Comment by sottol | Hacker News Reader

Comment by sottol | Hacker News Reader

Parent Full thread

Shameless plug if anyone is interested - I'm working on a $600-ish open-source, reasonably capable, but small and somewhat "tidy" hobby CNC machine with BOM cost around $600 that requires some DIYing.

It's meant to be an alternative to the Desktop CNCs like Nomad, Carvera, Bantam, ... moreso than a PCNC or other proper entry-level CNC.

The ultimate goal is to make it hobbyist-friendly, capable of easily cutting alumin(i)um and not taking up a lot space, not being messy or loud enough to require a dedicated workshop. Unfortunately, cutting metal is inherently loud so you probably would not be able to run it in an apartment as I'd hoped.

I've made a couple decisions around being friendly for people coming from the 3DP space around probing, using roborock CPAP as chipvac, running it mostly dry, fully enclosed. I'm also starting to work on computer-vision-based probing and the idea is to later enable a host of more user-friendly and safety-focused features and maybe integration with Kiri:Moto's CNC mode for "guided" CAM and so on - basically a beginner-friendly CNC that guides newbies using an integrated web-interface.

More info on Github: https://github.com/thingsapart/mini_nc

GH is a little outdated but I've been using the little machine to cut alu for a while (mostly parts for itself) and it's working quite well. There's more videos and such on the Discord linked in the GH readme - feel free to ask questions on the Discord, I try to respond as quickly as I can. The full model with all its components is completely open in Onshape (I know it's not ideal but how I learned CAD - link also on GH).

Fully enclosed with a chip vac is good. Chips all over the place is no fun. Especially with coolant.

Don't expect people to precision-cut wood for the frame. The Liteplacer people tried that for their pick and place machine, and most people never got a working machine. If it needs plates with holes in them, make them in bulk and sell them. Waterjets are good for that. The holes will be where they are supposed to be.

(The Liteplacer was a really good idea - a pick and place machine for assembling prototype PC boards. Camera controlled, with the input parts in partitioned trays rather than reels, it was slow but did the job precisely. The PixiePlacer seems to be the next generation of this. But, as with the Liteplacer, you can't just order the metal parts. You have to make them or have them made. There are commercial machines, of course, but they're for production, feed parts from reels, and are more expensive.)

Good point - there is a provision for laser-cut steel or alu plates that sit inside pockets inside the enclosure panels as I figured many would be turned off by a full plywood design.

The metal parts are symmetric so you can cut 2x of each - that is way cheaper on send-cut-send (afair only 25% extra for 2nd part).

> plywood design.

Coolant and plywood do not play well together.

The bottom panel is hdpe currently and "trayed", but you wouldn't run this machine with flood coolant anyway. mql might work but the idea was to cut dry, suck away chips and rely on coated end mills.

I've seen people experiment with diesel heater pumps for mql, might try that some time.

coolant always ends up very messy. even mql lubricated chips can be a relative mess compared to dry cutting.

> but the idea was to cut dry, suck away chips and rely on coated end mills.

You can go through a lot of end mills cutting dry. This is less of an issue for hobbyists who aren't turning large volumes of metal into chips and aren't using high-powered milling machines. The main limit on milling speed is getting rid of the heat. If you're willing to run slow, dry cutting works. Or if you only cut materials softer than steel.

At some point, you get Machinery's Handbook.[1] For most of a century, machinists' toolboxes had a built-in space for a copy of that book. Now it's available as an app.

[1] https://books.industrialpress.com/machinery-handbook/

I like to think of wood CNC as a step in the kit to something better. If you do your operations rights errors can cancel each other out and so you get better results by having a few extra steps. Make the wood CNC, then use that to cut the molds to make a epoxy-granite frame, then transfer the electronics to the new frame.

What about the lumen from opulo?

That's neat, but it's meant to get its parts from feeders. It's a small-volume production machine.

I uploaded a quick video of it cutting some alu recently if anyone's interested:

https://youtube.com/shorts/XUsj06iMbb0

At first I was skeptical, but that's an impressive demo for such a small machine.

The documentation on your github is a tad lacking however. :)

But good luck on your machine, I like your CPAP fan idea.

Documentation is definitely lacking - I just got the design to a point where I'm pretty happy with it. So far only 1 machine exists and the build has a few bits that are... less than ideal.

The plan was to build a second machine and optimize some of the assembly, take notes and document the build.

What's the advantage of this over a 3018 or 3030 machine? With some basic upgrades (you mentioned needing to diy anyway) you can easily cut aluminum on those for $500 or less.

I tried [1] - replaced the sides with 2040s, blind-jointed every extrusion, replaced X with MGN12H + 4 carriages, replaced the whole Z with 4080U and even bolted it into an MDF box to stiffen it up. The 3018 could cut alu, but not well. Maybe it was the 4080U but it just didn't work for me, it could cut alu but had lot of chatter.

For $600-800 it is fully enclosed, includes a decent spindle, wifi-enabled +offline RRF-based controller with folding/rotating LCD screen, 2 power supplies (24V + 48V for the spindle), a chip vacuum and probably some more I forget.

This machine was designed [3] specifically to cut alu rather well for < $1000, can run adaptive clearing toolpaths at 0.5mm optimal load and 3mm doc at 1800 mm/min with a 6mm end mill and produce decent chips. It can probably do more, my standard settings are 1200mm/min, 0.5 woc, 3mm doc. Mind you, this is all still hobby-level though you could still push the feeds and speeds a bunch I reckon.

[1] https://youtube.com/shorts/C0ngUJrWrB4

[2] https://youtube.com/shorts/XUsj06iMbb0

Not made in china though since many parts come from china anyway...

