CNC – Beta Table
This is simply the best set of plans I’ve seen for a DIY CNC machine. The instructions are clear, include LEGO style assembly drawings and include a BOM and pricing (from American suppliers). I learnt a heck of a lot from walking through the plans step by step. If anyone wants to build a CNC that has the best chance for success I wouldn’t hesitate to recommend this design.
This appears to be a very popular design and has notable features such as a torsion box base and dual guide rods each side. The down side for me was the use of leadscrews/threaded rod for the drive mechanism. From my previous attempt I found that 1/4 threaded rod developed too much whip if unsupported over 1 1/2′ or more and I wasn’t willing to invest the money into proper leadscrews or 1/2″ threaded rod for another test.
With these two sources in mind I went about designing a table that combined my favourite aspects of the two. It would have a torsion box base to resist warping and remain flat and accurate but would also utilize a timing belt drive system. I completed the design and sat back and reviewed my work. The design would have been stiff but included many duplicate pieces that would have been tedious to cut and nearly impossible to duplicate accurately. The heavily over constrained design made me return to the drawing board with a new mentality to keep the design as simple as possible.
This time I used the design posted on Instructables.com as my starting point and only made changes that would simplify the building process. The design had a fairly complicated gantry with lots of small tabs holding everything together. While the author claimed it could be made with a bandsaw, drill press and hand tools I was sceptical at how accurate it would turn out. I chose to keep the same base design but to use my design for the gantry and trolley. Having learnt my lessons with the stiffness of MDF in the past, the gantry design is centered around an ‘L’ section beam which would be the simplest part to make and would have more than adequate stiffness in the principle directions. I was finally happy with the design which give me confidence in its build-ability, precision/accuracy and aesthetics (I know this one shouldn’t count but I’m not going to invest my time into an ugly duckling). Time to start building!
Base
The base for this machine is pretty much as easy as it gets. Everything on the machine is made from 1/2″ MDF. The base is a single sheet with groves cut for 3/4″ aluminum tube as the linear rails. In the corners there are mounting block to secure the tube as well as braces glued to the sides to resist the tension of the timing belt. To finish it all off there are clamping blocks on top of the mounting blocks to hold the timing belt.
Routing the groves for the linear rails. 1/4″ wide, 1/8″ deep
Base sheet complete with groves, cutouts and holes for cross nuts
Test fitting of linear rails
Drilling holes on the mounting blocks
Completed set of mounting blocks
Base with linear rails and mounting blocks installed
Mounting block brace
Base with braces attached
Base nearing completion
Completed base
Gantry
Trolley
It Works!
I finally got the cnc up and running! To test it out and practice using Cambam and Mach3 I cut some trial projects in insulation foam.
1. Accuracy Test
To determine the accuracy of the machine a 2″ square and circle were cut. The results are shown in the picture below.
The results were far better than I could have expected. They are not great in terms of what one can expect from a cnc but the x-axis in particular has a large amount of spring in it. Once the stiffness issues gets fixed I can start worrying about backlash. Once I move on from cutting foam I will redo this test to see what effect cutting resistance has on the results.
2. Mach3 Road Runner
The Mach3 demo roadrunner was drawn using a roller ball pen. A second spring was inserted behind the pen insert and end of the pen body (inside the pen) to give resistance to downward pressure. This gives a consistent writing pressure and prevents the pen from being driven into the MDF and binding.
3. Involute Gear
Involute gear drawn using the same setup as above. G-code created using the gear generator in CamBam.
4. CamBam Drilling Tutorial
Created by simply following the CamBam drilling tutorial. Very easy to do and turned out very well.
5. Pulley
Drawn using the pulley generator in CamBam. This didn’t turn out quite as well as hoped. I was a bit excited to move on to fancier things so I didn’t try it again to determine if the problems were a result of the coding, the machine or the material. I have a feeling the foam is tearing on the tips causing the poor cut quality.
6. 2.5D Involute Gear
Again made using the gear generator in CamBam. Better finish than the pulley but inconsistent profiles for the teeth. 2″ dia, 1/4″ deep.
7. 3D Involute Gear
Same gear as above but with the top surface faced and the backside cut away.
8. Miter gear surface
Miter gear surface cut from a cad file from
Rush Gears. The depth increment is 0.01″. This one turned out really well with much improved consistency in the tooth profiles.
9. Hemisphere
Turned out really well until the Z-axis starting making grinding sounds. Two passes later it slipped ruining the piece.
10. Boat Hull
I’m tired of typing. The picture and video cover everything
