CNC design evolution, or a history of bad decisions

Well, maybe I’m being too hard on myself. I was going to make a post to introduce my latest build, which is a new and superawesome cnc router. The idea was to do that by showing the path that led to the current incarnation, which means I had to start by actually reviewing said path. Looking at where I started and how I went from there, it sure looks like a long series of bad decisions or perhaps some sort of mental retardation.
But like I said, I’m being too harsh. It’s rather a testament to my complete and utter cluelessness of anything even remotely related to cnc, electronics or even basic building skills when I started.

Gather ’round, relax and enjoy while I tell a story of beginnings, endings and great revelations.
It all started in the beforetime, a long time ago. I was an avid World of Warcraft player, with no interest in building or creating anything. I was good at what I did, the best in fact. Perhaps that is what made me feel like a goal had been reached, a change was due. I had recently decided to switch path in life, away from the world of healthcare (2 years of medicine and 2 years of physiotherapy studies is what it took to make me realize I hate (sick) people) and to start studying electrical engineering instead. As an engineer I believed you needed to have a genuine interest in your field of study (which my classmates’ utter ineptitude and lack of interest in anything technological later disproved), and I started as so many others have done both before and after me; I bought an Arduino. Specifically, the Sparkfun Inventors Kit.

A new paragraph for a walk down a new path. Ever heard the song “I set fire to the rain”? I didn’t set fire to the rain, but pretty much everything else got a taste of the flames (of sulfuron). I managed to build one working thing with what survived that conflagration though, one of the few builds that actually got used extensively. Check it out under “ambilight clone” in my “old projects” page.
Anyway, the second item I intended to build was automated window blinds. I started by buying three stepper motors and drivers. That is also about as far as I got with those blinds. As soon as I got the motors, I promptly let the magic smoke out of all three drivers. I then got new drivers and started googling what a stepper motor actually was and how I should get it to move. You know what you get when you google stepper motor? CNC. That’s pretty much how much it took to get me completely hooked. I rushed to the hardware store and, standing in the isles, designed and bought the parts for my first cnc router. I didn’t have a clue what I was doing, and you know what? It was horrible. It’s truly remarkable that I even imagined it could work like that.
Oh, it did work. I even made a pcb with that first version. But really, rubber wheels as linear bearings? Check out the project log in “old projects” if you feel like you need a laugh.

 

CNC collage

 

I wont fill this entire post with history though. Suffice to say, I soon built another, this time with plenty of research and even cad modeling. That one was insane compared to the first one, I loved it. For about a week. Then I wanted more. I spent about a year learning, reading and learning some more, and last semester I started designing the third iteration. This time I took my time, and as you can see from the picture above, I went through several designs before I settled on the one I’m about to start building.
I think I’m going to split this up into two blog posts, and describe the actual design work in the next one.

But first, let’s talk a bit about the ones I scrapped. The first one, the mdf monstrosity, is the machine that I actually built. It has some strong points and several weak ones. The major strong point is that it was cheap. Secondly, the stepper motors are decent. As for weak points, I used mdf as building material. That could have been enough to actually cut mdf and things like that, had I used a stronger design for the z-plate and linear bearing blocks for all the axises. Instead, I used skate bearings for Z. That was really stupid, probably the weakest point in the entire build. The rest of it is pretty balanced, and I suggest you read about it in the designated project log if you’re interested.

The first design of my new one was pretty much a redesign of the mdf machine, with the same concept and layout but with the weak points I talked about earlier addressed. I even made some FEA analysis of it. It wasn’t very good.
The later designs progressively changed bearing types, stiffened the gantry sides, lowered the fulcrums closer to the work area, switched to dual ballscrews and so on and so forth. I can’t really summarize 5 months of constant pondering in a few sentences. Look at the pictures and ask questions, I’ll happily answer all of them. Next blog post should cover my final design in a bit more depth.

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