Scott...envisioning this am I hearing you say that I should cure the "B" stage pre preg carbon fiber twill weave as a thin outer shell for cosmetics in a female mold with a vacuum bag, then put that skin into a compression mold with "B" stage pre preg behind the skin and bake it under pressure?

If so that makes a lot of sense in a production setting for doing multiple finished components, which is what I'm wanting to achieve!

I've been giving a lot more thought to this after hearing Zebra's comment and I'm wondering if compression molding may be the perfect fit?  I'm familiar with Vac Cast and have used it before to make mandrels for forming multiple layers of veneer into 3D components.  It's also used a lot for doing temporary molds for investment casting wax.

Would it work to make a two part male / female compression mold from my plug using Vac Cast that I'd use tooling gelcoat on?  My experience working with Vac Cast for investment casting molds is that it's poured into an aluminum body that has dowel pins through the aluminum that the keep it registered properly.

What are you guys thoughts on this?

I've attached some pictures how I've used Vac Cast for forming veneers over a mandrel with a vacuum bag for one of the components I’m producing using 7 plys of .023” birch veneer that is 0°/90° cross banded, then has an 8th ply of exotic hardwood for the face veneer using urea-formaldehyde adhesive, that is cured with heat under vacuum.

Once formed, they are put into a vacuum chamber and infused with liquid acrylic then baked to cure the acrylic.  This plasticizes the wood making them extremely durable and the only finishing required is with a buffing wheel and polishing compound.  Trimming for the outer edges and ends, along with the vents are then machined on a CNC router.

The advantage of using veneers over solid wood is it makes a wood component that has great dimensional stability, with no warp, twist or bow, without splitting or cracking.  It also allows you use book matched grain out of a two ply sequence from the flitch, so the right and left side of both halves match identically.

The part needs some consideration due to the tight rads and joggles. It lends itself to a prepreg layup and possibly curing the skin (1st layer) to get the outside surface correct to the mould.

Zebra...thanks for the quick response!  Having no clue what I'm doing, a lot of what I'm hearing hear could just as well be in Chinese and I think I'm asking too broad of a question, so I'm going to try and be more specific.

Can you explain compression molding, as well as what carbon fiber sheet molding compound is, and how I should approach the mold design?

I make carbon fiber stocks which are more complex than your pics. I use compression molding for smaller details.

OK…so I think I’m going to approach my questions differently as I’m not sure I’m hearing what I was hoping for, so I’ll do this in a question format with pictures.

In the following picture I’ve shown arrows where there are exposed edges that are seen, so this top edge needs to be cosmetically perfect both visually and dimensionally on the lower hand guard.

In these next two pictures of the lower hand guard you can see where there are critical surfaces on the front that need to be formed dimensionally to within +/- .030”. There are similar critical surfaces on the back end, as well on the inside on both ends.

In the next three CAD renderings you can see arrows pointing to an upside down isometric view of the upper hand guard where there are also similar critical surfaces on the back and front end, as well as inside.

I’m about half way through making the plugs for these two parts and my next step is doing the split molds.  I will be using an autoclave that has heat, vacuum and pressure, which you can see pictures of at: http://www.talkcomposites.com/21718/I%E2%80%99m-the-new-guy-from-Oregon-USA

Question 1.  Are these molds needing to be two halves that split down the middle, with molds on both ends, and a male mandrel coming in from the top, where all 5 sections are bolted together to form a completely closed mold?

Question 2.  Knowing that I want the outer visible surfaces to be cosmetically perfect with the orientation of the twill weave pattern, is it safe to assume that this needs to be all pre preg, or are there other options that includes infusion.

Question 3.  If they are all pre preg; how do I insure that I get the correct number of layers in the areas where the inside is built up, or is that strictly trial and error?

I’m using rapid prototypes on the plugs, as I find they are dimensionally more stable in terms of twist, bow and warping than production injection molded parts.  And they are of a material that lends itself to making changes using body putty and accept gel coat nicely.  I’m also making these where the vents in the sides will be CNC machined in afterward and then be clear coated on the finished production parts.

I sincerely appreciate your input here, as I have no real clue what I’m doing, other than what I’ve seen watching videos!

M14 ?? ...

I have made a number of gunstock parts using infusion, and it can work .. but getting a good "cosmetic" CF surface on the inside of such parts, really requires post processing, which in this case you will need anyway, since you DO want to UV protect something like this!!

I made mine by doing the inside and the outside as two parts, then bonding them together .. That had the advantage that I could make different "insides" to fit different bolt-rifle actions- Requiring only an amount of cutting in the outside part, to fit different magwells etc. --

"Sapere Aude"... Dare to KNOW!

The written word is the only truly efficient vehicle for transmitting a complex concept from mind to mind...

103% of all people do not understand statistics...

Do not adjust our mind, theres a fault in reality :-)

Your right…I probably am overthinking this!

I’ve attached some images of the parts I’m currently having injection molded out of 35% fiberglass filled high temp nylon using permanent CNC aluminum tooling I own, and I’m wanting to do these in carbon fiber as an alternative.

It’s important that the internal structural definition of the parts be as well defined as the outside, which includes both ends, so my thinking is the only way to achieve this is to vacuum infuse a closed mold with resin so I don’t get any voids.

I’d actually prefer pre preg as it’s easier to work with, and money isn’t the issue.  My concern is that due to the varying thickness in certain locations inside both ends, it may be difficult to get both fiber and resin to properly fill those areas adequately using pre preg.

If what you want to do is "produce" and sell multiple counts of this part, then Prepreg all the way through is the way to go. 

I have made quite a few small complex CF parts using closed aluminium moulds and infusion.  Getting "perfect" cosmetic finish on all surfaces of these has never worked faultlessly.

I decided to not bother, since I wanted to secure the parts against UV damage anyway, so all "non contact" outside surfaces are clear-coated.
(by "contact surfaces" I mean the areas of the part that is "covered" by the stuff they are clamped to/ screwed on to.

"Sapere Aude"... Dare to KNOW!

The written word is the only truly efficient vehicle for transmitting a complex concept from mind to mind...

103% of all people do not understand statistics...

Do not adjust our mind, theres a fault in reality :-)

Not really, no. I think you are over thinking this. It is certainly very possible to get cosmetically perfect finishes using infusion, there's no problem there.