Computer Controlled Machining

Group assignment:

  1. Complete your lab’s safety training
  2. Test runout, alignment, speeds, feeds, and toolpaths for your machine
  3. Document your work to the group work page and reflect on your individual page what you learned.

1x1 “modular” table (Alan)

Alan designed and made a flat-pack modular table for this week. The actual fabrication took place towards the end of Fab Academy, since an easily accessible machine was difficult to come by.

Foam Crawler Side Plates (Dan)

Dan designed, fixtured, and milled HDPE side plates for his foam crawler final project.

Dan also tested runout on his milling machine using the Total Indiacted Readout (TIR) method. TIR is how Dan was taught as a machinist to check runout of cutters before wasting valuable materials. With TIR completed ahead of the first part being machined, runout tolerances can be accounted for ahead of actual part machining. Dan believes TIR method prevents wasting valuable material to test runout.

Alignment of gantries fixturing datums, vises, and mounting holes should be tested with a dial indicator, or machined into soft jaws of fixturing. Fixturing holes in wasteboards should be machined into place and threaded insterts added afterwards to allow establishing datums to create alignment that is as tight as possible with a given machine.

SciGlider (Dan)

Dan designed glider with a 1.2 meter wingspan called the SciGlider

Speeds and feeds

All cuts were completed with to following two sets of settings: PreciseBits 1.6mm diameter fish-tail, diamond-cut router bit spun at 6,000 to 12,000 RPM with a 48VDC 400Watt DC Spindle Feed rate X & Y: 1200 & 2400mm/min Plunge rate Z: 230 & 1200 mm/min Depth per pass: 7mm (single pass) Spindle RPM 6000 and 12000

Foam materials

Depron foam sheet material was ~ 5-6mm thick and was also very flat. The DOW Protection Board III Fanfold and FOAMULAR® Fanfold DWB extruded polystyrene foam sheet insulation with plastic film on one side was wavy. The peak to valley measurements varied from 0.3 to 0.8 mm on both FOAMULAR® Fanfold DWB and DOW Protection Board III.

  1. Depron Extruded polystyrene Sheet 5.7 to 5.8 mm thick (sometimes difficult to source in USA)
  2. FOAMULAR® Fanfold DWB extruded polystyrene foam 5.1 to 5.4 mm thick (at most home improvement stores)
  3. DOW Protection Board III extruded polystyrene foam 5.1 to 5.4 mm thick (difficult to source, may be obsolete)

For application where flatness is important to function, Depron foam should be used. In most prototype RC aircraft and template applications DOW Protection Board III is a good low cost option.