If you are going to design and build your own CNC Router machine, the first thing you should consider designing is the Base Frame. Many people design their machines from the spindle down, but we are going to do it from the frame up.
Base Frame Oversight.
The base frame is and always will be the main structural element of your CNC machine. The base frame is what hold everything together and all your components will attach to.
The base frame design will depend on what materials and supplies you have got, the number of lead screws and motors your budget can cover. Firstly we need to cover the basics of the designs so we can buy parts to fit our design.
If for some reason you cant find a part for your design or your budget can not cover your design you will need to go back to the drawing board and optimise your design and materials you have used. This is a common problem found by most when designing and building a project.
Firstly take a look at other CNC designs you can find anything that will benefit your own design.
Also you must choose now whether you will be building a mobile gantry or mobile bed.
CNC Routers X Axis Frame Design
When your building your own CNC Router machine, the X-axis is the base frame axis, why because it supports the X-axis linear rails.
This part of the machine servers 3 main tasks:
1) Its the main structural element, acting as the base.
2) Supports the X-axis linear rails.
3) Supports the cutting table.
The most used designs for the base are.
Fully Supported Base Frame
with a fully supported frame is one of the graetest designs it is also the main design used in industrial and professional router machines.
The fully supported frame design means that both X-axis and Y-axis will rest on floor or other structure. There is nothing across the Y-axis gantry (connecting). This results in a very sturdy CNC Base design that will not flex under cutting table or its own or external weight.
For this frame design to be able to flex or deform the material would have to compress.
But keep in mind that the kind of flex we are talking about isnt a massive amount, and if we revert back to the question in step one and that was how accurate do you want to build your machine and hold that accuracy. A deformation of 0.01 is acceptable if you only expect 0.1mm with your machine.
There are also drawbacks with this design they are, You will need to add an extra stepper, lead screw, ball screw and proximity sensor or limit switch, so this alone will bump up the cost of your design. You could employ a fully supported frame design and only use one motor (stepper) and use a pulley belt system, but for this system you would need to ensure your motor is up to the job as it will be under a lot of load, this will be covered in the CNC drive system section where we will show you how to work that out. With the fully supported design you can get away with lighter materials, because it is supported against the floor and other structure.
Now on to the next design.
Full supporting frame vs full supporting linear rails.
This design is fully supported and does not have anything obstructing or sweeping across the axis while operating
later we will cover fully and end supported linear rails, but that is later for now we woill just cover this heading, so focusing on this frame design it is possible to have fully supported linear rails and
not have a fully supported frame like this. //////////////
partially supported X-axis fully supported Y-axis frame
The most common design found in the DIY hobby CNC router out there is this one.
This illustration shows Y-axis and end supports the X- axis frame.
In this design the gantry would be an undercarriage design that would link the Y-axis underneath utilising only one stepper motor lead screw and proximity sensor, this would allow for a fully supported linear rail setup, however the supported rail will still flex but know where near the same extent of a non supported rail.#
a downside to this design is that you would need to add feet either end of the frame allowing the Y-axis undercarriage to pass back and forth without any obstruction, this would still be classed as a X-axis supported system since the frame would not interfere with the gantry.
This makes a very sturdy design because the Y-axis has no flex within it, it also makes for a very strong cutting bed that is also very rigid, only downside is where we are supported the x-axis up with legs this will allow for the X-axis to deform under the Y-axis weight or cutting force.
Building this frame out f solid aluminium measuring 38mm x 115mm with X-axis length of 1520mm your frame will sag 2.5mm in the centre. That is only under its own weight this does not include gantry weight or anything else like cutting force.
This would be a nightmare if (back to step one) you decided you wanted a machine with a tolerance of 0.01mm in the z-axis, this machine would definitely flex and you could probably compensate for it, but the machine could and probably would vibrate and bouncy even while trying to cut a straight line.
If you choose to use this design I would say to use a small x-axis length 600mm to 800mm max this would lower the amount of sag in your x-axis.
This frame design is the easiest design to setup and get going but not without its known issues, there are other solutions out there for design.
Full Suport on X-Axis Partly Supported Y-Axis
For this design lets say you only have one stepper motor and lead screw available for your X-axis but still wish to obtain a high tolerance machine. What we could do in move the Y-axis gantry inside the base frame, this would allow for a fully supported X-axis the machine would not be able to cut under the x-axis frame, however using this system the y-axis would not be a fully supported.
With this design you can see, the X-axis is fully supported (its grounded) however the gantry would be able to cut through any frame within the Y-axis so limiters would need to be in place to protect the frame.
With this setup no matter how much weight was placed on the gantry or cutting bed the X-axis frame would not deform rather the material would deform then cause an issue.
However, for this frame to work the cutting bed would have to be separate from the overall machine, this means the machine table could deform if wasn’t built with adequate strength and support, there is also a pro to this design once the bed is set you could use your machine to plane it smooth and level.
This would mean the cutting bed is true to the machine.
When designing and building your own CNC Router Machine, you will have to decide what is more important to your design. Have a machine that remains constant or having a bed that will flex with your machine, this will be covered more when we cover the cutting bed.
Alternatives To The Above
there is always another alternative and depend how creative you wish to get with your CNC router design.
We could create a design in which both X-axis and cutting bed are both very supported, if you look at my design below you will see the X-axis is raised this allows for a small gantry in height it is also fully supported x-axis frame it sits on the ground and carry all the weight, as for the cutting bed it could easily be integrated into the design either fixed to the machine so it can flex with the machine or a free standing bed that will remain constant and milled to always sit true to the machine.
Mobile Bed Design
Personally not a fan, Why, well to make this machine the X-axis has to be twice the size of the cutting bed so if your bed is 500mm your X-axis would have to be 1m in length, large footprint small cutting bed.
But with the design the cutting bed is fully supported and attached to the machine it also allows for the machine to plane the bed to sit true so it does have its advantages
your only need one stepper motor and lead screw to get it to work this is a great design if you wish for a small high precision machine that will not break the bank.
Mobile gantry machines are great for PCB and engraving machines.
Considerations to think about
So when it comes to designing and building your own CNC router machine, firstly you will need to consider what material you will cut the frame from as it will play a big part in your overall design.
Different materials will have different tolerences and all will deform differently, but the most common materials to choose from are:
1) MDF, easy to work with relatively strong but will flex and warp if in a humid environment.
Will degrade over time and will need to be remade.
2) Plywood, only use structural marine ply very strong easy to work with and can create a good machine but over time will become weaker and lose precision.
3) Aluminium Stock, flat plate, angle ect again this is a great material, but aluminium can deform very easily over a small distance so if your machine X-Axis is 1500mm it will need a lot of support to stop it flexing.
4) Aluminium Extrusion, this is probably your best option it is design to have a very low deform over a long distance it strong and easy to work with but does come with a price tag. But your machine will last a long time and always remain strong and precise.
5) Steel. Your not going to get anything stronger than steel to build your machine but you will need a welder and you will have to take in to consideration the weight of the materials as they accumulate on your machine.
All 5 materials have pros and cons all can be used on your machine but consider aluminium and steel don’t mix this is a big NO NO as the aluminium on contact to steel will transfer all its ions to the steel causing galvanic corrosion and your aluminium will become worthless in months.
In future pages we will be covering placement of components and these should all be consider into your design especially when it comes to maintenance of your machine components.
For now just review your design you may consider different options for your design.
Do not rush your design it is important to find the issues within the design process before you start building as a minor error might mean a costly rebuild later on.
Next lets look at the Z and Y axis frame design.
Step 3: Designing and building the Y and Z axis.