How it works
A CNC or Computer Numerical Controlled Router these work pretty similar to a hand router where the operative would move the router to create what they wish to achieve.
All CNC machines work in a similar way, they use a computer programme that communicates with the breakout board which breaks down the signal to the Stepper drivers and then they turn the steppers to the right position of rotation.
A standard CNC router machine moves in three directions these are you axis, they are referred to as X, Y, Z directions. X and Y are normally the longest as they run front to back and left to right. Z is the height up and down and is normally the shortest this is to do with the torsion stress they will be explained in a different article.
See below the for a visual.
CNC Machines work very cost-effective they work all three axis simultaneously which reduces the amount of time the machine is running. This means you can create a high definition model accurately.
Ok so now we will go over the parts on a CNC machine, and how they all tie together the make your machine work.
T the right you will see an image showing the Parts.
There are many more parts to a CNC but you don’t need to know them just yet.
Now we can look at these parts in more detail.
The CNC Controller and Computer System
These two parts work directly together as the brain of the whole system. Telling the steppers and stepper controllers which direction to move and how much. You have to put your design into the computer software for it to do so.
Most of my designs start in SolidWorks and then get put in a cam program that formats it into a 2d digital image (dxf) they then allocate a tool path code such as g code.
The computer software then converts these g-codes into signals to the breakout board then on to the stepper drivers.
This is all done by varying the current and voltages.
Most CNC programmes like LinuxCNC and Mach3 are plug and play and only need a few things setup to get your system running. All will be explained in future articles.
The Spindle is the part that holds the collet which holds the milling tool that does all the cutting.
Think of the spindle as a standard wood router you would find in any tool shop.
They are rated in horsepower in English units and watts in SI units.
The spindle rotates at high speed 4000 to 30000 rpm (Revolution per minute) these motors are great for cutting through material like wood and plastic.
For cutting metals you would need a spindle that cuts between 2000 and 10000 RPM.
Most CNC machines that are purchased are capable of cutting through both metals and woods, this is limited thou to softer metals like aluminium.
When cutting materials like aluminium you will need a means of cooling this, this is normally done by using an oil mist system.
This cools the router bit and material being cut and enables the machine to make a smooth cut.
Some CNC spindles are controlled by a VFD or variable-frequency drive these can control the Spindle torque and speed this very useful when you use a variety of materials.
There are also other options to that could be installed on your spindle these are ATC this is an automatic tool changer.
You will even use a touch probe at some point for calibrating your z axis check that out here.
The Cutting Floor
The Cutting floor is where you will place your workpiece, so this is where the magic happens. The cutting bed comes in many different types but they are all essentially the same.
They are designed to support and secure your work pieces to the machine.
Two of the main cutting beds you will find are t slot and vacuum tables, t slots work very well but you have to be aware of the clamps on your workpiece, with a vacuum table you don’t need to the clamps the air vacuum holds the workpiece in place which is great.
Vacuum tables have some downfall’s thou these are, you can only really use flat workpieces with them due to the way they work.
T-slots are a lot better if your workpiece isn’t flat with the clamps you can virtually able to clamp anything it’s a little more time consuming but at the end, you will have a finished product.
There is even a hybrid table which combines both vacuum and t slot together this brings on the best of both worlds but comes at a cost.
The Linear System
Each axis has a linear system in place to move your machine to its desired location, these include stepper motors or servo, a linear bearing or rack and pinion, these make up the linear system.
The stepper is where the electrical pulses from the stepper driver are converted into rotations this, in turn, rotates the linear bearing, this is the same if you used a servo or rack and pinion system.
So we have two different types of motor these are steppers and servos, stepper motors are defiantly the cheaper of the two they offer great performance and are very accurate and reliable, but they can generate a lot of heat, and they are not usually closed loop.
Servos, on the other hand, are closed loop and this means after they have moved to their desired location they send a signal back confirming they have completed the task.
You only normally find closed loops on high-end CNC as they are reactively expensive to buy.
Controlling servos is still the same you will need a servo controller in place but they are not the same as a stepper controller.
The stepper or servo offers the power in the for of rotation motion which then needs to get converted to linear drive. This is where the lead screw comes into play, this is essentially like a threaded rod and a nut, the nut is held fixed to the gantry as the tread rotates the nut either moves up or down the thread creating linear motion.
With a rack and pinion the stepper motor or servo is attached to the pinion and the rack to the frame as the motor rotates it creates linear motion up and down.
Both systems have their benefits and drawbacks it’s just a matter of what’s better for your system.
There is more information on this here.
Pretty much all CNC machines you see today are gantry style CNC’s this is where the whole of the y-axis is suspended across the cutting bed. It’s suspended via two arms allocated either side of the cutting bed on the X axis linear rails.
By now you should have a good understanding of how a CNC system works. The Computer runs a program which sends signals to the breakout board where they are broken down to the drivers and the drivers send electrical pulses to stepper motors and the turned into rotational motion and the lead screw then converts this to linear motion.
This moves the spindle in 3 directions that can accurately cut your model.
So this has only covered the basics of how a CNC drive system works. If you’re like to find out more in-depth about parts and other related parts to a CNC, Please check out my other pages.
If you are now comfortable with how the CNC drive system works we can move on to the next section which will take a look at the different types and features that are available.
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