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3D Machining Strategies Comparison
3D machining takes very much longer than 2.5D machining. This can cause considerable management problems in Design and Technology classes in schools when the designs of perhaps 20 pupils need to be machined and time is short. This exercise was done to compare the surface finishes and machining times obtained with different machining strategies.
The billets were all urethane insulation foam (Therma Slab), which is much cheaper than rigid, closed cell modelling foam though its surface is somewhat friable until it is sealed with paint or PVA glue.
The billet dimensions were X=55, Y=55, Z=30
The 3D design was drawn in Inventor 5 and saved as an STL file.
The STL file was imported into DeskProto for code creation.
The cutter was a 6mm ball end and the maximum depth of cut was 25mm.
The cutting feed rate and spindle speed were the same for the four parts.
The parts were sprayed red after machining.
Domes 1 and 2
The cutter moved in a square spiral, starting at the centre and working outwards.
The tool step-over for Dome 1 was a coarse 2mm, machining time 25 minutes. Note the deep cusps and the poor quality of the profile of the circular base.
The tool step-over for Dome 2 was a finer 0.67mm, machining time 65 minutes. The cusps are much smaller and the profile of the base is smoother.
Domes 3 and 4
The cutter did unidirectional raster cuts first in the X and then in the Y directions.
The tool step-over for Dome 3 was a coarse 2mm, machining time 55 minutes. The cusps are smaller than those of dome 1 but the profile of the base is still poor.
The tool step-over for Dome 4 was a finer 0.67mm, machining time 150 minutes. This has the smoothest surface finish of all four domes but the machining time was very long.
Machining time could have been halved if bidirectional cutting had been used.
2.5D and 3D Machining
3D Machining Tips
Code-generating Software
Design Resources