tag:blogger.com,1999:blog-23681518.post2752461857816314657..comments2023-10-14T04:05:08.546-07:00Comments on Diary of a Technocratic Anarchist: Some crude load testsForrest Higgshttp://www.blogger.com/profile/17208965471464716174noreply@blogger.comBlogger17125tag:blogger.com,1999:blog-23681518.post-2035784436597702352010-03-05T15:18:38.168-08:002010-03-05T15:18:38.168-08:00Really interesting work, Forrest. Keep it up! :)...Really interesting work, Forrest. Keep it up! :)Robhttps://www.blogger.com/profile/00222764022709703493noreply@blogger.comtag:blogger.com,1999:blog-23681518.post-41428607876153280082010-03-05T08:10:36.485-08:002010-03-05T08:10:36.485-08:00I'm currently working on making better beams a...I'm currently working on making better beams and pillars (under the name hiroe on thingiverse) and was wondering if anyone had any ideas for alternatives to the pin and hole that forest says are fragile.<br /><br />I'm also wondering if post tensioning is necessary at this scale. my though is to use string to make a small tension at the edges between shapes. basically tying them together under tension instead of going all the way through. Having no physics or engineering background and never having dealt with post tensioning I don't know if this would be significantly weaker or not.Hiroehttps://www.blogger.com/profile/05691099566996575740noreply@blogger.comtag:blogger.com,1999:blog-23681518.post-46236407033570792392010-03-04T06:47:37.835-08:002010-03-04T06:47:37.835-08:00". However it will be difficult to secure rop...". However it will be difficult to secure ropes / braids to an end cap without letting any slack through your knot. "<br /><br />If you know your knots that´s no problem. Fibers are good for converting range of movement into<br />pulling force exponentially while<br />at the same time exponentially removing<br />error due to slack from the equation.<br />It´s called a wire rope and it´s<br />thousands of years one technology.The Editorhttps://www.blogger.com/profile/01641247429615484542noreply@blogger.comtag:blogger.com,1999:blog-23681518.post-27334632765632293472010-03-03T19:36:42.341-08:002010-03-03T19:36:42.341-08:00Plastics creep is certainly a very real problem. ...Plastics creep is certainly a very real problem. What I think I haven't communicated very well is that the light frame module that I designed is an extremely tentative experiment.<br /><br />I learned a lot doing the exercise. A few things...<br /><br />The pin and socket connection between modules was not a great ideal. It looks good but it's fragile.<br /><br />AoI can only be used for this kind of design work with extreme difficulty.<br /><br />Skeinforge as it stands now isn't very useful for this kind of work, either.<br /><br />Keep in mind that the module I designed was intended as a load bearing column, not a beam as such. Had I designed a beam I would have put more plastic on the compression side and mounted the post tensioning studding down towards the tension side instead of the middle.<br /><br />This is only the beginning of light frame design work. It isn't reasonable to expect that a first cut exercise will be anywhere near optimal. We're going to get LOTS better at this. :-DForrest Higgshttps://www.blogger.com/profile/17208965471464716174noreply@blogger.comtag:blogger.com,1999:blog-23681518.post-9446848395547185972010-03-03T19:20:56.812-08:002010-03-03T19:20:56.812-08:00Jonathan's comment on creep is an important on...Jonathan's comment on creep is an important one. Forrest: could you do us all a favor and see what happens if you leave your test object loaded for a few days? We might want to be looking for the highest possible modulus (least stretch under tension) so that the structure doesn't creep in compression from the tensioning members.<br /><br />(And I'm betting something like an eyebolt through a nut on the far side of a possibly fender washer should do it for all sensible loads...)paulhttps://www.blogger.com/profile/14797761477457158490noreply@blogger.comtag:blogger.com,1999:blog-23681518.post-51271587269482859802010-03-03T13:54:46.115-08:002010-03-03T13:54:46.115-08:00Rather off topic, but a very interesting read on n...Rather off topic, but a very interesting read on natural materials with high tensile strength:<br /><br />http://books.google.be/books?id=4QTfTINjQtUC&pg=PA207&lpg=PA207&dq=guitar+tensile+strengthMark Van den Borrehttps://www.blogger.com/profile/06387179974055444605noreply@blogger.comtag:blogger.com,1999:blog-23681518.post-73513642908800906692010-03-03T13:42:46.521-08:002010-03-03T13:42:46.521-08:00Indeed! Piano wire comes to mind immediately.Indeed! Piano wire comes to mind immediately.Forrest Higgshttps://www.blogger.com/profile/17208965471464716174noreply@blogger.comtag:blogger.com,1999:blog-23681518.post-33392688460340395672010-03-03T13:31:42.813-08:002010-03-03T13:31:42.813-08:00As a professional guitarist, I can't help but ...As a professional guitarist, I can't help but think of musical instrument string technology.<br /><br />My technical knowledge is too limited, but the strings and tensioning mechanisms from the musical world might inspire some solution here.Mark Van den Borrehttps://www.blogger.com/profile/06387179974055444605noreply@blogger.comtag:blogger.com,1999:blog-23681518.post-80142893944227225442010-03-03T13:06:33.700-08:002010-03-03T13:06:33.700-08:00Hi Forrest.
