Computer-controlled Machining Week #8

Introduction

This week we have two main assignments:

Individual Assignment: Make (design+mill+assemble) something big
Group Assignment: test runout, alignment, speeds, feeds, and toolpaths for your machine

Design something big

For this assignment, I decided to build a laptop stand that I can use while laying down in bed.
I used Fusion 360 to design the laptop stand. The laptop stand consists of 4 parts: tabletop, Mousepad, legs and supports.
Leg part: two pieces of this part will be fabricated (front and back legs)
Table-top part: one piece of this part will be fabricated
Mousepad part: one piece of this part will be fabricated
Supports part: four pieces of this part will be fabricated
I designed the laptop stand parts to press-fit together, for this purpose I created dog-bones in the female part (the front and back legs), where the supports will press-fit, and T-bones where the tabletop and mousepad press-fit
For the parts to actually press-fit together nicely, I needed to test for the tool tolerance. For this purpose, I designed two small test parts, one male and one female. I first created a parameter named "tolerance", so that I can change it easily during tests. The final tolerance that made the parts pressfit nicely was 0.2 mm.
I put the tolerance parameter into consideration while designing female dog and T-bones, while I kept the male part dimensions the same.
After finsihing the design, I exported the 4 parts in DXF format to prepare for fabrication.

Mill something big

I used Autodesk ArtCam software to create the toolpath for the CNC machine.
First, I created a new model and started with setting the dimensions of the plywood sheet (600 mm x 900 mm)
Afterwards, I imported the DXF files of my design into Artcam, and aligned the parts on the sheet
Then, I started with setting up the material.
Setting the material thickness is not that trivial! The "commercial" thickness of the plywood sheet that we used is 9 mm. However, the actual thickness varied from 9.1 to 9.6 mm in different parts of the sheet!
So to be safe, I set the wood thickness to the maximum measured thickness 9.6 mm.
Now, it is time to create the toolpath. Press 2D toolpath icon, the Profiling window will open.
Set the finish depth again to the maximum measured wood thickness 9.6 mm.
The most important step of the process, setting the tool to a 4 mm endmill. I set the default machining values including the spindle speed, feedrate, and plunge rate.
The stepdown is set to 3 mm, which means that the endmill will go down 4 times to finish the cut along the wood thickness
Finally, I calculate the toolpath.
It's important to simulate the toolpath afterwards to make sure that all the lines and specially the press-fit female parts are detected in the toolpath.
Finally, I save the toolpath's gcode, and choose the format that is compatible with our CNC machine.
Now, it's time to prepare for cutting, fixed the plywood on the CNC bed.
And, fixed the 4 mm endmill to the spindle
Now, I used Mach3 Sotfware to control the CNC machine. Starting with powering up the machine and pressing the "reset" button to get into safety mode.
To set the zero point, I started to move the endmill until I reached the desired zero point then I set it on the software by pressing the zero X, zero Y and zero Z buttons.
Now, I import the gcode that I exported earlier, and I can see the associated toolpath on the screen's corner.
Finally, I press "Cycle start" to start the excuting the code.