PROJECT OVERVIEW:
– to become acquainted with how to operate a 3-axis milling machine
– to design an object that could be assembled without the use of fasteners, relying only on press fit joinery
– effects of scale, and building components were to be considered
MATERIAL:
– 1/2″ plywood
DESIGN CONCEPT:
The above photos are of a small container and a box full of hardware that needs to be organized and easily accessible, otherwise it will not be used. My design intent was to develop a system of compartmentalized, stackable trays. Due to limited space, the overall dimensions of the base tray are 13″ x 13″ x 4″. The press fit, mortise and tenon joint relies completely on friction which is weak, and weakened with each re-assembly. Because of this weakness, the compartment divider parts mechanically lock the assembly together, solidifying the structure.
TRIAL / TEST 01:
After measuring the materials thickness with calipers, and adjusting the drawings tolerances appropriately, I was ready to cut parts. The first test was performed on the techno CNC, which does not have an automatic “dog-bone” tool. The solution to this was to plunge the bit through the material at the necessary corner locations, leaving a through hole the diameter of the tool. The cut file, seen below, highlights the holes and specifies their corner locations.
Fueled by the machines air compressor, the heat caused by the friction of the bit vs the material caught the sublayer of MDF on fire. The fire burned downward as it was being pulled through the material by the machines air compressor. The fire went undetected until it was visible on the outer layer of plywood. At this point, the fire had spread completely through the base layer of the waffle patterned material, the middle layer of MDF, and through the top layer of plywood.
TRIAL / TEST 02:
The second test was performed on a different CNC mill, the ShopBot PRSALPHA 120. This machine does not have a vacuum table, so the material to be cut must be fastened to the machines routing base. The cut file was adjusted to ensure the mandatory 1-1/4″ offset from the materials boundary. All parts were cut out successfully.
FINISH / ASSEMBLY:
All parts were sanded, and all edges were chamfered at a 45 degree angle to promote ease of assembly.
Side walls were installed first, followed by the structure solidifying, divider parts.
Below are photos of the edge detail before, and after, divider parts were installed.
parts fully assembled
TROUBLESHOOTING:
Due to tight tolerances, when the first middle divider part was installed, a sharp corner ripped the veneer off the ply. The solution to this was to chamfer the corners at 45 degree angles. The best, longterm solution is to mill a small radius at this, or similar situations.
On one of the two trays, the tolerance was too tight when installing the second divider part onto the assembly. The part failed at the middle joint as seen below. My next investigation is to loosen the tolerance in this middle joint condition.
CONCEPT 02 SKETCH DIAGRAMS:
Concept 02 begins to investigate half, single, and double height, compartment spaces.
COMPLETE FABRICATION 