Threaded Rod vs Pitch January 05, 2016 05:55AM |
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Re: Threaded Rod vs Pitch January 05, 2016 07:55AM |
Registered: 11 years ago Posts: 5,780 |
Re: Threaded Rod vs Pitch January 05, 2016 08:19AM |
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Re: Threaded Rod vs Pitch January 05, 2016 11:00AM |
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Re: Threaded Rod vs Pitch January 17, 2016 04:14PM |
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Re: Threaded Rod vs Pitch December 15, 2016 06:31AM |
Registered: 11 years ago Posts: 1,277 |
Perfect one to ask this then. I was just told to ditch the two leadscrew one motor design I made and go for three leadscrews. What say you? I will have a 1/4in tool plate 12inx12in as the printing surface so how much torque of a single motor should I go for? Any links to a motor to handle that would be awesome if you have it. I am using a ramps.Quote
the_digital_dentist
With 200 steps per rev motors and microstepping, almost any pitch is OK. My printer has 1/2" pitch (egads! Imerial units!) acme screws in the Z axis and I can set any desired layer thickness without any artifacts. I would try to stay with metric pitch screws.
In many printer designs the X axis is lifted by two Z screws. If the screws get out of sync the X axis alignment is thrown off. Contrary to what some may think, aligning it accurately is a slow and painstaking process. For that reason, I recommend that if you're using multiple Z scews, connect them together with a belt and drive them with a single motor. That is the only way to ensure that the screws always remain in sync.
Re: Threaded Rod vs Pitch December 15, 2016 07:00AM |
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Re: Threaded Rod vs Pitch December 15, 2016 08:17AM |
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Re: Threaded Rod vs Pitch December 15, 2016 06:44PM |
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Re: Threaded Rod vs Pitch December 16, 2016 02:20AM |
Registered: 11 years ago Posts: 1,277 |
Thank you for the link.Quote
the_digital_dentist
I use the Oriental Motor web site's motor sizing tools: [www.orientalmotor.com]
It seems to work pretty well once you figure out what to enter into the forms.
Re: Threaded Rod vs Pitch December 19, 2016 10:12PM |
Registered: 7 years ago Posts: 17 |
Re: Threaded Rod vs Pitch December 20, 2016 02:22AM |
Registered: 11 years ago Posts: 1,277 |
Mine will be from eBay with anti-backlash nuts already with it. Not sure why Dentist wouldn't answer about his thoughts on this matter.Quote
lukaCX
I just built a triple leadscrew core xy with 60cm Z travel. I have robotdigg mgn12 rails for the Z axis.
It seems to be working fine no wobble or banding as far as i can tell. The kind of tricky bit is getting everything square and in sync.. Also buying high quality leadscrews because if they are not all machined the same that can lead to z banding...
Re: Threaded Rod vs Pitch December 20, 2016 08:15AM |
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Re: Threaded Rod vs Pitch December 20, 2016 04:00PM |
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Re: Threaded Rod vs Pitch December 20, 2016 07:53PM |
Registered: 11 years ago Posts: 1,277 |
Thank you.Quote
the_digital_dentist
I'm not a mechanical engineer, just a dentist and electrical engineer. A while back I would have said use three screws (assuming you use them properly), but these days I'd probably try two and see if the result is acceptable because it is cheaper and easier to do, and add a third screw if two doesn't work well enough. A lot will depend on the guides you use and how they are arranged in relation to the bed and the screws, the quality of the screws (forget threaded rods), and the sort of tools you have available.
I'm putting a belt drive Z axis into my coreXY design, with the belt lifting the bed at the center of two sides of the bed, which is how I would arrange two screws if I were using screws. The bed support is attached to two linear guides. The limited testing I've done on the assembly indicates that it will perform acceptably, but there is more testing to do and there is one major issue to sort out- the bed drops when the motor is disabled or power is cut off. I have multiple possible solutions to that problem, so it is manageable.
Wrong as lift Z during retraction is why you need an antibacklash nut. I plan on a closed loop belt and I learned about two motors sharing the same channel from the Prusa machine.Quote
lukaCX
Backlash doesn't matter in Z because you only need to go down and gravity acts as anti backlash..... It would make a difference if you used z-hop or something...Ditch the anti backlash parts of the nut you dont need them(it can even cause you more trouble than be of any use)
I think that the setup difficulty is the same with either 2 or 3, except that you have a leadscrew plus to sync...You are still syncing the leadscrews together with one belt(If you do choose to go with 2 leadscrews please use an endless belt to do so DO NOT USE 2 motors for each screw..... I would recommend you look at some triple leadscrew bots(http://www.thingiverse.com/thing:612857) read the summary it should clarify things.....
