bedding 17 hmr with j-b weld?
- Thread starter jr.fish
- Start date
Use jb weld, it works awsome! I prefer the JB "marine weld", it's the strongest epoxy they make. I've used it several times on bedding projects and it holds up as good as, or better than Marine tex which i know a lot of benchrest and silhouette guys use.
Avoid jb kwik though, it sets too fast and is not nearly as strong.
The most important factor is you must mix it exactly 50/50, Dont "go easy on the hardener" or it wont set properly. Also you need to make sure it is mixed very thoroughly to activate the chemical reaction properly. Do this and it comes out very very hard. If you have problems after it has set you will have to grind it out with a dremel... and yes you want it to be that hard.
It takes 15+ hrs to set, so you have lots of time to correct any problems you might run into with positioning. Another tip is to mix it about 1/2 hour before you are going to use it so it wont be so runny and will stay where you put it.
Also i prefer johnsons paste wax for a release agent.
Avoid jb kwik though, it sets too fast and is not nearly as strong.
The most important factor is you must mix it exactly 50/50, Dont "go easy on the hardener" or it wont set properly. Also you need to make sure it is mixed very thoroughly to activate the chemical reaction properly. Do this and it comes out very very hard. If you have problems after it has set you will have to grind it out with a dremel... and yes you want it to be that hard.
It takes 15+ hrs to set, so you have lots of time to correct any problems you might run into with positioning. Another tip is to mix it about 1/2 hour before you are going to use it so it wont be so runny and will stay where you put it.
Also i prefer johnsons paste wax for a release agent.
The JBWeld may work "alright" but there are definately better suited products for the job. The main issue that needs to be addressed with epoxies is the shrinkage rate. The off the shelf general epoxies tend to shrink a couple percentage points when fully set. The amount of shrinkage is directly related to the amount of solids content in the epoxy vs the resin content. Devcon 10110 has a high solids content for example and has a shrinkage rate below 1 %. I use ProBed 2000 because its shrinkage is even less, and I prefer the type of solid contents they use in the mixture over the Devcon's. It can also be purchased cheaply in a size much smaller than the Devcon can be purchased.
One way around the shrinkage issue is to use only a thin skim coat, either on the stock directly, or after a preliminary heavy layer has been bonded first (using two stages).
One way around the shrinkage issue is to use only a thin skim coat, either on the stock directly, or after a preliminary heavy layer has been bonded first (using two stages).
No, Jb weld DOES work excellent and has a shrinkage rate of 0.0 and tensile strength equal to any other steel epoxy, and at a fraction if the cost.
ht tp://jbweld.net/products/jbweld.php
The shrinkage rate is not accurate. All epoxy resins shrink...that is a known fact. The amount of fillers to resin ratio determines the amount it shrinks. Tensile strength has little to do with this application, it is compressive strength that applies since you are pulling an action (either with or without pillars) into the material. Along with removing any movement between the stock and the action, the secondary purpose of bedding is to provide a foundation that does not compress between the action and the attaching screw/bolt heads. This in turn provides more consistant bolt torque.
There is a term called "specmanship" you ought to familiarize yourself with if you take a companies claims or specs into consideration. They spend umpteen dollars to provide specs on products that the average joe is intended to see and use as comparison to their competitors claims. All posted general specs on any product can be "legally" backed up with specific data that contains the fine print and explanations how the testing was done. Rarely is this procedure of testing agreed upon between manufacturers or mandated to be followed by an overlooking body such as the government.
To give you an example of how shrinkage rates can be reduced to zero or near zero by a testing facility....
Epoxy product is cast into a tube measuring 1 meter long and parralel end points are measured in the casting die with CMM machine to within +/- 3 microns.
Cast product is removed and measured again and shows a 1% decrease in size measuring .9900000 meters (+/- .000003 meters).
Same product is cast in a die measuring .01 meters long, removed and remeasured. At the same shrinkage rate of 1%, you have now exceeded the tolerance of you measuring machines capability and the number gets rounded to 0.0%....bingo, you have succeesfully decieved the public with totally legit data.
I worked specifically in this field for many years producing specs for products that are designed to "sell" the product. Terms such as "accuracy, percentages/ volume, weight, density; tolerances, limits, repeatability and hundreds more are extremely difficult for layment to understand and are "dumbed" up for the public to interpret exactly how we intend them to be interpreted. One of the best ones to date are when a digital caliper is produced with a resolution of .0005 on the scale. 99% of the public thinks it is accurate to half a thousandths of an inch because of this when in fact the caliper measuring faces could be out of parallel more than 10 times this amount.
Something else to consider. Talk to top level benchrest competitors or their gunsmiths. Ask them if they use JB Weld or another product for bedding that is proprietary made for the application. Devcon 10110, Marine Tex, ProBed 2000 and to a lesser extent Accraglass are the go to products used. Personal preference seems to go to the ones that are easiest to mix properly, have the right viscocity, produce the right combination of compressiveness without sacrificing to be too brittle.
Ok... I get it, you know more about epoxy than I do.
I've used JB marine weld and had zero issues. I've also used marine Tex and acraglass. Same, no issues. Jb marine weld is the cheapest and easiest to work with IMHO. Would I use it to bed a Cooper or high end custom centerfire rifle? No. But for the average 17hmr with little to no recoil I hardly think the type of epoxy used will make any difference other than cost.
We are splitting hairs here. The op asked if jb weld will work and for his application I think it would be perfectly suitable. There is no need to go spend $40-$100 on industrial spec epoxy.
I've used JB marine weld and had zero issues. I've also used marine Tex and acraglass. Same, no issues. Jb marine weld is the cheapest and easiest to work with IMHO. Would I use it to bed a Cooper or high end custom centerfire rifle? No. But for the average 17hmr with little to no recoil I hardly think the type of epoxy used will make any difference other than cost.
We are splitting hairs here. The op asked if jb weld will work and for his application I think it would be perfectly suitable. There is no need to go spend $40-$100 on industrial spec epoxy.
No problem, and in this sense I agree it would be hair splitting. I've both pillared and bedded countless rifles over the years. In reality, there is a bit of uncertainty as to the out come on some rifles that get bedded. Sometimes its remarkable, other times no difference. The guys that do this all the time use the best stuff they can get because it narrows it down as to why its no different, if thats the case. Even with the ProBed 2000, if I used the fumed silica that comes with it to thicken it up a bit, I end up with more air bubbles. Some epoxy is too thick to let the bubbles rise out of the mix when you set the action in it.
I have a neat trick for getting the bubbles out of acraglas, or any epoxy for that matter. After you apply the epoxy to the stock, rest it on a vibrating power tool. I use an orbital sander without the sanding pad, but I've also used a bench grinder which worked just as well, just sit the stock on it for a few seconds and it's like magic, you can watch the bubbles just rise up out of the epoxy. Works amazing! I found that little gem in Bob Brownells' book "gunsmith kinks II".
