{"id":70,"date":"2008-12-04T08:04:38","date_gmt":"2008-12-03T21:04:38","guid":{"rendered":"http:\/\/www.madox.net\/blog\/?p=70"},"modified":"2008-12-08T13:58:31","modified_gmt":"2008-12-08T02:58:31","slug":"rapid-prototyping-mechanical-iris-diaphragm-new-improved","status":"publish","type":"post","link":"http:\/\/www.madox.net\/blog\/2008\/12\/04\/rapid-prototyping-mechanical-iris-diaphragm-new-improved\/","title":{"rendered":"Rapid Prototyping – Mechanical Iris Diaphragm (New & Improved!)"},"content":{"rendered":"
\n

Last time<\/a> around I ran into two major issues.<\/p>\n

    \n
  1. Tolerance between moving parts was too tight.\u00a0 My pivot pins on the inner ring were pretty much jammed into their holes…<\/li>\n
  2. Fragility of the part.\u00a0 Using 1mm diameter pivot pins using the detail material (weak) was not a good idea.\u00a0 Coupled with the tight pin problem above, it meant I accidentally snapped a couple of pivot pins off the blades when I tried to rotate close the iris.<\/li>\n
  3. Coarse triangulation of the exported STL which made the two rings too ‘blocky’ to rotate freely with each another.\u00a0 My fault, fixed by (labourously) tweaking\/experimenting with Alibre’s Export.<\/li>\n<\/ol>\n

    So how did I fix it all?<\/p>\n

    <\/p>\n

    The design<\/h2>\n

    This message thread<\/a> on the Shapeways forums details a few experiments other people have tried printing ‘living hinges’ and moving parts direct from 3D print.\u00a0 Appears the magic number is >0.1mm gap between two components to avoid them fusing together…so I went for a margin of error and aimed for >0.25mm gap.<\/p>\n

    While reading it all, my previous design came as 26 individual components…which probably annoyed the hell out of Shapeways staff while shipping it.\u00a0 With the improved tolerances, I tweaked the design to combine all components into one assembly to be printed in one go hoping it’ll work ‘out of the box’.\u00a0 Yes thats right, printing in ‘one-piece’ and hoping it works!<\/p>\n

    A few other tweaks here and there; making it smaller to save cost, making the pivot pins thicker, putting a covering skin on it to hide\/contain the blades and around an hour later…<\/p>\n<\/div>\n

    \"The<\/a>
    The result...<\/figcaption><\/figure>\n

    One thing to note is that this only took an hour because I cheated and reused my previous Alibre Design files.\u00a0 Being a parametric modeller, all I had to do in most instances is edit some dimension values on the sketches I’ve set up on the previous design.\u00a0 Easy!<\/p>\n

    I also didn’t bother doing math calculating on how long the sliding slot should be, simply judged it by eye by sliding\/rotating the blades in assembly mode to see approximately how much movement I’ll need to achieve full closure\/opening.\u00a0 This is seeming more and more like an Alibre<\/a> advertisement isn’t it?<\/p>\n

    The painful STL export again…<\/h2>\n

    One rant though is with the STL export – its non-intuitive, the help file instructions were that helpful and it all came down to trial and error.\u00a0 I learnt :-<\/p>\n

      \n
    1. Tweaking the normal deviation setting is a bad call.\u00a0 Making it smaller will result in either a humungous file or Alibre crashing out.<\/li>\n
    2. Tweaking the surfaces setting is too painful.\u00a0 It either had a negligible effect on things or I was simply doing it wrong…<\/li>\n
    3. Tweaking the maximum cell size worked!\u00a0 Well kind of.\u00a0 It basically asks the exporting to enforce a triangle plate size to be smaller than what you specify, so a small value generates alot of triangular cells.\u00a0 This is not optimal because even if you had a large flat triangular sheet that could be very well represented by one large triangle, it’ll now be forced to make it into 893475 triangles…<\/li>\n
    4. Why kind of?\u00a0 Because the Shapeways design validator crashed\/errored out of me when I had the cell size too fine (0.1).\u00a0 I had to nudge that back to (0.2) before Shapeways accepted the file.<\/li>\n<\/ol>\n
      \"Smoother<\/a>
      Smoother STL than last time...<\/figcaption><\/figure>\n

      Naturally I used Meshlabs to validate the triangulation and remove duplicate vertices again.\u00a0 This step is required to allow it to pass Shapeways validation, it also cuts the STL filesize by 80% typically.<\/p>\n

      Oh I forgot to explain why it was painful.\u00a0 Learning items 1-4 above probably took me oh over 2-3 hours?\u00a0 [Though I still remained productive by fixing my girlfriend’s Nintendo DS…].<\/p>\n

      Waiting for the shipping again<\/h2>\n

      Actually waiting to find my wallet to click the order button \ud83d\ude42 Lets see how this turns out!<\/p>\n","protected":false},"excerpt":{"rendered":"

      Last time around I ran into two major issues. Tolerance between moving parts was too tight.\u00a0 My pivot pins on the inner ring were pretty much jammed into their holes… Fragility of the part.\u00a0 Using 1mm diameter pivot pins using the detail material (weak) was not a good idea.\u00a0 Coupled with the tight pin problem … Continue reading “Rapid Prototyping – Mechanical Iris Diaphragm (New & Improved!)”<\/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":[],"class_list":["post-70","post","type-post","status-publish","format-standard","hentry","category-engineering"],"_links":{"self":[{"href":"http:\/\/www.madox.net\/blog\/wp-json\/wp\/v2\/posts\/70","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.madox.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.madox.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.madox.net\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/www.madox.net\/blog\/wp-json\/wp\/v2\/comments?post=70"}],"version-history":[{"count":4,"href":"http:\/\/www.madox.net\/blog\/wp-json\/wp\/v2\/posts\/70\/revisions"}],"predecessor-version":[{"id":98,"href":"http:\/\/www.madox.net\/blog\/wp-json\/wp\/v2\/posts\/70\/revisions\/98"}],"wp:attachment":[{"href":"http:\/\/www.madox.net\/blog\/wp-json\/wp\/v2\/media?parent=70"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.madox.net\/blog\/wp-json\/wp\/v2\/categories?post=70"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.madox.net\/blog\/wp-json\/wp\/v2\/tags?post=70"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}