6 1/2" diameter tubing with quality finish on the inside

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#1

I searched the forum and couldn’t find anything on a tube with the finish on the inside, I apologize if this has already been discussed…

I need to make some 6 1/2" (Doesn’t have to be exact as these are cosmetic), internal diameter tubes- between .030 and .060 in thickness, and varying lengths up to 3 feet.

I’m currently setup for vacuum infusion and would like to keep with that process if possible.

What has been your most productive way of doing this? I have wrapped PVC tubing, but it’s just too difficult to remove once cured. Plus, the finish on the outside of PVC is not exactly the best finish.

I’ve thought of dis-solvable mandrels, but I have zero experience with those products.

Thanks in advance for any and all feedback.

#2

Use a thin walled piece of aluminum tubing for your male mold. If you heat the tube from the inside it will expand. Then when your carbon laminate cures it will be the larger diameter. After all the curing is done put it in a freezer to maximize tube shrinkage. The CTE differences between the aluminum and the carbon will allow you to remove the tube.
This works very well with prepreg and heat shrink tape or a very slow cure resin.

#3

Thanks! Will try to do it this way next week.

#4

How perfect a finish are you wanting? I’ve always found the easiest way to make tubes to be by wrapping paper over the tube and then wrapping that again in flash tape or clear packing tape. Then laminate and use shrink tape for consolidation. The paper allows the carbon to slip right off the mandrel, and the tape allows you to remove the paper from the inside of the part.

The finish isn’t perfect though obviously, you will get lines where your tape edges overlap etc.

#5

The finish needs to be really pretty. I honestly didn’t want to spend too much time on these… Hopefully, AVT’s technique will work perfect for me. Thanks!

#6

I wrap the tube in glossy window tint film and then wrap the carbon fiber around that. The inside finish comes out mirror smooth and the window film is easy to remove.

If the piece is just cosmetic , you could also just wrap any tube that is already smooth on the inside.