Guys,

How much SS powder do you add to the epoxy to strengthen it against impact? What do you look for in terms of consistency when doing this?

Using some epoxy from K&G that I have found to be brutally strong for knifemaking ... way better than anything else I've seen (such as devcon, west epoxy systems, etc). Is actually pretty thick stuff to begin with.


Thanks!

Hi Mike!

Happy New Year.

If you're talking about bedding, there's really no need to mix any custom epoxy.

The three most popular choices are Acraglas Gel, Marine-Tex, and Devcon Steel Putty.

One target stock builder whose work I admire uses the Devcon. He beds some big boomers, and if this product didn't work, he wouldn't use it.

flaco

Flaco,

I have an epoxy I know very well, and know it holds up better than any of Brownell's, Devcon, or West product. I have it in stock and routinely buy it in 8 oz quantities. Guess what I'm gonna use. The rifle being bedded is a boomer. It has already cracked Acraglas.

I just want to know how what consistency the mixed steel/epoxy should have.

Mike,
I think I remember something like 25% by volume, of powdered metals.

I am just using striaght marinetex, since harry turned me on to it 2 or 3 years ago.

Didn't mean to offend, Mike.

It's just that, well, an epoxy that's great for knifemaking might have characteristics different from one great for bedding.

My reasoning is that to some degree, any time one adds an ingredient to an epoxy, it--to some degree--adulterates the product's balanced chemistry.

So.

While your K&G may exhibit perfect characteristics for knifemaking, adhesion, I'd imagine, and to some degree shock resistance, it might not be best when subjected to the kind of compression that a bedding compound routinely undergoes.

I'd agree that Acaglas probably has least compression resistance of the three I mentioned. Still, it's designed for this use.

It's my understanding that McMillan uses Marine-Tex.

Finally, there's no doubt that the makers of Devcon have, through trial and error, blended epoxy/steel proportions to maximize the strength of their product.

And it's recommended by at least one builder of world class target rifles. Where results are measured in thousandths of an inch. At, say, 600-1000 yards.

Now.

If you're so inclined, feel free to blaze a new trail here. If you can come up with a better method, and care to share, I'm certain we'll all be indebted to you.

I doubt you can screw up too much by just mixing in a little steel. Until it looks good and spreads good.

But I wouldn't. A whole bunch of folks smarter than I have been building these custom rifles--professionally--for a long time, and I like to follow their advice.

Let somebody else make the mistakes.

And... if there's any appreciable benefit to be gained--other than the convenience of having K&G in stock--I'll be very surprised.

Good Luck.

flaco

Flaco,

In real life before I retired I was a PhD chemist and over the years automated a polymer testing laboratory that had every piece of testing equipment known to super science.

The K&G stuff has both better adhesion, compression modulus, and shear modulus than either Marine-Tex or Acraglas. They are good but relatively inexpensive epoxy formulations.

Mike,

Is the metal powder actually going to make it stronger, or is it used as a thixotroph ? I may be wrong here, but I think something like fumed silica (which is a metal oxide) might work better. Probably wouldn't take as much either. I have used it in epoxies in construction,but we weren't concerned with overall strength, we just didn't want the product to sag when applied as a cove base. Fumed silica is actually very common in several different industries. If you've ever worked with it you know it's pretty strange stuff. One of the guys that worked for me called it horse feathers. The sack it came in weighed about as much as the product itself.

Here is a link to a company that makes it.

fumed silica

Hello,
Save yourself a lot of time and effort and use the MarineTex. Understand about your testing, lab, etc., but can tell you over the years the Service Rifle teams over many, many hours of field testing have found the MarineTex really works fine over very extended firing periods. It simply works and if it did not would not be used as widely as it is with those shooting for both "busines" and pleasure.

I have bedded dozens of rifles with Devcon Steel Putty, and it is easy to work with. I don't have to fight gravity or time. I have never had one break.
If a 220 gr 300WM bullet acclerates from 500fps to 2000 fps in .4 ms
F= ma = 220 gr 2000-500 fps/.4ms

=220 gr/7000 gr/ pound 1500 fps/.4ms
= .0314 pounds 3750 fps/s
= 117 pounds
At ~20k psi compression strength of epoxy, the acceleration force is negligible.
The problem is when the 117 pound force builds up some speed, it is like 117 pounds of force on a hammer, it can hit hard. That is what the recoil pad is for, to spread the deceleration over time and area.

Dsiteman,

They've also found that heavier weight bullets generating more recoil are harder on the weapon and bedding than projectiles up to 172 gr or so.

I am bedding a .458 that generates something like 300+ percent of the recoil of a 30-06 loaded with 180s to 2700 fps.

