Gunsmithing Bedding with or w/o coating?

[Punisher29073]

If you were bedding an action in Devcon, and you were going to coat this rifle in Duracoat(1-1.5 mils thick), would you bed prior to coating or coat prior to bedding? Is the thickness of the coating enough to make a difference in the bedding?

Ryan


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[...]

definitely bed AFTER coating.....1.5mils doesnt sound like much.......until you have to fit an action into a perfectly bedded stock.

 

[GH41]

What he said ^^^^^^^^ If you could keep the coating at 1.5 mils (You cannot) it still adds up. Remember.. It adds up on all sides.

 

[Punisher29073]

That was my inclination. Thanks. Just wanted to make sure I wasn't over thinking it.

ryan

 

[Wannashootit]

I Cerakote after bedding and no indications of any problems caused by it. I'm not going to risk any cosmetic issues from release agents, etc on a finished rifle if I can help it. Will the epoxy flex one thou ea side to make contact when the action screws are torqued down? Dunno- guess I should pass that along to my son the Engineering major studying Materials Properties

 

[FCrifles]

I like to bed after coating, you just have to be more careful.

 

[...]

I Cerakote after bedding and no indications of any problems caused by it. I'm not going to risk any cosmetic issues from release agents, etc on a finished rifle if I can help it. Will the epoxy flex one thou ea side to make contact when the action screws are torqued down? Dunno- guess I should pass that along to my son the Engineering major studying Materials Properties

Devcon has a cured hardness of shore 85D......to put that into perspective, a hardhat has a hardness of shore 75D.......and a compressive strength of 8,260 PSI......i really wouldnt count on it moving much if any from the torque of an action.

now.....Devcon shrinks .0006 inch per inch......assuming you have 1/4" at most.....you are going to shrink .00015".....which in the grand scheme of things.....nothing significant.

now the problem you run into with the coating is ensuring a uniform thickness........which is almost impossible to due.....you could have one area 3 mils....another area .5 mils.


noooooow, the fuck does all this mean?......well essentially the more variables you introduce after the bedding, the less consistent your bedding will be.

but is a discrepancy of a mil or two in the bedding going to cause accuracy issues?....honestly i cant say.......the engineer in me wants to say yes.........the practicalist in me wants to say, eh, probably not to any significant degree....especially considering all the other issues that are going to effect accuracy.

 

[WeiserBucks]

I posted a similar question awhile ago, everyone recommended bedding after the coating was applied. I went that route and everything came out great , especially for my 1st DIY bedding job .

 

[LRI]

Devcon has a cured hardness of shore 85D......to put that into perspective, a hardhat has a hardness of shore 75D.......and a compressive strength of 8,260 PSI......i really wouldnt count on it moving much if any from the torque of an action.

now.....Devcon shrinks .0006 inch per inch......assuming you have 1/4" at most.....you are going to shrink .00015".....which in the grand scheme of things.....nothing significant.

now the problem you run into with the coating is ensuring a uniform thickness........which is almost impossible to due.....you could have one area 3 mils....another area .5 mils.


noooooow, the fuck does all this mean?......well essentially the more variables you introduce after the bedding, the less consistent your bedding will be.

but is a discrepancy of a mil or two in the bedding going to cause accuracy issues?....honestly i cant say.......the engineer in me wants to say yes.........the practicalist in me wants to say, eh, probably not to any significant degree....especially considering all the other issues that are going to effect accuracy.

Sooooo, if I go buy a .025" thick piece of inconel, titanium, kryptonite, or whatever, and I have a sheet of this stuff sitting on my table, does that mean I can't bend it? After All, it has material properties that far exceed anything quoted by an epoxy manufacturer.

Let's put this into context:

The stock will flex to accommodate a .003" deviation in dimensions. (which is what 1.5mil works out to on both sides) No bedding is going to magically resist this when it's applied at maybe a .02" in film thickness by most who skin bed a stock. I surface inlets to generate a .05" film thickness and it will still distort. Sit and figure the tensile psi loading of a guard screw once. That is mechanical advantage in one neat little package. It will pull the thing together.

A very compelling argument has been made that to some degree the distortion is desireable. It's been proven at some level, although much more beta testing is needed to really validate it.

