<p>By &quot;better&quot; I mean &quot;more precise&quot;...</p>
<p>With respect to a RepRap P3Steel or Wilson II, I am getting some 330 mm T8 leadscrews for the Z-axis movement.</p>
<p>There seems to be a choice between a <em>lead</em> of 1, 2 or 8 mm - the <em>pitch</em> is 1 mm in the first case and 2 mm in the last two cases<sup>1</sup>. However, there is precious little information about the advantages and disadvantages of each lead size in <a href="http://reprap.org/wiki/Threaded_rod#Leadscrew" rel="noreferrer">RepRapWiki - Threaded Rod - Leadscrew</a>.</p>
<p>It seems to me that using a leadscrew with a 1 or 2 mm lead could result in a more precise Z-axis movement, as one rotation of the stepper results in a smaller increment in height. Therefore the layer thicknesses could be smaller.</p>
<p>However, is the minimum layer thickness not, also, dictated by the thickness of the filament, horizontal speed of the print head, nozzle size, etc.? Thus, at some point there would be no need for a super fine vertical resolution from the leadscrew, as it may be constrained by other limiting factors.</p>
<p>Of course, conversely, the use of a 2 mm lead would mean that the stepper would need to &quot;work&quot; four times as hard, than when using 8 mm, in order to raise the print head the same distance, as well as making the movement, during a &quot;home&quot;, take four times as long (or, if you will, four times slower). In the case of a 1 mm lead that would become eight times...</p>
<hr />
<h3>TL;DR</h3>
<p>Is it worth getting a leadscrew with a 2 mm lead, or is 8 mm sufficient?</p>
<p>By extension, would a 1 mm lead be even better, or just overkill?</p>
<hr />
<h3>Footnote</h3>
<p><sup>1</sup> Nomenclature:</p>
<ul>
<li><strong>Pitch</strong> is the distance between the adjacent threads;</li>
<li><strong>Lead</strong> is the distance that a nut will turn with one rotation, and;</li>
<li><strong>Start</strong> is how many starting (or thread entry) points at either end.</li>
</ul>
<p>So, for a leadscrew, with a <em>pitch</em> of 2 mm, if there is only one <em>start</em> to the screw then the lead is the same as the pitch. However, if there are four <em>starts</em> to the screw, then the lead will be 8 mm. If there are two <em>starts</em> to the screw, then the lead will be 4 mm. And so on.</p>
<p>For more information, see <a href="https://en.wikipedia.org/wiki/Screw_thread#Lead.2C_pitch.2C_and_starts" rel="noreferrer">Wikipedia - Lead, pitch and starts</a>.</p>

[{'answer_id': 4034, 'author': 'Carl Witthoft', 'author_id': 2191, 'author_profile': 'https://3dprinting.stackexchange.com/users/2191', 'pm_score': 3, 'selected': True, 'text': "<p>Based on what I've learned over 8 months of printing:</p>\n\n<p>What matters the most is getting a very accurate zero relative to the bed surface.  An offset of 30 or 40 microns can strongly affect first-layer adhesion.  Now, unless you put in some of the advanced auto-levelling sensors, the repeatability of the Z-axis limit switch may outweigh the precision of the lead screw itself.  But if you've got a good limit sensor, then the more precision in the lead screw, the better you can set (and repeat) the position of the first layer. </p>\n\n<p>I don't see a significant difference in strain on the drive motors if they have to run longer per mm of z-drive - just make sure the lead screws are clean :-)</p>\n"}, {'answer_id': 4038, 'author': 'Greenonline', 'author_id': 4762, 'author_profile': 'https://3dprinting.stackexchange.com/users/4762', 'pm_score': 3, 'selected': False, 'text': '<p>From <a href="http://www.protoparadigm.com/news-updates/accuracy-vs-precision-and-threaded-rod-vs-leadscrews-in-3d-printers/" rel="nofollow noreferrer">Accuracy vs Precision and Threaded Rod vs Leadscrews in 3D Printers</a>. I have highlighted the relevant parts:</p>\n<blockquote>\n<p>In general, FFF/FDM printers use relatively infrequent, small, precise\nmovements on the z-axis and consistent, fast movements on the x and y\naxes. <strong>A single start leadscrew with the tightest pitch possible\n(highest thread density, smallest pitch) is generally going to be your\nbest bet for the z-axis</strong>, while you may or may not need something a\nlittle steeper to get the speeds you\'d like from your x and y axes.\nWhile this may seem somewhat arbitrary given the precision of movement\nyou can get from a stepper motor, an important factor to remember here\nis torque.</p>\n<p><strong>A more aggressive leadscrew will require more torque to drive</strong>. We have\none kit printer we bought a couple years ago that has an overly\naggressive multi-start leadscrew for the z-axis. The small motors\nincluded in the kit do not have the torque required to reliably start\nupward movement of the carriage, leaving it sitting there skipping\nsteps until the carriage is given a little upward nudge to get it\ngoing (no, it\'s not a lubrication issue or a driver that needs turning\nup).</p>\n</blockquote>\n<p>So, a 2 mm lead is preferable to a 8 mm lead, as not only is less torque required, but also more precise movements are obtainable.