CNC Circuit Mill/V2 Design Rationale

Frame

The function of the frame is to move a part of the frame in 3 dimensions (relative to its base).

For performance, a good frame has:

• Precision

• Rigidity

• Speed

• Force

For design, fabrication, and assembly, a good frame also has:

• Uniform Dimensions and Other Parameter Values

• Ease of Fabrication, Assembly, and Disassembly

• Modularity

• Durability

• Scalability

For the CNC Circuit Mill, a good frame also has:

• Workpiece mounting platform

• Large working volume of moving part relative to the mounting platform.

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Major Frame Type

• Selected - Mobile gantry design (XYZ all linked) allows tremendous scaling potential.

• Mobile bed (X alone, YZ linked) requires a greater non-axis frame to support both X and YZ; scales ineffectively.

Minor Frame Type

• Selected - Blocks on plate (Non-axis frame is a plate; X axis begins with 4 blocks on this plate)

Frame Material

• Selected - 6061 Aluminum Alloy for rigidity, ease of machinability, and accessibility

Axis Drive

• Selected - Stepper motors provide high resolution in a simple open-loop system

• AC or DC motors with encoders necessitate complex closed-loop control systems

Spindle Drive

• Selected - Outrunner Brushless DC Motor has maintenance-free operation, over 90% efficiency, commutator-free long lifetime, precision speed control possible, quiet operation, more torque than inrunners

• Brushed DC Motors require regular maintenance, short lifetimes, noisy operation

http://www.youtube.com/watch?v=fPLdHeRQp_w

http://www.rcgroups.com/forums/showthread.php?t=1118773

http://www.tcrconline.com/documents/electric%20flight.pdf

Rotary-to-Linear

• Selected - Leadscrew and Nut for high velocity ratio and lifetime operation

• Belts stretch and have low velocity ratio

Axis Supports

• Selected - Precision Shafts for ease of manufacturing and direct mounting

• Precision V-Rails

• Precision Extrusions

Block Dimensions

• 2 uniform dimensions (40mm, 75mm)

• 40mm to accommodate the mounting circles of leadscrew nuts.

• 70mm to accommodate the mounting orientation of stepper motors.

Sleeve Bearing Mount Dimensions

• Mount hole diameter (18mm)

• Mount circle diameter (32mm)

Leadscrew Nut Mount Dimensions

• Mount hole diameter (12.7mm)

• Mount circle diameter (19.05mm)

Stepper Motor Mount Dimensions

• Mount square side length (31mm)

• Mount hole diameter (3mm)

• Center hole diameter (22mm)

Collar Dimensions

• Length (10mm)

• Outer diameter (25mm)

• Inner diameter (12mm)

• Setscrew (M5x0.8, Xmm Lg, 2.5mm drive)

Coupling Dimensions

• Length (30mm)

• Outer Dimensions (15mm)

• Inner Diameter (3mm OR 5mm OR 1/4" OR 1/8")

• Setscrew (M5x0.8, Xmm Lg, 2.5mm drive)