Step 19: X-Axis Motor Mount
The structure of the CNC is almost complete. There are only two more pieces to build, the x-axis motor mount and the mount for the router. I may not get to the router mount right away, skipping straight to the electronics. First, let's get the x-axis motor out of the way.
The x-axis motor mount is the easiest because, first, you've done two already and you're an expert, and last because there are few obstructions in your way. In this build, just like the last, the process is exactly the same. There is one minor change, but it will be preferred by most builders. Each motor mounting hole will contain a screw and three nuts. One nut lodged into the hole in the mount. Two nuts between the mount and the motor. These nuts will add extra support by tightening one to the motor side and one to the MDF side. This way, the motor is stabilized and the nut against the MDF is tensioning with the nut in the hole so the nut in the hole will not have the tendency to move.
Many readers have asked me to divulge the motors that I'm using. I will talk a tiny bit about my choice in motors and later I will provide a bit more information on motors in general. I am using stepper motors with the following specifications: 305 oz-in of torque, 2 amps, 6 volts and 200 step/revolution. Now, I'm sure about 50% of the readers are completely confused now, and I have a habit of attempting to articulate these things into laymen terms; however, this will deserve some extra homework. I will give you the two cent version, stepper motors are not motors for climbing stairs. Nor do they dance, or walk for that matter, but wouldn't that be cool. I gave a bit of a clue in the specifications (200 steps/revolution). That is to say, stepper motors are like motors that rotate at specific angles. In my motor, one step is 360/200 degrees. What is that 360? It's the full rotation of a shaft or object. Turn yourself around one time and you've turned yourself 360 degrees. Now, if you turn yourself 1/200 of a turn that relates to 360 degrees, then you've turned... 360/200 = 1.8 degrees. So, if you tell my stepper motor to make one step, it will turn 1.8 degrees. Oh, and not all stepper motors are created equal. there are various power, torque and current specification.
Just to leave a little to the imagination, I will explain the torque and leave the rest for later. The torque is the spec of 305 oz-in. that really means ounces (where does the z come from?) per inch. If you know cars then you've heard this convention before (foot-pounds of torque). The more feet-pounds of torque, the more rotational strength given other specific conditions applied to the motor, but let's not go there. The inch - ounce is the same thing as saying: the motor will push 305 ounces one inch away from the shaft of the motor. It's like putting a stick at a right angle to the shaft and applying 305 ounces at that point.
There are many factors that go into the decision for a motor. How much torque is needed? What tool or spindle will used to cut material? What material will be cut most often? What accuracy will I need (related to steps/revolution or resolution as I like to refer to this)? And How much am I willing to spend on the motor and/or electronics to drive the motor? These are the basic factors you will need to determine before purchasing the motors? Ok, so why did I purchase these motors? I liked the price! Ok, ok, the torque is pretty good too, and as far as I know, this is the best resolution you can find. And yes, there are other technologies out there like servos, basic motors with encoders and the like. these will be discussed at a later date.