Gunsmithing lapping scope bases vs. bedding to receiver

[tarfu64]

Forgive me, I am new to the bolt-gun game so bear with me on my question.

In looking at all the posts regarding bedding scope bases, has anyone ever taken a couple thousandths off the "high" side of the base to get it in alignment to the receiver, instead of the whole bedding process? Seems to me this would be just as stress-free, unless this would change the MOA of the base possibly?

Looking at it, I would rather have metal-metal contact than metal-epoxy-metal contact, or am I way off base here? Seems counter-intuitive to in essence "shim" the base.

Thanks for the schooling here, BTW. I have learned an enormous amount from you guys.

 

[Keith Johns]

Re: lapping scope bases vs. bedding to receiver

I like the idea of perfect base to receiver contact more than epoxy, but how are you going to get it perfect? And how long would that take?
It's probably just as good and faster to bed it.

Seekins bases have a groove that makes up a sort of lug for the base to contact the receiver. Mine didnt make contact without bedding it. I didnt put bedding between the receiver and base, but just in the lug Recess so it makes perfect contact.

Many ways to skin a cat. A lot of ways probably work as well as the others in this case

 

[Mgordon]

Re: lapping scope bases vs. bedding to receiver

Check out this thread I started a while back.

http://www.snipershide.com/forum/ubbthre...699#Post1069699

 

[Glen Seekins]

Re: lapping scope bases vs. bedding to receiver

Think about it this way.

Assuming the rings are not lining up because of the base fit..

Making your base fit would be the way to "fix" the issue. lapping to compensate for a base that doesnt fit is just a bandaid..

 

[cdmurphy]

Re: lapping scope bases vs. bedding to receiver

You have two possible sources of misalignment for your scope rings: The rings themselves can be off, or the base can be off. With modern, high quality rings, the problems are much more likely to be in the base, or more specifically in the base's fit the action. Ideally, you want the base, or bases to be perfectly straight and in alignment, then any remaining issues with the rings can be fixed by lapping. If they are lapped while on a straight base, then they will fit properly on any other straight base or at any other spacing on a straight base. If you lap them on a bent or offset base, all you are doing is ruining your rings for use on anything but that base, at that spacing.

The reason everyone recommends using epoxy to correct base to action fit issues is that it works really well, and it's easy. Obviously in a perfect world, metal to metal contact would be better, but there really aren't any user friendly ways to accomplish that. You could always re-machine the bottom of your base, and the top of your action, but that is well beyond the capabilities of most shooters or gunsmiths. If you have way too much time on your hands, look into "scraping", it's a technique used for generating cast iron gages, surface plates and the like. Basically you use a very thin layer of pigment based marking compound on the surface you are trying to match, and press the piece you are trying to make fit up against it. This will result in a few colored spots where the two make contact. You then scrape off a little bit of material at all the colored spots on your workpiece. You repeat this spotting, scraping process over and over until you eventually wind up with evenly distributed points of contact all over your workpiece. It is very time consuming, but if done right, it is possible to make steam tight joints using this method with nothing more than some ink, a scraper, and a lot of time. This general technique can also be applied with grinding stones or wheels if the materials are too hard to scrape.

- Cameron

 

[USMCj]

Re: lapping scope bases vs. bedding to receiver

I bed the base and lap just to be sure. I mean why skip such a easy step and risk damaging a socpe. It takes 5-10 minutes to lap rings, if you are going to be too lazy to do both, Ide suggest taking up another hobby.

 

[tarfu64]

Re: lapping scope bases vs. bedding to receiver

Thanks for all of the replies, but I think something is getting lost in translation. I'm not talking at all about lapping rings, I do that regardless. I'm specifically speaking to the base to receiver fit, nothing to do with the scope rings. Looking at all the "bedded my base today" threads, I find that in some cases it appears from the pics that a few thousandths taken from the front or rear of a base (where it contacts the receiver) would take care of the inequities of base to receiver fit. Instead, I see skim coats of epoxy between the base & the imperfections of the receiver to even things up ("stress free"), when what appears to be 5 minutes of elbow grease and some 400 wet or dry would do the trick and allow metal to metal contact between the two. I'm NOT saying that I think the bedding process is wrong-I'm not that bright to know- I'd just like to get a feel for what we are trying to accomplish and possibly a better way when I go to do this. Thanks again.

