Friday, July 30, 2010

CNC - Beta Table

With my first attempt at building a CNC machine not successful and beyond repair I returned to the drawing board to design a new one from scratch. This time I took note and carefully studied the design intent of published designs that have been built and proven. Returning to my previous research gave me two paths:

CNC plan on posted by oomlout:
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.

Joe's CNC:
This appears to be a very popular design and has notable features such as a torsion box base and duel guide rods each side. The down side for we 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 favorite 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 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 sceptically at how accurate it would turn out. I chose to keep maintain the same base design but to use my design for the gantry and trolley. Having learnt my lessons with MDF 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!

Building logs can be found following the links below:

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