Strictly speaking thixotropy applies to reduced viscosity upon the application of a shear force which returns when the shear force is removed. Not quite sure that it applies in this situation as one is applying substantial compression and shearing forces and the risk is that the polymer will break. Obviously one would not load the mix with so much metal powder that it substantially reduces the linking and cross linking of the polymer to the point that its bulk and shear moduli are substantially reduced.

The section of the stock that supports the receiver recoil lug is backed up by a milled chunk of 7075 aluminum epoxied into the stock so as to create the front of the windowed magazine. The block has substantive length and height so that it's adhesion to the stock should be substantial. Worse thing that can happen (other than breaking the stock behind the tang of the receiver) is that the bedding epoxy may break up.

At any rate, am going to try it anyway as I have the stuff.

Your point(s) are well taken, but on the other hand(as they say!) the dedicated marksman type shooter, match shooter, military shooter, etc. will fire seveal times more rounds in a rifle than several people in a lifetime will in a 458 rifle. "Exposure to constant torture is the true test of loyalty and integrity" I rest my case and good luck.

Mike,
from brownells,

quote:

ATOMIZED METALS
Atomized (finely powdered) metals can be added to Acraglas Gel to increase both tensile and compression strength along with increased impact resistance. This feature allows you to duplex-bed guns using reinforced Acraglas Gel where the recoil lug contacts the bedding and either un-reinforced Acraglas Gel or regular Acraglas for the rest of the bedding. These metals can be added in ratios ranging from 1 part metal to 4 parts of mixed Acraglas Gel, all the way up to 1 part metal to 1 part of mixed Acraglas Gel.

We offer four metals in atomized form: ALUMINUM - Very malleable with excellent machinability for easy drilling, tapping, shaping; polishes to a light gray finish. STEEL - Offers a full 10% increase in tensile and compression strength over unreinforced Acraglas Gel. Less machinable than aluminum reinforced; heavier, too. Resulting finish is a dull black that does not polish well and requires metal working tools for trimming or shaping. STAINLESS STEEL - All the attributes of steel particles but with a medium gray finish and no fear of rust formation on surface of bedding. BRONZE - Between aluminum and steels in workability; finishes to a "metalflake" highlighted, medium brown color and shapes easily using same tools as aluminum.

quote:

adulterates the product's balanced chemistry.

.. only if you don't mix according to directions... X parts resin, Y parts hardener, then add the powdered metal.

AIR BUBBLES hurt bedding epoxy... powdered metals has been used for 30+ years

There is no better epoxy on the market than Devcon Period !.

There are as good as but none better than !.

Epoxies come in so many different formulas I would be here for a week just to define the different properties . Devcon makes a SS epoxy also .

When filleting and feathering Aerospace composite joints I would call for 10-17% to be added . Any more than that is unnecessary and serves no real purpose for strength .

More is for Thixothropic thickening of the epoxy and actually weakens the connection .

For compressive strength it's another matter more Metal powder the better , but then comes the trade off point .

Shoot Straight Know Your Target . ...

thixotropy pertains to fluid states. it also refers to a change in viscosity. adding powders to epoxy to thicken it is not a thixotropic function. it is nothing more esoteric than "thickening."

silica, fumed or not, is not a metal oxide. it is a metalloid oxide.

adding steel or other non-reactive structural metal adjuncts to epoxy will not affect the epoxy's chemical properties. adding nascent sodium might, though....

When referencing viscosity in any liquid or paste it's done in Cp where resin is concerned . Paints generally are done by Zahn or Ford cup measurements .
Viscometer
an instrument that measures the viscosity of materials. An example below .
CONVERSION TABLES
Viscosity

1 cP = 1 mPa·s
1 P = 100 cP
1 Pa·s = 1,000 mPa·s
Sample Volume

1 L = 1000 mL
1 mL = 1000 mL
1 gal = 8 pt. = 3.7 L
1 pt = 16 oz.
Torque Range

LV = 673.7 dyneocm
RV = 7,187 dyneocm
HA = 14,374 dyneocm
HB = 57,496 dyneocm
5xHB = 287,480 dyneocm
Temperature

°C = 5/9 (°F-32)

Adding more of any element or compound to a predetermined mixture does in deed effect the base property value !. More metal powder effects strength as well as elasticity of the epoxy .

Remember this if one adds to much of anything too an epoxy the epoxy can fail or worse yet CATCH FIRE simply by raising it's extothermic value . As can disproportionately mixing the catalyst ( hardener ).

You may take that too the Bank !.

Shoot Straight Know Your Target . ...

delloro,

You're absolutely correct that fumed silica is a metalloid oxide. I wondered if anyone would catch that, but I decided to use the term that Cabot used on their web page to avoid confusion.

Did you also know it's fiberglass ?.

That's the process for making fiberglass Fuming Silica . He is correct about that .

Shoot Straight Know Your Target . ...