That's just the glad bake (accept no substitute).
You have to put it on dry or it'll never come off!

PK

One of my boys built a mandrel for 2" rocket tubes. Its pvc pipe mandrel that has a cut(split) down the length. It has 4 round blocks that fit into the mandrel to hold it in shape. We just coat the pvc with wax , lay the glass ,then when set, just knock the blocks out of the mandrel and it collapses and we pull it out of the new f/glass tube.
Works good

Steve

I wonder if it would be better to put two slits in second tube such that it could sit inside the first tube, with the slits at 180 degrees to each other? I'm thinking that that would keep the cross-section more consistant along its length.

While doing a bit of work on the N project 6" rocket that may be viewed in the following build thread viewtopic.php?f=6&t=1840 we took some of the drying/curing time to throw together a mandrel jig.



The idea is that the mandrel sit on one side, (gets a wrap of Mylar) and the material feeder sits on the other.
The jig has yet to have some bolts added to it on the ends where the axle slots are. Tension will be applied by way of rubber bands wrapped around the axles and anchored to the bolts.

The idea is that the feed material can be applied within the guidelines and accurately monitored for straightness by the user. The tension will keep the mandrels from unwanted spinning.



The mandrels are constructed from 2 sections of PML full length coupler tubing glued together using LOC Stiffy couplers. They are marked with reference lines for constructing tubes in lengths of 48" & 60" and in both 3" & 4" diameters.

Both mandrels have ply centering rings sized to match the tube ID and the centre axle which is a length of 25mm steel conduit. The conduits were "foamed" in place using a low density high temp 2 part foam.
The foam and the CR's give the mandrel a measure of stiffness.

After the foam had cured, the mandrels were sanded to take away any high spots, and a wipe of West Systems 105 Epoxy resin and 207 Special coatings hardener. The epoxy was wiped on using a Chux wipe, then any excess wiped away with a clean chux.

A light sand using 400 grit paper has been given to the tubes. The tubes will receive another wipe of the epoxy before the waxing process begins.

Mate thats looks better then the saw horses you were using...

Here y'all go.......after the final wipe of West Systems 105 epoxy resin & 207 hardener.................



I gave the suckers some quality sanding time with 320 & 400 grit paper before using a foam roller to apply the epoxy, then wiping off with a nice clean Chux wipe.

Ready for the Hi temp wax now............

Beer in shot for build validity!

Well guys I had another attempt at laminating a mandral , and I would like to say it all went well , came off so easily just a twist and it came off , was supprised . Goes to show the right prep work is the key.( Dont neglect the prep work ) will save a big headache later on. I brought the fiberglass from VOLKSGLAS 3 meters of 130 cloth , only 30 dollers cheap as. Wrapped it about 5 or 6 times it is 1400mm long but will cut it down to 1200mm, its weight is 340 grams. thanks to everyone that gave me advice on rolling fiberglass body tubes. Next stage nose cone.....

Excellent news diesel

What "wall" thickness did you end up with?

What diameter tube is it?

Well done Diesel, I might have to try that one of these Days/years!

Scoop, I noticed on your photo of the completed Mandral that the tube spirals are still there. I presume after you wax it and add the glad bake that this will not matter....

With the Mandrels shown in the pictures we use Mylar for the barrier wrap.

Although the spirals are still visible, the tube has been filled with wipes of high gloss epoxy. You are correct in assuming a wax coating is applied before the barrier wrap though.

The Mylar is NOT applied in the same way as the gladbake (accept no substitute) ie spiral wound, but is cut to either butt joint and finished with scotch tape or slight overlap and join with 3M Super 77 spray adhesive.

It is a 60mm diameter tube and only about 2mm wall thickness , will only be a medium power rocket . But saying that still pritty strong for only 2mm thick.

2mm is VERY thick, I've flown a 2mm wall glass tube >Mach1...
.... 1-1.5mm is thick..

PK

2mm is VERY thick, I've flown a 2mm wall glass tube >Mach1...
.... 1-1.5mm is thick..

PK[/quote]
Well PK I just guest it was 2mm but after looking at it proberly is closer to 1mm.

Here's a couple of pictures of a 4" tube we pulled off the new mandrel.

I dunno what weight the cloth was as it was part of the batch that PK picked up off the net, plus a couple of wraps of 200gsm plain weave to add some finish.
Wall thickness ended up being around 1.2mm and the resin to cloth ratio very good, it is reasonably light for it's 1,000mm length. In the end, I think we agreed that this tube will make an outstanding 98mm MMT for someone.

Our application process of the Mylar could possibly do with an improvement in the process, because it is difficult to get it on without issue with less the three pairs of hands.

We can also improve on the cutting technique for the "heavier" weight glass cloth to ensure a straight overlap or seam.

And finally, the application of the plastic wrap after the peel ply needed to be a little tidier, to prevent some ripples in the outer finish.

I saw diesel's glassing from the mandrel today and it looked top quality! well done mate. Now I just need to ask, whats the chances of you making me some 16" dia lengths??

p.s. Im serious!!