G's webpage

In order to understand the basics of CNC milling and machining, an intensive research was performed to discover all the variables that affect the CNC machining process.

There are many components that must be taken into consideration when CNC machining, and those mainly are based on the material undergoing machining, the tools used, and the machine itself.

So the next step is to test the different outputs we get by variating the settings of the machining process.
In this section we will test the alignment of the Shopbot we have in our fab lab, and then test the various outcomes we get when we change the speeds, feeds and toolpaths.

To achieve that, we prepared a file with different settings for the test.

Getting to the actual testing, first we had to identify our material that would be cut and the bit we are going to use.

We went with Plywood (15mm)
And a 1/4 Inch, single flute, upcut milling
The bit supplier where we got ours from has specified that the chipload should be between 0.004 and 0.006 so we had room to adjust our variable settings as long as we were in the specified scope.

We decided to go with a chiprate of 0.005 which is in between and adjust the spindle speed and feed rate while maintaining the chiprate based on the equation stated above
So the Chiprate is a constant 0.005:

CR = RPM x FeedRate

Setting 1: CR = 10,000 x 50, 3 passes (1xD)

Setting 2: CR = 14,000 x 70, 3 passes (1xD)

Setting 3: CR = 18,000 x 90, 3 passes (1xD)

Above were the Settings we used to perform our tests, each of these was done twice. Once while using the climb setting and the other in conventional setting. The picture below is the test that was made, going as follows from left to right:

Setting 1 Climb, Conventional

Setting 2 Climb, Conventional

Setting 3 Climb, Conventional

This is the raw result, after sanding it would look much smoother.
We also did another test with one pass instead of 3, for this test we had to recalculate the chip rate as it has to be divided on the face of the drill, so the 0.005 chiprate has to be divided into 3 as it is now handling triple the load. The pass was successful and the picture of the settings and final result are found below.

Conclusion

14.800mm

Individual Assignment

Design

For my design, I decided to do something related to my final project. Which basically needs a tall structure, I cannot say this is the best design for its purpose since the most efficient structure would be standing on 4 pillars. But I wanted to try and design something that would be a bit of a challenge to design in accordance to my level of skills. I decided to do a tripod which would have joints on the top and bottom. Since the tripod would be much easier to handle and falls in well for my final project, only I am not too sure the plywood would be able to handle the tension I am going to need to exert on it. If it fails to be of use for my final project, I have other designs in mind that would include what we are going to learn in the upcoming weeks. That way there is noway what I did would go to waste.

The steps taken to achieve this design are as follows:

First I designed my structure using Fusion360

I first started drawing a rectangle with the dimensions of the actual board I was going to cut since it was basically my only limitation. I then started designing my 2D parts within this rectangle to make sure i would not design something that would exceed my limitation and face drawbacks habing to go back and design again.

Since my design revolved around a tripod, I started designing the poles as they were the largest and most crucial parts of my design

Then I went ahead and started designing the joints I will have to make to pressfit these poles together. Since it is a tripod, I went with a circular pattern with 3 openings (fittings) 120 degrees apart so they are equally distant.

Then I went ahead and chose where to put the openings for the pressfits on the poles, I added some more along the edges of the poles in case I would need to add some more supports to the structure later on. Since I would be using the same measurements for all steps, I set 3 different parameters, one for the kerf, one for half the kerf (going from the center of a lign), and the semi circles to achieve the T-Bone design.

And lastly I did some triangles that would fit around my structure and support it externally. I could not do them big enough to support the structure from the bottom, but it did reinforce the top area of the tripod.

And finally save the file in .DXF format

G-code Generation

Now with the 2D design complete it is time to move on to the CNC.

As stated above the CNC we have at the Berytech Fablab is the ShopBot. In order to generate the Gcode we have to use the V-Carve software.
The steps to set up V-Carve are as follows:

First you have to open the file (Import)

Input Board Dimensions (As in our case, if you dont have a vaccum bed make sure you take into consideration the edges that are held down)

Now move your design accordingly to the board, the way you set it up is up to you. But try being as efficient as possible

Your cuts are generally going to fall into two categories, inner and outer cuts. for this step, select your inner cuts (jump to steps after the selecting the exterior cuts down to saving the toolpath)