Gunsmithing Questions about epoxy for filling fibreglass stock

[rcampbell]

I have an old fiberglass stock I want to experiment with. I want to fill it so I can inlet it again with my little milling machine. My question is about the type of epoxy I should be looking for. I started out by looking at some epoxies that are used for aircraft parts.

Here's an example of one of the epoxy systems I've been looking at: http://www.aircraftspruce.ca/catalog/cmpages/polyepoxy.php

According to the specs it has a flexural modulus of 515,000 psi and a tensile strength of 9600 psi.

My question is, are these number sufficient for what I'm looking to do with it? Are there some general guidelines I can go by when looking for an epoxy? Will this stuff adhere to the fiberglass that the stock is made out of?

 

[bohem]

Re: Questions about epoxy for filling fibreglass stock

The easiest, cheapest route that I can suggest which I know will work is sold at boat supply stores. "West Systems"

It's not really exceptional at anything except 1 thing. It works on LOTS of things.

It will be plenty for what you're looking to do.

Also, you don't want to just use straight up epoxy here, you want a filler and for that I'd suggest some short chopped fiber glass. West Systems also sells a filler that's almost like a dust. It comes in a pringles size/shape can and costs about $15 for the can full of fluff.

Prep the stock with some rough sandpaper, scuff things up really well to get good adhesion.

Clean it with a tack-free cloth and MEK or Acetone (you might want to wear nitrile when handling these things).

Whip up a batch of that goop with filler in it, work it into the corners well and fill'r up.

 

[E. Bryant]

Re: Questions about epoxy for filling fibreglass stock

+1 for bohem's whole post. I've used the West System stuff quite a bit on firearms projects and a bunch of other stuff (including a composite chassis for a solar race car in college), and it's worked quite well.

Just be careful when mixing larger batches (more than an ounce or two) - spread it out over a cutting board or piece of glass and "fold" it with your applicator to mix it, instead of using a cup. Else it may "cook off" if the exterior temperature is high enough. Plus, you're more likely to avoid bubbles by mixing it by folding on a flat surface.

 

[dinc]

Re: Questions about epoxy for filling fibreglass stock

Fill out your profile so we know where you are.

Tap Plastics has a lot of information about glassing supplies, epoxy, fillers, cloth, and you can get small amounts for experimenting. Their staff will usually answer lots of questions informatively.

Boat supply stores usually have West Systems epoxy. I used to get 1 hr epoxy at Home Depot but haven't seen it lately. A rough rule is the longer epoxy takes to set the stronger it is.

There are different epoxy fillers for differant applications. Ground glass for thickening and strengthening, microballons for lightweight (not for strengthening), and chopped glass for stongest filler. You can add metal filings for strength but sometimes adheasion is a problem.

 

[Al_Ski]

Re: Questions about epoxy for filling fibreglass stock

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: E. Bryant</div><div class="ubbcode-body">+1 for bohem's whole post. I've used the West System stuff quite a bit on firearms projects and a bunch of other stuff (including a composite chassis for a solar race car in college), and it's worked quite well.

Just be careful when mixing larger batches (more than an ounce or two) - spread it out over a cutting board or piece of glass and "fold" it with your applicator to mix it, instead of using a cup. Else it may "cook off" if the exterior temperature is high enough. Plus, you're more likely to avoid bubbles by mixing it by folding on a flat surface. </div></div>

Yup. Use the West Systems Epoxy, the filler is called micro balloons. The strength and sanding ability can be controlled by the volume of filler you add to the epoxy.

 

[rojkoh]

Re: Questions about epoxy for filling fibreglass stock

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: rcampbell</div><div class="ubbcode-body">I have an old fiberglass stock I want to experiment with. I want to fill it so I can inlet it again with my little milling machine. My question is about the type of epoxy I should be looking for. I started out by looking at some epoxies that are used for aircraft parts.

Here's an example of one of the epoxy systems I've been looking at: http://www.aircraftspruce.ca/catalog/cmpages/polyepoxy.php

According to the specs it has a flexural modulus of 515,000 psi and a tensile strength of 9600 psi.

My question is, are these number sufficient for what I'm looking to do with it? Are there some general guidelines I can go by when looking for an epoxy? Will this stuff adhere to the fiberglass that the stock is made out of?</div></div>

If you're patient, I have about 75% of all commercial bedding products and I'm about to start testing them for impact and shear.

Only delay has been weather and working out a way to cast blocks.

I normally use ACRAGLAS for semi-auto rifles because I know if it's strength and durability to stand up to constant pounding for semi auto's like the 14 types. Putty will not stand up this well, with the except of some of the newer products I haven't tested like Devcon titanium. I will be testing them.

Quick note: I bedded my first M1A in 75, a Devine Tx rifle. I did it with ACRAGLAS and it lasted 2 and 1/2 barrels (USGI NM barrels which was the only NM barrels available in those days).
Equate that to 7-10,000 rounds per barrel.

 

[Whiskey Tango Foxtrot]

Re: Questions about epoxy for filling fibreglass stock

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body">The easiest, cheapest route that I can suggest which I know will work is sold at boat supply stores. "West Systems"

It's not really exceptional at anything except 1 thing. It works on LOTS of things.

<span style="color: #3333FF"> </span>
It will be plenty for what you're looking to do.

Also, you don't want to just use straight up epoxy here, you want a filler and for that I'd suggest some short chopped fiber glass. West Systems also sells a filler that's almost like a dust. It comes in a pringles size/shape can and costs about $15 for the can full of fluff.

Prep the stock with some rough sandpaper, scuff things up really well to get good adhesion.

<span style="color: #3333FF"> </span>
Clean it with a tack-free cloth and MEK or Acetone (you might want to wear nitrile when handling these things).

Whip up a batch of that goop with filler in it, work it into the corners well and fill'r up. </div></div> <span style="color: #3333FF"> </span>

<span style="color: #3333FF"> </span> Clean BEFORE and after you sand.
I have been using WEST system for a couple of decades, used to build high performance vacuum bagged carbon fiber sailboards and now build race car parts with it. There are better resins but west is pretty darn good.
I also use it for bedding

 

[sirhitalot]

Re: Questions about epoxy for filling fibreglass stock

use alot of ballons and put the cup in a bath of ice and water while you mix / wait for it to start to go in "attack" mode. If it gets too hot, ad some salt in the water / ice mixture and the temp will fall to 0 deg. F / -15 deg C. Even the smallest amount of West systems epoxy can overheat...

 

[rcampbell]

Re: Questions about epoxy for filling fibreglass stock

Wow thanks for all the input guys. I'm quite familiar with making stocks from Rutland laminate, but this whole epoxy/fiberglass world is a little confusing for a newb.

I had a look at West Systems website. I assume you are referring to the 105 system? I noticed one of the fillers they have is microfibers, is this what you are referring to?

Also, what would be the difference between using that and using chopped strand mat (CSM)? Could I just get a "regular" fiberglassing resin and use CSM to fill my stock in?

Thanks in advance for the advice and patience.

 

[ejg]

Re: Questions about epoxy for filling fibreglass stock

Goal is: very strong bond with the existing stock, good compression strength and no overheating while curing.
Forget Polyester resin for this. Choose a laminating Epoxy resin with a low viscosity which helps add a higher content of solids. Also choose a resin/hardener with a very long pot life.
What we use for filling an inlet is the same aero approved resin that we also use for making a stock. Pot life well over two hours. Fill with a cocktail of aluminium powder, 3mm carbon, 0.2mm glass and some micro balloons. Using a few different sized fillers helps increase filling or packing ratio.
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