The stock will budge, the bedding will yield, and I'd bet a steak dinner the gun will shoot just fine. It's just duracoat which is nothing more than watered down tractor paint from Sherwin Williams. Polane T if I recall.

Good luck.

 

[Punisher29073]

Thanks. Much more technical than I can debate answers given, but it sounds as if it may not matter. I went ahead and coated the barreled action last night to give it a weeks cure time before my Grayboe stock gets here Monday. I have to have the rifle together by next Friday in order to shoot the MPA match on 4-8,9 and my 6.5cm match rifle barrel gave up the ghost during their club match 3 weekends ago. I was hoping it was operator error, but after shooting groups for the last 2 weekends to confirm, it has opened up to 2" groups and the throat is so long I cant even get near it with mag length rounds.

Ryan

 

[Wannashootit]

I wouldn't take that steak dinner bet from Chad. I looked at the Devcon specs before I decided which way I was going to do these long ago, then just figured regardless of shrinkage, elasticity, and all the shit I'm not technically qualified to evaluate there wasn't a strong likelihood that 40-50 in/lbs of torque wouldn't pull the action down to the bedding.

I think this is one of those many areas of minutiae that we often get into that make for interesting discussion, but (as he noted) have no effect on the results at the target. Perhaps a thin layer of Hi-Spot Blue along the very bottom of the receiver channel would confirm contact (meaning the necessary flex occurred) and resolve the question (?)

 

[...]

Sooooo, if I go buy a .025" thick piece of inconel, titanium, kryptonite, or whatever, and I have a sheet of this stuff sitting on my table, does that mean I can't bend it? After All, it has material properties that far exceed anything quoted by an epoxy manufacturer.

Let's put this into context:

The stock will flex to accommodate a .003" deviation in dimensions. (which is what 1.5mil works out to on both sides) No bedding is going to magically resist this when it's applied at maybe a .02" in film thickness by most who skin bed a stock. I surface inlets to generate a .05" film thickness and it will still distort. Sit and figure the tensile psi loading of a guard screw once. That is mechanical advantage in one neat little package. It will pull the thing together.

A very compelling argument has been made that to some degree the distortion is desireable. It's been proven at some level, although much more beta testing is needed to really validate it.

The stock will budge, the bedding will yield, and I'd bet a steak dinner the gun will shoot just fine. It's just duracoat which is nothing more than watered down tractor paint from Sherwin Williams. Polane T if I recall.

Good luck.

nooo....in fact im pretty sure you could bend it without too much issue.....but ide bet you that steak dinner you couldnt squeeze it any.......same applies with the bedding compound, once that is cured, your gonna need some gusto to get that to compress any (which is what you would see on the bottom of the action)

now on the sides of the action....if you are dealing with a wood stock.....you could probably get the stock to flex 3 mils...........but on a composite stock like a manners/ Mcmillan.....i really dont think you are going to get that stock to budge much at all.....but even if it does....that still leaves the bedding under the action that isnt compressing.

now like i said before......i really dont think a 3 Mil discrepancy is going to cause accuracy issues.....that im pretty sure of ..if you bed your action, then coat it with a reasonable thickness of paint......i really dont see it causing a noticeable shift in accuracy......this whole hullabaloo over bedding compressing is just an discourse in theoretical behavior of the material.

 

[Threadcutter308]

Sooooo, if I go buy a .025" thick piece of inconel, titanium, kryptonite, or whatever, and I have a sheet of this stuff sitting on my table, does that mean I can't bend it? After All, it has material properties that far exceed anything quoted by an epoxy manufacturer.

Let's put this into context:

The stock will flex to accommodate a .003" deviation in dimensions. (which is what 1.5mil works out to on both sides) No bedding is going to magically resist this when it's applied at maybe a .02" in film thickness by most who skin bed a stock. I surface inlets to generate a .05" film thickness and it will still distort. Sit and figure the tensile psi loading of a guard screw once. That is mechanical advantage in one neat little package. It will pull the thing together.

A very compelling argument has been made that to some degree the distortion is desireable. It's been proven at some level, although much more beta testing is needed to really validate it.

