Well, then… given my state of affairs as of late, I’m excited to share something more notable!
So, I designed my own parametric CNC mill. Straight from my imagination. Which is to say I absolutely could not come up with an industrial grade machine on the first round, especially on a shoestring budget. As far as my creations go, it’s about the most involved project I’ve undertaken on my own. It’s been alive for nearly a year, and despite a slow start, I’ve been getting ever more glitch free running hours out of it.
I conglomerated a short list of project ideas a couple weeks ago, some that are essential and some just for kicks. I finally made it to an essential project: tightening up the play in the axis. I haven’t had a chance to do all the improvements I need to do, but this was a remarkable start!
I clocked a good number of runtime hours in, feeling pretty stoked on the new mastery of shape that my machine empowered me with. Then, I thought I’d do something neat and cut out a perfect little pocket for a bearing to sit in. I barely set it in place before the obvious issue struck me down: the perfect circles I thought I cut were clearly perfect ovals. Observing the machine more closely, I finally saw all the little wiggles along the drive train. The Z axis was easily secured with a couple washers, but the other two required more effort. Basically, the linear bearings were just all around sloppy. I shim-shiminy’d all the shims I had, but ultimately the failure was in the design. I skimped on the linear bearing brackets, opting for a mere one bracket per point of contact. It was a hundred dollar decision that cost me dearly in quality. Lesson learned!
Moving on to the project at hand, I was really really tempted to clamp these pieces of HDPE to the mill for the heavy lifting and let my fingers work the magic on the keyboard. Circles being out of the question, all I really needed was good depth control and one firm axis. As I endeavored to get the two pieces positioned and imagining how the rest of the operation might go down, I got the feeling that maybe this wasn’t the best approach.
Sitting against the wall, boxes piled on top and underneath, was my beloved Mark V. Most of my audience is wondering who Mark is, but I’m sure someone out there will read this and chuckle. It may seem peculiar that this antiquated old pile of metal has such value in my eyes, but I’m more connected to this thing than I care to discuss at the moment. Not this exact machine, but the Shop Smith in general. Much like the Volkswagen in its conception, this piece of Deutsch engineering was built with serviceability and ubiquity as focal points. Unlike Volkswagen, these folks stuck to their guns, but don’t let me get started on that rant! Since the Mark V’s debut in 1953, they have made very few but very thoughtful changes. My machine is a 70’s model, but absolutely any accessory ever made will fit without adaptation. I can still buy replacement belts, motors, quills, etcetera if it ever breaks. If I decide I have too much money one fairy tale day, I can upgrade the whole headstock. Ooh, digital rpm display! <Homer drool>
I would say my CNC is standing on the shoulders of a giant. I’m sure the purists will tell me all about the lathe being king and what-not, but I have the capacity for a compact, light machine. I’m doing what I can with what I got! I also have to point out that, despite being an older model with fewer of the stabilizing revisions, I am fairly confident in the accuracy of cuts it can produce. So, with a sacrificial layer expertly mounted to the fence (eh hem) I started making shavings.
Now, one aspect that dissuaded me from using the mill was thinking about all the passes I would have to make. It’s just plastic, so it should cut like butter, right? Well, sort of. It is high density plastic, so I couldn’t just hog off a quarter inch per pass. However, the Mark V has a 5/8 inch chuck as well as a 1/2 inch collet and I have a wider selection of bits to work with. A half inch end mill made for easy chewing of most of the block. From there, it took a couple of tedious hours to nibble the notches down using a cheap Dremel bit, but I really wanted that nice 1/8 inch bead profile to match the slot in the 80/20 extruded aluminum.
At the end of it all, I did have to wonder if all the time I just spent on these things was worth it or if I should have just bought another set of brackets (maybe not 80/20 brand!) Considering my going rate and backlog of profitable work waiting to be done, these 4 brackets cost me at least a hund-o. I would have spent the same plus shipping on brackets, so I figure that it’s a wash as long as my parts don’t wear out too fast.
As I went to mount them, I realized that I probably did better than just saving on shipping. I did spend a fair bit of time installing shims on the rest of the bearing pads. Somehow, I didn’t quite have enough to go around, either. I realized this as I had taken all my measurements off the Y axis rails but wanted to see if the parts would look better on the X axis. With all the shims needed to get the pads nice and tight, my parts wouldn’t fit alongside the brand name brackets at all. However, they did fit the Y axis just beautifully, and I get to save all that time not having to shim and adjust.
In the words of Ace Ventura, “Like a glove!”