Have been busy over the last few days working on a design for a B/C axis head for the 5 axis CNC machine that will produce all of the plugs for the bodywork and a few other parts. This design incorporates a belt driven dual axis run by Nema 34 motors with encoders.
Also utilizing an air cooled 3kw 18,000rpm high speed spindle with an ER20 collet system will allow me to use various tools for machining MDF or different foams.
The Nema34 motors will use an HTD belt drive system with a 6:1 drive ratio. The 8.5nM stepper motors with the 6:1 ratio will produce 51nm of torque to maneuver the spindle and provide enough strength to hold position while machining some harder materials.
Since the goal is to machine some MDF and different foams, I want to make sure I could keep the dust and swarf out of the drives and bearings so covers (likely made from fiberglass or carbon fiber) were designed that could easily keep all the crud out.
Still in progress is the B rotational axis. Need to figure out an efficient way to design the bearings and mountings for the radial and thrust loads. You can also see the encoders on the stepper motors here. They will provide feedback to the control system so that the machine is always aware of how much each axis is currently rotated. This awareness is handy for the machine to not twist itself up as the wiring will have enough give to rotate 1 full rotation in each direction.
Can see the 6 bolt mounting pattern here for the high speed spindle.
The spindle mount itself is actually an aluminum extruded rectangular tube with one side cut off. This will reduce the amount of seperate parts and also how much machining is required.
The axis of the spindle motor is perfectly lined up with the axis of the B rotation which will help create much more efficient toolpaths and result in quicker machining times.
When setup properly, an HTD belt drive can provide a nearly backlash free power transmission. With belts and pulleys at nearly any size you can imagine, it’s easy enough to design around the parameters you need for your application.
The choice to go with stepper motors over servos was price and simplicity. The amount of accuracy needed didn’t require the use of a servo and the amount of power in the size of package was easily achieved with the Nema 34 motor size. Since my other CNC machines were built with stepper motors, I also felt more comfortable with the setup of these, plus the use of an encoder gives me everything I need.
Will be posting more on this machines build in the coming weeks and months as I juggle different projects. Stay tuned!