hey all,
I’m in the process of making several bolt action rifle stock molds and am looking for a material to solid fill the reciever and barrel channel areas. I would like to find a material that is heat resistant, lightweight, has strong compresive strength, and is relatively inexpensive. I know this is alot to ask of one product, but I need to find something. Each one will require about 80c.i. After the stocks are molded and filled they will be inletted on a cnc. Thanks!
Jon
Epoxy foam? Does not need a CNC as well…
herman, thanks for your response. I need to clarify that the material will have 2, 1/4" screws going through drilled holes in the fill to attatch the action solidly to the stock. The stocks will be molded with a flat top (no inletting) to accomadate a variety of inletting options. I’m not sure if foam would have the strength for my application. I’ll see if I can find a picture of one of the leading manufactures and post it up soon.
Jon
Here is a couple of pics showing the fill material in a popular manufacturers composite stocks. I don’t know where, but recently I read they were using a material similar to the stuff being used on the inside of bowling balls. I have no idea what this stuff is. I’m sure its not lightweight, but that feature is of lessor importance.
Jon
I would try epoxy + carbon rovings. Heat resistance will be determined by the epoxy used. Use as little epoxy as possible. I’m not sure how well this will machine though?
What do gunsmiths use? There must be a commercially available product specifically for firearms.
wedge,
I’m pretty sure they aren’t using any carbon in the fill as they would be going through truck loads of end mills. There are high temp epoxies available for the final “bedding” process, but that solid fill is a mystery and the big guys intend to keep it that way. I am determined though to find a suitable product for my stocks.
Jon
That material looks more or less solid to me, not a lightweight material.
You could opt for a special mix of 600 kg/m3 epoxy foam (water is 1000 kg/m3) mixed with short glass fibers. At least, that is my thought.
I do not wear guns, nor do I fancy bowling… I do recall having seen a broken bowling ball (must have been at Mythbusters…) which from memory was a very high density foam of some sort.
1: it can be a chopped fiber, or even some other filler like ballons, and a HIGH fvf. You can see it in the first pic, which can be fibers grouping, or density changes in other fillers.
2: it might also be a blowing agent, meant to aerate the material. Like PVC foam…it is NOT foam as we normally think of it. Some tool boxes are made from it.
3: might be compression molded/injected. The fibers and resin would have to be compatible to machine well. If you have the right tools for prodction, anything is possible.
I overread about the carbon. Carbon is not as bad as glass in machining. Just the dust is conductive, which is annoying.
I would really give it a go with a thick epoxy resin, some short fibers and some blowing agent.
riff & herman,
Thanks much for your response! As a novice I’m unfamiliar with the products and terms you listed, specificly “fvf” and “blowing agent”. I did a search on “fvf” and found a technical report on fiber volume fraction but haven’t had a chance to study it yet. Am I looking in the right direction? If you would, please offer a very brief description in laymans terms or direct me to some information to educate myself further. The time you all have taken in answering my posts is very deeply appreciated. It’s great to have such a powerful resource with experts around the globe to a novice such as I!
Jon
FVF is yes, Fiber Volume Fraction, ie: how much stuff you got in your resin. More stuff, higher fiber volume. This way you can create a thick paste, or filling agent that is light weight. The resin is there just to hold it together. More resin, less fibers, means it will be heavier, and maybe crack under high loadings and shocks.
blowing agent is a chemical that creates a foam in a matrix, be it thermoset resin, or thermoplastic. Makes a lighter weight product, in the shape you want in a mold, verses machining foam to the shape.
I have never used it, but I have dealt with plastics enough to understand it slightly 
2 comments:
-more fiber means heavier. Resin has a density of 1,2 kg/dm3 (sorry for metric), carbon some 1,8, aramide 1,5, glass 2,8.
So the higher the Vf (fiber volume fraction) the heavier the product. (and stronger)
On blowing agent: here is a video of a rudder made with epoxy foam. (turn of the sound, unless you like “synthesizer greatest”… )
[ame=“http://www.youtube.com/watch?v=1Pm3EC0YpM4”]Sicomin - YouTube[/ame]