Re: Threaded Rod vs Pitch December 21, 2016 10:30AM |
Registered: 7 years ago Posts: 17 |
Re: Threaded Rod vs Pitch December 21, 2016 11:25AM |
Registered: 11 years ago Posts: 1,277 |
Exactly, which I started doing as it seems to really help in the final prints for me. No idea if that will be needed with the new setup or not but for 2 or 3 dollars more I might as well go with the anti-backlash nut.Quote
lukaCX
Sorry for not being clear, thats what i meant ...You would only need to use an anti backlash nut if you used commands like z hop....
Re: Threaded Rod vs Pitch December 21, 2016 04:19PM |
Registered: 11 years ago Posts: 5,780 |
Re: Threaded Rod vs Pitch December 21, 2016 05:28PM |
Registered: 11 years ago Posts: 1,277 |
"You should not need antibacklash nuts" Coulda woulda Shoulda so I did. An ounce of prevention and over engineering, and all of that. I would rather have something not give me any issues like this beotych of a Prusa I3 Rework has. It never hurts to have anti-backlash nuts on everything especially when we are talking about 3 dollars or less in difference.Quote
the_digital_dentist
Antibacklash nuts work by keeping the nut's threads in contact with the screw's threads. In a vertical lift mechanism, assuming no binding occurs, gravity will ensure that the threads are always in contact. You should not need antibacklash nuts even if you do Z lift on retract. If you're designing this device to work on the ISS, that's another matter...
Re: Threaded Rod vs Pitch December 21, 2016 06:57PM |
Registered: 7 years ago Posts: 17 |
Re: Threaded Rod vs Pitch December 22, 2016 11:07AM |
Registered: 11 years ago Posts: 1,277 |
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 ) 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? "
Re: Threaded Rod vs Pitch December 22, 2016 02:04PM |
Registered: 11 years ago Posts: 5,780 |
Re: Threaded Rod vs Pitch December 22, 2016 03:32PM |
Registered: 11 years ago Posts: 1,277 |
I can understand that but one would think the anti-backlash nuts must wear out something fierce then because it has more drag and the tool is being pushed back by the material.Quote
the_digital_dentist
On CNC mills and routers, the material you're cutting pushes back on the tool. If there were backlash it would immediately show in the part you're cutting. In 3D printing, there's no resistance to the movement of the tool other than its own inertia (and gravity in the Z axis).
Re: Threaded Rod vs Pitch December 22, 2016 05:25PM |
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Re: Threaded Rod vs Pitch December 22, 2016 06:24PM |
Registered: 11 years ago Posts: 1,277 |
I see anti-backlash nuts in Delrin too.Quote
the_digital_dentist
The nuts are usually brass and the screw is steel. As the nut wears, the spring keeps it pushed against the screw threads. Eventually you have to replace it, but it can probably run for quite a while before wear becomes a problem.
Re: Threaded Rod vs Pitch December 28, 2016 01:49PM |
Registered: 9 years ago Posts: 1,873 |
Re: Threaded Rod vs Pitch December 28, 2016 02:49PM |
Registered: 11 years ago Posts: 1,277 |
For a company but with hobbists they are just too expensive.Quote
JamesK
I think CNC grade anti-backlash is usually done with ball-screws - the screw analog of a linear guide. That's a different league of thing entirely.
Re: Threaded Rod vs Pitch January 01, 2017 11:58AM |
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Re: Threaded Rod vs Pitch January 01, 2017 12:30PM |
Registered: 11 years ago Posts: 1,277 |
One of the many privileges of being in the rust belt too. Here? Nada. The makerspace here had to move from my city (due to taxes/rent/crime) to 30 miles away and I am not sure what happened to them but it is all new or not at all for me.Quote
the_digital_dentist
It's true that quality ball screws are pretty expensive when purchased new. But that's not the only way to get them. You can buy used parts or pull them out of scrapped machines as I did to get the precision ground ball screw that is in the Y axis of my printer. I paid $0 for it - just one of the many advantages to belonging to the Milwaukee Makerspace.
We have almost 300 members at the MMS. When someone needs something, and as people get to know each other and the sorts of projects they work on, people start looking for opportunities to get tools and materials that others in the group can use. People know what I do and frequently give me parts that may be useful for the next printer. The local scrap yards know who we are and will set stuff aside for us (especially t-slot aluminum extrusions). Several of the members routinely scan the local auctions for tools and materials we can use. Many members work for industrial companies and talk them into donating materials and equipment to us (we're a 503C nonprofit, so donations are tax deductible for the donor).
Re: Threaded Rod vs Pitch September 02, 2017 05:27AM |
Registered: 11 years ago Posts: 1,277 |