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Hello, I've been working on a metal additive manufacturing machine for a while now and I'm still trying to figure out if there are any real drawbacks to using a chain drive to turn 4 screws. My weight capacity on the bed is around 350 lb which is why I was considering using a chain opposed to a belt. I'm not sure of the limitations of using chain and now this might affect accuracies.
Any advice or information is greatly appreciated.
Roller sprockets and chain drives have a lot more slop than timing belt type drive mechanisms. If your machine is basically a MIG welder with motion control, that might not matter, since the process is inherently imprecise. But if you're building a laser sintering machine, you'll want as much precision in your stages as you can get.
Thank you for your response, that's more or less what I had expected. I suppose the best option is to go with a counterweight and use belts. I guess I could add weight to the counterweight as the print increases in Mass. Or at least gas struts to counteract the weight of the print bed itself.Quote:
Originally Posted by awerby
I'm using a micro plasma arc welder. I wouldn't really consider it comparable to Mig or lasers so it's hard to say.
I had considered using worm gears at all four corners because they won't back Drive. Although I have already purchased a 400 watt Servo with brake.
What's the difference between micro-plasma and MIG? It sounds like the same thing, just smaller. I'm not sure why you'd need a counterweight; it doesn't seem like the micro-plasma head will weigh much, and there are no cutting forces to contend with. I don't think it would make much sense to move the whole bed, when all you need to do is move the head. I also don't think a long rubber belt would work too well in the presence of the arc welder; the UV radiance and metal spatter wouldn't do it much good. Rack and pinion would probably be your best bet, and keeping that mechanism sheltered from the arc mess would extend its life.
That's very true about the belts. Initially, yes I thought it didn't make much sense to move the bed. Although plasma arc welding is one of the fastest welding methods. My gantry is using direct drive 400w servos with 10mm ball screws. I don't think that at higher speeds I would have much rigidity even with a steel Construction and the bed is essentially a static load moving only fractions of a mm at any time.Quote:
Originally Posted by awerby
I'm not at all going for much penetration of weld. It's essentially hardfacing. So the rate at which that is possible to print as a bit unknown.
Regardless of if the bed or Gantry is moving vertically wouldn't a gear reduction on the screws at least reduce the backlash? I've heard of people having problems with repeatability. I'm not sure if a gear reducer would have any effect on the repeatability specifically.
Adding more gears typically increases backlash, rather than reducing it. It does reduce speed and increases torque, but each gear has to have a little gap for clearance between each tooth, so it adds up.
So if I move the Gantry instead of the bed I would think I would have less backlash throughout the print since the Gantry would just be moving up. Where if I were moving the bed down instead it would be creating backlash every time at moved. I could still see heat from the welder definitely being a problem with belts. The more I think about it the more I lean towards using spiral bevel gears with shaft connected in an H shape turning ballscrew at each end.