What is the mandrel made out of? Suggest dry ice packing the tube if it is metallic. Liquid Nitrogen has been used by others.

Warren

The mandrel is Carbon Fiber... already tried the liquid nitrogen, when that wasnt successful we tried liquid nitrogen on the inside of the mandrel tubing with a gentle blowtorch to the outside tube with no success... I cant even easily cut the new tube off without risking damaging the mandrel (a rocket I really want to fly again). I'm trying to think of some sort of mechanical tool we can use to get leverage to pry the mandrel out or the tube off but havent come up with anything yet...

What a bummer....

I assume the new layer is completely hardened. If it is soft and even the slightest bit malleable it will deform and not slide.

Can you place a coupler on either the mandrel or the new tube so that the two pieces have clean overlaps – with the tube overhanging on one end and the mandrel exposed on the other? Then you can take a pipe clamp or similar long clamp and then apply a smooth but very extremely firm compression between the two. I did this when I had a copper pipe mandrel stuck to the carbon fiber tube I was making. I actually had a large socket (yes, from a socket wrench set) that I could slip over the exposed end of the mandrel and butt up against the carbon tube. Once it broke free I was able to pull them apart relatively easily.

I've used a lathe as an arbor press before to get a tube off of a mandrel. I set the chuck to hold the mandrel then backed it off ever so slightly. I then put a live center in the other end with a cap I turned to fit inside the mandrel with a lip. I slid the tailstock tight and then cranked the wheel on the tailstock to apply pressure. It took a few tries but there was a 'pop' and then everything slid. It didn't slide easy but I was able to get it out.

Edward

You can use some motor casings, a threaded rod from Home Depot, and an airframe to press-fit the mandrel out, similar to Edward's method, below. For details and pictures, see page 2 of my 38mm carbon thread:

http://www.rocketryplanet.com/forums/showthread.php?t=2808&page=2

But your biggest challenge will probably be getting something with an edge that's the outer diameter of your rocket mandrel. Check on McMaster to see if they have a thick washer with the right ID. I got one that was 1.5" ID for my problem and with a little dremel action it was just right. I assume the mandrel is your 29mm rocket?

How was your mylar covering configured? My dumb mistake was to use intermittent scotch tape on the overlap, and then the vacuum bag squished the epoxy under the overlap. I have some process improvement ideas for the next time, but I'd like to know what not to do.

Thanks for the ideas guys! One problem I have is one end of the mandrel has fins on it, and not much room to grab on which further complicates the situation. I am also wondering if the vent holes in the mandrel are causing small depressions that are binding the tube. Problem is these holes are very hard to locate in the rocket so drilling them through the outside may be hit or miss and then I have a rocket and a coupler with several very large vent holes. The pipe clamp may be one of the best options to help create mechanical leverage.
Adrian - I used a continuous piece of scotch tape to join the mylar and then ptfe coated that.
Right now I'm trying to make sure it is fully cured by placing it in my oven (car in the sun) to see if this is possibly a problem of the epoxy not being fully cured.
Ill let you know how this turns out. -Sean

What little I know I learned from Mick Kelly on the Composite Rocketry group and from John Coker's website. In the end, the answer comes down to NEVER use a non-metallic mandrel - you'll never be able to get enough of a expansion differential to pull off a well-made tube.

On the other hand, I'm really lazy - I'd just as soon buy the airframe made to my specs and have had both Curtis Turner of PF and Mick Kelly make airframes for me. Far easier than doing it yourself without proper equipment

Warren

Thanks for all the advice - finally required an 80 ton press at a machine shop to get it half off, but it bottomed out on the shop floor, so then I made a sort-of press with all thread and some bolts I cranked on to get the rest out. Ended up with a beauty carbon tube we used to couple a 54mm Mongoose on top of Doug Krohns 4 inch rocket. We just got back from BALLS and flew this successfully a CTI M1300 DT staged to a CTI L730 - we hit 37,600 and fully recovered the sustainer, the booster only got the drogue out and the main got stuck so a little damage - and the carbon fiber coupler - barely a scratch. Thanks for the advice! -Sean

Congratulations!!!! 37K+ is impressive.

Warren