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My CNC milling machine

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poorchava:
Hello,

I wanted to show you my CNC milling machine which I have been building for ~4 months now. It's already functional, yet needs some major tweaks.

Specs:
-work area of 300x295x130mm
-construction material: 18mm plywood (~3/4" for you metrically-impaired :) ), M5 bolts and nuts
-drive transmission: hardened steel trapezoidal thread drive screws 16mm OD, 4mm pitch + hardened plastic nuts
-linear motion assembly: fully supported 16mm hardened steel rods + linear bearings in mounting brackets
-actuation: NEMA23 size 0.9 N.m 1.9A/phase stepper motors, microstepping driver of my own design based on TB6560, homemade/ghetto optocoupler board + lpt + Mach 3
-max. velocity 1400mm/min for X and Y, 600mm/min for Z (ghetto optocoupler board craps out @ 7-8kHz)
-spindle: Kress 800FME (800W 10k-29k RPM). tested with tools up to 1/4" OD
-materials machined: softer aluminum alloys, MDF, plywood, solid wood, PCB laminate, all kinds of plastic

Details:
I've build the machine out of plywood for numerous reasons: it's cheap, easy to work with using relatively inexpensive tools, can be obtained in any construction&garden&DIY mall/market (plus they will cut those to rectangles of chosen dimensions for free). It's also less sensitive to moisture than eg. MDF. General arrangement is that work table moves back and forth (Y axis), the carriage with spindle moves right to left and are attached to static base. Z axis is mounted on carriage together with the spindle. I've chosed the supported rods because they are easier to mount than unsupported type (no end-brackets) and they are most rigid of all "affordable" solutions (unaffordable being linear guides like THK, Rexroth, Hiwin etc). Motors are mounted on brackets made of 9mm and 18mm plywood and are coupled to the drive screws using reinforced garden hose and hose clamps (ghetto method but very cheap and entirely sufficient for this purpose). Threaded rods have been purchased as 2 1m pieces and then cut to length with angle grinder. Then they were mounted in a jig comprising of 3 16mm ID needle bearings bolted to 50mm of mdf scrap boards, rotated using ordinary power drill and ground with the angle grinder (i'm not really happy with the outcome). Whole machine is 55cm x 70cm x 50cm excluding motors (which stick out and add ~15 cm on each side). It weighs about 45kg.

Photos:

nctnico:
You'll probably get problems due to resonance. You can make the large panels much stiffer by putting a grid (with irregular sizes so there is no resonance frequency) made from wooden strips on them and add an extra panel (doesn't need to be very thick).

robrenz:
Awesome job!  Your choice of how the axes are arranged is excellent. The only thing I see that would improve the rigidity of the frame is to glue in a piece of plywood that fills that hole under the Y axis.  Just cut a hole big enough for the X axis drive to fit through. That would really decrease deflection in the Y direction and raise the resonant frequency of the frame. The low modulus of elasticity of wood tends to have wooden frames act as very effective "speakers".  You could also trim the sideplates from where they meet your Y axis base to where they meet the baseplate (remove a triangle of material) and it would not significantly reduce your rigidity but would greatly increase accessibility of the work zone.  Those two unsupported "triangles" will act like a huge tuning fork with large surface area generating wonderful howling noise when excited by the machining vibrations.

Keep up the great work and keep us posted on your progress.

poorchava:
Believe me I'm aware of resonances and not the best rigidity of the frame (found out the hard way - ~$20 endmill -> bin).

I can't mount a panel on the backside and obscure it completly, because the table moves outside of the frame. Also, this gives me opportunity to load something long (like 2m board) and cut it into pieces (it's handy as i don't own a circular saw).

In longer run I'm definitely going to put some reinforcement in the back of the machine.
Similar thing goes for sides. I'm planning to attach another 18mm (or even two of those) to the sides as it would improve rigidity alot. Unfortunately such large pieces of plywood would add a lot of weight. I'm generally planning to move this machine to the basement (or to entirely different location as I'm planning on moving out with my girlfriend in nearest half a year or so). attaching sides and back reinforcement would easily push the weight above 65kg which makes it unportable for two people (i have narrow staircase which makes it impossible to use the help of 3rd person).

In the end i intend to reinforce this machine ALOT.

edit: some videos




edit2: ac for cutting off triangulat pieces in the front - i agree. I've thought about that from the beginning, but having everything rectangular/square made it easier to align. I'm considering cutting off those when I add the additional side panels. The access to work table is not so bad, but of course cutting these corners would improve it alot.

robrenz:
 Two stiffeners on each side like this pic will do more for your Y axis stability than more layers and won't add much weight.

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