8. Computer controlled machining¶

Group Assignment

Test runout, alignment, speeds, feeds, and toolpaths for your machine

Individual Assignment

Make (design+mill+assemble) something big

Group Assignment¶

Do your lab’s safety training.

The safety elements of the Fablab Vigil are:

Eye protection goggles.
Cotton work glove with nitrile coated palm.
Earmuffs for ear protection with three positions.
Disposable foam earplug.

The anatomy of drill bit

There are various types of bits basis of its type of cutting length region

Direction of cut

The direction of cut affects the life of a tool, the quality of the cut and the material you are working with. When selecting a tool it’s important to consider the type of material you are using, the needs of the customer and the specifications of the CNC machine being used.

Cutting speed

Cutting speed is the peripheral speed of the tool. Sometimes you may need to calculate cutting speed mathematically. Or, you might use a cutting table. Whichever way you do it, you need to know the cutting speed and RPM for the tool you have selected on the CNC machine you are using. Sometimes cutting speed is confused with feed speed. Just remember that cutting speed is in relation to the tool itself while feed speed is in relation to the movement of the tool.

Spindle and feed speed

Feed speed is the rate at which the workpiece moves into the cutter. It is always determined in relation to the spindle speed. Using the wrong feed speed can produce too much dust or burn the workpiece. To determine the optimum feed speed you can use a feed speed table or calculate it mathematicall.

Out and Inside Cut

There are different type of cut types for different kinds of situation, as tool has its own thickness. Thus you need to choose what dimension you want exact and what part you want to be eliminated

Milling tool setup

The CNC milling machine we have in the Fablab is NomadTech, here is a picture:

What I must take into account are the cutting parameters according to the manufacturer:

This is the program:

Shear Tolerance Test Design¶

We will use 9mm MDF as raw material.

To test the progress and trajectories of the cutting machine, we will design the test piece in 3D CAD, Onshape.

We will use the tip of the 6 mm drill bit. For a better drill cut we increase the measurement by 6.1 mm the corners.

Then, we proceed with the design of the second piece.

We show two isometric view of the assembled parts.

(a)

(b)

We prepare the pieces for cutting in DWG file..

Downloads of parts 1 and 2 in DXF format.

Cutting process¶

DWG files are loaded into Corel before cutting begins.

The Corel file is then loaded onto the machine (Blue Elephant CNC Router) and cutting begins. A video of the process is shown.

This is how the cut pieces look, after a smooth grinding and cleaning of the shaving hairs that are impregnated.

Then with the caliper we measure the slot of part A.

The measurement is 9.4 mm

Then with the caliper we measure the slot of part B.

Slot measurement is 9.4mm

We proceed to join the pieces,

We see that they come together smoothly, y

Leaving both pieces perfectly united

This is a bottom view of the tolerance test

We see that the tibon are superimposed one on top of the other as it should be.

A view of the final assembly.

Individual Assignment¶

1. Design of an ecological shelf¶

What I am going to work with is a wall shelf as shown in the image. The shelf will be a gift for my son Aryan.
I give initial measurements of length, width and height.

The design is done in Onshape. I start by drawing the horizontal surface of the shelf, on the floor plan.

I give a 4 cm radius rounding to the edges of the front part. I add three landmarks to each side of the base.

I make two through holes of 2 x 1.8 cm and a cut that will serve for the arm of the shelf. 2 x 1.8 cm. Then I duplicate it to the opposite side.

The second piece is the arm of the horizontal platform. I give you the respective measurements.

The third piece is the base that rests on the wall. I give it a through perforation of 5.08 cm 1.8 cm. I also added two external half circumferences of 0.8 cm in each corner so that when milling there is no internal half circumference left.

Finally I make the assembly and show it in 3 views on the shelf.

I cut the pieces using the milling machine. For this case, request the services of a third party, since the equipment is not yet available at the IES FPGV.
There are 5 pieces, in a first test it is seen that they assemble perfectly. It is necessary to apply some pressure so that it settles to the bottom.

2. Assembly¶

I proceed to assemble the shelf.

This is a right side view.

I forgot to make the half circles in this part of the piece. That’s why it doesn’t fit perfectly. To solve this I will have to scrape it with a file.

Bottom view of assembled shelf.

Top view.

A preliminary presentation before bolting it to the wall.

Using a wall drill, make a hole, place a plastic plug, fix the shelf and bolt it with a 4.5-inch screw.

This is how the shelf designed in 18 mm thick MDF material turned out.

Finally the shelf is being used. My son Aryan and I are happy.

Conclusion: I can conclude that with computer controlled cutting, many good things can be done, for example for a house, school, etc.

Correcting errors¶

My local evaluator told me that I should correct the errors. The correction was done manually on the Router machine in the FabLab Vigil which already had the equipment.
I turned on the router and the milling cutter I put it at 10000 rpm, then using the program I lowered it little by little until I passed the end. I repeated this for all the corners.