7. Computer-controlled machining¶
This week, our assignment was to make something big. I will be making shelving to fit underneath my desk in my garage.
CAD Work¶
I decided to make shelving that could fit my CNC machine and 3D printer inside it. My desk is fairly tall, so I will fit my CNC machine on top of my 3D printer.
I started by creating a small box for the area I had to fit my shelves. I then designed my shelving around that. Finally, I added tabs to hold the parts together. I will be using slot fit joints since they allow me to assemble the final product without needing glue.
I then created a copy of the fusion document that I could modify. I laid the shelf parts flat and used the project feature to create a sketch from them.
It was at this point that I realized I had made a mistake. For the slot joints to fit together firmly, I changed the width of my joints by a small amount. However, I accidentally made my joints wider instead of thinner, and this would have the opposite effect on my joints. Thankfully, I had used parametric design in my file. So, I changed my value from +.011 in to -.011 in, and I was slammed with a plethora of warning messages. Fusion 360 did not like me changing a positive number to a negative number, and a variety of extrudes, sketches, projects, and other features was messed up. Instead of fixing each issue one at a time, I opted to restart.
I made a new fusion file, and to avoid these problems I decided to only work in the 2D plane. I also simplified my design to remove a section that would hold my CNC machine, as I do not think that the slot fit joints will be strong enough to hold more than 5 pounds. My new design is much simpler and is just one row of shelving with a back.
I imported the file into Corel draw to turn it from a .DXF file to a .SVG. I did this because we will be using the program Aspire to create our toolpaths, and it does not support .dxf files. In Corel, I used the virtual segment delete tool to clean up my file, since .dxf files exported from Fusion 360 include construction lines.
Finally, I imported the .svg file into Aspire. I used sliding joints for my shelves, so I started by creating a separate layer for my slots. This will make it easier to create different toolpaths at different heights.
Next, I created dogbones for all my slot joints. This allows the round tool to cut out a square hole that my pieces can slot into. To do this, I had to first use the join vector features because the .svg file was imported as separate lines instead of one. After using the join command, I then used the dogbone feature to draw the dogbones.
After finishing my drawing, I created the toolpaths. I first created the toolpaths for the sheet, then for the slots with the 2D profile toolpath option. For the slot, I used the inside cut option, and for the sheet, I used the outside cut option. I enabled tabs for the sheet and disabled them for the hole slot joints because they were small enough that the tool would cut away all the material.
Finally, I created the toolpath for the sliding joints with the pocket toolpath option. I set the cut depth to .25in.
Next, I exported the toolpath and I was ready to cut.
Cutting¶
The next day, I went to the lab to cut. I followed the workflow for our lab’s PRSalpha shopbot. First, I calibrated the X and Y axis with proximity switches and calibrated the Z-axis to the table. Next, I attached the plywood sheet to the table with wood screws.
I then imported my Aspire project to the computer that controls the shopbot. I dragged my pieces into the bottom corner and recalculated my toolpath. I used the merge toolpath function to combine all the toolpaths into one toolpath and saved it. Before cutting, I moved the shopbot to the coordinates 2,1 and zeroed it so that it would not cut through the wood screws and I ran the cut.
Assembly and Problems¶
The cut turned out really well, and after chiseling the tabs and sanding, I started assembling the shelves.
The slot fit joints fit together very well, but the sliding joints did not fit together well. There were a couple of problems with my sliding joints - I hadn’t made a dogbone on the pocket toolpath, so the machine did not cut all of the pockets out. I could have fixed this by lengthening the toolpath or by adding a dogbone. The other problem was that the shelves were very tight and didn’t fit well at all. They were a bit too wide, and while assembling I tried to force them in but I ended up bending out the wood. I also tried cutting down the width of the shelves with a table saw, but the wood was too damaged to hold the shelves.
To fix this problem, I decided to use slot fit instead of sliding joints with my shelves since I had success with them. I redesigned my shelves and side plates around slot fit and updated my aspire project. Now I am ready to cut out my shelves whenever I can get in the lab again.
Once I got back into the lab, I started by milling out the aspiring project file I had created. I followed the workflow and processes previously described to mill out my shelves.
However, there were some problems. The major one was that the slot fitting shelves were so tight that when I pushed them in, it actually warped the shelves slightly out of their perpendicular angle. This resulted in them being out of square, and the other side piece was unable to align and fit in.
The shelf was able to support considerable weight- it was able to hold the CNC machine- but I will be redesigning it so that the other side can fit.
Unfortunately, I ran out of time this week to finish the project. I will resume this week’s assignment at a later date.
UPDATE- week 12¶
I got behind during machine week, so I had some catching up to do before I could return to machining week. I eventually was able to return to and complete this week.
I started by redesigning my fusion sketch file with larger tabs. I made no other significant changes to the design. I then imported it into aspire and generated the toolpaths.
I then milled out my shelves, following the workflow and safety protocol.
However, I discovered a major issue that my tight tabs had masked- stability. My shelves were only supported at two points in the middle, which created an axis that the shelf was able to rotate around. This resulted in major instability. If I wanted to hold anything, I had to keep the center of mass of the held object inside of the thin rectangle that was creating the axis. Obviously, this was a poor requirement for a shelf, so I once again redesigned and remilled my project.
This time, I designed it so that there would be 2 tabs per side, 4 in total. This would remove the problem with the axis in the middle of each shelf.
One final time, I milled out my shelving using our lab’s workflow.
It did hold together, and I found that it was easily able to hold plenty of weight. There was one last minor problem with my design that could be fixed- I had accidentally made the tabs for the shelves 1 inch tall instead of the thickness of the material, .5 in. This resulted in loose joints that decreased the overall stability of the shelving. This can be remedied by adding some inserts to fill up this space and tighten the joints.
However, it was functional. The top shelf held up, supporting the weight of my personal PCB mill. The bottom shelves’ dimensions were laid out perfectly to hold some cardboard storage containers used by our lab for soldering materials.
Reflection¶
Overall, I learned quite a bit about the processes and design rules for machining. I became quite efficient at making Aspire toolpaths (after milling and designing 4 times), and I slowly became more knowledgeable in the best types of joints to use. It was very frustrating to constantly deal with different issues after solving a previous one, but I do feel like I learned a lot about joinery through this ordeal.
Group Assignment¶
This week’s group assignment was to test run out, alignment, speeds, feeds, materials, and toolpaths for your machine as well as taking the safety training through our lab. Since all of us have used the shopbot through our school’s engineering classes, we have already taken the safety course. Our group’s documentation for this weeks assignment can be found on our group page
All my files for this week can be found on this zip file