how the company is managed.

axegon_5• 5 years ago

No, I'm not full on RMS here, if there's a proprietary software that I could use and I can use it under linux, god speed. Sadly adobe and autodesk are reluctant to add more support, despite the demand.

skybrian2• 5 years ago

I'm liking Onshape for CAD. There's a learning curve, but it seems logical in a geometric puzzle-solving sense.

I read a bit about resin-based 3D printing (stereolithography). The amount of detail looks impressive but it sounds expensive and messy due to the toxic chemicals and fumes. How do you deal with that?

jtms• 5 years ago

Messy yes, fumes yes, but the printers themselves are now less expensive than a decent FDM (filament) printer and the resin itself is relatively inexpensive as well.

axegon_5• 5 years ago

Very much depends what type of resin you use. The one I use has practically no odor and is water washable. In addition, there is an air filter(which is annoyingly sold separately) for that printer so even less of an issue. I was initially planning to shove it in the basement but after a few prints I figured it doesn't make a lot of sense.

quartesixte3• 5 years ago

Unfortunately 3D printing can only go so far and some things must be CNC milled.

bsder2• 5 years ago

With something like a FormLabs Form 2, 3D printing can go really far. And, with a Form 2, you will be printing parts from the get go and not dorking around with the printer all the time.

My biggest problem is still when I want to do something in Stainless Steel. I really wish I had some way to deal with Stainless without needing a gigantic machine.

zimpenfish• 5 years ago

Which I reckon is me being too used to cli-tools and hardly ever going outside the cli world

You might get some mileage out of OpenSCAD if you can define your object parametrically (I used it to make a Switch controller middle-bit.) Or there's stuff like https://github.com/fogleman/sdf which I've used to make resin-printed buttons for my mother.

(I also cannot get the hang of Blender despite dipping into it for a couple of weeks every year since about 2013.)

axegon_5• 5 years ago

https://github.com/fogleman/sdf

Holy crap, why have I not seen this before?!?!!? I was even planning to start coding something like this myself. This is awesome! Thanks!!!!

Yenrabbit• 5 years ago

I remember avidly reading this whole thing when it came out (and a lot of the rest of the blog) despite not having a CNC myself. Always great to see someone sharing knowledge from their own deep interest in a topic.

Guerrilla guide to CNC machining, mold making, and resin casting (2015)

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