</p>\n<hr />\n<p>With respect to the layer heights, I found this nugget of information, from <a href="http://www.3ders.org/articles/20151127-ditch-the-threaded-rod-in-your-reprap-3d-printer-and-upgrade-to-a-lead-screw-z-axis.html" rel="nofollow noreferrer">Ditch the threaded rod in your RepRap 3D printer and upgrade to a lead screw z-axis</a></p>\n<blockquote>\n<p>It\'s always better to use layer heights that are a multiple of your\nfull step. If you trust in your micro-stepping you will get poor\nresults because torque is very poor and the motor won\'t stop very\nprecisely. Best approach is to use a lead screw (whose longer step\nallows the gravity to work for you and eliminate backlash) and a\nstepper driver configured to 1/4 micro-step for low noise, but not for\nmicro-layering. I always use multiples of my full step and have\nprinted 0.040 (1 step), 0.080 (2 steps), 0.120 (3 steps and so on), 0.200,\n0.600 and 0.800 mm (of course using 2 different nozzles). Do you need\nmore than that?</p>\n</blockquote>\n<p>See also <a href="https://www.reddit.com/r/Reprap/comments/4yd9t7/lead_screw_opinions/" rel="nofollow noreferrer">Reddit - Lead screw opinions</a></p>\n<ul>\n<li>the general consensus is that a 2 mm lead is preferable to a 8 mm lead:</li>\n</ul>\n<blockquote>\n<ul>\n<li>Lower the lead the better for an Z-Axis screw to allow for more precision.</li>\n<li>No need for anti-backlash nuts for a Z-Axis if it has a decent amount of mass/weight to it.</li>\n</ul>\n</blockquote>\n<ul>\n<li>1 mm will slow the printer down, but provide 0.005\xa0mm (5μm) vertical movement:</li>\n</ul>\n<blockquote>\n<p>That\'s going to be awfully slow when homing. While you really don\'t\nneed speed for the z-axis, there\'s not much point in going with such a\nlow pitch... you won\'t be printing anywhere near the layer heights\nthat can achieve. In the end I guess it\'s not a big deal, but I don\'t\nsee any reason to go below about a 4\xa0mm pitch. A 1\xa0mm pitch with a 1.8°\nstepper gives you 0.005\xa0mm increments. Anything under 0.02\xa0mm (which is\nsort of ridiculous anyways) is just unnecessary. Just my thoughts.</p>\n</blockquote>\n<ul>\n<li>(As Tom <a href="https://3dprinting.stackexchange.com/questions/4031/would-using-a-leadscrew-with-1-or-2-mm-lead-en-lieu-of-8-mm-result-in-a-better/4038#comment5535_4038">points out</a>) An 8\xa0mm lead can result in the weight of the X-axis gantry (especially in a P3Steel) overcoming the idle torque of the stepper. As a result of this, the X-axis gantry can end up sliding down the leadscrew, in particular at power down:</li>\n</ul>\n<blockquote>\n<p>I have lead screws on my Z and it readily falls down if you kill the power. Regular threaded rod is much better at keeping it in place without power.</p>\n</blockquote>\n<p>and</p>\n<blockquote>\n<p>That\'s one of the problems with 8mm lead ;) With 2mm lead it will hold itself. The stepper motor provides a fair amount of resistance even when powered down.</p>\n</blockquote>\n<hr />\n<h3>TL;DR</h3>\n<p>Be wary of leadscrews with a <em>lead</em>, as opposed to a <em>pitch</em>, of 8 mm, as there are disadvantages, when compared to a lesser lead of, say, 4\xa0mm, or 2\xa0mm (or 1\xa0mm for leadscrew with a pitch of 1\xa0mm):</p>\n<ul>\n<li>Higher torque may be required</li>\n<li>Less accuracy</li>\n<li>Possibility of slippage, of the X-axis, once power is removed, or stepper is disabled<sup>1</sup></li>\n<li>Anti backlash nuts required</li>\n</ul>\n<p>However, their major (if you can call it that) advantage is a higher maximum movement speed.</p>\n'}, {'answer_id': 6975, 'author': 'David Hsu', 'author_id': 11272, 'author_profile': 'https://3dprinting.stackexchange.com/users/11272', 'pm_score': 2, 'selected': False, 'text': "<p><strong>Longer lead</strong></p>\n\n<p>Pros:</p>\n\n<ol>\n<li>Faster movement (mostly benefits homing)</li>\n<li>More standard</li>\n<li>Weak motor friendly</li>\n<li>Might be slightly more stable (sideways) than shorter leads because of more starts creating more contact with nut (?)</li>\n</ol>\n\n<p>Cons</p>\n\n<ol>\n<li>Backlash</li>\n<li>Less resolution (unless using 0.9 degree motor but see note<sup>1</sup>) although this is ignorable since it's still very high. It's already around 5x higher than xy axes using the longest leads<sup>2</sup>.</li>\n</ol>\n\n<p><strong>Shorter leads</strong></p>\n\n<p>Pros</p>\n\n<ol>\n<li>More accuracy if you turn off microstepping. it can give you more resolution, but it's useless resolution unless you print with &lt; 0.01&nbsp;mm layer heights<sup>3</sup>. Turning off microstepping trades away this useless resolution for increased accuracy. But this comes at the cost of (much) louder drivers.</li>\n<li>Less backlash</li>\n</ol>\n\n<p>Cons</p>\n\n<ol>\n<li>Stronger motors maybe needed</li>\n<li>Slower homing</li>\n</ol>\n\n<p>The reason why companies prefer longer leads is because shorter leads simply add useless resolution and slows down movement.</p>\n\n<p><strong>Footnotes</strong></p>\n\n<p><sup>1</sup> It makes more sense to use higher degree motors to drive shorter leads than vice versa because of higher torque.</p>\n\n<p><sup>2</sup>  0.0025&nbsp;mm vs 0.0125&nbsp;mm</p>\n\n<p><sup>3</sup> or using a probe to autolevel, which causes the z axis to go up and down in very small increments </p>\n"}]
['https://3dprinting.stackexchange.com/questions/4031', 'https://3dprinting.stackexchange.com', 'https://3dprinting.stackexchange.com/users/4762/']