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CNC-2116 - Up and running, sort of (2015-03-21)

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Yvan256:
After seeing crashwg's CNC machine and especially the results he got when he milled that 4" wooden token, I've decided to build my own CNC machine too. Seeing dexxy's MechMate cutting panels for his Neon Copy was also inspiring.

For the last five years or so,  I've collected easy-to-do ideas about linear slides, motor couplings, anti-backlash nuts, etc. Just like an arcade cabinet, there's a lot of topics to cover and different ideas depending on the available budget and tools.

My problem is that I have many projects on hold because I can easily design things in Sketchup but I have a hard time actually building them. It's easy to make a Neo-Geo side panel in Sketchup, it's another thing to be able to cut it properly with all those angles and curves. Having a small CNC would make the job of cutting the required parts so much easier. I'm not planning on doing RCBs (routed circuit boards), so even a so-called low-precision machine would be just fine with me.

So, I'm trying to build a really simple, very extremely low-cost 3-axis CNC milling machine: CNC256.

* Cutting area of 24 x 20 x 2 inches (60.96 x 50.8 x 5.08 cm - I know Canada is supposed to be metric, but being so close to the USA, almost everything from wood to bolts is almost always in feet and inches). I could have gone for 24 x 24, but the machine is already going to be wide enough as it is. Big enough for desktop arcade cabinets and big enough for the panels of a future project, which at last count needed over 50 precisely-cut panels.
* I've bought four stepper motors (1.8 degrees, 24v) at an electronics surplus store for around 8$CAD each, I think. It's been too long, I can't even remember which year I bought them. (update: I contacted the store, they were only 4$ each) Why four? At that price, and given that it's a surplus store, I wanted to have at least one backup motor.
* I'm making my own stepper controllers to reduce the cost. So far I've got (good) preliminary results with an Atmel ATtiny85 and four TIP120 for my first tests. I plan to use one ATtiny84 (the ATtiny85 doesn't have enough pins to control the motor and receive signals) and one ULN2803 (two lines wired in parallel for each motor winding to allow 1A per chip) for a total cost of around 4$CAD per axis (plus taxes and shipping, required pcboard that I'll make myself, etc). It won't have extra-smooth motion or power-saving features, but at around 15$CAD to control all three motors this is a hard deal to beat. The cheapest controller for 3 motors seem to be around 35$ on eBay which is more than twice the cost of my controllers. And by building it myself, and with a microcontroller, I control and know everything from A to Z, and I'll be able to update the software later if I want to (microstepping, etc).
* For the "CNC computer" itself, the thing that drives the motor controllers, I plan on using Grbl instead of an actual x86 computer. With the external clock, power supply, etc it's going to cost about 10$ for the "computer". I'll still need a way to transfer g-code files to it... probably via an SD card, a small LCD display, small joystick and buttons (I plan on using arcade parts for that). The goal is to have an autonomous machine that doesn't require an external computer connected to it.
* Inverted V-groove skate bearings linear slides (idea by larry104) - I dropped that idea because the nuts grind on the aluminium angle and it's near impossible to adjust them properly.
* Fake V-groove skate bearings on aluminium angle, idea taken from Ro-Bot-X's Weblog, who modified an idea from TinHead, who modified the idea from the blackToe... The plan is to go with the Route-X design, change the aluminium angle when it wears out (if it wears out enough to need replacing that is, after all I'm not planning on using the machine more than a few hours per week) and upgrade to real v-groove bearings later and possibly steel angle much later on. That should allow easy upgrades, one at a time to lower costs, and without needing to re-cut any panel.
* For the motion, I'm going with regular threaded rod (low-cost) with home-made HDPE nuts. My father has donated enough HDPE blocks to make 12 nuts - three for the machine, nine backups!)
* I planned on using the Dremel tool I already have for routing, but regular 1/4" routing bit won't fit and according to most people a Dremel is just too under-powered for such a job. Seeing the videos on YouTube vs proper trimmers/routers, I have to agree.
* I'm recycling a lot of particle board panels from older/abandoned/failed projects. So far I had enough to make the whole Y and Z axis.
* I also plan on adding a mini Shop-Vac with a home-made cyclone dust separator similar to that one. My father has both a full-size and mini shop-vac so I'll be able to compare the two and see if the mini is enough for the job.
Bill of materials (prices in Canadian dollars with taxes):

* 32 skate bearings (ABEC5): 30$
* Four stepper motors (NEMA 23, 24v, 1.8 degree per step): 16$ (three for the machine, one backup)
* Two 8 feet long, 1/2 inch wide, 1/8 inch thick aluminium angles: 36$
* Particle boards: 0$ (already had those, recycled from older projects)
* Three Motor controllers: 13$ (not bought yet)
* Threaded rod: 10$ (not bought yet)
* Nylon nuts: 0$ (home-made, HDPE plastic blocks donated by my father, not done yet)
* Various bolts, nuts, washers: around 10$
* Power supply for the microcontrollers and motors: unknown (not bought yet)
* Computer: unknown (not bought yet - I know the ATmega328 costs 4$, but the other parts are a bit unknown right now)
* Shop-Vac mini: 40$ when on sale (not bought yet)
* Cyclone system of the shop-vac: 2$ (plastic pipe connectors, one angled and one straight. I plan on finding the plastic bucket and tubing for free)
* Total so far/planned: around 166$ (rounded up)
Please note that since some parts came from surplus stores or some parts are different, I used average prices for those parts. I'm also going to need more wood panels to complete the whole thing.

I still need to get a small trim router, but I'm setting the budget for that at 100$CAD maximum. I'll be checking for units on sale.

Attached is a cutting size capability comparison between standard size/popular kits sold on the internet (the two models of blueChick, the two models of blackToe and the Mechmate).

drventure:
Looking forward to this thread. I've wanted to do the same thing, but don't really have space.

Maybe after you're build, I'll find space  :)

Yvan256:
Some new parts arrived today. I already had 16 bearings, but due to the design I'll need more. Local stores only sell extremely high-end skate bearings, so my brother brought me this pack of 16 bearings when he visited. Adds 14.80$CAD to the build cost, or 0.93$CAD per bearing. Still cheap to replace when they fail.

Thanks Daniel!

syph007:
Glad to see you start this thread.  Im in Canada too and have been wondering how hard sourcing parts will be.   Can I ask where you found your steppers?

Yvan256:

--- Quote from: syph007 on August 15, 2011, 10:48:11 am ---Glad to see you start this thread.  Im in Canada too and have been wondering how hard sourcing parts will be.   Can I ask where you found your steppers?

--- End quote ---

I got my steppers at Accès Électronique. They have four stores, all in the Quebec province. Never mind their website, their stores usually have a much bigger selection. Since it's a surplus store, the selection varies all the time.

The inventory number for my motors is 51925. I added two photos to my first post. For an idea of scale, the square part of the motor mount is 56mm wide/tall.

I emailed them to ask if they had any left, and the price. They don't have this motor for sale anymore which isn't surprising since they're a surplus store (am I glad I bought four), but the price was only 4$ each. I'm sure most of their stores currently have similar motors at around the same price.

If I had known how good they were, I would have bought a dozen.

Tip: try to get 12v motors, you'll have less trouble finding a power supply for your motors... i.e.  power supply from old PCs.

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