I worked 62.5 hours straight without sleep --- milling, lathing, drilling, welding, gluing, bolting, and writing custom software for my new custom-built CNC machine. It weighs 2000 lbs, runs at a max. linear speed of 18.23 ft./sec, consumes 6000 W of power, positions with +/- 10^-6 inch accuracy over 12 ft., eats live chickens, and is day-glow orange in color.
OK, so I'm kidding. Made you read, though.
The truth is I am actually going to build a machine. Whether it eats live chickens will depend on what parts I pull together.
I have decided to document my little adventure, with the hopes of sharing as much information as possible. My diary may do any one of the following: inspire, motivate, or discourage. Hopefully at the very least the common denominator will be that the information will make an impact.
To be honest I haven't put much thought into this project yet. A while back, a friend of a friend donated parts to an old ShopBot to Kelvin and I. Kelvin put some work into it and created the SB CNC machine which some of you have seen. It works beautifully. Now I want my own.
At this point, there's no set design or 'plan' that I'm following. It's going to develop as it goes, so it will be interesting.
Let's get started.
Last weekend I visited my family and cousin Kam (littleKam) in So. California. While at my brother Pat's house, I picked up four Ametek servomotors. Last year Pat converted a standard manual milling machine into a CNC machine and he had some motors laying around not in use. I was glad to take them off his hands, and here they are:
They are Ametek 965922-101 servomotors, rated at 12 amps (peak), nominal 38 VDC, and I think capable of delivering a whopping 600 oz-inches of torque. The 5/8" diameter output shaft seems to suggest that they can deliver some umph! Each motor weighs a fair amount, too. On the bottom of the motor is an optical encoder. I don't know the counts/revolution, but will figure it out at some point.
Some CNC's use stepper motors, DC motors that are designed to move in steps, for example, 200 steps per 360-degrees. Steppers are easy to work with and can be operated without a sensor feeding back information about what position the shaft is in. In this case, the motor can be run in open-loop. Steppers are controlled by applying pulses to step the motor from on position to the next. It's a simple setup and great for CNC-type machines where a tool has to be positioning relative to a workpiece in 3D.
Other CNC's use servomotors, a motor with a sensor attached to the motor's shaft. A controller is needed to sense the shaft's position and then adjust the input voltage/current appropriately to control the (angular) position of the shaft. These motor/sensor/controller systems are a bit more complicated, and if the sensor was to ever fail with the controller active, the motor can spin out of control to infinity and beyond. Of course there are ways to minimize this, but in general they are slightly more complicated.
There are advantages and disadvantages of using either steppers or servos. Everybody seems to have their own opinion, so I'm not going to contribute to the debate. However, I've been intrigued by servos and have built similar setups at my day job, so I figured since the motors were free I'd make the best of them. As for the controller and power supply, it depends on my budget and avaiable time, but I'll try to build as much from scratch as possible without nuking myself --- bzzz, bzzzz... I always keep in mind that electricity is extremely dangerous and always double, triple check my connections before turning on power. It doesn't take much current to stop one's heart!
Anyway, in addition to the motors, I also picked up some modular aluminum framing to create the skeleton of the CNC machine. I haven't decided on the size of the machine yet. For now I'm just collecting parts and dreaming.
I will do my best to update this thread as I go and hope that it materializes into something worthwhile. Feel free to ask or inquire about anything or better yet, make suggestions and point me in the right direction. Until next time.
