CNC Mill

I’ve finished up the machine, and sold it. On to other projects.

1) 2F, 4mm DOC, 1.6mm WOC, 0.02 FPT, 150 m/min, 90N Too much DOC/WOC and not enough feed-per-tooth? Significant chatter 2) 1F, 2mm DOC, 0.6mm WOC, 0.08 FPT, 150m/min, 45N Dropping DOC & WOC and increasing FPT seems to reduce chatter 3) 1F, 1.2mm DOC, 0.4mm WOC, 0.16 FPT, 75m/min, 54N Even less chatter 4) Non-adaptive climb milling 1F, 0.8mm DOC, 0.4mm WOC, 0.16 FPT, 150m/min, 72N Looks good

Frame This was the basic frame, made up of only extrusions and joints. I added the linear modules and custom plates, spindle and fixture plate Finally the enclosure, motors and limit switches Electronics I can’t be sure of the quality of these power supplies, so I’m using one for the steppers and another for the spindle. I hope this prevents noise from the spindle affecting the steppers.

G2Core is a motion control system, similar to grbl, mach3/4, linuxCNC, etc. It runs on a 32-bit ARM Cortex M3 Arduino Due, which means plenty of power for additional features. Due Pinout Configuration in G2core Term Meaning machine BOARD + SETTINGS_FILE CONFIG Specifies default BOARD/SETTINGS_FILE for a machine BOARD Specify board type and revision BASE_BOARD Specify underlying hardware platform SETTINGS_FILE Specify default settings Enable Motors and Axes Create a new SETTINGS_FILE, settings_defaultdue....

I stumbled on an excellent resource, Principles of Rapid Machine Design Bamberg, E. (2000). Principles of rapid machine design. It covers design and manufacturing principles, calculations and simulations, and experimental data. Design Principles Stiffness Budget “One of the most important criteria is the effective stiffness of the tool/work piece interface, measured in force per unit deflection $N/\mu m$.” Bamberg states that values of 10 to 25 are desirable for machining....

The parts are going to take a while to arrive, so in the meantime I’m refining my design again. I went from a XY-Z configuration to Y-XZ. This frees up space in both the x and z axes and should make it easier to put additional reinforcement as well as a future 4th axis. The y-axis table also extends out of the frame, which will make it easier to load/unload the machine....

When we last left off we managed to get 20 μm, I’m going to try to improve on it. Spindle Brace Adding Stainless steel sheet metal (5 mm) brace between the spindle and rear column Aluminum sheet (4 mm) at the bottom reduces deflection (at 110 N) from 20 μm to 16 μm. Column Brace Adding a 60 x 200 x 5 mm stainless steel plate reduces deflection from 16 μm to 14....

Design Goal (Quantified) After a few more weeks of research and reading up I have decided to use deflection at the spindle as my primary design goal. I plan to use depth of cut (DOC) + width of cut (WOC) to estimate the acceptable deflection. Depth of Cut DOC in aluminum ranges from 0.254mm/0.76mm/1.6mm (Shapeoko Wiki) to 2.54mm (Vince Fab) and 6.35mm (Shapeoko Forum). Recommendations for the Tormach PCNC1100 is also 6....

Tripteron The Tripteron is a 3 DoF parallel cartesian robot. It is decoupled, which means each axis can be controlled independently and isotropic, which means it’s dexterity is unchanged throughout the workspace. Practical Limitations But there are some serious obstacles to building a parallel CNC as a first machine. It needs many precise, high strength joints. Precise because any backlash gets magnified by the length of the chain. Strong because the length also results in a large moment....

Overview Notation $$ \begin{aligned} &\Theta &&: \text{Joint velocities} \cr &\Theta_{a/p} &&: \text{Active/Passive} \cr &W &&: \text{Twist} \cr &V &&: \text{Velocity of end-effector} \cr & \Omega &&: \text{Angular Velocity} \cr & X &&: \text{Generalized coordinates} \end{aligned} $$ Outline Inverse Kinematics : Relates position Inverse Jacobian : Relates velocities (in generalized coordinates) Inverse Kinematic Jacobian : Relates velocities (in cartesian coordinates) Inverse Kinematics Inverse kinematics are a way of getting joint coordinates from a desired end-effector pose....