{"id":292,"date":"2023-03-24T05:10:32","date_gmt":"2023-03-24T05:10:32","guid":{"rendered":"https:\/\/danlacroix.a2hosted.com\/wordpress\/?p=292"},"modified":"2023-04-07T04:16:18","modified_gmt":"2023-04-07T04:16:18","slug":"differential-screw","status":"publish","type":"post","link":"https:\/\/danlacroix.a2hosted.com\/?p=292","title":{"rendered":"Differential screw"},"content":{"rendered":"\n<figure class=\"wp-block-image size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/danlacroix.a2hosted.com\/wp-content\/uploads\/2023\/04\/20230325_175346_e_comp_rot-1024x483.jpg\" alt=\"\" class=\"wp-image-432\" width=\"665\" height=\"313\" srcset=\"https:\/\/danlacroix.a2hosted.com\/wp-content\/uploads\/2023\/04\/20230325_175346_e_comp_rot-1024x483.jpg 1024w, https:\/\/danlacroix.a2hosted.com\/wp-content\/uploads\/2023\/04\/20230325_175346_e_comp_rot-300x142.jpg 300w, https:\/\/danlacroix.a2hosted.com\/wp-content\/uploads\/2023\/04\/20230325_175346_e_comp_rot-768x363.jpg 768w, https:\/\/danlacroix.a2hosted.com\/wp-content\/uploads\/2023\/04\/20230325_175346_e_comp_rot-1536x725.jpg 1536w, https:\/\/danlacroix.a2hosted.com\/wp-content\/uploads\/2023\/04\/20230325_175346_e_comp_rot-2048x967.jpg 2048w\" sizes=\"auto, (max-width: 665px) 100vw, 665px\" \/><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">This was an attempt to make a differential screw. I got interested in them after watching this video from Tom Lipton of Ox Tools\/Berkeley Lab. Tom&#8217;s channel is amazing and has lots of ideas for precise, useful and clever projects.<\/p>\n\n\n\n<figure class=\"wp-block-embed is-type-video is-provider-youtube wp-block-embed-youtube wp-embed-aspect-16-9 wp-has-aspect-ratio\"><div class=\"wp-block-embed__wrapper\">\n<iframe loading=\"lazy\" title=\"Precision Mechanics\" width=\"660\" height=\"371\" src=\"https:\/\/www.youtube.com\/embed\/7RC8WL2ngfA?start=1073&#038;feature=oembed\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share\" referrerpolicy=\"strict-origin-when-cross-origin\" allowfullscreen><\/iframe>\n<\/div><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\">How differential screws work<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Main principal<\/strong> &#8211; Differential screws allow you to make really precise adjustments using two screws with slightly different thread pitches &#8211; one screwed into a fixed part and one screwed into a moving part. The moving part will move a tiny bit relative to the fixed part due to the differences in the pitch. Another way to think of it is that the coarse pitched screw advances by a certain amount and the fine pitched screw backs off by <em>almost<\/em> the same amount, resulting in a large reduction from the input movement to the output movement. Screws are already good for adjustment since they convert large rotational movement into small linear movement, so stacking this effect with the differential screw effect results in surprisingly good precision. Regular adjustment screws only go up to about 100-120 threads per inch so this is one of the only ways to get more precision while still using some type of screw mechanism.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><a rel=\"noreferrer noopener\" href=\"https:\/\/en.wikipedia.org\/wiki\/Differential_screw\" target=\"_blank\">Wikipedia &#8211; Differential screw<\/a><\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"330\" height=\"157\" src=\"https:\/\/danlacroix.a2hosted.com\/wp-content\/uploads\/2023\/04\/DifferentialScrew.gif\" alt=\"\" class=\"wp-image-459\"\/><\/figure>\n<\/div>\n\n\n<p class=\"wp-block-paragraph\">The effective TPI is calculated as:<\/p>\n\n\n\n\n\n<p class=\"ql-center-displayed-equation\" style=\"line-height: 42px;\"><span class=\"ql-right-eqno\"> &nbsp; <\/span><span class=\"ql-left-eqno\"> &nbsp; <\/span><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/danlacroix.a2hosted.com\/wp-content\/ql-cache\/quicklatex.com-4d13a57503cb718cc68ec49e748feebf_l3.png\" height=\"42\" width=\"255\" class=\"ql-img-displayed-equation quicklatex-auto-format\" alt=\"&#92;&#91; &#92;&#102;&#114;&#97;&#99;&#123;&#49;&#125;&#123;&#84;&#80;&#73;&#95;&#123;&#101;&#102;&#102;&#125;&#125;&#32;&#61;&#32;&#92;&#102;&#114;&#97;&#99;&#123;&#49;&#125;&#123;&#84;&#80;&#73;&#95;&#49;&#125;&#32;&#45;&#32;&#92;&#102;&#114;&#97;&#99;&#123;&#49;&#125;&#123;&#84;&#80;&#73;&#95;&#50;&#125;&#32;&#61;&#32;&#80;&#95;&#123;&#101;&#102;&#102;&#125; &#92;&#93;\" title=\"Rendered by QuickLaTeX.com\"\/><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Combinations<\/strong> &#8211; Some common combinations are:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>10-24 with 10-32 (96 TPI)<\/li>\n\n\n\n<li>1\/4&#8243;-20 with 1\/4&#8243;-28 (70 TPI)<\/li>\n\n\n\n<li>1\/4&#8243;-28 with 10-32 (224 TPI)<\/li>\n\n\n\n<li>M4 x 0.7 with M5 x 0.8 (254 TPI)<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">If you combine metric and imperial threads you can get some crazy combinations like 4064 TPI for a 10-32 and M5x0.8 screw &#8211; just a quarter thou per revolution!