Saturday, 12 December 2009

CNC router projects

YO, I had been contemplating with the idea of owning a CNC machine for some year now. (proably since chilhood when i learnt the word CNC). Buying one is out of the question, too expensive and again, against the Ghetto engineering Ethos. Which leaves the only option to make one!

I started out with a budget of a £ 100 and intended to use an arduino as the brain for the machine.I started the build and £ 100 pounds later i ended up with something that looked like this:
The frame was built out of pine wood strips , screws and plastic cuboid thingies held it together.I used plastic, aluminium extrusions and plates, steel rods for railings and an M6 all thread rod as lead screw.

I purchased 2 stepper motors off the makerbot website , that i had just discovered! i intended to use an RC servo for the z axis, ghetto engineering frugality...

I later regreted that decision and bought another stepper when I realised that mixing servos and steppers would complicate the controlling electronic. SO that was changed! I bought some stepper controller ICs from farnell and set to design a CNC controller from scratch, which i did get to work on a breadboard stage, but i realised that i had set myself a herculean task that involved reinventing the wheel when i came to writing the source code to change g-code into actual stepper control signals, and my good senses kicked in and i started looking for a decently priced stepper controller! i found a decent 4 axis stepper controller manufactured and sold by a chap in Hungary , that was as godsend, it worked brilliantly!

So as i tested The machine with a biro as a tool and figured out how to rig a z axis meanwhile and make a cheap cutting tool..
here is the first job ever done on the machine ( there was no z axis hence the line between each letter).

Considering I had not designed this, I had merely built it on the fly, I was chuffed by the results! I built and tested a couple of rotating tools to to mount on the machine ( to cut depron foam to make rc planes and uavs)

after installing a the cutter bit!

Below are a couple of clips of the cnc machine being tested!

After a few succesful test cuts, i decided to design a monster machine with a bed of 1000mm x 1000m , big enough to place a whole sheet of 6mm depron and cut aircraft kits. I also wanted an indexing turntable to be able to explore the third dimension and cut 3d objects...

So i set of to Portugal on Holiday and spent my evenings sipping moscatel de setubal and sketching my next project. When I got back to Leeds, I sat at my pc for about a Week with my best friend Solidworks and got cracking transposing my sketches into a 3d ASSEMBLY, printed the engineering drawings for my components. I burst into a an evil Laugh full of glee when when I compiled my Bill of Materials and the cost came up to £200 pounds, this included a nice electric circular saw essencial for the precise MDF cuts required for the jobs, with G clamps bought at the pound shop - a pound for 3 G clamps. ( still using them to this day) ; Ghetto engineering indeed. I recycled the steppers and controller from the Mark 1 cnc router and got building for a fortnight.

From concept to reality...

Left, sketches made on holiday while sipping Moscatel de setubal

Back from holiday, the solidworks assembly drawn, plans for the parts draughted and printed, BOM sorted and cost finalised. OFf to screw fix and B&Q we went.... Transporting the timber in my Toyota Ago was a fun experience...Gotta love the cutting service B&Q offer, I had designed the parts in a way that i only had minimal cutting to do after the chap at the timber yard sliced my mdf sheet!

Gantry assembled! I later redesigned it and rebuilt it a bit taller for extra z- axis movement!

Y -axis carriage added, the movement is soooo smooth! hardly any friction. Bearings Recycled from hardly used Roller blades from my teenage years. Recurring theme, Ghetto Engineering baby!

Installing the gantry on the base! Scary moments! its make or break! will the alignment be true?will the axes be perpendicular??

OF course no, the axes were at 87 degress. over small Jobs, insignificant but when cutting large jobs, makes all the difference! the gantry was later rebuilt taller as mentioned above and the y axis carriage rail could pivot for adjustment after final assembly! Lesson learnt!

Testing the motion, for such a heavy gantry, i was pleasantly surprised that no much force was required to move it! using an M6 all thread rod as a leadscrew(purpose built lead screw are soooo exorbitantly priced) should provide a lot of force!!

Voila! Now i just need to Shoulder Press this beast to my Lab/office/bedroom and install the motors, lead screw, end stop optical switches, the cutting tool and finally the work surface!

SO much Fun to be had!

ouple of weeks later! motors and everything installed.Before trying a test cut with a cutting tool, I used a felt tipped pen to test out the machine after calibrating the scaling and adjusting the axes for true perpendicularness or is it perpendicularity?does it work? course it does!! Remember your 6 P's

Planning and

Here is the first time I tested the machine:

Note, I decided to get the machine to write SEXY , not because I think the machine is hot,Nor because I am vain, but becuase the word is short and provides a a combination of curves and angled lines perfect for testing a CNC machine, a bit like the " hello world" used in electronics when testing...
Anyway, lets mount the cutting tool and see how it goes!

Time for the first test cut using a rotary tool ( of my own design, my dremel is used too often to be sacrificed for this project!, i used a speed 480 motor from an old aircraft, we all fly brushless these days.., used a motor shaft adaptor to hold the dremel end mill bit, and joined that to the motor using a shaft linkage from a RC boat,Used an little turned aluminium thingy from a sliding door as a flywheel to gyro stabilise the business and reduce vibrations.The bearing was salvaged from a burnt out brushless motor.I know dont ask, Ghetto engineering.Everything is recycled.

Hmm, it works, lets try it for the purpose it was designed for! cutting aircraft kits! lets see the first kit cut!

Verdict: accurate beyond my wildest dreams, but A bit slow. Must gear the leadscrews to increase the working speed. Sadly I never got to modify the machine for more speed. I Am currently out of a job and job hunting. Shelling £50 quids to buy aluminium pulleys and toothed belts is a out of the question, so between applying for jobs, i decided to recycle the parts and build a smaller mark III machine. Faster but with a smaller footprint,using cheap plastic gears from hobbicraft. 65 pence per gear, bargain.

Mark 3, was built on the fly, having learnt from my mistakes and previous designs , i was able to whip up this version within 3 days recycling components from mark I and II. I still have to complete this baby, but it promises to be as accurate as mark II. Motor tests, (not fimed yet) promise super fast cutting speeds!

Watch this space!

Fropessional Engineer Nick!

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