Hi I’m the new guy here!  (See http://www.talkcomposites.com/21718/I%E2%80%99m-the-new-guy-from-Oregon-USA)

I want to produce a mold that will allow me to have finished molded surfaces both inside and out on the component I'm producing, which will have a high degree of structural definition both sides.

From some videos I’ve seen it appears I need to make a closed mold for vacuum infusion, which may require the mold to split lengthwise and again on both ends with this particular part.

The exposed outer surface of the finished part needs to be a cosmetically perfect twill weave pattern and the only way I can figure out how to orient the fiber do this is pre preg on the 1^st layer.

The subsequent layers don’t need the cosmetics, so do they need to be pre preg, or can they be vacuum infused with wet resin in the same mold then baked in the autoclave?

Is it possible to use the same resin to infuse the mold as what's in the pre greg so you're not using two separate resins, with one being "B" stage", then curing them together in the autoclave as a single consolidation?

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. 

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!

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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.

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 :-)

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!

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

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?