Comment by mfi | Hacker News Reader

Comment by mfi | Hacker News Reader

I just finished my latest project, building a CNC-machine from scratch using an Arduino Uno, GRBL and 40x 3d-printed parts. It’s able to mill wood and aluminium, up to ~20mm thick.

As with all my other projects, I think they should be executed in the open where other people can learn from my mistakes and get inspired to build their own things! Therefore I’ve spend a lot of time writing a free complete tutorial of the build, documenting every step with text and detailed images, creating a complete bill of materials (including STL-files for the 3d-printed parts) etc. I don’t want any dependencies on DIY-websites, so I’ve hosted it on GitHub, where anyone can clone it locally.

I built this machine to gain more knowledge about mechanical engineering, electrical wiring, stepper motors, GRBL, CAD, CAM etc. Also, I guess I can build new fun things with the machine? Overly-engineered birdhouses maybe?

Setup:

* It’s running on an Arduino Uno, CNC-shield and GRBL.

* 40 parts are 3d-printed (all the red parts in the video)

* It’s based on Ivan Miranda’s blueprints, but I’ve adjusted some parts and structured the bill of materials.

* It uses 2x 19:1 geared NEMA17 stepper motors for the Y-axis and 1x for the X-axis. The Z-axis is using a standard NEMA17 motor.

* HTD5M belts and pulleys are used for X-axis and Y-axis. GT2 belt and pulleys are used for the Z-axis.

If you have any questions, feel free to contact me. You’ll find my email in the top of the guide :)

Nice work! You made a lot of great design choices.

+1 to those that recommend upgrading your extrusions and motor mount on future iterations. The rigidity is well worth it.

If you are ever deciding between belts and ballscrews, I recommend ballscrews. It is worth the extra $$.

For the milling of aluminum, I suggest adding a compressed air nozzle. It will make a huge difference in milling AL. Also, some of the new bits are fantastic at hogging out aluminum. For reference see pic at https://drive.google.com/file/d/1BWvOOwmaQljwhdBzYNvilYDKdsy...

We built our own 5-axis CNC too, to do large envelope parts trimming. It looks like Frankenstein, but works pretty well. See a pic at https://drive.google.com/file/d/0Bydp4fsq-EhtUndOTlZTcU1fTEU.... We use it to trim the chassis parts for our baby car seats at https://kioma.us

Keep on building!

I understand you put thought and time into your approach and it was a hobby to learn more abotu the process (and thus you know about MPCNC but decided to make your own). I've also build similar systems and I've learned some timesaving tricks that have paid off in terms of hobbyist enjoyment.

I really like buying the majority of the parts from a place like OPenBuildsPartStore, rahter than assembling frames from channel manually. Time/cost/quality tradeoff is hard to beat here.

I strongly recommend switching to Grbl_Esp32 https://github.com/bdring/Grbl_Esp32 with external controllers (this board https://www.tindie.com/products/33366583/6-pack-universal-cn... with these plugins https://www.tindie.com/products/33366583/external-stepper-mo... and these controllers https://www.amazon.com/STEPPERONLINE-1-0-4-2A-20-50VDC-Micro...). That's what I ended up with because tuning current using the little pots is dumb, and you want a TON of current going to those huge motors. ESP32 + Grbl has a bunch of nice features that aren't in plain old Uno GRBL.

My system has high torque NEMA23 with no gears (same motor for all 3 axes), I can't see any situations where adding more torque to the X or Y axes using a smaller gearer stepper makes sense.

"I can't see any situations where adding more torque to the X or Y axes using a smaller gearer stepper makes sense."

Generally agree. Torque is only needed to a specific threshold. If it requires a lot of torque, then that's probably a good sign to slow the movement down (for the sake of the machine's longevity).

On the contrary, plenty of tools need to move and chip otherwise they'll get dull, cutting speed is a function that increases a machines' longevity. But cutting speed does require a solid mechanical setup, drivers that can source some current and a drive train that does not suffer from over or undershoot ('slop').

"plenty of tools need to move and chip"

Not sure what you mean by that. I dont know all the tools in the world, but generally a chipped tool gets less sharp. Even something like obsidian would get less sharp in regards to the intended use with a random chip as compared to a well knapped tool.

"cutting speed is a function that increases a machines' longevity."

I'm not sure you are using cutting speed the same way I'm talking about movement. Applying too much lateral torque to a router bit is how bits break, bearings wear prematurely, etc. You don't need much torque to move the router.

If you want faster cutting speed, then the RPM of the bit can be increased, or using a different bit design. You can cut faster and it still shouldn't require much torque for the movement.

