I created two sanding guides to help me either draw the parabola shapes (or ideally, sand the shapes) of the conduit ends of the MadCow 2.6in BOMARC.
I then created an alignment guide to help position the ramjet cones when applying epoxy (an assembly step that felt like I was definitely going to mess it up).
*To use the sanding guides:*
The idea is that these guides can straddle the end of the conduit (over the wing, in the case of the rear guide). You can then use them to mark the conduit for cutting/sanding, or leave them in place to provide a visual guide while doing a rough-sand or cut.
You might consider drilling the straddle-bits (don't know what to call them...ears?) to allow you to fix them in place with stick-pins. Alternately, use painter's tape or masking tape to adhere them while you work.
You may have to modify the straddle-bits on the STL or cut down the printed part to fit your conduit, depending on how it's worked out for you (sanded already, different clamping arrangement than mine, etc.).
*To use the alignment guide:*
DRY-FIT THIS FOR SIZE AND ALIGNMENT BEFORE TRYING WITH ADHESIVE! Put a little bit of epoxy or wood glue on the mounting surface of the small ramjet cone, and insert it in the hole of the positioning guide (from the side with the 1mm depression).
Carefully place the guide and small cone onto the large cone, using the 1mm depression to align them. The 1mm depression should just fit the front of the larger ramjet cone.
Holding the small cone onto the large one with a fingertip, carefully lift the alignment guide off of the small cone. Carefully clean any excess adhesive off the aligned parts (or wait 'til dry and sand...).
Clean excess adhesive off of the alignment guide before doing the other cone. (un-cured epoxy comes off pretty well with a paper towel wet with rubbing alcohol).
I printed these in PLA on my Printerbot Simple 1401 (Yes, still. Upgraded with drive belts. Works fine). Used 20% infill, no support needed. Printed with .5 nozzle, 40mm/sec .2mm layer height.
I printed each piece independently. The long one fits: you may have to mess around with initial positioning or skirt width. The long sanding guide took about an hour, the short one 40 min., the ring about 30 min.
The cone alignment tool was poorly sliced by Cura: I had to trim out (with an Xacto knife) and sand a thin, spurious top layer. It printed nicely otherwise: perfectly sized to my parts on the first try.
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