The stock will budge, the bedding will yield, and I'd bet a steak dinner the gun will shoot just fine. It's just duracoat which is nothing more than watered down tractor paint from Sherwin Williams. Polane T if I recall.

Good luck.

"Tractor paint".....now that's funny stuff. I think the most recent comments by Chad and others basically boil down to "at the end of the day, it doesn't make any difference, practically speaking". I've done it both ways in the past. I used to bed first, then paint/finish, because the finishes available 20 years ago were quite delicate. Conversely, I bedded a Cerakoted Bighorn TL2A with Devcon in a Manners T2A this weekend and everything turned out just fine. I think you run into a problem if you apply the finish/Cerakote/Durakote thicker than a French Whore's makeup, then you'll have interference issues. I recently saw a Cerakote job that was so bad, I could barely make out the S/N on the action because of how thick the Cerakote was applied.

But, with the durability of the new finishes, I don't have any problem bedding with Cerakoted barreled actions.

 

[Yoteslayer50]

I have done it both ways if I do bed before paint I cover bedding with tape to keep paint off. Painting the bedding makes me feel like I'm trying to cover a crappy bedding job up just my 2 cents

 

[300sniper]

Maybe having a .001-003 of interference fit is a good thing? I mean if you're after a stable union, .004-.006 of press fit (and a minor plug weld) keeps your 1ton truck axle tubes secured to the cast center section. I doubt there are any negative issues with this kind of fit in an open top situation such as a cylindrical receiver in a open top composite stock.

 

[LRI]

nooo....in fact im pretty sure you could bend it without too much issue.....but ide bet you that steak dinner you couldnt squeeze it any.......same applies with the bedding compound, once that is cured, your gonna need some gusto to get that to compress any (which is what you would see on the bottom of the action)

now on the sides of the action....if you are dealing with a wood stock.....you could probably get the stock to flex 3 mils...........but on a composite stock like a manners/ Mcmillan.....i really dont think you are going to get that stock to budge much at all.....but even if it does....that still leaves the bedding under the action that isnt compressing.

now like i said before......i really dont think a 3 Mil discrepancy is going to cause accuracy issues.....that im pretty sure of ..if you bed your action, then coat it with a reasonable thickness of paint......i really dont see it causing a noticeable shift in accuracy......this whole hullabaloo over bedding compressing is just an discourse in theoretical behavior of the material.

But we're not talking about squeezing it. The mere fact that a stock would likely have pillars fitted mitigates the compression you are describing. Its the fundamental purpose for using them.

What were dealing with here is a cylindrical body attempting to be squished into another cylindrical body (that's been split in half). The argument is the added film thickness from an applied finish skews the relationship.

It's been my experience that it doesn't. Stocks distort quite easily It is not difficult to budge a thou or two. It's not hard to budge one 10 or 20 thousandths. A painful lesson I learned 14 years ago when I started inletting them... By budge I mean I can bend it across its length. In this application I can "bellmouth" the showline a few .001's with no fear.

Carbon Fiber: Wings, boat hulls, fishing rods, the list goes on... None of these products are static pieces of granite. They flex, compress, elongate, etc... CF is really good at doing that.

 

[bikerman9967]

But we're not talking about squeezing it. The mere fact that a stock would likely have pillars fitted mitigates the compression you are describing. Its the fundamental purpose for using them.

What were dealing with here is a cylindrical body attempting to be squished into another cylindrical body (that's been split in half). The argument is the added film thickness from an applied finish skews the relationship.

It's been my experience that it doesn't. Stocks distort quite easily It is not difficult to budge a thou or two. It's not hard to budge one 10 or 20 thousandths. A painful lesson I learned 14 years ago when I started inletting them... By budge I mean I can bend it across its length. In this application I can "bellmouth" the showline a few .001's with no fear.

Carbon Fiber: Wings, boat hulls, fishing rods, the list goes on... None of these products are static pieces of granite. They flex, compress, elongate, etc... CF is really good at doing that.

carbon is a good example. it moves all over the place. we have some laminates which are over .75 thick and you can still bend it somewhat.

 

[Edds]

How thick is the film of release agents being used?