I suspect he means that you want to move quickly through aluminum, especially if you don't have active cooling. If you move slowly you can get problems like chip welding and everything goes south.

I actually didn't have enough torque to move the router through lots of material until I moved to some fairly serious stepper drivers and configured them to use max current and voltage (IE, I got a 48V, max 20A power supply). Even then, if if accidentally move the router bit while it's not spinning into the work, the motors stall well before the bit breaks (1/4" carbide end mill).

I guess if they're getting welding there's no sprayer set up. Some emulsified oil (10% Ballistol) usually works great for lube and cooling, even in small quantities.

Yeah, that makes sense. That sounds like it's really not that much torque the way you describe - just above functional minimum and no where near too much (eg people forcing it through and breaking bits).

They possibly meant "plenty of tools need to move chips".

A common problem that causes chatter and poor tool life is not taking a large enough chip. Large chips stabilize the tool (the rotation of the tool pulls it into the part) as well as allowing for a more continuous, uninterrupted cut (whereas too small of chips cause the flutes to have to re-engage the cut over and over, and the number of engagements and tool life have an inverse relationship).

True. My point was that it shouldn't take very much torque to match the cutting speed with the movement speed. Even if you increase cutting speed you can keep the same torque (for movement) by increasing movement speed. It should be a balancing act with torque (for movement) being fairly constant in the range to provide continuous engagement, with the cutting and movement speeds changing.

>I can build new fun things with the machine? Overly-engineered birdhouses maybe?

I don’t have space for a workshop. I live in an apartment. So I’m pretty limited in the sorts of materials and tools I can use. 20mm of wood is probably quite useful. My table top and shelves aren’t 20mm thick. If this can go through MDF I’d say it’s really useful.

this sort of machine could easily carve 5-10mm of MDF in a single pass. It's awful loud though, even when enclosed.

What I recently made: a terrain map of california cut into plywood. It's several feet by several feet (~600mmx600m), 0.75" (almost 19mm deep at the lowest points in california) and wall-mount-worthy.

Sounds really cool! Got pics?

Unless you have an incredible dust collection system in place, I would seriously reconsider any potential plans to cut MDF in your apartment. The particles are very fine and you will find it everywhere. And that is to say nothing of the particles that you'd be inhaling.

What a fantastic project. Is the design parametric, in other words, are there parts that would need to be scaled up to have larger x, y or z axis or are those all off the shelf and are the various STL files for the components the same if the design is scaled up?

Glad you like it, most cred should go to Ivan Miranda for the core design, I just executed, updated some parts and wrote a guide around it :)

No, it's not parametric in that way. But it is possible to extend the "mill-bed" by:

* X-axis: Increase length of frame and bridge profiles. Buy longer MGN12H rails used for the X-axis.

* Y-axis: Increase length of frame profiles. Buy longer MGN12H rails used for the X-axis.

* Z-axis: Increase the vertical beams between lower and upper frame. Buying longer MGN12H rails used for the Z-axis and a longer acme rod.

Awesome. Can it mill aluminum? If so, would you consider replacing some of the 3D printed parts with machined parts?

Yeah it can! Ivan Miranda, the guy who has created the blueprints actually updated his machine with aluminium parts, milled on the CNC-machine. That might be something I'll do in the future!

Von Neumann probe when?

Right after you figure out how to 3D print solid rocket fuel without things going 'bang' prematurely.

If you print Potassium Nitrate/Sorbitol[0] with direct granule extruder[1] you could do it. But this will probably need additional toolhead for engine body[2] (plastic-fiber composites DO have enough strength to survive using KNSB in engine, I've seen tests, but those are not publicly available) and for ceramic nozzle[3]. With some experimenting, probably doable.

[0] http://www.nakka-rocketry.net/sorb.html

[1] https://hackaday.io/project/181165-my-machinery-2021-direct-...

[2] https://www.sciencedirect.com/science/article/pii/S221282711...

[3] https://reprap.org/wiki/Ceramic_Extrusion

The CNC Shield is a blessing, shame the Gerber files aren't being published for newer versions.

100%, it helps so much with the wiring.

https://www.pcbway.com/project/shareproject/CNC_Pro_Shield_V...

very cool! thanks for sharing. I don't have the equipments to drill holes on aluminum parts, I will probably need to use https://8020.net/ to build one.

Aluminium is quite soft, so it might work if you have access to a screwdriver and a step drill

I’m not an expert here but I’ve heard 8020 is expensive enough such that purchasing a drill press would probably be cheaper, if feasible, correct?

