Threaded Rod vs Pitch
Posted by mogey336
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Re: Threaded Rod vs Pitch December 21, 2016 06:57PM |
Yes my mistake , even if you do a z-hop move you need to accelerate more that 9800mm/s 
) To quote Jetguy on this matter: "Here's the problem you fail to account for when using an antibacklash leadscrew nut for an X and Y axis and further, why on a Z axis it is an added cost with no benefit.
An antibacklash nut contains is a second nut that is spring loaded to ensure the inevetible last between the threads is forced to one side. However, this is a tradeoff. The strength of that spring determines how much additional friction and lack of efficiency that nut has in turning mechanical rotation into linear force. But the real kicker is, that 3D printers are generally high speed forward and reversal style of motion in XY with high inertia. Thus, suddenly, that undampened spring allows the backlash to be realized because intertia+ opposing reversal force is more than enough to overcome the spring force. Again, it's a double edged sword. If you use a really stiff spring, the drag created now will cause the motor to skip steps at high speeds and acceleration rates but also greatly inscreases wear on the threads in the nuts themselves. So you could eliminate backlash but at the cost of friction and wear with a major performance hit to top speeds and acceleration rates.
Conversly, usign anti backlash on a Z axis is a waste of money. Gravity and weight of the overall Z stage is more than sufficient to act as the spring in any normal anti-backlash nut. Z stage never does rapid moves and specifically reversal moves that would overcome gravity (9.8m/s).s So again, this is putting an expensive and extra drag nut in a location already subject to sufficient preload in 99.999999% of cases. If you consistently operate in that 0.000001% use case, you obviously are an astronaut and printing in outer space.
So, from the above statements, it's pretty obvious, look at industry and Stratasys and 3D systems don't use leadscrews for XY for the above reasons, and Makerbot and all the clones don't require antibacklash nuts on Z because gravity does it for us.
So ask yourself, why pay for more expensive parts if they offer zero benefits? Shouldn't you put that money to use elswhere for desirable features that DO impact print quality? "
) To quote Jetguy on this matter: "Here's the problem you fail to account for when using an antibacklash leadscrew nut for an X and Y axis and further, why on a Z axis it is an added cost with no benefit.An antibacklash nut contains is a second nut that is spring loaded to ensure the inevetible last between the threads is forced to one side. However, this is a tradeoff. The strength of that spring determines how much additional friction and lack of efficiency that nut has in turning mechanical rotation into linear force. But the real kicker is, that 3D printers are generally high speed forward and reversal style of motion in XY with high inertia. Thus, suddenly, that undampened spring allows the backlash to be realized because intertia+ opposing reversal force is more than enough to overcome the spring force. Again, it's a double edged sword. If you use a really stiff spring, the drag created now will cause the motor to skip steps at high speeds and acceleration rates but also greatly inscreases wear on the threads in the nuts themselves. So you could eliminate backlash but at the cost of friction and wear with a major performance hit to top speeds and acceleration rates.
Conversly, usign anti backlash on a Z axis is a waste of money. Gravity and weight of the overall Z stage is more than sufficient to act as the spring in any normal anti-backlash nut. Z stage never does rapid moves and specifically reversal moves that would overcome gravity (9.8m/s).s So again, this is putting an expensive and extra drag nut in a location already subject to sufficient preload in 99.999999% of cases. If you consistently operate in that 0.000001% use case, you obviously are an astronaut and printing in outer space.
So, from the above statements, it's pretty obvious, look at industry and Stratasys and 3D systems don't use leadscrews for XY for the above reasons, and Makerbot and all the clones don't require antibacklash nuts on Z because gravity does it for us.
So ask yourself, why pay for more expensive parts if they offer zero benefits? Shouldn't you put that money to use elswhere for desirable features that DO impact print quality? "
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Re: Threaded Rod vs Pitch December 22, 2016 11:07AM |
I take anything Jetguy says with less than a grain of salt BUT the rest of what you said does have a valid point and the drag part is something I always thought would go up with an anti-backlash nut (with drag comes more wear). Now on X and Y on a CNC mill/router they use them exclusively so there must be a reason and they go painfully slower than our 3d printers do.Quote
lukaCX
Yes my mistake , even if you do a z-hop move you need to accelerate more that 9800mm/s
An antibacklash nut contains is a second nut that is spring loaded to ensure the inevetible last between the threads is forced to one side. However, this is a tradeoff. The strength of that spring determines how much additional friction and lack of efficiency that nut has in turning mechanical rotation into linear force. But the real kicker is, that 3D printers are generally high speed forward and reversal style of motion in XY with high inertia. Thus, suddenly, that undampened spring allows the backlash to be realized because intertia+ opposing reversal force is more than enough to overcome the spring force. Again, it's a double edged sword. If you use a really stiff spring, the drag created now will cause the motor to skip steps at high speeds and acceleration rates but also greatly inscreases wear on the threads in the nuts themselves. So you could eliminate backlash but at the cost of friction and wear with a major performance hit to top speeds and acceleration rates.
Conversly, usign anti backlash on a Z axis is a waste of money. Gravity and weight of the overall Z stage is more than sufficient to act as the spring in any normal anti-backlash nut. Z stage never does rapid moves and specifically reversal moves that would overcome gravity (9.8m/s).s So again, this is putting an expensive and extra drag nut in a location already subject to sufficient preload in 99.999999% of cases. If you consistently operate in that 0.000001% use case, you obviously are an astronaut and printing in outer space.
So, from the above statements, it's pretty obvious, look at industry and Stratasys and 3D systems don't use leadscrews for XY for the above reasons, and Makerbot and all the clones don't require antibacklash nuts on Z because gravity does it for us.
So ask yourself, why pay for more expensive parts if they offer zero benefits? Shouldn't you put that money to use elswhere for desirable features that DO impact print quality? "
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I await Skynet and my last vision will be of a RepRap self replicating the robots that is destroying the human race.
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