On to the Park tube repair and repainting. The outer finish is polyester resin, often known in the marine world as gelcoat. Polyester resin is how fiberglass things were made before epoxy came along. It still sees use due to lower bulk cost than epoxy, but it has some major drawbacks. It's brittle (leading to the well known stress cracks around holes), darkens and yellows as it ages, has really noxious fumes, and surfaces exposed to air won't cure unless you use a wax additive or PVA to form a barrier layer. I briefly used polyester resin for glassing rocket bodies a long time ago, but then epoxy showed up and I switched over for good. My Park/Cave tube has really gone yellow and I have stress cracks around a majority of the holes. So I have no appetite for putting any more polyester resin on it. Fortunately, I don't think I will need to do that.
Someone around here probably knows details of the original build process for the tubes. Mine has a single lengthwise seam lap about 1mm high, suggesting that they did the layup flat and then rolled it up with something wrapped around it to give the outside shape. They were not painted; the dyed-in-the-mass poly resin was the outer surface.
It needs structural reinforcement around all the attachment points...the tube is too thin to withstand the loads from all the small-gauge hardware that was used. That's actually going to be straightforward, in the form of 6oz glass patches on the inside, wetted out with West System epoxy. I already did this once already 25+ years ago when I relocated the finder; the patch has held up fine, so I'm going to replicate that everywhere else there were (or will be) holes drilled. I'm also looking to machine or 3D print some contoured backer plates to reduce stress on the tube. (Bleedover here - we use tube backers with thin glass and cardboard rockets all the time).
My finishing plan is to sand the poly down, eliminate the seam and cracks as much as possible, and then prime / paint gloss white with a 2-part epoxy system. I have 40 year old things painted with that stuff that are still bright white, so I'm pretty sure this will effectively eliminate the fading and yellowing for as long as I'm around.
First things first...I need a tube cradle fixture that will hold the tube horizontally on a table and not let it spin. Started by dicing up some 3/8" ply that I had hanging around.
Anti-spin done by adding some strips of the 1/16" silicone rubber sheet, glued down with clear silicone seal. Good stuff.
The finished cradles. The whole cradle build took about 25 minutes.
Rotating ring removal. The ever-useful deadblow hammer was essential for getting them started. The rings are a pretty close fit, so I'm going to have to watch it on the paint thickness. Before removing them I made temporary witness marks with a sharpie to indicate the front/rear and orientation, since they were match-drilled and have preferred orientations. After they're off, I'll engrave permanent marks on the inside. They were secured with a too-small number of too-small bolts. The outer rings are missing some paint so they're in the "gotta paint this" pile now.
Removing the aluminum badge plate. Gentle use of a heat gun and putty knife did the trick.
It took a couple of hours to sand off the seam and stress cracks. I used #320 on orbital sanders. My old cheap Ryobi bit the dust halfway through - RPM drop, bad smell, bits of plastic flung out thru the vents, pad stops rotating. Replaced it with a Bosch 5" unit that is twice as sturdy, half as loud, actually catches the dust, doesn't make my hand feel numb, and probably won't melt its own gears.
The sanded tube ready for fiberglass patches. If you look closely you can see all the holes. The HOLES...yikes. As I was thinking about where to put the patches, it occurred to me that I need to revisit the location of some things on the tube like the guidescope (Dalek: "Moderniiiize!") and the rotating rings (too far aft when you are hanging more stuff up front).
Edited by Dave Cook, 14 December 2020 - 12:57 AM.