There is also handheld drill press rigs that may be useful.

You might also want to look at the mostly printed CNC, which uses standard conduit/pipe for the frame.

https://docs.v1engineering.com/mpcnc/intro/

Be warned these plans require you to drill a couple holes in the conduit. I managed with just a handheld drill though the holes weren't quite aligned. Definitely use a file or hacksaw to create a flat spot on the conduit where you want the hole so the drill bit doesn't wander as easily.

Or a center punch (helps on flat metal too).

One favorite trick of mine is to print out 1:1 drill pattern drawings and center-punch through the paper onto my metal workpiece for all the drill locations. Fast and accurate.

Basically, 2D printers (you know, those $150 things) are exceptionally high precision and accuracy tools for making 2D drawings. I've been using printers for years and it never occurred to me you could use it to print a (for example) 10cm square.

You can if you are really nifty do limited scale PCB manufacturing this way.

https://www.instructables.com/Creating-Printed-Circuit-Board...

Fusion360 seems to try to prevent you from exporting PDFs with the free hobbyist version. One tip that I discovered was to create a CUPS printer on a Linux VM that saves PDF files.

(I found it printed slightly off sized if I sent a 2D drawing straight to the printer.)

Yeah, you have to correctly configure the output to get dimensional accuracy. but it shouldn't involve finding some magic scaling factor for X and Y that makes things accurate.

I've used Inkscape to make basic shapes, and pay for Fusion 360. TBH I've never actually thought to take one of my 3D Fusion models and use it to make a 2D template for drilling. That makes sense...

Inkjet yes, laser no.

My favored approach to offset drilling / drilling on curved surfaces is to use an endmill. Doesn't wander, goes straight in. Of course, you need an endmill for that approach, but id you're building a CNC those should be in ready supply.

interestingly you can also mill a flat or indexes to mate tubes together. I’ve also contemplated making one-piece saddles to mate extrusions, filling the gaps with zero-expansion epoxy.

Tubes and extrusions you buy cheap rarely have dimensioning and tolerance you’d want to accept out of the box. To get what you need, best just to use geometry of hole centers, and adjustable fine parts.

I set a limit of 1/128 inch on any garage woodworking projects. This is 8 mil (thousandths of an inch) or 0.2 mm. Wood and plastics (and even aluminum) fluctuate from moisture and temperature enough to make this a lower limit of reasonable value, though I’m getting closer to 5 mil in router precision. It’s not a fine carpentry shop and I’m not making anything that really needs better than eyeball precision (hand marking) which would be about 1/32 inch.

Applying geometric dimensioning and tolerance to design has been a liberating experience. I’m not a mechanical engineer or even otherwise anywhere close to the industry so I really had no idea how to assess or compare designs.

Since the mostly printed CNC already requires a 3d printer, you might as well print a jig to help drill those holes. https://play.fallows.ca/wp/tools/3d-printer/mpcnc-drilling-j...

I use a cordless hand drill to drill and tap aluminum all the time (as does this project). adjust the speed until you are pulling out long ribbons instead of dust. you can use a little oil, but its not necessary. the only issue is trying to stay perpendicular to the work, but usually a little deflection doesn't matter. also pay attention to 'wowing', where instead of drilling your perfect round hole the drill bit starts to bounce around a triangle or pentagon and you end up making too big a hole. its often best to start with a pilot drill and then a final pass to clean it up. also its often easier to use a centering drill to setup the holes. it provides a pocket for the drill to rest in so that it doesn't wander, and you can use the centering drill to fine-tune the hole pattern before you make it permanent.

To easily stay perpendicular to the work, use a tap guide block. You can 3D print one or drill one out of stock on a reasonably square drill press.

I picked up a used drill press for $45 or $50 (I don’t remember now), and a tap and die set from Amazon for about $20. 10/10 would recommend if you have the space.

Believe it or not, aluminum can be treated the same as wood when it comes to tools. Any drill that can drill wood can drill aluminum.

You mention aluminium. Any plans to add a lubricant sprayer?

what material did you use for 3d printing? I would think PETG or ABS is probably best?

I actually used normal PLA

PLA is actually the stiffest of those materials, just keep it cool enough that it doesn't warp! I expect that would only be a problem around the spindle which can get quite hot, and maybe stepper motor mounts.

You most definitely want to avoid PETG as it is pretty... flexible...

PLA is the way (the MPCNC, for example, is designed with PLA in mind) in this case, as with ABS you most likely need higher printing temps, bed temps, an enclosure to keep even the slightest drafts out...

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