After spending an hour or so mulling over my design of the z stage, it struck me that the rigidity/levelness of the building platform could be compared (badly) to the three possible motions of a airplane: pitch,roll and yaw. Building a solid build platform and xy stage that didn't wobble required a system that restricted any pitching, rolling or yaw movement. A quick summary of past z stage efforts
four threaded rods - pitch,roll, yaw all unrestricted (skipping of threaded rod caused all three, unstraight threaded rod cause yaw issues and general headache)
bearing design - pitch, yaw restricted (with the bearings pressing on the insides of the aluminum angle frame), roll restricted (nothing stops the platform from tilting side to side)
this revelation put me in a bit of a panic, as I didnt know what the solution could be. But then it came to me. I already use a captive system that prevents pitch yaw and roll -the x stage and its rollercoaster inspired linear guide.
You might be thinking "gee thats a heck of a lotta bearings", and you'd be right. In fact the total used in the printer is now equal to 20 (not as many as Mendel's 32, but still quite a hefty number). With each bearing costing 2 bucks, that's an additional 40 bucks worth of bearings (and they're from a surplus store, so the actual cost might be higher).
You may also think sticking with a teflon slider like the y stage would be a better option. And it might. But ball bearings are much more forgiving then teflon sliders (at least in my opinion in this early "prototyping" stage) in cantilevered systems such as the y and x axis. So until we get more people and money to test these options -which we will look for once our prototype works, reusing the ball bearing idea seems to be a safe bet.
Enough with the chit chat, lets see some model pictures and some photos of the actual metal bot.
The machine and its progress so far. Looks rather simple for now I know. The aluminum angle frame was unfortunately drilled on a drill press, which means there are a lot of parts that aren't straight and square. It's so bad that the frame doesn't even sit level on the ground (I think it has to partially do with the fact that i force bolted the pieces together, causing them to bend ever so slightly). The piece halfway down the machine with the lettering is the clear polycarbonate plastic bottom platform with the protective cover on it.
A closeup of the countersunk bolting arrangement on the angle frame. You can already see some of the gaps in the junctions of the frame pieces. I'm planning on re-drilling the holes on a milling machine next week in order to fix the bent frame issue.
A closeup of the x stage rollercoaster-inspired bearing and the attached y stage drive motor. The orange strips are kapton tape -their smoothness makes the sliding motion a lot quieter. The amount of trouble needed to secure the motor to the y stage has made me renounce locknuts for future versions, and instead embrace lockwashers and standard nutes (like that used on the angle frame).
A closeup of the underfriction wheel and side friction wheel, as well as the homemade pulley idler using a standard ball bearing with flanges made from washers. It works fairly well, and reduces the cost of having to purchase specialized idler timing pulleys.
That's everything for now.
-Eric
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