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CNC machining or 3D printing

CNC beats 3D printing for bathroom use

DeskProto developers need of course to extensively test the software, so it is very helpful when a nice hobby application comes up that can be used for a next test run. This project results from the frustration of finding a pile of brushes in the bathroom (for the shared electric toothbrush) without knowing which one is yours.
The idea is to create a brush-holder that clearly indicates the user of each brush.
A nice maker-project: make your own custom solution instead of buying a standard product.

While 3D printing currently is in the spotlight as technology for making parts, the lowcost filament printers that are used by hobbyists are not suited for this application:
  • for reasons of hygiene: such 3D printed part is porous and thus cannot be kept properly clean.
  • the holder's pins will easily break when printed in layers ("delamination", depending on their orientation in the 3D printer).
  • for a good stability the holder needs to be heavy, which means solid. Adding all required material as filament will cost much time much filament.
  • for CNC machining the material cost will be much lower than for 3D printing.
The alternative making technology CNC machining is perfectly suited for this application: an appropriate material (food-safe, easy to be cleaned, strong) can be used, and the surface can be machined perfectly smooth so dirt won't stand a chance. Lowcost CNC machines are available for any hobbyist user.

Rhino Screenshot of the design in CAD
DeskProto screenshot with geometry and toolpaths
First the design in Rhino, next STL and DXF in DeskProto

The design of the brush-holder is pretty straightforward: a mono-block form, with 4 pins on top to hold the (for this family) four different brushes. The size of the pins was measured from the two-brush holder (too few positions) that came with the electric brush. A sloped side was created for the text to be written on. On all edges a fillet has been applied, as that looks better and will make the part easier to clean. The illustration above shows the part, created using the Rhino CAD software.

The geometry then was exported as STL file, and opened in the DeskProto CAM software to calculate the toolpaths. The text was created in Rhino as well, and exported as 2D DXF file. "C L M R": for each brush one character to name its owner. This DXF file then was opened in a DeskProto 2D Operation.

Roughing operation on the machine
Machining the text with a small cutter
After he roughing operation, and next engraving the text.

The brush-holder was machined from a block of Delrin (POM), which is easy to machine, approved for use in the food industry, and has a low water absorption. The block was clamped down using both a mechanical clamp and a piece of doubly sided tape, as Delrin is known to easily pull out of a clamp under the cutting load. Later the clamps were removed for the final few toolpaths.

The ball-shaped tips of the 4 pins have been machined first (see the toolpaths in the DeskProto screenshot above): when machining these after the roughing operation the pins would bend while trying to machine this radius. The text was machined using a small cutter (1 mm diameter), by projecting the 2D toolpaths onto the geometry, at 0.5 mm depth.

The resulting brushholder in the bathroom
The resulting brush-holder. Four Philips 'Sonicare' brushes: one for C, L, M and for R.

While machining it was nice to see the results of the new sorting algorithm that was introduced in DeskProto V6.1: the pins were completely machined one after another, instead of (as in V6.0) travelling from pin to pin for each Z-level. This sorting almost halved the total machining time for the waterline toolpaths over the four pins (compared to V6.0).

The picture above shows the resulting brush-holder is use: no more bathroom wars about missing brushes or about brushes that allegedly have been 'illegally' used.
A very practical maker project !