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A micromaxx size carbon body rocket.

Scott PowersScott Powers 11/24/2015 at 03:252 Comments

It has been a while since I have worked on this project. One of the last attempts I did a while ago utilized a bit of release wax and PVA on an aluminum tube. The idea was to create a part with better tolerances, however that part seems to be permanently bonded to the mandrel. It was hoped that exposure to cold would shrink the aluminum mandrel more than the carbon, however it just wasn't enough.

Another attempt after that utilized the paper and tape method using an aluminum mandrel. This gave a nice part with good concentricity, but alas the ID was too large to be useful.

Today I decided to take a step back and make some fiber glass parts. I was hoping to have gotten the first carbon part fairly quickly, but it seems there is enough iteration that needs to happen that the first rocket might end up using fiberglass to reduce the cost of experimenting.

Instead of using packaging tape as my release layer with paper under it, I am trying to use a section of plastic film from a page protector. A section that allowed for ~2 wraps around the mandrel was cut from the protector, and wrapped around the mandrel. The film was then taped once in the center with a small piece of scotch tape. I am hoping that this with both be easy to remove, as well as not so thick as to make the part useless.

Discussions

Daren Schwenke wrote 11/24/2015 at 04:21 point

I think you were on the right track with the wax/pva.  It also helps if you polish your mandrel.  Still having issues... heat the tube from the inside with a propane torch a bit.  Stay below 100C.  Let it cool, then try again.  A hammer helps break the surface tension as well if carefully applied.  :)

If not, and you have nothing to lose... keep going.  Your AL tube is going to expand 10x faster than your composite.  When it cools again, you may have created some space where none existed before. You are going to weaken your composite doing this and it could fail violently and/or release toxic stuff depending on... lots of variables.  Do it outside, wear leather gloves, face shield...

Don't get your AL too hot, or you'll be buying a new tube as you'll destroy the tempering.

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Scott Powers wrote 11/24/2015 at 05:02 point

While the wax/PVA setup is a fairly common method, I am hoping to have this be more easily reproduced by others.  As far as heating with a torch, with such a small part I am worried about damaging it.  Thanks for the tips though.

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