8. Computer controlled machining¶
A new week has started bringing new adventures and different assignments .As a group assignment we have to test runout, alignment, speeds, feeds, and toolpaths for our machine. In addition i had to make something big (on a CNC machine) as an individual assignment .
What is CNC?
CNC machining is a manufacturing process in which pre-programmed computer software dictates the movement of factory tools and machinery. A CNC machine is a motorized maneuverable tool and often a motorized maneuverable platform, which are both controlled by a computer, according to specific input instructions. Instructions are delivered to a CNC machine in the form of a sequential program of machine control instructions such as G-code and then executed. The program can be written by a person or, far more often, generated by graphical computer-aided design (CAD) software.
What To Consider While Doing CNC ?
Type of Tool Used
Selecting a tool to use on a CNC machine mainly depends on the type of material being used, the type of work to be done, the quality of finish and the number of components to be run.
Since CNC milling is subtractive method. It requires various kind of tools to carve out material. The choice of Drill Bit would determine how your product will come up
Type of Milling 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
Group assignment¶
Check this direct linkfor the group assignment
Individual assignment¶
For the individual assignment, that required making something ‘big’I decided to design a book shelf to put it beside my desk . I choose Fusion 360 to design my parametric model , this method facilitate your work because if you want to change some dimensios you don’t have to cancel every thing you nedd just to press ->change parametres and change what ever you want
I created new sketch to define the bookshelf profile the first step is to create a big rectangle using the dimensions i have alrady define in the parametres ,
then on this big rectangle i had to design three other rectangles for the different pieces like the top and the shelf
so the first piece i designed is the left side and i used it to make the top by extruding the upper part as much as the width distance
I used the miror to make the right side then i used the same method as before to create the bacK ,the shelf, the bottom shelf and the kick
After that i modified all the bodies by adding joints as showing bellow
I created a ground where i put all the cutting parts
While making corners, milling tool doesn’t give sharp corners thus joinery fails in the CNC product.
Thus fillets are used to compensate that.That’s why i decided to take an extra little bite out of each interior corner in the form of dogbone
To design pressed fit joint on Fusion 360. A “dogbone” add-in has to be installed. The purpose of dogbone is to add circle at all corners of a slot. This is because vertical end mill cutter cannot cut square corner.
To to include dogbone add-in, I had to follow the steps on this
- Download file from the following web link
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Follow the instruction in the same download page.
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When the dogbone add-in is properly installed, a new icon will appear in the create tab
The add-in really facilitates th work i need to select the interior edges and enter the tool diameter which i defined befor on the parametres called cutter(6mm) then the dogbones automatically appear
to define thestock i created a new setup and i choose my axes X,Y,Z
I used a 6mm Flat end mill with 1 Flutes for wood cutting
Now it is time for the milling operation . I started with inner cutting going to the outer cutting to guarentee a better result. so i had to press 2D >> 2D contour and select the inner holes like the following on the picture .
After finishing with all the cutsfrom inside i had to move to the outside so new 2D >> 2D contour and select the outer cutting
The last step is togenerate the Gcode
For the making Process Iused Victor VR0907B cnc machine,
Characteristis
Table dimensions: 900mm x 1000mm
Max working size: 900mm x 700mm
Z-axis travel: 110mm
Table: T-slot
Max. travel speed: 7000mm/min
*Voltage: 220V
Motor: Stepper motor
Spindle speed: 18000rpm/min
Spindle power: 1.5kw
Tool diameter: 3.175 to 6 mm
Accuracy: 0.01 mm
Controller :NcStudio
Software: Type3
Format: HPGL G code
Unidirectional transmission: ball screw
Weight: 300kg
Machine Size: 1000 × 1260 × 1300mm
Since the machine size doesn’t exceed 1/1.26m ,it wasn’t possible to put all the pieces together on the same wood plate , the so i had to use cut 3 wood plates (1/1m) to cut all designed parts
I t wasn’t really easy but i enjoyed the result , i assemble the design pieces and my bookshelf looks great e
Check my bookshelf fusion file