This is a really good result - I'...Hi Forrest.<br /><br />This is a really good result - I'm impressed at how much load a few grams of polymer can take!<br /><br />On using polymer cables for tensioning: keep an eye out for plastics that creep/relax over time. I believe that Kevlar has very little stretch, and might be suitable for the job. However it will be difficult to secure ropes / braids to an end cap without letting any slack through your knot. Some form of ratchet fastener or tightening mechanism would need to be fabbed in.<br /><br />Paul: a friend of mine is doing a Masters on rapid prototyping, and apparently the reprap fused-deposition method isn't very strong in tension - the layers tend to delaminate (pull apart). Possibly Forrest could fabricate a member with a hole in each column and use multiple tensioning members to overcome this?Anonymoushttps://www.blogger.com/profile/02653510977776837607noreply@blogger.comtag:blogger.com,1999:blog-23681518.post-46358385467627704042010-03-03T08:30:22.886-08:002010-03-03T08:30:22.886-08:00exciting to see this, forest! well done. i'm ...exciting to see this, forest! well done. i'm kind of excited to see the first usable structure printed out of these, say a mendel (or even a darwin) with these replacing a lot of the larger threaded rod segments. <br /><br />for down the road, i really like the suggestion of using a cord with some method of post tensioning. it seems pretty innovative to replace much of the threaded rod vitamins with some RP parts and a spool of some thin cable or filament, tied to some tensioning end fasteners.Peterhttps://www.blogger.com/profile/09748593214168860068noreply@blogger.comtag:blogger.com,1999:blog-23681518.post-12997475144518165932010-03-03T07:28:30.453-08:002010-03-03T07:28:30.453-08:00paul: There are a variety of braided cables and m...paul: There are a variety of braided cables and monofilaments that could be used for the tensile member in post-tensioned beams. How you attach them to the end plates and how you put them in tension are the big issues. I haven't got time to tackle those problems right now, so I am content with using small diameter studding, lockwashers and wingnuts. Those work easily and are very easy to acquire at just about any hardware store.Forrest Higgshttps://www.blogger.com/profile/17208965471464716174noreply@blogger.comtag:blogger.com,1999:blog-23681518.post-7003353463667151902010-03-03T07:00:19.938-08:002010-03-03T07:00:19.938-08:00Hurrah!
And you'll get even better behavior i...Hurrah!<br /><br />And you'll get even better behavior if you put the reinforcement through the columns -- what you have here is essentially a 15mm depth because the part below the metal doesn't really have any strength in tension. (So your deflection is largely the result of compression in the upper section.) Speaking of which, has anyone designed a fabbable barb fitting for making joints that can easily be assembled but are then strong in tension?<br /><br />A look at a table of materials properties shows that pretty much anything has more tensile strength and modulus than ABS/PLA/etc. I would tend to go with kevlar cord, which is readily available and terrifyingly strong. The issue will be how to make end plates (washers?) that will distribute the load.paulhttps://www.blogger.com/profile/14797761477457158490noreply@blogger.comtag:blogger.com,1999:blog-23681518.post-50057077521947002462010-03-03T06:58:34.540-08:002010-03-03T06:58:34.540-08:00Marcus: That's possible, but it adds a lot of...Marcus: That's possible, but it adds a lot of extra material to the module. For gritty reality, however, this module design was really pressing the envelope for Art of Illusion. I was barely able to get this assembly to work. Making it even more complex just wasn't practical. <br /><br />I was thinking about trying different designs last night and found that AoI's dodgy boolean operations module kept limiting what I thought possible. I finally broke down and bought an entry level copy of Alibre to see if their boolean operations module was going to be more robust.<br /><br />LogbLogb: I responded to your comment where you made it originally on the Reprap blog.<br /><br />mfsamuel: Triangular might well be more efficient. Singe I was thinking about rectilinear problems when I designed this one, I stayed with the square cross-section because it was easier to integrate into the rest of my design.<br /><br />Todd: I have 40 kg of polypropylene and 8 kg of HDPE which might go a ways towards answering that question.Forrest Higgshttps://www.blogger.com/profile/17208965471464716174noreply@blogger.comtag:blogger.com,1999:blog-23681518.post-10646719149441520482010-03-03T05:43:36.518-08:002010-03-03T05:43:36.518-08:00UHDPE is being used for stays in on racing sailboa...UHDPE is being used for stays in on racing sailboats. You might be able to use that.Todd Bateshttps://www.blogger.com/profile/17658318994782111042noreply@blogger.comtag:blogger.com,1999:blog-23681518.post-86108435468208975442010-03-03T05:32:43.496-08:002010-03-03T05:32:43.496-08:00looks good, but wouldn't a triangle cross-sect...looks good, but wouldn't a triangle cross-section resist flexing more and be less material to print?Anonymoushttps://www.blogger.com/profile/02659008091237945194noreply@blogger.comtag:blogger.com,1999:blog-23681518.post-49089364836771480262010-03-03T04:08:54.165-08:002010-03-03T04:08:54.165-08:00What about integrating end-caps ir cross-supports ...What about integrating end-caps ir cross-supports between diagonal corners into each segment?The Editorhttps://www.blogger.com/profile/01641247429615484542noreply@blogger.comtag:blogger.com,1999:blog-23681518.post-59486513438259430872010-03-03T00:55:51.166-08:002010-03-03T00:55:51.166-08:00This obviously has great potential to further the ...This obviously has great potential to further the self replication. As I see it there are two major flavours of drive and motivation in the reprap movement. personal-fab and self-replication. They both bare many parallels and coexist great in the movement but closer to goal i personally belive design choices will diverify and there will be a split. What is your major drive and if you had to guess, what will be the hardest part to replicate?LogbLogbhttps://www.blogger.com/profile/14807132044313536063noreply@blogger.com