<span style="font-weight: bold">USMCj</span> with all due respect who the hell is talking about being lazy??? If anything, lapping the bottom of the base would possibly be more time consuming. This thread has nothing to do with being "too lazy".

 

[cdmurphy]

Re: lapping scope bases vs. bedding to receiver

The only problem with lapping using 400 grit wet/dry sandpaper is that you won't get perfect contact. The extra thickness of the paper will tend to enlarge the radius on the underside of your base slightly. This will lead to contact only in the center of the base, and not out at the edges where you need it for stability. Also if the paper is loose and not glued down, you will tend to remove more material along the front and back edges where the paper buckles slightly as you pass the base over it.

The other main benefit to epoxy bedding beyond a stress free mounting, is that you are bonding the base to your action, taking most if not all the stress off the standard 6-48 screws, and allowing for much heavier recoil without problems.

- Cameron

 

[tarfu64]

Re: lapping scope bases vs. bedding to receiver

Cameron, that makes sense. Especially regarding the unifying aspects of the epoxy base to the receiver, I now "get it". This is the way it should go.

Thanks again to everyone for all the fine help.

 

[nashlaw]

Re: lapping scope bases vs. bedding to receiver

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: USMCj</div><div class="ubbcode-body">I bed the base and lap just to be sure. I mean why skip such a easy step and risk damaging a socpe. It takes 5-10 minutes to lap rings, if you are going to be too lazy to do both, Ide suggest taking up another hobby. </div></div>

My thinking, too. I lap the rings and get less cosmetic damage to the scope body(fewer ring marks). Last night I set up a buddy's .270W and lapped the rings in about 10 minutes, cleanup included.

Little fuss or muss and good return for the time/effort/material expended.

 

[918v]

Re: lapping scope bases vs. bedding to receiver

I agree.

Just because you bed the bases don't mean they will be perfectly in line with one another.

Just because you bed a rail don't mean it is perfectly straight. Cheap rails are often bowed out or inward so you end up with a crooked rail even if you bed.

Lapping is good insurance.

 

[monteboy84]

Re: lapping scope bases vs. bedding to receiver

There is no such thing as machined surfaces mating perfectly, it's a fact of life that we have to deal with imperfections. No matter how you lap or machine the base and/or receiver top, it will never work the way that a proper epoxy bedding will.

The quality of modern epoxies is such that epoxy to metal is nary any weaker than a full metal-to-metal surface mate. Devcon is your friend

-matt

 

[Clark]

Re: lapping scope bases vs. bedding to receiver

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: tarfu64</div><div class="ubbcode-body">Forgive me, I am new to the bolt-gun game so bear with me on my question.

In looking at all the posts regarding bedding scope bases, has anyone ever taken a couple thousandths off the "high" side of the base to get it in alignment to the receiver, instead of the whole bedding process? Seems to me this would be just as stress-free, unless this would change the MOA of the base possibly?

Looking at it, I would rather have metal-metal contact than metal-epoxy-metal contact, or am I way off base here? Seems counter-intuitive to in essence "shim" the base.
</div></div>

I have BOTH milled and then glassed the bottom of the scope mounts.

Years ago Steve Acker in "Home Shop Machinist" showed how hold Weaver mounts in the mill vise with V blocks, and then cut a new concave radius on the bottom with a fly cutter.
I have modified a pair of V blocks to give better access for this process.

When the receiver is drilled and tapped off center, the process of making oblong the mount screw holes and counter sinks are referred to, derogatorily by my peers, as "wallering out".