SwarfySteve
Plastic
- Joined
- Jun 5, 2017
Background
November operations included: rewriting the g-code to leave more material and manually parting off (in attempt to reduce chatter/marring).
Tool
The Pocket NC is a 5-axis CNC mill. The control is a BeagleBone Black single board computer running Machinekit. The only tool used is a 0.125 inch, single flute, flat end mill. It is optimized for cutting wax and plastic, and is made of uncoated carbide. When installed in the tool holder, the tool reaches roughly 1.125 inches.
Workpiece Material, Fixturing, and Machining Strategy
Stock used is a 2” x 2” x 2” (really 2.05 ± 0.05 inches per axis) block of Delrin plastic. The stock would only be fixtured once, however parting off would be executed manually.
The part would then be fixtured a second time to apply a fine surface finish to each broad side of the block.
Speeds and Feeds
The program was written with a max spindle speed of 9,000 rpm and max feedrate of 40 inches per minute. However, it was programed with wax in mind and not Delrin. To compensate for the difference in material, the feedrate override was supposed to be set to 80%.
Spindle speed and feedrate for the “manual” finishing operations would have been 10,000 rpm and 30 inches per minute respectively.
Conclusions
Much went wrong this November. For one, an 80% feedrate override was forgotten causing quite the office annoyance. Second was a crash halting all operations. The parting off was to be exectuted manually after the g-code file completed. Before proceeding manually, some chips needed to be cleared as they were a visual obstruction. A MDI command (G00 X0 Y0 Z0 A0 B0) was entered to move the table and spindle/tool to a maintenance friendly position. This caused the tool to collide with the stock resulting with an end mill broken into 3 pieces. A crash report was created. November’s operations will be executed again more carefully for this month upon reception of a new tool. The stock and broken tool are pictured below.
November operations included: rewriting the g-code to leave more material and manually parting off (in attempt to reduce chatter/marring).
Tool
The Pocket NC is a 5-axis CNC mill. The control is a BeagleBone Black single board computer running Machinekit. The only tool used is a 0.125 inch, single flute, flat end mill. It is optimized for cutting wax and plastic, and is made of uncoated carbide. When installed in the tool holder, the tool reaches roughly 1.125 inches.
Workpiece Material, Fixturing, and Machining Strategy
Stock used is a 2” x 2” x 2” (really 2.05 ± 0.05 inches per axis) block of Delrin plastic. The stock would only be fixtured once, however parting off would be executed manually.
The part would then be fixtured a second time to apply a fine surface finish to each broad side of the block.
Speeds and Feeds
The program was written with a max spindle speed of 9,000 rpm and max feedrate of 40 inches per minute. However, it was programed with wax in mind and not Delrin. To compensate for the difference in material, the feedrate override was supposed to be set to 80%.
Spindle speed and feedrate for the “manual” finishing operations would have been 10,000 rpm and 30 inches per minute respectively.
Conclusions
Much went wrong this November. For one, an 80% feedrate override was forgotten causing quite the office annoyance. Second was a crash halting all operations. The parting off was to be exectuted manually after the g-code file completed. Before proceeding manually, some chips needed to be cleared as they were a visual obstruction. A MDI command (G00 X0 Y0 Z0 A0 B0) was entered to move the table and spindle/tool to a maintenance friendly position. This caused the tool to collide with the stock resulting with an end mill broken into 3 pieces. A crash report was created. November’s operations will be executed again more carefully for this month upon reception of a new tool. The stock and broken tool are pictured below.
