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Is Over-polishing a barrel a thing?

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PumaCarl said:
elh0102, I think your conclusions and observations are spot on.


Here's another JB story: I bought a pb bolt gun and in running the bolt I could hear the machining marks catching somewhwere. It sounded like a high pitch zipper zing. Now, everyone always talks about old bolt guns and how they get smooth over time, which is true and got me thinking about it. How many times did hunters shoot there rifles? Seriously. In days of old, who had the time or the money, or the horse, that could carry that much ammo to seriously break in a bolt gun? Not many, which is why it would take so long. Few, and I'm guessing here, would just sit around working the bolt either. I believe most of the old smooth guns came from the factory with a level of finish that is just lost these days. So, I decided to do a second experiment with JB and I slathered my bolt with it and ran my action (I $h!t you not) 5000 times. It did get a little bit smoother but there is sometimes just a little bit of the zing left. JB does a great job at being more abrasive than lead and getting at it, but it is not wearing down steel. I attribute whatever smoothness I got to simple wear of the steel on steel.
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You are referring to lead-lapping in your post I assume?

Hand-lapping is mostly what we do with airguns.

There is also fire-lapping but that can be destructive if not done expertly.

Hand lapping can be achieved with a tight fitting cotton patches on a pull-pull line with the barrel in a smith's vice.
 
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Some general comments about the materials and supplies associated with polishing versus lapping...

Patches or felts are suitable for polishing with a fine abrasive (like J-B), the goal being to remove microscopic surface roughness (fretting) to extend cleaning intervals. That is, make the bore less prone to stripping off and accumulating lead. Being compressible, the patches or felts conform to the variable shapes and dimensions of the bore to scrub all surfaces. For all intents and purposes, no material is removed...it's simply blunting and smoothing the microscopic hilltops of the surface fretting. By "no material" I don't mean literally no material but it will not change the baseline bore dimensions in any way measurable by instrumentation found outside of a space telescope lab.

Whereas cast lead is used for lapping, the goal being to level surfaces, remedy tight spots, etc. Because the goal of lapping is to actually manipulate the bore dimensions, it is generally done with abrasives far coarser than J-B.
 
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NO! Directly from my smithing workbooks, "lead-lapping" is what you are referring to, it is NOT the only form of lapping by a long shot.

Lead lapping does not give consistent results along the length of the bore and that is purposefully done. The donor slug sluffs off as it moves from the breach to the crown, leaving a *tapered bore.

Fire-lapping achieves this in PB's but is destructive in mild steel airgun barrels.

Lapping is defined as two surfaces rubbing together with an abrasive in-between them and yes, you are lapping with a grit on a tight patch.
 
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We agree on the first part:
Firewalker said:
Lapping is defined as two surfaces rubbing together with an abrasive in-between them
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but not on this part:
Firewalker said:
and yes, you are lapping with a grit on a tight patch.
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The idea that lapping may be performed with a soft material is incongruent with every source I can find. For example, the very first result that comes up when I search "difference between lapping and polishing" uses this very point to make the distinction.

from https://www.sciencedirect.com/science/article/pii/B9780815514244500081
Lapping produces a rough surface processed with coarse abrasives and a hard plate tool, while polishing produces a mirror-like surface processed with fine particle abrasives and soft pads.

With lapping there is an emphasis on flatness:

from http://www.southbaytech.com/appnotes/54 Lapping & Polishing Basics.pdf
Lapping is the removal of material to produce a smooth, flat, unpolished surface.

And from https://www.linkedin.com/pulse/difference-between-grinding-honing-lapping-polishing-andres-bellot
Lapping achieves high flatness and surface finish levels, whereas polishing enhances aesthetic appeal.
Lapping provides exceptional flatness and surface quality but is limited to small areas. Polishing focuses on aesthetic appeal and produces highly reflective surfaces.

A soft "lap" cannot produce a flat surface. It can only remove asperities from the surface. Whatever degree of flatness the workpiece had to begin with remains unchanged.

Firewalker said:
Lead lapping does not give consistent results along the length of the bore and that is purposefully done. The donor slug sluffs off as it moves from the breach to the crown, leaving a *tapered bore.
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I disagree here as well. The sloughing nature of the slug has very little to do with achieving a given result, whether that goal is a uniform bore or a tapered bore. It is almost entirely upon the operator as to what result is attained. He must stroke different zones of the barrel as necessary to achieve the result he wants.
 
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Okay, so your point is there is a whole spectrum of lapping substrates ranging from hard to soft. That's fair.

At the same time, it's quite the reach to characterize lead as soft in the context of a conversation where it is contrasted with cotton. And you use the term "soft plate", which seems perfectly fine to describe a lead lap. However I'm looking for cotton lapping plates and it's getting frustrating because all the commercially available lapping plates seem to be rigid materials.
 
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Called off due to incoming rain..

Even Wikkipedia gets in on the discussion:

"The other form of lapping involves a softer material such as pitch or a ceramic for the lap, which is "charged" with the abrasive. The lap is then used to cut a harder material—the workpiece. The abrasive embeds within the softer material, which holds it and permits it to score across and cut the harder material."
 
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Firewalker said:
softer material
Click to expand...
A material merely being softer does not qualify it as a lapping material. Why not? Because a material which is too soft cannot achieve any meaningful shaping or flattening. Every source I can find on the topic of lapping is crystal clear in its purpose being to flatten, shape, contour, "improve the form accuracy" or some similar verbiage.

From the same article you cited:
Lapping can be used to obtain a specific surface roughness; it is also used to obtain very accurate surfaces, usually very flat surfaces. Surface roughness and surface flatness are two quite different concepts.

I wouldn't say lead is the maximally best material to develop very flat surfaces. But cotton, even the compressed cotton of a tight patch, very nearly represents the least good way to develop very flat surfaces.

Cotton is pretty good for polishing and buffing though.
 
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Well, if 100,000 gunsmiths are using the word lapping to describe running a tight cotton patch and abrasive back and forth through a bore...then yes, 100,000 gunsmiths are using the wrong term.

But just to be clear, that wouldn't imply to me that a given individual is being deceptive or malicious, any more than it did when you asserted "yes, you are lapping with a grit on a tight patch." People very innocently substitute one word for another all the time, and in certain contexts it falls into the realm of a distinction without a difference. But in the context of this thread, the distinction is relevant. And as of yet, I have been unsuccessful in locating a single source online, credible or otherwise, that supports the idea lapping can be performed with tight cotton or the like.

Strange, indeed.
 
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I lap every day at work. I use a very expensive lapping machine. I remove material to achieve a goal. I can lap flat or concave. People refer to a lot of things in life using a word that is by definition wrong. We can’t be so anal about it to get in an argument.

IMG_4523.png
 
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