Cox:Minitech

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Summary

The Minitech MiniMill Computer Numeric Controlled milling machine provides traditional milling operations on a desktop scale. CAD/CAM software allows for the conversion of CAD files to toolpaths that can be used to drive the milling machine in an automated fashion. Alternatively, simpler coding is possible, as well as manual orthogonal movement through a controller program.

Mode of Operation

A NSK high speed spindle capable of speeds beyond 20000 RPM is connected to the mill, which allows travel in 3 axes. A 4th rotary axis is also available. A controller and driver box couple the mill to a PC. 3 collet sizes are available: 0.125" , .1875", and .25" diameter. A variety of tooling is available to work with most materials.

Guidelines for Use

Preparing the Work

The key to successfully machining a part with high precision and quality is having a properly secured piece of stock that will not shift during the course of machining. Securing the work to the deck is easier said than done, and usually is dependent on how you plan on machining the piece of raw material. The user has several options when it comes to securing material to the deck:

• Small Aluminum Vise
• Nuzzler Clamps
• Precision Vise
• Direct Attachment
• Rotary Axis (with or without tailstock)

Preparing the Toolpath

The user can choose one of 3 methods of moving the spindle to make a part:

• Manual Control
• G code
• Using Visual Mill

Manual control is performed by "Jog" or "Point commands in FlashCut. With "Jog" you are able to move in one direction at a time, while in "Point" you can move in a straight line from one point to another. These are only recommended for surfacing or rough cutting of material, as it is a very inefficient way of movement.

G code is a programming language that allows one to create very efficient toolpaths for objects with limited geometric complexity. As the G programming language was designed for much larger and complex milling machines, several commands such as changing the spindle speed or auto tool changing is not supported on the MiniMill. Check the FlashCut CNC manual for the specific commands available. The most frequently used commands are:

• G00 Rapid Tool Movement
• G01 Interpolated Tool Movement
• G02 and G03 Circular Movement (Clockwise and CounterClockwise)
• M98 and M99 Creating Subroutines

Materials in Stock

• 6061 Aluminum
  • Rods
  • Sheets
  • Bars
• Teflon
  • Rods
  • Angles
  • Channels
• 316 Stainless Steel
  • Rods
  • Sheets
  • Pipe
• Copper
  • Sheets
  • Rods
• Polycarbonate
  • Sheets
  • Rods
  • Block
• Machinable Wax
  • Blocks
• Delrin
  • Plates
• Acrylic
  • Sheets
• Brass
  • Rods

Part Gallery

Lessons Learned

• Loud, high frequency noises usually mean you are rotating the bit at too high of a speed. Turn down the speed of the spindle. You may also have to reduce the feed rate as well to prevent stalling.
• Nuzzler clamps tend to make sheets bow up in the center if you only use them on a pair of sides. This may cause inconsistencies in the depth of cut. Try using more nuzzler clamps on all the sides, and be mindful of the bowing.
• If you accelerate the feedrate of the machine too much, the stepper will trip an over-current sensor and lose track of its position. It makes a loud noise and will ruin the build if you dont stop toolpath execution in time. The best way to avoid this is to keep feedrates below 20 in/min, and limit the overdrive of your program.

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