{"id":1327,"date":"2012-05-01T15:03:31","date_gmt":"2012-05-01T14:03:31","guid":{"rendered":"http:\/\/svarthaletracing.se\/?p=1327"},"modified":"2012-05-02T14:06:20","modified_gmt":"2012-05-02T13:06:20","slug":"1327","status":"publish","type":"post","link":"https:\/\/svarthaletracing.se\/?p=1327","title":{"rendered":"A little about surface roughness"},"content":{"rendered":"\n<!-- powered by embed-javascript plugin ver. 1.1 beta (sw-galati.ro) -->\n<span style=\"font-size:10px;\"><a href=\"http:\/\/wordpress-plugins.sw-galati.ro\/\">Powered by Wordpress Plugins<\/a> - <a href=\"http:\/\/wordpress-plugins.sw-galati.ro\/\">Get the full version!<\/a><\/span><br><script type=\"text\/javascript\" width=\"100%\" height=\"900\" src=\"http:\/\/svarthaletracing.se\/linusn_js\/calculateRa.js\"><\/script>\n<p><strong>P\u00e5 svenska<\/strong><\/p>\n<p>Inte f\u00f6r att vi direkt specificerat ytfinhet p\u00e5 v\u00e5ra ritningar f\u00f6r pulsjeten, men jag snubblade \u00f6ver begreppet i ett annat projekt. Ytfinhet \u00e4r ett m\u00e5tt p\u00e5 hur &#8221;j\u00e4mn&#8221; en yta \u00e4r. Detta \u00e4r f\u00f6rst\u00e5s v\u00e4ldigt viktigt att kunna m\u00e4ta, f\u00f6r att kunna specificera hur t.ex en fr\u00e4st\/slipad\/svarvad yta ska se ut. Ytfinhet kan anges\/m\u00e4tas p\u00e5 ett flertal s\u00e4tt, och ett av de vanligaste \u00e4r <em>Ra<\/em>, vilket anger en slags genomsnittlig avvikelse fr\u00e5n den t\u00e4nkta &#8221;normallinjen&#8221;, d.v.s den linje\/yta man vill \u00e5stadkomma vid bearbetningen. <a href=\"http:\/\/sv.wikipedia.org\/wiki\/Ytfinhet\" target=\"_blank\">En kort Wikipediaartikel om ytfinhet<\/a>.<\/p>\n<p>Jag ramlade \u00f6ver ett &#8221;problem&#8221; d\u00e4r man beh\u00f6vde fr\u00e4sa en &#8221;3-dimensionell&#8221; yta, d.v.s inte plan, utan b\u00f6jd i alla ledder. F\u00f6r detta anv\u00e4nder man oftast en fullradiefr\u00e4s (&#8221;ball nose&#8221;), och genom att k\u00f6ra v\u00e4ldigt m\u00e5nga g\u00e5nger t\u00e4tt ihop kan man \u00e5stadkomma en yta med n\u00e4stan vilken form som helst. Fr\u00e5gan \u00e4r bara; hur sm\u00e5 steg i sidled m\u00e5ste man ta f\u00f6r att uppn\u00e5 en viss ytfinhet.<\/p>\n<div id=\"attachment_1363\" style=\"width: 124px\" class=\"wp-caption alignnone\"><a href=\"http:\/\/svarthaletracing.se\/wp-content\/uploads\/2012\/05\/ballNose.jpg\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1363\" class=\"size-full wp-image-1363\" title=\"ballNose\" src=\"http:\/\/svarthaletracing.se\/wp-content\/uploads\/2012\/05\/ballNose.jpg\" alt=\"\" width=\"114\" height=\"240\" \/><\/a><p id=\"caption-attachment-1363\" class=\"wp-caption-text\">Fullradiefr\u00e4s \/ Ball nose<\/p><\/div>\n<p>Jag gjorde n\u00e5gra ber\u00e4kningar. F\u00f6ljande parametrar ing\u00e5r:<br \/>\n<em>d<\/em>: Fullradiefr\u00e4sens diameter<br \/>\n<em>s<\/em>: Stegl\u00e4ngd<br \/>\n<em>Ch<\/em>: &#8221;Cusp height&#8221;, d.v.s h\u00f6jden p\u00e5 de &#8221;r\u00e4nder&#8221; som uppst\u00e5r mellan varje steg.<br \/>\n<em>Ra<\/em>: Den resulterande ytfinheten<\/p>\n<p>Prova g\u00e4rna formul\u00e4ret nedan&#8230;<\/p>\n<p><a href=\"http:\/\/svarthaletracing.se\/wp-content\/uploads\/2012\/05\/cuspHeight.png\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone  wp-image-1362\" title=\"cuspHeight\" src=\"http:\/\/svarthaletracing.se\/wp-content\/uploads\/2012\/05\/cuspHeight.png\" alt=\"\" width=\"315\" height=\"258\" \/><\/a><\/p>\n<form>\n<table>\n<tbody>\n<tr>\n<td>Tool diameter (<em>d<\/em>):<\/td>\n<td><input id=\"toolDia_input\" type=\"text\" value=\"12\" \/> mm<\/td>\n<\/tr>\n<tr>\n<td>Step size (<em>s<\/em>):<\/td>\n<td><input id=\"stepSize_input\" type=\"text\" value=\"0.5\" \/> mm<\/td>\n<\/tr>\n<tr>\n<td colspan=\"2\"><strong>Results<\/strong><\/td>\n<\/tr>\n<tr>\n<td>Cusp