- March 16, 2016 at 6:45 am #9169
After 1st test fit of this redesign of the totem design to make it parametric, I heard a little bit of a crack when tightening the bolts which got me thinking of a way to improve the design. I did only print it at 20% for testing instead of 40% which is the recommended density for the original corners. There is also a 4mm gap on the main parts at the middle of the pipes & where the spacer & belt tensioning parts go. The spacers & belt tensioning parts are 3.5mm thick & my final printed parts of those measure 3.6mm. My 1st thought was to make those parts maybe .2mm thicker. While taking a 4 mile hike in Pisgah forest yesterday I started toying with the idea of splitting the top & bottom parts of this totem design into more pieces & then realized I could do the same for the middle joiner part. So with this redesign, those 3 parts become 11 smaller parts. The 8 parts that touch the EMT are all the same part. They are the height of where the EMT would touch where the part goes flat, so there are 3 flat plates to the design. The middle plate is 4mm thick & the outer plates are whatever thickness you want. I am using 6mm for the outer plates to start with so I can use M5x70mm bolts if I can. The total printing time of these parts will be more, but splitting them apart seems like it could make this assembly stronger. You should also be able to print the 8 parts that touch the EMT on their side. With the simpler design of the individual parts they would be easier to print in ABS & might be able to rout them out of wood or aluminum. I am printing these in PETG & should be able to test it later today or tomorrow. Does this sound like a good idea?
Here is a screen capture of what I am talking about. I just realized after looking at this screen capture again that the bottom spacer & belt tensioner are located at the wrong Z depth.
Attachments:March 16, 2016 at 10:24 am #9189
As most of the time happens with an idea that sounds good to me, I do not see something until putting it together. I usually try it anyway because sometimes it leads to something better I did not think about until trying it. Splitting the parts apart around the EMT tends to push those parts away, so I gave up on splitting the middle joiner part. The EMT is still held in place quite well at the top & bottom & it does not move when I try to rotate the pipe. I did not hear any cracking when tightening the bolts this time. As you can see from the close up photos, it does flex the top & bottom plate, but since I am using PETG plastic currently it is working pretty good. Will see how it holds up over time. It was also a little more trouble putting all these pieces together since they had a tendency to go where they wanted to. I am probably only going to use 1 corner with that part for now.
Here are a couple of close up photos of it installed.
Attachments:March 16, 2016 at 10:47 am #9194
The most important part is to make the part, whatever it is, between the two conduits 1 piece. It holds the critical dimension. I made tons of new corner blocks over the last year trying to improve upon mine. I am pretty happy with the new one, not perfect but better than the current design. The other thing is, the corner has very little stress on it in any direction, it is always divided by 4. There should be next to zero force pushing the emt in or out of the hole so giant clamps aren’t needed, gravity is working in the z negative direction/4, then z positive is resistance against the tool and the material contact/4 (should also be small with a sharp tool. To me the important part is the connection between the emt center piece and the leg. The leg and foot is taking all the horizontal forces, The highest I think, also divided by 4. https://www.dropbox.com/s/w8aheb61yybqp4f/corner5.avi?dl=0March 16, 2016 at 11:59 am #9195
Ok, thanks for the structural info. I have already printed 3 of the tall corners & one of this totem design, so will see how well it works when cutting and will use your design if it does not hold up.
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