<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Build and results<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">I printed swappable blocks to test different thread combinations and joined long sections of threaded rod together with a printed shaft coupler. The flexure is just to get stiction-free linear motion from a 3D print which allows for more accurate readings. Unfortunately, my setup was kind of a disaster.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/danlacroix.a2hosted.com\/wp-content\/uploads\/2023\/03\/20230325_175437_e_comp-642x1024.jpg\" alt=\"\" class=\"wp-image-368\" width=\"294\" height=\"469\" srcset=\"https:\/\/danlacroix.a2hosted.com\/wp-content\/uploads\/2023\/03\/20230325_175437_e_comp-642x1024.jpg 642w, https:\/\/danlacroix.a2hosted.com\/wp-content\/uploads\/2023\/03\/20230325_175437_e_comp-188x300.jpg 188w, https:\/\/danlacroix.a2hosted.com\/wp-content\/uploads\/2023\/03\/20230325_175437_e_comp-768x1224.jpg 768w, https:\/\/danlacroix.a2hosted.com\/wp-content\/uploads\/2023\/03\/20230325_175437_e_comp-963x1536.jpg 963w, https:\/\/danlacroix.a2hosted.com\/wp-content\/uploads\/2023\/03\/20230325_175437_e_comp-1285x2048.jpg 1285w, https:\/\/danlacroix.a2hosted.com\/wp-content\/uploads\/2023\/03\/20230325_175437_e_comp.jpg 1420w\" sizes=\"auto, (max-width: 294px) 100vw, 294px\" \/><\/figure>\n<\/div>\n\n\n<p class=\"wp-block-paragraph\"><strong>Asymmetrical loading<\/strong> &#8211; With designs like this you want all your loads to be symmetric so nothing is twisting or bending. I decided to chance it with this design and put everything above the plane of the flexure but this caused deformation in the print and resulted in jerky motion.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Bad threads and thread engagement<\/strong> &#8211; Even with preload springs, the motion was very uneven. In Tom Lipton&#8217;s video he uses a brass screw for smoother motion and has far more threads engaged. My setup just had nuts set into plastic. There was a lot of clearance between the rod threads and the nut threads and the nuts rocked in their plastic sockets. The stick\/slip action in the nuts also made the readings jump around a lot. The shaft coupler also wasn&#8217;t tight enough which meant the the whole thing wobbled and tended to buckle since the threaded rods were so long.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Stiffness<\/strong> &#8211; Some parts were too stiff and some parts were too flexible so it was easy to bend things in a way that changed the reading significantly. I didn&#8217;t have the equipment for it but I think a screw with both external and internal threads like in Tom&#8217;s video or the inside of a micrometer would be better &#8211; much more rigid and everything would move at the same time so there wouldn&#8217;t be uneven motion.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>This was an attempt to make a differential screw. I got interested in them after watching this video from Tom Lipton of Ox Tools\/Berkeley Lab. Tom&#8217;s channel is amazing and has lots of ideas for precise, useful and clever projects. How differential screws work Main principal &#8211; Differential screws allow you to make really precise &hellip; <a href=\"https:\/\/danlacroix.a2hosted.com\/?p=292\" class=\"more-link\">Continue reading <span class=\"screen-reader-text\">Differential screw<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[11,13,14],"class_list":["post-292","post","type-post","status-publish","format-standard","hentry","category-mechanical_flexures_precision","tag-flexures","tag-mechanical","tag-precision"],"_links":{"self":[{"href":"https:\/\/danlacroix.a2hosted.com\/index.php?rest_route=\/wp\/v2\/posts\/292","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/danlacroix.a2hosted.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/danlacroix.a2hosted.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/danlacroix.a2hosted.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/danlacroix.a2hosted.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=292"}],"version-history":[{"count":25,"href":"https:\/\/danlacroix.a2hosted.com\/index.php?rest_route=\/wp\/v2\/posts\/292\/revisions"}],"predecessor-version":[{"id":490,"href":"https:\/\/danlacroix.a2hosted.com\/index.php?rest_route=\/wp\/v2\/posts\/292\/revisions\/490"}],"wp:attachment":[{"href":"https:\/\/danlacroix.a2hosted.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=292"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/danlacroix.a2hosted.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=292"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/danlacroix.a2hosted.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=292"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}