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Threaded Rod vs Pitch

Posted by mogey336 
Threaded Rod vs Pitch
January 05, 2016 02:55AM
I'm designing V slot 3D printer and I'm asking
Is there a relationship between threaded rod and pitch for accuracy
I mean what are the best option for 8mm threaded rod 1.25mm pitch or 2mm pitch for good accuracy for printing

Edited 1 time(s). Last edit at 01/05/2016 03:56AM by mogey336.
Re: Threaded Rod vs Pitch
January 05, 2016 04:55AM
1.25 mm vs 2 mm isn't enough of a difference to matter. Either will work fine, except that you won't find lead screws with either of those pitches.

If you use threaded rod(s), your next post (or maybe a little later) here will be asking how to get rid of the Z banding in your prints. If you want the thing to perform well, and I assume you do or you wouldn't be asking about screw pitch, forget about threaded rods and get proper lead screws. Threaded rods are always bent and will cause Z-banding. Like everything else they put into crappy kits, threaded rods are there because they are cheap, not because they are good.

If you make cheapness your goal, that's where you'll end up. You won't get to greatness by aiming at cheapness. My advice: look at a bunch of crappy (i.e. cheap) kits, pay attention to details- look for commonalities, then do almost anything they don't do, because almost anything you do with performance in mind will be better than what they do with cheapness in mind.

Edited 1 time(s). Last edit at 01/05/2016 04:58AM by the_digital_dentist.

Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Threaded Rod vs Pitch
January 05, 2016 05:19AM
Thanks for your reply
I will go with lead screw
my question is if i have to get a better accuracy i have to buy it smaller pitch or not.
or any pitch
Re: Threaded Rod vs Pitch
January 05, 2016 08:00AM
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.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Threaded Rod vs Pitch
January 17, 2016 01:14PM
You can get an 8mm (diameter) 30cm long lead screw including brass nut for like $7.

Look for TR8*8 (p2) which is the most common and thus the cheapset. Can even get an anti-backlash nut for them at only $10.

TR8*8 (p2) Means 8mm diameter. One full rotation is 8mm and the pitch is 2mm. It has 4 starts. If you use a US based calculator they have the pitch at 8mm (real pitch 2mm * 4 starts=8mm)

Pitch usage is different between the US and everywhere else.

Edited 2 time(s). Last edit at 01/17/2016 01:16PM by dintid.

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Re: Threaded Rod vs Pitch
December 15, 2016 03:31AM
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.
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.

As far as the leadscrews go I was looking at 2mm pitch single start so one full revolution raises by 2mm not the 8mm I see a lot of machines use and even on a small (Replicator size) bed when the power is off it wants to fall so with a 6-9 pound 12in sq. bed it will fall like a lead weight with that.


_______
I await Skynet and my last vision will be of a RepRap self replicating the robots that is destroying the human race.
Re: Threaded Rod vs Pitch
December 15, 2016 04:00AM
Without knowing more about your design I can't really say. My 1/2" lead Z axis doesn't drop when the power shuts off. In my printer, if the X axis dropped when power was off it would be a problem because the nozzle might crash into the bed. Does it matter if the bed drops when the power is off? Put a rubber bumper or a spring at the bottom of travel and let it drop. That will make it easier to prep the bed for the next print...


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Threaded Rod vs Pitch
December 15, 2016 05:17AM
Well, the main question to you was about the three leadscrew versus the two leadscrew and your thoughts on it.

As far as the Tr8*8 vs the Tr8*2 quad start or single start I am sold on the single start since it shouldn't allow it to drop but what I do not know is for a bed of that size and weight what size Nema 17 would I need using either the two or three leadscrews?


_______
I await Skynet and my last vision will be of a RepRap self replicating the robots that is destroying the human race.
Re: Threaded Rod vs Pitch
December 15, 2016 03:44PM
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.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Threaded Rod vs Pitch
December 15, 2016 11:20PM
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.
Thank you for the link.

Trying to get your thoughts on the three leadscrews versus the two leadscrews is like pulling teeth, lol.


