Puzzle
Computer Controlled Machining Project
Requirements
Create parametric puzzle using press-fit jigsaw joints to interlock panels.
Mill puzzle pieces from OSB sheet on the Onsrud.
Design and create puzzle image using vinyl cutter and apply to pieces.
Design
This week's goal was to design and fabricate something big... so I made a big ass puzzle. I used Fusion 360 to create a parametric sketch defining each puzzle piece and the jigsaw press-fit joints.
My original plan was to engrave an image directly into the surface - which you can see in the image below - because I thought it would be fun to expeiment with 2.5D milling (variable depths).
I started by cading the full boundary of my assigned OSB sheet (48in. x 96in.) and used it as a grame to ensure that all puzzle pieces fit within the available material.
The geometry was modeled so that all the pieces could be milled individually and reassembled.
When designing for CNC, I made sure to account for the tool kerf (where each cut removes material equal to the tool diamater, 0.125in.). Because of that, I arranged my puzzle pieces with textra space between contours to leave enough margin for the endmill and to prevent kerf overlaps.
Mastercam automatically offsets cuts to the outside of the parts, so I sketched the puzzle piece outlines at their true dimensions.
I also considered the limitations of the tool's physical reach. Narrow gaps or tight internal corners can't be milled precisely because the bit can't fit. One solution could be to use dogbone fillets.
However, I figured this would disrupt the look of the engraved surface I was planning, so I opted for interlocking press-fit jigsaw joints instead. This choice preseved the smooth, puzzle like aesthetic while still allowing precise alignment.
Unfortunately, after the shop manager and I reviewed the files, we realized that the engraving workflow would require additional time than I could afford, so I decided to pivot and focus on routing the puzzle geometry itself.
I then exported the design as DXF files from Fusion 360 to prepare for toolpath generation in Mastercam.
To bring back some of the visual interest from my original engraving idea, I decided to use vinyl graphics instead. I converted a McLaren F1 car cartoon image to an SVG, aligned and split it across the puzzle pieces so that I could vinyl cut each segment individually and apply them to their respective puzzle pieces.
Milling
Before bringing the DXF files into Mastercam, I double-checked that each was ready for toolpath generation, that is, the geometry was clean, closed and continuous, with no small gaps or overlapping edges that could break the tootlpath.
Another key factor is verifying arrangement on the stock. I confirmed that all pieces were spaced with enough margin for the 0.125in. end mill diameter and for secure hold down.
Because OSB sheets can flex or lift, I made sure to leave room around the perimeter for screws to clamp board unto the vacuum table since OSB can warp during milling, causing it to no longer stay flat on the table for maximized suction.
After confirming the DXFs were clean, I imported them into Mastercam to create the cutting toolpaths for the Onsrud. I defined the stock thickness (0.433in. OSB as measured in the group assignment), selected a 0.125in flat end mill, and assigned spinde speed (18,000RPM) and feed rates (300in/min) as recommended by the shop manager.
The outline toolpath was programmed with 2 stepdown passes of approximately 0.22in. per layer to cut through the OSB sheet.
Once the setup was done, I loaded the toolpaths into the CNC router. One side of the OSB sheet is noticeably rough while the other side it smoother. I put the smoother side down on the Onsrud table for better vacuum.
The entire milling process took about 30 minutes, after which I separated each puzzle piece and lightly sanded the edfes to smooth out splinters and tool marks.