How deep could any pitting be? Give me a grinder and 30 seconds and the pitting is gone. Then another couple minutes to "scary sharp."
Most chisels that actually get used a lot end up an inch or so shorter than they started from sharpening over and over and over again over their many years of use.
Decades ago, before you could stop at the local big box and buy new set of disposable chisels for 30 bucks, cabinet shops had to use theirs down to the nubs. It was very common to see chisels ranging from a foot long down to a couple inches. They sharpened and sharpened for years and years and used just about every inch.
I am a sharpening (near) fanatic. All chisels, pocket knives, hunting kniv es, machetes, planes, kitchen knives and my woodturning tools must be nasty sharp. Always. I sharpen my kitchen knives every single time I use them, and my pocket knives (I carry two) usually about once a week or so.
You learn that the time invested on those mirrored edges prized by some are only worth the effort on some cutting instruments, and they are few. I wi ll set aside fine carving tools and certain specialty chisels, but the rest , not a chance.
Most of the carbon chisels are 10XX, usually something like 1084 0r 1087, a nd hardened only to about 55 RC or so... usually less. Makes a good cutter for a short bit, but nothing spectacular. Some are lesser steels, hardene d to even lower points, and worse, incorrectly hardened. This is unlike a g ood plane blade (like a Hock) which are I believe 1095, and IIRC, hardened to about 57-58RC. Harder and better steel, but harder for some to sharpen. The reason they don't harden the steels to higher RC points is because mos t people can't sharpen properly anyway, and people like me that use a cutti ng tools a lot sharpen (and plan to) frequently.
Since 10XX chisels won't hold their edge to my satisfaction, I usually only sharpen to 320gr on my rougher chisels, and 600gr on my finish. Now on a couple of my pocket knives that have VG10, 154CM, and even D2 that are hard ened up to about 60RC, one a bit north, the mirror finish on the edge is wo rth it.
You used to see those chisels ground down like you described because in som e uses a toothier edge yielded better results for cutting. But even a more coarse edge requires sharpening. So off the tradesmen went to their favor ite sharpening device, and the chisels paid the price for poor sharpening t echnique. Like so many pocket knives that have been ground to nothing, the same happens to wood chisels. Until they were stolen, I had a great set o f SEARS chisels that were made in the 70s, and they were my favorites. Har d enough to hold and edge pretty well, but soft enough to sharpen in the fi eld.
I just got a set of Buck Bros. chisels earlier this year at HD, and they ar en't even good enough to call junk. They are worse than awful, completely useless. You can get a razor edge on one, and it is gone in a few cuts. I am trying out some new ones from Amazon as I need a good 3/4" chisel in my kit, always.
Seeing your post made me think of some of the told timers I worked with in the 70s and 80s that had ground off about 2" on some of their chisels and t hey looked like some kind of specialty chisel. I didn't know for some time that they actually had sharpened those bad boys that much.
It's the back of the chisel or blade that becomes pitted. You can't grind those pits out as they're not generally concentrated at the cutting edge, but rather further away from the bevel. You'd have to grind off most of the blade to eliminate the pits.
Yes, pits in the cutting edge itself, or on the bevel side can be ground away. Pits on the back, not so much, and they affect the quality of the cutting edge.
Unless they're either humongous or exceedingly numerous, the fractional area lost would be miniscule. If there's one in the current edge area, it'll go away too if the edge is ground back if it can't be honed away.
seems to contradict the instruction from the maker
quote "Directions. For light rust on steel or cast iron, spray RustFree? on a rag and wipe surface. Do not spray directly on surface, as it may cause spotting. For heavy rust, spray directly on rusted surface and scrub with Scotch-Brite? pad. Wipe off and repeat if necessary. RustFree? works best above 70° F.
CAUTION! RustFree? is acidic and should be used with care.
Test on hidden area before use. Can cause spotting on cast iron and steel. Rinse off painted surfaces thoroughly and neutralize with soap and water. Do not use on guns or black oxide tools. Can dull paint and plastics. Not for spot cleaning of table tops. Do not use on polished cast iron surfaces."
Again, I'd like to see this pitting and ask if it would matter at all. We're talking wood chisels, here, not surgeons' scalpels. I imagine all that pitting would do is create a "serrated" edge at those tiny points. I suppose if it were an issue one could end up using those chisels to "hog out" wood and save their finer ones for finishing up for nice, clean edges.
Why do you refuse to "learn" anything from anyone in here? If you're so worried about those four issues, then I suggest you get out of woodworking altogether because they are all pretty much daily parts of the craft.
First of all, I was referring to your words, "a putty knife to scrape away most of the rust then a wire brush." That's considerably more than simply rubbing the surface with a Scotch pad. It's akin to 40grit belt sander vs. 220 sandpaper to knock off the nubs from cured lacquer.
Using the Scotch-Brite? pads essentially ensures the acid is getting to all the rust. I have found it to be unnecessary for about 80% of my rust removal.
Seriously, rehabbing old power tools is a hobby of mine. Usually when I get one, whatever metal surface isn't painted with be deeply rusted. I've tried EVERY technique purported on the internet short of sandblasting. The only ones that work involve phosphoric acid because of the chemical and physical reactions it has with rust.
When I first started, I went with RustFree's directions and found the scrubbing unnecessary. For tough, deep rust, all that is necessary is to let the product sit a minute or two longer. The reason they tell you to scrub is the same reason they tell you to NOT use it on polished surfaces. Because it will cause spotting. The spotting is the acid somewhat "etching" the metal. Metal workers with use phosphoric acid as a metal priming technique to give the metal some "bite" for powder coating. But that's all it will do. It's not an aggressive or dangerous acid like hydrochloric. That's mostly why they suggest scrubbing; get it on and get it off quick. It does work fast, by the way.
So, here are the conclusions I came up with for using it. The places you have deep seated rust on old tools are NOT going to end up being a smooth polished surface anyway. They are likely cast parts, that have a rough texture to begin with. Like on a saw: the trunnion, the underside of the table, etc. Any parts you that should be smooth, polished surfaces-- like the tables tops of a saw or jointer, or chisels-- are going to need ground out, sanded, and polished anyway. So any "pitting," spotting, or etching done by the phosphoric acid is a moot point, because it'll be sanded out in the process of smoothing out a polished surface.
I'll see if I can get some pictures. I've had plane blades where the back was pitted over more than 50% of the surface. It wasn't possible to grind the cutting edge back beyond the pitting without making the blade too short to seat in the plane.
You'll note my original point was for cutting tools, not just chisels.
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