_______
I await Skynet and my last vision will be of a RepRap self replicating the robots that is destroying the human race.
Re: Threaded Rod vs Pitch
December 19, 2016 07:12PM
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...

Edited 2 time(s). Last edit at 12/19/2016 07:16PM by lukaCX.
Re: Threaded Rod vs Pitch
December 19, 2016 11:22PM
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...
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.


_______
I await Skynet and my last vision will be of a RepRap self replicating the robots that is destroying the human race.
Re: Threaded Rod vs Pitch
December 20, 2016 05:15AM
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.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Threaded Rod vs Pitch
December 20, 2016 01:00PM
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 20, 2016 04:53PM
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.
Thank you.
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.....
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.


_______
I await Skynet and my last vision will be of a RepRap self replicating the robots that is destroying the human race.
Re: Threaded Rod vs Pitch
December 21, 2016 07:30AM
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 08:25AM
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....
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.

Where my two acme rods will be is dead center on each side and adding another in the back would require a lot of work to do and I am not sure I could find a closed loop belt of that length. Lets hope it will not be needed.

Edited 1 time(s). Last edit at 12/21/2016 08:27AM by Dark Alchemist.

_______
I await Skynet and my last vision will be of a RepRap self replicating the robots that is destroying the human race.
Re: Threaded Rod vs Pitch
December 21, 2016 01:19PM
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...


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Threaded Rod vs Pitch
December 21, 2016 02:28PM
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...
"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.


_______
I await Skynet and my last vision will be of a RepRap self replicating the robots that is destroying the human race.
Re: Threaded Rod vs Pitch
December 21, 2016 03:57PM
Yes my mistake , even if you do a z-hop move you need to accelerate more that 9800mm/s smiling smiley) 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 08:07AM
Quote
lukaCX
Yes my mistake , even if you do a z-hop move you need to accelerate more that 9800mm/s smiling smiley) 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? "
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.


_______
I await Skynet and my last vision will be of a RepRap self replicating the robots that is destroying the human race.
Re: Threaded Rod vs Pitch
December 22, 2016 11:04AM
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).


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Threaded Rod vs Pitch
December 22, 2016 12:32PM
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).
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.


_______
I await Skynet and my last vision will be of a RepRap self replicating the robots that is destroying the human race.
Re: Threaded Rod vs Pitch
December 22, 2016 02:25PM
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.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Threaded Rod vs Pitch
December 22, 2016 03:24PM
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.
I see anti-backlash nuts in Delrin too.


_______
I await Skynet and my last vision will be of a RepRap self replicating the robots that is destroying the human race.
Re: Threaded Rod vs Pitch
December 28, 2016 10:49AM
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
December 28, 2016 11:49AM
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.
For a company but with hobbists they are just too expensive.

Off the subject but I have become a non fan of V-Rail wheels as I have some on this 3d printer I am building and there is nothing on but the X 20x40 with each side being on the side rails with the wheels. Delrin is bad as no weight and in the morning I can move them and where they were sitting have become flat. I know this because I can move them by hand and every complete rotation I feel the flat but after moving it back and forth a dozen times the wheels are smooth moving again. I can only imagine what will happen when I load them down with the X and extruder motors. Before anyone asks I have left them about to fall off to semi tightened to fully tightened and by that I mean where the wheels are tensioned. I have never played around with Delrin before but this is too bloody soft so I may have to buy some Polycarbonate wheels on the load bearing wheels.


_______
I await Skynet and my last vision will be of a RepRap self replicating the robots that is destroying the human race.
Re: Threaded Rod vs Pitch
January 01, 2017 08:58AM
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).


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Threaded Rod vs Pitch
January 01, 2017 09:30AM
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).
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.


_______
I await Skynet and my last vision will be of a RepRap self replicating the robots that is destroying the human race.
Re: Threaded Rod vs Pitch
September 02, 2017 02:27AM
One thing the Dentist mentioned above is dead straight they will lose sync but according to Prusa just slam Z all the way up until you hear the motor(s) doing the ratatatatat sound for a few seconds as it will not hurt the motors and both motors will be back in sync. This is his way he tells everyone to do it on his MK2 series of printers.


_______
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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