Understanding long Lead Screws April 19, 2017 11:03AM |
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Re: Understanding long Lead Screws April 19, 2017 01:11PM |
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Re: Understanding long Lead Screws April 19, 2017 02:10PM |
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Re: Understanding long Lead Screws April 19, 2017 02:36PM |
Registered: 7 years ago Posts: 34 |
Quote
the_digital_dentist
I think constraining all four corners of the bed support is likely to end in the mechanism binding at the slightest misalignment. Two bearings should be enough if everything is perfectly inflexible, so three should be plenty in the real world.
Belts vs lead screws is a personal choice. Belts look like a cheaper alternative initially, but when you solve the bed-drop problem, I suspect the cost ends up about the same. Belts do make it pretty easy to build the Z axis to any arbitrary length. In a printer with a very long Z axis belts may be better than screws because they can't produce lateral forces that will create Z wobble in the print. It can be difficult to build a very tall machine rigid enough to withstand the lateral forces that offset motor couplers, etc. can produce in a screw driven system- in that regard a very tall machine is similar to a small, cheapo machine with a rickety frame. In a very tall machine when the bed gets loaded with a massive print (that's why you're making it tall, right?), the screws may bow under the load and that may produce some of those dreaded lateral forces when they rotate. In a belt driven Z axis the belts will stretch a little, but won't create any lateral forces.
Re: Understanding long Lead Screws April 19, 2017 08:37PM |
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Re: Understanding long Lead Screws April 20, 2017 10:22AM |
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Re: Understanding long Lead Screws April 20, 2017 12:00PM |
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Re: Understanding long Lead Screws April 21, 2017 01:55PM |
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Re: Understanding long Lead Screws April 21, 2017 02:05PM |
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Re: Understanding long Lead Screws April 21, 2017 02:36PM |
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Re: Understanding long Lead Screws April 21, 2017 08:38PM |
Registered: 7 years ago Posts: 34 |
Quote
DjDemonD
Has anyone ever tried or considered a rail supported z axis which climbs a rack using a pinion gear like a mountain railway? Then it wouldn't matter how tall it is, provided the pinion gears were geared highly enough not to roll back down the rack on power off.
Re: Understanding long Lead Screws April 22, 2017 08:25AM |
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Re: Understanding long Lead Screws April 22, 2017 08:50AM |
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Re: Understanding long Lead Screws April 22, 2017 10:02AM |
Registered: 7 years ago Posts: 34 |
Quote
the_digital_dentist
I corrected a math error in my post. In the example, a 200 um layer, if it were solid plastic covering the bed, would have a 0.945 micron error at the completion of the layer. That's about 0.5%, of the layer thickness and that amount only occurs if the layer is solid plastic covering the entire bed. Prints that do that are pretty rare. The error accumulates slowly, and the z axis mechanism still steps in the specified layer thickness. There will never be a single layer with a 42 um thickness error because there's no filament dense enough to weigh 1kg in a single 200um layer.
A 1kg print will be 42 um taller than designed and a 2 kg print will be 84 um taller. As the kids say, meh.
The flatness of the bed, even tooling plate, will vary by that much, and first layer thickness will vary from the design value depending on how you zero the print bed. Top layer infill is rough and you will get different thickness measurements depending on where you place your caliper. In the end, the error due to belt stretch is on the same order as and is masked by the other errors. If you gotta have um accuracy in the height of a 2 kg print, smooth the top surface with a piece of sandpaper.
Re: Understanding long Lead Screws April 22, 2017 10:50AM |
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Re: Understanding long Lead Screws April 22, 2017 11:34AM |
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Re: Understanding long Lead Screws April 22, 2017 03:16PM |
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Quote
the_digital_dentist
You're still not getting it. In my example, the distance from the nozzle to the bed will never be more than 200.945 um. The error is cumulative and the total error in a 1kg print is 42um. There will never be a layer that's 242 um thick.
Re: Understanding long Lead Screws April 22, 2017 03:19PM |
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Re: Understanding long Lead Screws April 22, 2017 05:15PM |
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Re: Understanding long Lead Screws August 27, 2017 02:16AM |
Registered: 6 years ago Posts: 14 |
Quote
the_digital_dentist
I think constraining all four corners of the bed support is likely to end in the mechanism binding at the slightest misalignment. Two bearings should be enough if everything is perfectly inflexible, so three should be plenty in the real world.
Belts vs lead screws is a personal choice. Belts look like a cheaper alternative initially, but when you solve the bed-drop problem, I suspect the cost ends up about the same. Belts do make it pretty easy to build the Z axis to any arbitrary length. In a printer with a very long Z axis belts may be better than screws because they can't produce lateral forces that will create Z wobble in the print. It can be difficult to build a very tall machine rigid enough to withstand the lateral forces that offset motor couplers, etc. can produce in a screw driven system- in that regard a very tall machine is similar to a small, cheapo machine with a rickety frame. In a very tall machine when the bed gets loaded with a massive print (that's why you're making it tall, right?), the screws may bow under the load and that may produce some of those dreaded lateral forces when they rotate. In a belt driven Z axis the belts will stretch a little, but won't create any lateral forces.
Re: Understanding long Lead Screws August 27, 2017 09:30AM |
Registered: 11 years ago Posts: 5,780 |