CS:R ANH 2-Layer Skins

In 2009 when I started designing R2 Parts life was a lot simpler. The major design tool at the time was Autocad, a 2D drafting program. I could do with it everything that I learned in my "mechanical drawing" class in High School. Plus a bit more! Six years later and the world, myself included, has moved on to 3D design tools. But we still find a need to design 2D things. Seemingly, for some reason, that's gotten harder instead of simpler.

Chris Reiff, and a team of R2 Builders, developed what is now called Club Spec: Revisited and published a huge volume of documented changes to the existing set of R2 drawings (now called Club Spec: Legacy). For more information see the wiki. The files were made available in a number of 3D engineering formats, none included the veritable Autocad formats. Curiously enough, one tool I had used extensively to convert  adobe .pdf documents into autocad .dxf format, Pdf2Dxf, would no longer work on the published .pdf files. Let me show you why that was a problem for me.


It's a little difficult to see at this size, the images link to larger versions, just click on them. On the left is the .pdf version of the front skin. On the right is the .igs [IGES format] version of the skin that's been imported into Geomagic Designs cad software. The notable difference is that double line gap around the skin panels is missing on the .igs version.
The other difference is not apparent until you get into editing the design file. On the left are two door panels that are on either side of the coin slot feature.

The curved portion of the right hand panel, the curve is represented by two lines meeting at 90 degrees and a circular arc of 90 degrees. The extra dot is the center of the arc.

The left hand panel is represented by a spline.which creates a problem because the portion of the line going to the left isn't aligned with the horizontal axis. It hooks slightly, an artifact of the conversion of .igs into a different format.

While the problems above deal with the source data, the other problem a prospective R2 Builder faces is that you need two sets of files for the skins, an "inner set" that provides a foundation and an "outer set" that provides the panel details. You need both sets for the Front and Rear Skins. To make things worse, you typically need those files in .dxf format to feed to the cutting programs that control the machine tools that make the actual skins! Since I'm building a CS:R frame with a removable rear door, I decided to take the plunge, and create a set of files for the CS:R ANH droid.

To the left is a composite of the front outer skin file (blue) placed over the front inner file (purple).

Below are the two files taken separately.

Each image links to a larger version of the image file.


To the left is a composite of the rear outer skin file (blue) placed over the rear inner file (purple).

Below are the two files taken separately.

Each image links to a larger version of the image file.

There are two additional factors that need to be taken into account when creating skin files:

First the skins need to be adjusted to take into account the wrap diameter - my calculations follow:
A CS:R droid is 18.25" in diameter.  The inner skins wrap around a frame which is 18.09" in diameter.
Frame at 18.09" + 2(.040" inner skins) = 18.17" diameter of inner skins. [ 57.0827" in circumference ]
Inner skins 18.17" + 2(.040" outer skins) = 18.25" finished droid diameter. [ 57.3340" in circumference ]
Looking at the circumference numbers the outer skins are  ~ .2513" wider [57.3340 - 57.0827] than the inner skins.
This implies that panel edges that are aligned in the center of the Droid will be off by ~ .125 on the edges closest to the seam
unless the inner skins are scaled in the horizontal direction by ~ 0.44 %. [ .2513/57.0827 = .0044]

Second to allow for the practical needs of the builder the edges need to be oversized so the skins can be trimmed to fit.
I have added .0625 to the top/bottom edges and for overlap at the joints .125 on each end for lapping/trimming the joint.

My thanks to John (galaia2004) for confirming my calculations and pointing out an omission in the original skin files and
John Z (Ziz) for providing the missing measurements.
The two forum threads where the skin files are discussed are:
http://astromech.net/forums/showthread.php?22983-CS-R-ANH-Skin-files-posted-in-dxf-format-Questions-on-adjusting-for-wrap
http://astromech.net/forums/showthread.php?18329-Club-Spec-Revisited      around post number 142

I have made the adjustments noted above and you can download a .zip file that has .pdf and .dwg versions (noted as V2) of the front & rear, inner & outer, skin files made slightly oversize and with the inner layer shrunk .44%.



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