Design thoughts: enclosure, Z-axis, and alignment. July 15, 2019 01:07PM |
Registered: 6 years ago Posts: 5 |
Re: Design thoughts: enclosure, Z-axis, and alignment. July 15, 2019 02:05PM |
Registered: 6 years ago Posts: 134 |
Re: Design thoughts: enclosure, Z-axis, and alignment. July 15, 2019 02:59PM |
Registered: 11 years ago Posts: 5,780 |
Re: Design thoughts: enclosure, Z-axis, and alignment. July 15, 2019 03:09PM |
Registered: 6 years ago Posts: 5 |
I intend to do just that, for much of it, and will likely have to order precision-cut extrusion (most likely Misumi, unless someone at my makerspace is willing to pitch in, or we can make use of of the local tech school's gadgetry for milling), but that's a ways off. I haven't touched any real CAD in a very long time, so I expect that will eat up a good bit of my free time, as I get other details worked out. I will likely buy some things before that's done, but that would be rails, pulleys, etc., for which I would want to get actual dimensions to use in the rest of it.Quote
piper3d
Before going into buying mood I would recommend starting with SolidWorks or Fusion 360 assembly. This way you will not be buying parts 2 or 3 times and may not need to cut anything, but order precisely cut pieces.
Re: Design thoughts: enclosure, Z-axis, and alignment. July 15, 2019 03:39PM |
Registered: 6 years ago Posts: 5 |
I was thinking that, but it would be nice to use such ubiquitous material. And, that when I just sketch things out, the necessary width and height for a given print volume just keep adding up .Quote
the_digital_dentist
I think 2020 t-slot is too small for a printer that size, even with PC side panels. The moving mass on the XY stage is at the top of the machine. Throwing it around at 100mm/sec or more will make the whole thing want to move around. 2020 is pretty flexible stuff, especially when the pieces get to be 500-600 mm long.
The specific driving I will probably just experiment with. A simple idea, which I've seen in some very large printers, are counter weights, which would be trivial to implement, combined with gearing down by belts (9:2 is easy enough, just browsing RobotDigg). It would be easy to try, and easy to move away from if it doesn't work well enough. With the actual supports, rails, and vertical belts arranged well, changing the Z motor section of it shouldn't be much trouble.Quote
the_digital_dentist
You really only need two rails to guide the Z axis. Lifting the bed at three places is the most stable way to go and could be done easily with belts all driven from a common drive shaft. Put two of the belts close to the two linear guides and the third on the opposite side of the bed. You're going to need some method of preventing the bed from dropping when motor power is lost/cut. Since the bed assembly will be heavy, you'll want some gear/belt reduction of the drive to multiply motor torque. If you use a worm gear drive you'll get the lifting power you need and stop the bed from falling. I made a worm gear box that used a small, 40mm long NEMA-17 motor to lift the 3.5 kg bed assembly + 4kg load in my printer. Unfortunately the gears turned out to be poor quality and I didn't end up using it. The gears have to be very high quality to prevent repetitive Z axis artifacts in the prints.
That's a good point. I'll compromise from the start, then, and design it to be enclosed, even if I don't initially put a door or top on it.Quote
the_digital_dentist
I would think long and hard about building a large machine without the ability to print ABS. If I were printing large objects that represent a substantial investment of time and material, I'd want them to be around for a while. PLA is not a material you can count on. It gets brittle when it absorbs moisture from the air and melts in a hot car. You can't use it around anything that gets warm, let alone hot. PETG is marginally better.
Re: Design thoughts: enclosure, Z-axis, and alignment. July 15, 2019 04:36PM |
Registered: 11 years ago Posts: 5,780 |
Re: Design thoughts: enclosure, Z-axis, and alignment. July 15, 2019 05:13PM |
Registered: 6 years ago Posts: 5 |
That's why I originally was thinking to just eschew ABS printing for specialized variants of lower-temp plastics. Heat-wise, I would be fine with the right filaments, but I think you were right about long-term moisture. Smaller PETG prints I have are worse than cheap eye glasses. That will mean either mimicking your X axis, or making a sturdier than normal rod-based X axis, that can itself be more forgiving. I've seen that done to good effect on these here intertubes, but I have also noticed that such machines making good prints always use printed bearings, tuned to their specific rods.Quote
the_digital_dentist
Printing ABS isn't just about enclosing the machine. When you heat things up they expand. You have to allow for that or you may have problems, especially in a corexy mechanism made using linear guides. Linear guides are great bearings but they aren't tolerant of misalignment, even the relatively small misalignment that can result from thermal expansion.