The Octagon Port

I went through two and a half design iterations before coming up with my final version of the octagon port design. How do you do a half of a design you might ask? It's easy, you get half way thru a revision and then you see that someone else has posted a better way to take care of the same problem.

	This was my version 1 design. It was derived directly from the R2BC drawings. I put the bevels on the top/bottom and left/right pieces so that the 4 corner pieces are all the same. Click on the image for a 3D .pdf version.
I cut a set of parts	But I didn't anticipate how hard it would be to keep them in alignment. - Back to the Drawing Board!

I was just about finished adding a set to tabs to the top edges of each of the corner pieces and matching cuts in the top edges of the top/bottom and left/right side parts when Stephen posted a flat pack octagon port design on astromech.net. He solved the problem I had in the first design rather elegantly. I modified his version by adding tabs and slots to the outer box. It makes it easier to glue the box together. Here's how the design is developed using Alibre Design's 3d CAD software

	Each face is projected onto a separate plane to create the top/bottom and left/right sides of the box. The edges are extended at the corners and tabs are inserted. I didn't bother putting fillets on the tab edges as I did with the egg crate designs. The slot is cut oversize so that the rounded edges of the tab have extra space. The cut corner is projected onto a parallel plane and then the bevels are cut on the edges. This has to be done twice, once for each corner. (Only one shown here).
This is the stack of discs that make up the center of the port. Click on the image for a 3D .pdf version. Note the pocket cut into the bottom of the largest disc.	I've hidden the left side of the assembled port so you can see how the disc stack fits. Click on the image for a 3D .pdf version.

Here's what the result looks like

	The stack of disks with an 8-32 screw for alignment
make sure the pocket is facing the bottom of the stack then clamp and glue
	The tabs & slots with the rubber bands hold the box together. The clamps insure a tight joint. Apply glue just to the joints between the bottom and the sides.
Insert the corners and glue the remainder of the joints.	be careful how much force you use to clamp the corners It's not visible below, but I spread open one of the box edges which dosn't matter, since it's not visible when you mount the octagon port behind the skin.
That little sliver of pink box edge will have to be filed off by hand to get a smooth fit to the skin
	Above: the disc stack in placed in for the photo. Paint first Left: The spider web slots are cut with a .0625 dia bit so they come out slightly rounded. A few minutes with a needle file sharpens up the outer corners.

A note on cutting the parts. If you choose to CNC cut your parts here are some hints. I use 3 cutting bits. A 90 degree v-bit for the bevels, A .125 end mill for most cuts and a .0625 end mill for sharpening up the spider web pattern. I cut the bevels first. Then, using the .125 end mill I rough cut the spider web. I switch to the .0625 end mill and re-cut the spider web. Then I go back to the .125 end mill to cut the screw holes, pocket and profiles. Locating the cut line for the bevel cuts is a little tricky. Although the V-bit edges meet in a sharp point, the bit is also about .050 thick. The result is that the bevels start about .025 away from the cut line. Don't want to cut your own? You can try this parts source.

The design drawings are available as both Autocad .dwg files and Adobe .pdf files download drawing files with the understanding that the drawings are copyright to Media-Conversions and are not to be used commercially. (That note also appears on each of the drawings). With thanks, and credit, to Stephen for the idea of making the octagon into a square box!

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