Since we have gained a full understanding of the X-axis frame designs, step2 concerning a DIY CNC router design, it is also necessary to consider the Y-axis assembly and design.
For those that enjoy DIY projects, the gantry design is quite common to people who are actively involved with CNC routers. This design finds a wide application because it is one that works the way it is intended. There are different designs which you can adapt and may be most suitable depending on the type of material available, the parts, and the limits of your budget.
Of all the “DIY CNC routers,” the gantry design has been determined to work best. Regardless of this, there are certain things you need to note about the design.
Stability and balance are two essential design features which your gantry should possess. Your CNC gantry should have a design that ensures it is able to withstand any force that will be acting on it. This protects the lead screw, bearings, and motor from encountering strain and stress which are in excess.
Defining the forces that will be acting on the gantry is the first step to take in order to come up with a gantry design that will be able to counter the forces.
To fully grasp the concept of what happens in the CNC gantry, we need to understand the following;
Centre of gravity/mass
The Technical Explanation: CNC Router Forces
The design works by using a CNC drive system which is fixed at the bottom to either push or pull a gantry from left to right or vice versa. As this is happening, a router spindle is being moved downwards, and it begins the cutting action.
The movement of the gantry and that of the cutting action are in the opposite directions. This opposing motion between the two produces the cutting force in the design. The differences in the acceleration of the gantry, the chip load, and the revolutions per minute (RPM) of the spindle are the factors that determine the cutting force. The gantry material, the type of bit, and the RPM are the factors that determine the chip load.
As a reminder and for those of you that need to learn, force is equal to the mass of the body multiplied by the acceleration of the body. The unit of force is either in Newton in SI unit or lb-f (pounds of force) in the English system.
In the gantry, you will have a moment which is produced by the action of the cutting force. The moment is the product of the force and the perpendicular distance. Its SI unit is the N- while it is lbf-in in the English system.
To determine the position of the centre of gravity of the system, the weight of the gantry is needed. The centre of gravity is used as a term for the point at which your machine will be balanced.
To counterbalance the weight of the spindle hanging over the Y-axis linear bearings in a DIY CNC router, the upright side arms of the gantry are usually bent backwards.
In the design of a DIY CNC router, the centre of gravity of the gantry assembly should lie between the two linear bearings.
For a design with a moving bed and an immobile gantry, your CG should be located at the midpoint of sidearm bottoms of the gantry.
This is to give you the guarantee that the machine will not topple over and will remain in balance. It also equally distributes the loads on the bearings of the machine.
Below are some essential aspects you must always consider when you decide to carry out a DIY CNC router project;
When creating a distance from the linear bearings and lead screw of the X-axis to the bottom of the linear bearings of the Y-axis, the distance should be as small as you can obtain. You can also make the distance to be almost equal to the distance from either the top or the bottom of the Y-axis linear rods to the centre point between them.
The material you use in the fabrication of the spindle plunge arm should be strong and not easily bent. For the spindle plunge arm which is located on the Z-axis assembly, you must ensure that the length of the arm is the smallest length possible.
You should determine the centre of gravity of the gantry. This can either be by calculation or through a rough estimate, and the spindle should also be taken into consideration. To get the best out of your design, you should try as much as possible to have your centre of gravity between the linear bearings at the front and back of the X-axis of all the arms on the gantry. The arms are essential for balance. (CG should be located at ½ D4 and as close to X-axis lead screw as possible)
When considering the distance of separation between the upper and lower Y-axis linear bearing rods/rails, you should choose the maximum distance of separation. To allow the maximum distance of travel for Z, do not forget to account for the clearance below the bottom rod. (Maximize D3)
For the best DIY CNC router, you need an excellent gantry design. While this is the case, DIY projects are often limited by the budget and materials available. This means you have to make estimations and have mental pictures of how you can use the materials available to get a design that will work.
To analyze your design, you can contact us, and we can provide you with a free analysis. We perform an exhaustive analysis which includes;
Dynamic simulation of your machine
Specific CG location
Material stress and strain analysis
Other aspects which are important in CNC router do it yourself projects include;
- Motor placement
- Lead screw placement
- Linear bearing attachments