Advanced Epoxies for Bedding Platform

[Stocky]

The past few weeks I have had what you might consider to be an awakening in the world of epoxies as a result of my own endeavors to keep large fiberglass / plywood rockets from flying apart at supersonic velocities. This could all be somewhat irrelevant one could argue, as we have some great products available (i.e. Acraglas, Devcon, Marinetex, etc.) but allow me just a moment to encapsulate my findings and see if anyone has any thoughts.

I have no affiliation with anyone in the epoxy industry, just offering these discoveries as food for thought, perhaps as fodder to take this whole bedding thing to the next level.


Here's a few facts:

• Epoxy does not mix chemically at a 1:1 ratio. More in the range of 3-5 resin to 1 hardener.
• Fillers are added to arrive at this convenient mixing figure.
• Gels and putties have such additives, that's why they are gels and putties.
• Such additives can easily be mixed in by the user to desired results.
• Epoxy cures to an inert plastic solid that sticks to nothing.
• Adhesion comes from a property called keying and results from the epoxy soaking into the material and hardening.
• Therefore, the thinner the epoxy and the longer it takes to cure, the more it soaks in.

Kind of nukes the 'steel putty is the best' concept, no? Thinner the better from a bonding perspective, but see below.

Since we are concerned with perfection as opposed to 'it's worked O.K. for 20 years why change' for the sake of this discussion, here's what the adhesion pros do outside the sporting arms industry. A great example would be some engine mounts in a yacht - we want them to fit the base of the motor perfectly, have the required adhesion to the structural components of the yacht and be able to take the pounding that a pair of turbo-diesels can dish out over a period of years. But they wouldn't want the engines permanently affixed, might have to pull them for service. Just a set of perfectly mated mounts with the mounts permanently mounted to the boat.

That ought to cover anything we'd dish out... for the purposes of this discussion we'll use West System 105 resin because it is available with a variety of hardeners to vary curing time as well as fillers to increase viscosity, it's a complete epoxy system. We need to make it thicker because it's not going to stay in place and make a good mold of the engine mounting bracket (barreled action) when it's in it's neat form - about like Karo syrup. (neat = no additives)

1. Start by degreasing and subsequently roughing up the area in question to increase the surface area of adhesion.
2. Mix up some resin with the appropriate cure-time hardner 'neat'
3. Thoroughly wet-out the area of the stock until the thin mixture saturates the material.
4. Add the desired filler (fiberglass fibers, aluminum shavings, colloidal silica, etc.) to balance of mixture.
5. Lay-in thickened mixture.
6. Replace barreled action and finish as usual.

First off one of the most important points I take away from all this is that by wetting-out the stock with neat epoxy one would achieve a far stronger bond with the stock that all the steel in the world mixed into some kind of putty. It'd be far better to wet everything out neat & add your own filler to increase strength and/or thicken the mixture when ready. This way you'd have an homogenous adhesive platform penetrating deep within the stock with required strength and 'body' in the required areas surrounding the receiver.

One example would be the West Systems 404 High-Density filler is designed just for that -

"404 High-Density filler is a thickening additive developed for maximum physical properties in hardware bonding where high-cyclic loads are anticipated. It can also be used for filleting and gap filling where maximum strength is necessary."

I doubt if I'd use that particular filler unless I needed to bed a really big boomer in a thin stock, but it is recommended for motor mounts so I'd think it can take it. Weatherproof too. There's fillers designed for body, strength, weight reduction, etc., seems to me that the something as flexible as this could be tailored to the conditions that the particular rifle would be subjected to.

Has anyone ever tried anything along these lines? What fillers have you experimented with?

Food for thought anyway ...

- Don

Research links:
Epoxy by the Leading Epoxy Manufacture | WEST SYSTEM Epoxy - West Systems Home
WEST SYSTEM | Use Guides - Education in the epoxy world
Aeropoxy Home - More great epoxies - I use 6029 & 2032 a lot

 

[AJ Peacock]

Interesting post.

I don't know that we need much in the way of adhesion (wetting down stock etc). I've never seen any of the typical bedding materials 'not adhere' to a stock.

Assuming that all the leading epoxies, steel putty's etc. have good shrinkage properties. My #1 criteria is ease of use. Devcon steel putty fits my methods as good/better than anything else I've tried. No objectionable smell, good working time, ease of mixing and perfect thickness for bedding stocks.

AJ

 

[treeman59]

if you don't have to work on the bedding with sharp tools powdered glass works really well as a filler and can be added more or less to acheive desired consistency. but it is hell on cutting edges on files and chisles

 

[Stocky]

Interesting post.

I don't know that we need much in the way of adhesion (wetting down stock etc). I've never seen any of the typical bedding materials 'not adhere' to a stock.

Assuming that all the leading epoxies, steel putty's etc. have good shrinkage properties. My #1 criteria is ease of use. Devcon steel putty fits my methods as good/better than anything else I've tried. No objectionable smell, good working time, ease of mixing and perfect thickness for bedding stocks.

AJ

I have has them not adhere, especially the putty HS Precision supplies with their Win 70 stocks. Falls right out. No way I'd use it or any putty.

 

[kiwi3006]

I have started making my own fibreglass rifle stocks and am using the West systems 105/206 system for the shells with 6oz cloth.
To make the action area I use the same resin/hardner combo and add 403 filler until I get the consistency I am after. This seems to be working well it has taken about 20 shots from my 7mm mag so far with no problems.

I did bed the action with acraglass though, but only because that was what I used in the past. I don't imagine the West systems being any weaker.

Here is some tech info from the West Systems and Devcon websites. The west systems is stronger in compression yield and flexural strength. Not quite a fair comparison as the West systems had 14 days to cure while Devcon had 7 days to cure.


West Systems

Devcon

Stu.

 

[zupatun]

I use West Systems 105 quite a bit, but for carbon fiber and fiberglass applications mainly. This stuff is the bees knees for most applications where you'd glass something.

That said, I think there are other very good systems for various applications on the market. I think the key is to also think about shrinkage during curing and thermal expansion of the final set material.

I haven't looked into what filler/West Systems epoxy combo would have the ideal properties, nor have compared them to Marine-tex, Acraglas, Devcon et al, but I think that would be the next step toward evaluating your proposition here.

Matt