This would be a lot more interesting if it could cut steel and titanium. I guess that is more difficult.

Added: a dumb question, if the main cutting device is a router with a spinning bit, how do you cut angles? One thing I'd like to make is a 4mm hexagonal hole in a piece of steel, to turn little hex drive screwdriver bits and the like. Is it even possible to make that with a mill, or do you need a different machine?

That's usually done with something called a rotary broach.[1] This is a clever trick. You first make a round hole. The rotary broach is a hex-shaped cutting tool. Both workpiece and tool are clamped in a lathe. But the center of the tool is slightly offset from the rotational center of the workpiece. Both spin, but the eccentricity makes it cut a hexagonal hole. Here's the process.[1]

A milling machine can cut a hexagonal hole, but the inside radius at each corner cannot be smaller than the radius of the cutter. A 4mm hex hole would require a tiny cutter to do a good job. Here's that process for a larger hole.[2]

If the hole goes all the way through, just get a hexagonal punch. Might need to drill a round hole first.

Or just buy a 4mm socket with a T-handle. Cost US$4.99.[3]

[1] https://www.youtube.com/watch?v=_AYEFjbGaL4

[2] https://www.youtube.com/watch?v=zOqSIRuBgCY

[3] https://www.amainhobbies.com/rc4wd-metric-hex-twrench-tool-4...

Thanks, yeah, a separate 4mm socket with a handle is certainly a possibility, but I liked the idea of a 4mm hex hole in something like this, to accompany the holes that are already there:

https://knifeworks.com/crkt-9100kc-eatn-tool-black-oxide-fin...

I'll look at the rotary broach video. Yes the hole would go all the way through, so a punch sounds ok. Anyway it's not about making this one hole. It's more an example of the kind of stuff I'd like to do with metalworking gear if I had access to it and knew how to use it.

It does sound like hard materials are an obstacle as well. Aluminum is a start though.

Ah. Here's the tool for that job - a Roper-Whitney hand punch.[1] This is like a hand paper punch, but stronger. Costs $85. Made in USA. With a punch and die, you get clean edges on the hole on the exit side. Scroll down for how to order the specific punch and die you need. Hex punches are not common, but are available. If you fill out their form, and tell them you need to punch 3CR13 stainless, they'll tell you what to order. Might need something with more leverage than the small hand punch. Lubrication helps.

Most machine shops will have such a punch, but they won't have a 4mm hex die in stock.

Or you could drill an undersized round hole and file it out to a hex hole. Maybe use the existing round carabiner hole.

There are touch-up kits for guns, called "gun bluing", to make your shiny new hole black.

This is all do-able but way more trouble than it is worth.

[1] https://www.roperwhitney.com/our-products/no-5-jr-hand-punch...

Cool, thanks, yeah for a single hole, doing it by hand with a needle file sounds more practical. Does something like this seem CNC-able?

https://sakparts.com/products/can-opener-diy-tool-part-for-8...

The idea isn't to duplicate an existing can opener, but rather to make custom specialized tools to fit into a SAK, or replacement knife blades out of specialty knife steels (i.e. very hard, so probably difficult to machine). It wouldn't just be for SAK's but also for other folding knives, each with its own special cutting pattern to work with its pivot and locking system.

Titanium is another material of interest, for ultralight gear.

All of this is probably impractical at the hobbyist level with limited work space, though. Oh well.

DIY knife forging is common. Search "knife forging". Look around for classes and forges with training. There's a huge amount of info on knife making and metallurgy. People obsess on this stuff. A good knife is a trick of metallurgy. The blade must be hard at the edge to be sharp but ductile in the body so as not to be brittle. How to do this is well understood today, but there was much mystery around it for centuries. If you're fascinated by metalworking, but don't have to make machine parts, that's a hobby direction.

Victorinox knife manufacture.[1] Stamp, heat treat, grind, polish. They're not exotic blades, just good manufactured stainless steel parts.

A primer on machining titanium.[2]

[1] https://www.popularmechanics.com/adventure/outdoor-gear/a351...

[2] https://www.harveyperformance.com/in-the-loupe/titanium-mach...

Sure, knife forging is one thing, but the idea of making replacement blades for folding knives sounds like it takes machining, because of the weird shapes needed at the pivot end, especially for weird locking mechanisms. It would be nice to be able to do that at a semi-commercial level if one were to get into it at all. Victorinox is on a completely different scale, making millions of units of whatever. But forging is for making one or two of something, while CNC machining is interesting for making a few hundred.

In practice I don't have it in me to pursue something like that for real. It's just interesting to find out about.

If I simply wanted to make knives, then no machining would be needed, just some cutting discs and belt sanders. It's the specific thought of making replacement blades for existing folders that seems to want more automation. I guess there are existing shops that can do that type of thing from a CAD drawing though.

We (ob. discl., I work for Carbide 3D) have a video series on doing this:

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

Thanks! That looks like just what I want. I looked at the first few seconds just now, and will watch the whole thing later.

Knifes are done with heat treating. you need to get the steel red hot and follow the proper cooling process. You machine soft iron to close then make it too hard to machine, finally grindit to the perfect size.

Steel is sooooooooooooo much harder than al, it’s not even in the same ballpark. Aluminum is about as hard to cut as wood. For non round holes, you are looking at approximations or broaching. Look up manual hex broaching

that looks like a nice project, reminds me of the ghost gunner 3 machine. I like the safety note too. might hop into discord sometime next week. thanks for sharing!

Reply on news.ycombinator.com