height (<em>Ch<\/em>):<\/td>\n<td><input id=\"cuspHeight_output\" type=\"text\" readonly=\"readonly\" \/> mm<\/td>\n<\/tr>\n<tr>\n<td>Ra:<\/td>\n<td><input id=\"ra_output\" type=\"text\" readonly=\"readonly\" \/> \u00b5m<\/td>\n<\/tr>\n<tr>\n<td><input onclick=\"javascript:calculateRa();\" type=\"button\" value=\"Calculate\" \/><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/form>\n<p><strong>In English<\/strong><\/p>\n<p>Not that we really specify surface roughness on our drawings for the pulse jet, but I stumpled upon this working with another project. Surface roughness is a measure of how &#8221;even&#8221; a surface is. It is of course important to be able to measure, and specify how a machined surface should look.<br \/>\nSurface roughness can be measured\/specified in many ways, and one of them is Ra, which indicates the average &#8221;height&#8221; of the machined surface&#8217;s deviation from the theoretical surface. <a href=\"http:\/\/en.wikipedia.org\/wiki\/Surface_roughness\" target=\"_blank\">A large Wikipedia article about this<\/a>.<\/p>\n<p>I needed to machine a &#8221;3 dimensional&#8221; surface, i.e. not a plane, but a curved surface. A common way of doing this is to use a ball-nose cutter, and by making several passes close to each other achieving the intended surface. This will of course result in a slightly distorted surface, so the question was; how small steps should one take between each pass to achieve a certain surface roughness (Ra)?<\/p>\n<p>I made some calculations. The following parameters are used:<br \/>\n<em>d<\/em>: The diameter of the ball-nose cutter<br \/>\n<em>s<\/em>: Distance between each pass<br \/>\n<em>Ch<\/em>: Cusp height, i.e. the height of the resulting &#8221;ridges&#8221; between each pass.<br \/>\n<em>Ra<\/em>: The surface roughness of the machines surface.<\/p>\n<p>The form above can be used to calculate these parameters.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>P\u00e5 svenska Inte f\u00f6r att vi direkt specificerat ytfinhet p\u00e5 v\u00e5ra ritningar f\u00f6r pulsjeten, men jag snubblade \u00f6ver begreppet i ett annat projekt. Ytfinhet \u00e4r ett m\u00e5tt p\u00e5 hur &#8221;j\u00e4mn&#8221; en yta \u00e4r. Detta \u00e4r f\u00f6rst\u00e5s v\u00e4ldigt viktigt att kunna &hellip; <a href=\"https:\/\/svarthaletracing.se\/?p=1327\">Forts\u00e4tt l\u00e4sa <span class=\"meta-nav\">&rarr;<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[26],"tags":[],"class_list":["post-1327","post","type-post","status-publish","format-standard","hentry","category-faktarutorguider"],"_links":{"self":[{"href":"https:\/\/svarthaletracing.se\/index.php?rest_route=\/wp\/v2\/posts\/1327","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/svarthaletracing.se\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/svarthaletracing.se\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/svarthaletracing.se\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/svarthaletracing.se\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1327"}],"version-history":[{"count":37,"href":"https:\/\/svarthaletracing.se\/index.php?rest_route=\/wp\/v2\/posts\/1327\/revisions"}],"predecessor-version":[{"id":1374,"href":"https:\/\/svarthaletracing.se\/index.php?rest_route=\/wp\/v2\/posts\/1327\/revisions\/1374"}],"wp:attachment":[{"href":"https:\/\/svarthaletracing.se\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1327"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/svarthaletracing.se\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1327"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/svarthaletracing.se\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1327"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}