What is the best method to make large diameter tubes?  Diameters will range from 8in to 24 in.  The outside is the finished side.  This will be a large on-going product run, so I don't mind investing in equipment, but can't afford a large autoclave, but possibly could get an oven that size.  So that leaves me with OOA prepreg and Vac infusion.




I personally think that the easiest way will be to get cylindrical Acrylic tubes made in the desired inner diameter and build on the outside and vac infuse.  The issue with this is that I'll have to take the time to sand and clear the outside to get the desired finish. 

The second option is to do the same thing, but build on the inside of the form.  I don't see a problem doing it this way on the larger diameter tubes since its not to hard to get a vacuum bag on the inside, but the smaller ones might be an issue.  I've heard of using bladders to inflate on the inside, but have never seen it in action.

The problem with using prepreg in an oven is that I don't know what kind of temps the acrylic forms can sustain without failing.

What are the other options? 

I think that if I were making this I might use a polished steel or stainless steel tube of the correct ID (polished inside) and mould your tubes in pre preg.

The metal will make for a great durable mould, you will need to split the mould along it's length but just in one place so that the mould can spread after the cook since it will want to shrink back to its original size. Without a split of some kind a metal tube will clamp onto the carbon tube and will not release.

Tape over the join in the mould with a Teflon tape, this will make a reasonable looking seam.

The surface will look great but being epoxy it will not have any UV stability, so the tubes may need a spray clear coat for UV?

good idea.  It may actually be cheaper to have a shop roll metal forms than acrylic. 

I don't have any experience with acrylic. For me if a simple shape can be done in metal then you will have a great mould that can not really get damaged. Usually the common method is to make a composite mould and that's is fine but it will likely cost more than a metal mould and will also be less durable.

Of course you need an oven to process pre preg but that's not such a big hurdle.