Mandrel for sleeving cardboard tubes? (and other questions)

SolarYellow

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I've seen people sleeving cardboard tubes with no mandrel, and with motor tubes used as mandrels. I noticed that fleabay and aliexpress both have metric-sized metal tubes available for cheep shipped direct from China. Has anyone gone that route for a mandrel? I'm a little worried about it getting banged up in transit; extrusions are normally pretty dang straight off the equipment.

I'm so far only thinking about a one layer light-sleeve reinforcement of a 24mm tube. Not a lot of options for full composite in 24mm, and the ones that are available are pretty heavy. I don't think I need that much strength, but think I'll need more than just cardboard.

It looks like the shrink tube is probably the way to go, as peel ply adds texture that needs to be filled and shrink tape leaves a spiral edge that needs to be sanded off. I do have a vacuum pump, but no other bagging equipment.

For people using plastic nose cones and sleeved tube (is that anybody?), what do you do to the cone to make the diameter match the tube? Just sleeve all or part of the cone? Use plastic putty/filler and sand it fair?
 

tsmith1315

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I noticed that fleabay and aliexpress both have metric-sized metal tubes available for cheep shipped direct from China

True enough to pull a tube from it?

Maybe try a full length coupler from BMS to brace the airframe a bit before wrapping? Only a couple bucks for 34". I've wrapped HPR tubes without vacuum, not that bad of a chore.
 

SolarYellow

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True enough to pull a tube from it?

Maybe try a full length coupler from BMS to brace the airframe a bit before wrapping? Only a couple bucks for 34". I've wrapped HPR tubes without vacuum, not that bad of a chore.

If I knew an aluminum extrusion hadn't been bent by mishandling, absolutely. It'll be as straight as any ruler/scale/whatever, which is why they make those things out of it. In the case of a short cut shipped from China, I'd put it between some V-blocks and spin it under a dial indicator before using it. I'd worry about the rocket flying straight before I worried about not getting a cardboard-inner layup off it. We have methods...

Mach 1 has filament-wound fiberglass in BT-50 (24 mm) size, $9/foot. Possibly less expensive overall, and certainly less trouble, than glassing a paper tube.

Solid glass ends up so heavy that the performance capability of a 24mm motor is completely neutered. And the solid carbon tubes, which I haven't found in 24mm yet, are still pretty heavy per foot, nevermind the price. I don't see either of them making sense for a performance-oriented LPR/MPR up to 29mm. Adding a single 0.013 inch layer of carbon to the outside of a cardboard tube gives it the needed strength without excess weight, based on the builds I've seen and work I've done so far. Remains to be validated with my own build and measurements, however.
 

prfesser

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Solid glass ends up so heavy that the performance capability of a 24mm motor is completely neutered. And the solid carbon tubes, which I haven't found in 24mm yet, are still pretty heavy per foot, nevermind the price. I don't see either of them making sense for a performance-oriented LPR/MPR up to 29mm. Adding a single 0.013 inch layer of carbon to the outside of a cardboard tube gives it the needed strength without excess weight, based on the builds I've seen and work I've done so far. Remains to be validated with my own build and measurements, however.
True, though the Mach 1 product is pretty thin-walled, 24 mm i.d., only 25 mm o.d., same wall thickness as paper tube.
 

prfesser

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Most standard 18 and 24mm cardboard tubes are 0.013-0.016 inch thick.

0.5mm is 0.020 inch.
Sorry about that, you are absolutely correct. Standard BT-50 has a wall thickness of 0.013", so the fiberglass tube is about 0.007" thicker. I don't know whether the difference in weight matters in SolarYellow's application.
 

rharshberger

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Sorry about that, you are absolutely correct. Standard BT-50 has a wall thickness of 0.013", so the fiberglass tube is about 0.007" thicker. I don't know whether the difference in weight matters in SolarYellow's application.
In a minimum diamter situation the weight difference may be a non-issue, there a number of times I needed to add weight to small MD rockets to hit the optimum weight for max altitude.
 
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