3D Printing 3D-printed LPR tube end sanders

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Jun 8, 2017
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Someone else posted this idea on the Rocketry Forum recently and I thought it was brilliant. I apologize for not linking to it or naming the author, but I can't find it again. I took their idea and printed mandrels that fit inside BT-5, BT-20, BT-50 and 29mm tubing. Each mandrel is printed with a 3.3mm diameter through-hole, which I tapped with a M4 tap to take an M4 buttonhead screw and metric washer. I found that moistening the tap with my spray bottle of alcohol provided better lubrication without having to resort to Tap-Magic or other oily lubricant. I used the 3.3mm tap size (0.130") because I had a bunch of M4 screws lying around. But you could use the same hole and try a #8-32 tap (needs a 0.136" hole) or ream out the current hole with a #29 drill. If you decide to use #8-32 fasteners, the hole in the end cap will also need to be drilled out with an 11/64 bit.

I have metric and imperial punches that go up to 30mm and 1 3/16". So I used a 4mm central punch concentric with the larger punch to make discs of sandpaper. I use 3M blue Stik-It sandpaper but non-adhesive paper should work just as well. For the 29mm sander I stuck the 37mm end cap to the sandpaper and used a snap knife to cut around it, then chased the edges with a file to clean them up.

I have a home made body tube cutting jig that makes really clean and accurate cuts so I don't need to do a lot of sanding. But for a really clean and dead square edge I wipe the inside of the tube edge with a touch of BSI Insta-Cure CA then slide the sander in and give it 4-5 twists. Voilá, a sharp and square edge in a matter of seconds. Much more precise than a sanding block or belt sander, which is what I used before.

If anyone has the link to the original post for this idea, please let me know so I can give proper acknowledgement.

I'm not sure if it was the first instance of it, but Roger Lipke submitted it to the Sport Rocketry magazine. It was published in the July/August 2023 edition, page 36.