Carbon fiber stock build

[nksmfamjp]

I plan and laying up the cf in each half mold, pressing together and adding a form of internal pressure. Think vacuum bag process from the inside. The stock will already be together when removed.

Ok. Got it now!

 

[aron]

You may be able to get by with not needing a vacuum if using prepregs as the excess epoxy is significantly less than with a resin transfer mold technique. I would also consider molding in your hardware (flush cups, t nuts, etc). That way you are not having to go back and cut the fibers to keep them as long as possible.

 

[jrock]

I thought about doing a mold where I would use expanding foam to pressurize it. I have an ultralight MPI stock and it appears it is set up for that method. However, I decided to go with a foam core with the expectation of using vacuum bagging to expel excess epoxy. Epoxy is where the weight is. I planning to do the sleeve method as it make more sense from a strength perspective...and may be easier/quicker to layup. I'm currently planning to use an aluminum model of the action and bottom metal area. I'm assuming when I vacuum bag, it will create a tight fit up and no trimming around the bottom metal area will be required. The MPI stock has a lot of epoxy around the action area which I plan to try and limit with this method. Its all theoretical at this point. It may not be the quickest method to start up but it should be pretty quick to use once setup.

I also want to make CF magazines like Seekins

 

[Tidus56]

isnt making a mold easier then making multiple foam stocks to wrap and vacuum

I thought about doing a mold where I would use expanding foam to pressurize it. I have an ultralight MPI stock and it appears it is set up for that method. However, I decided to go with a foam core with the expectation of using vacuum bagging to expel excess epoxy.

So we have tried both a foam core and using foam to pressurize and fill the space. We actually ended up getting better stocks with the foam core. We have made a few stocks without any pin pricks or fish eyeing or any other mistakes in the exterior shell. The key to that was putting the epoxy down on the mold, giving it thirty or so minutes and then laying the actual wetted out CF and adding the foam core. We used a ton of nuts and bolts to squeeze the mold together super tight. It made for a perfect exterior of the stock. I will pull the gunstock that's the closest to what we want and take a few pics of it and add here.

 

[jrock]

So you did a compression mold from the outside instead of doing a vacuum bag. I like that idea as I'm not really keen on the consumables for vacuum bagging...or cost of a vacuum pump even though I have other uses for such an item. Plus the exterior of the vacuum bagging process would need quite a bit of cleanup.

 

[Tidus56]

So you did a compression mold from the outside instead of doing a vacuum bag. I like that idea as I'm not really keen on the consumables for vacuum bagging...or cost of a vacuum pump even though I have other uses for such an item. Plus the exterior of the vacuum bagging process would need quite a bit of cleanup.

Yes, we made two molds that were identical. Then we added one layer of duct tape lol to act as the thickness of the CF on the foam mold. Then we actually put a 3D printed part to hold the space that our CF chassis would later take up. If you saw my 2 pictures ago you can see a foam with a CF chassis in it. Closed up the mold and then poured the foam using 2 pound marine grade foam.

 

[jrock]

I like your ideas. Lets talk molds. More so interested in the foam mold for material type and release agent...or was the duct tape the release agent?

I'm planning to make a blank from MDF for trial testing the geometries. I assume the finish on the foam doesn't need to be perfectly smooth. If that is the case, do you think I could make a foam mold directly off the MDF? Then make the true CF mold off the MDF after it has been smooth coated with epoxy to ensure a good outside finish on the CF?

 

[jrock]

I was thinking of doing something like this video to make a foam mold and CF mold to account for the CF thickness.

 

[Tidus56]

We buffed and polished our molds. Then used mold sealer and mold release, we did this both under and on top of the duct tape. We put the duct tape on basically perfectly, it took an eternity. However we did find a release paper that we purchased and we're going to use before everyone went back to school. We also used a wax on top of all that, just a light layer and then we buff it away just before the mold was used.
we used the same plug for both the foam mold and the stock mold. The plug was the finished form of our stock, coated in a poly coat so it would release. We had a few issues with the plug releasing in the initial process. I would treat your foam mold the same as your final mold. But no the foam doesn't have to be perfect just real good.

 

[Mram10us]

Great info, guys! Keep it coming. Decided to mask the inside of the stock with painters tape then pour in hot wax. Easily removeable, hard when cools and already a release agent. Learning a lot from your experience, Tidus.

 

[JimmyO]

So we have tried both a foam core and using foam to pressurize and fill the space. We actually ended up getting better stocks with the foam core. We have made a few stocks without any pin pricks or fish eyeing or any other mistakes in the exterior shell. The key to that was putting the epoxy down on the mold, giving it thirty or so minutes and then laying the actual wetted out CF and adding the foam core. We used a ton of nuts and bolts to squeeze the mold together super tight. It made for a perfect exterior of the stock. I will pull the gunstock that's the closest to what we want and take a few pics of it and add here.

I suggest watching the following video of Sako making their carbon fiber stocks.



To duplicate their exact process would likely be cost prohibitive, but it provides some great insight on what could work.. Adopting their method of using a CF sleeve over the foam core, rather than CF sheets, is going to make the stock exponentially stronger.

What I am having a hardest time envisioning is how to get adequate overlap of the CF sheets when using a two piece mold. If you don't have the overlap, you essentially end up with an epoxy seam running the entire length of the stock. I would be very fearful that long term recoil could end in catastrophic failure.

 

[Tidus56]

I suggest watching the following video of Sako making their carbon fiber stocks.



To duplicate their exact process would likely be cost prohibitive, but it provides some great insight on what could work.. Adopting their method of using a CF sleeve over the foam core, rather than CF sheets, is going to make the stock exponentially stronger.

What I am having a hardest time envisioning is how to get adequate overlap of the CF sheets when using a two piece mold. If you don't have the overlap, you essentially end up with an epoxy seam running the entire length of the stock. I would be very fearful that long term recoil could end in catastrophic failure.

Yeah we watched it when we first started up. We also saw what gunwerks was doing and our buddy used to work at Christensen arms. So we looked at a bunch of processes. We decided the hand layup was the best for us at the risk level. As for seams You just wrap a piece around the seams on the foam if that makes sense. Then you overlap and create I believe it's called flashing that has be cutoff. It was getting a stiff enough mold with it closing tight enough that's been are overall issue. It also took us an enternity to make the inletting/chassis area. I will say as a whole the chassis is very cool that we made and functional.

 

[Mram10us]

Ive watched tikka and mcmillans stock building vids. Lots of good stuff

 

[Mram10us]

Filled the stock with hot wax. Dried hard and used a potato peeler to knock it down. Doesn't need to be perfect just has to be flat and allow no mechanical locking when pulling the forms apart