Monday, June 8, 2009

CNC, Pt. 10: First Test

Everything was moved back out into the garage and all the power supply, controller, and computer parts were mounted into a single tidy computer case.

You'll notice the computer we're using is one of those little ViaC3 mini-ITX setups. They're small, relatively cheap, and have everything built into the motherboard.

Mike made a quick model in Lightwave3D and imported it into DeskProto. DeskProto is a tool that creates machine code (in G-Code format) from 3d models. From there it's just a quick trip to the machine's hard drive to run the file. And here it is, our very first test cut, hacked into a 2x4.

It's fair to note that while the machine is far from done, this is a pretty significant milestone. The first goal: a machine that could cut intricate shapes into wood for use in furniture (or whatever) has been achieved. There are several other goals ahead though.

Friday, June 5, 2009

CNC, Pt. 9: Computer

After a great deal of debate, trial, and research, we loaded a computer with FreeDOS and TurboCNC. To sum up the argument, windows based controllers, in my experience, suffer from an endless chain of issues associated with the use of hardware abstraction layers to provide "security." Linux works well, and offers EMC2 (free), but after a few arguments between myself and the system I decided this was a good place for pure simplicity.

TurboCNC reads control code (G-Code), interprets and outputs directly to the controller. Simple, straightforward, constistant, and free to mess around with. Donate the guy some money once you decide TurboCNC is awesome. Same goes for FreeDOS. These guys put a lot of work into their software for our benefit, and should be rewarded.

It took less than 5 minutes to get TurboCNC moving the machine, where we ran a few test files just to see everything work together. Messing around we were able to achieve some pretty good speeds (up to about 140 IPM, not bad for a heavy machine under powering its motors). Also, at 75 IPM the machine feels totally unstoppable. You can push and pull with all your might and it just keeps tracking along regardless. Also, there is no discernible play or flex in any dimension. When the motors are held constant it feels like everything is just welded in place. I do believe this thing is going to work:

Thursday, June 4, 2009

CNC, Pt. 8: Wiring

The whole apparatus was then moved onto my kitchen counter for wiring and testing. All the parts for the power supply, which consists of a large toroid transformer (changes 120V household A/C current to 32V A/C Current), a bridge rectifier (converts AC to DC), and a couple of large capacitors (help keep the power source stable). The final output is 30 volts at more amps than I can make use of.

Stepper motors, for those who have never messed with them, are motors with many sets of magnetic coils that can be energized independently. When one set is energized the motor jumps to a certain position. Energize the next set and it jumps again. By this principle we can control how much a motor turns and how fast. It does, however, make for complicated controlling mechanisms.
The motor controller board was another ebay purchase. It is possibly to save a load of money and build your own controller, which is exactly what I have done in the past, but things have changed since then. My (time X money) = constant ratio has shifted a bit, leaving me with the ability to afford a premade controller, and not a lot of time to build one from scratch. Your situation may closer resemble standard college life.

Wednesday, June 3, 2009

CNC, Pt. 7: Z Axis Motor Mounts

The mounting of the Z axis motor was done using more 1/4" aluminum plate. It was at this point, or somewhere close to it, that we decided that the Z axis plate needed more structure to prevent it from flexing under load. Aluminum L brackets were added, which had the benefit of looking pretty cool.

Tuesday, June 2, 2009

Reasons to work late

CNC, Pt. 6: X and Y Axis Motor Mounts

Time to mount the motors! All the ball screws needed to be turned down on a lathe so that a standard coupler could be used to attach them to the motor output shaft. This is a very laborious and time consuming process that is probably best left to someone else. Being a masochist, I went ahead and turned them down myself on my mini-lathe. The outer surface, to about 1/8" depth, is extremely hardened steel. To the point that it cannot be cut with a standard bandsaw blade. It's really tough stuff.

The actual motor and ballnut mounts are made from welded steel plate, then ground flat on a plane sander. It is most important to get the mounts to a perfect 90 degree angle, as any adjustment in this dimension has to be done with shims. When completed I only needed a shim under the Y axis ballnut mount, which was cut out of a cheap auto parts store feeler gauge set.

Monday, June 1, 2009

CNC, Pt. 5: Bed Plates

The next step is to mount the beds for the X and Y axes (that is, the two horizontal axes). This is probably one of the hardest parts of the construction process. I used tapered (countersink) screws to keep the hardware beneath the bed surface, but if I had to do it all over again I would have used a regular low profile machine screw and milled a flat spot into the bed plate to provide a little more adjustment. As it stands now, the screws have to be tightened in stages and in pattern to get the to just the right position.

The Z axis rails are then bolted to the Y axis bed plate. The holes for mounting are tapped directly into the aluminum.

And the same process again for mounting the Z plate- shown here with a 1/4" high speed router attached.