"Sharp enough to shave the hair off a flea's leg" is sharp enough for me (or plane iro
Now I'm going to start out with a disclaimer: "I am in no way an expert in the area in which I'm about to bloviate". If you want expert advice go to Chris Swartz's web page or read Ron Hock's book THE CUTTING EDGE. These guys are experts of the highest degree and there are many, many others. I'm only going to tell you what I've found works for me through my experiences sharpening plane irons, blades, cutters, whatever you like to call them. It's all pretty simple, unless of course you are a perfectionist, which I'm not, (but I play one on TV). I've found that the key to a well tuned, super performing plane is a sharp cutting iron. Others like flaaaaaat bottoms, I like sharp cutters. I've owned Junkers, I mean real crapalinear planes, that I can get to work reasonably well by sharpening the iron to as fine a degree as I can within the limits of my capacity. There are those who would scoff at such an idea and you might just be one. But why should one scrap grandpa's old Shelton or Capewell smoother just because it's not a Bailey? Answer: you shouldn't. Maybe it will never perform like a Bedrock, Bailey, Bridge City or even a good early Sargent, but it will do everything it was designed to do and do it pretty darn well, so long as the iron is clean and sharp.
I think most or our homeowner predecessors had a plane sitting on a makeshift workbench in the 1950s garage for looks. I don't believe many really used them for much simply because the didn't know how. My dad was one of those guys. I think he got his old Stanley from a church rummage sale and thought it looked cool and might come in handy to shave down a swollen door sometime. Well, it did look pretty cool but it never moved from the workbench to do anything except once that I remember when my mom got tired of waiting for my dad to actually trim the swollen and sticking door and told me to do it. So, I did. Now that door never quite looked or performed correctly after that but it didn't stick anymore and she was satisfied.
I took woodshop in high school and I loved it so much that I took three classes of it, two of which were teacher's assistant or "TA" for which I got the admiration of the shop teacher and a couple extra credits. Yep, we learned about planes, what they were used for and how they kind of worked. We got tested in making shavings and it was the only thing I didn't do well in that class because I didn't know about sharpening them. Consequently the plane became a useless tool to me much as it had my father until about 5 years ago. I learned then what I should have learned in high school. Planes are good when they are sharp and boat anchors when they aren't. Unless its a collector, it has to be sharp to be able to do what it was intended to do. I even sharpen my collectable planes because I believe that they should be in working condition.
I sell a lot of planes and none leaves my shop unless it's sharp enough to "shave the leg hairs off a flea", pretty sharp though not sharp enough for everyone but most folks shouldn't be trusted with things that can kill them by just
looking at them. So, if you're like me and want an iron that will make "wispy fine shavings" but don't have enough time to make it surgical grade, read the next few paragraphs and you might learn a little bit. AGAIN, I'm not an expert.
The first thing I do is set the bevel angle on my grinder. Yea, I know. the purists are already condemning me to hell because you should never use a power tool on a cutting blade. Well I do. My grinder is variable speed and I use the slowest speed. Deal with it. I try to set the guide plate on the grinder at 25 degrees so it's useful to have an iron that's already there to use as a guide. Set the bevel side down on the grinder plate with the known bevel touching the grinding stone. Then match up the bevel to the edge of the stone as close as you can get it. You can fine tune the bevel later. Now very gently run the dull iron across the stone which is turning at very slow speed until you have a nice even bevel across the entire edge. Now remember that this process causes friction and that steel is going to get hot so it's really important to douse it in water a lot to keep it cool. Get that black/blue steel streak and the metal is going to be really brittle and chip out. So, keep it cool. Once you have a nice even bevel you can go to step two. Flattening the back side (or front side depending on your point of view.
I use diamond sharpening stones first to do this starting with extra extra coarse. Hold the flat side of the iron flat against the edge of the stone and move it laterally across the surface. It's probably the most tedious part of the process but also the most important. The flat side of the iron needs to be flat, flat flat and you can tell when it is when the scratches from running across the diamond plate are evenly distributed across the iron. Sometimes it takes me several hundred strokes to get there. If the area is badly pitted you have two choices. Work harder or throw the darn thing away. I never throw them away so I just keep working on it until the pits are gone and all I have is clean bare steel. It also makes it easier if you angle the blade up a degree or two so that the focus of the friction is on the leading edge of the blade. Some folks use a small flat steel ruler as a guide by laying it along the edge of the diamond plate and running the iron across it laterally as they lap against the plate. The angle can be increased by moving the edge of the iron closer to the ruler and decreased by moving the edge farther away. Any imperfections close to the cutting edge are removed more quickly as the steel is ground away.
Now you've learned the technique you just have to repeat it on progressively less coarse materials. Next one I use is an extra coarse, then a coarse, then a medium, fine and extra fine diamond plate. After that I go to wet/dry sand paper at 400 and 800 grit. I do use a Japanese wet stone at 4000 and 8000 grit down the road a bit at the very end of the process but I'll talk about that later. What you end up with is a not so clear mirror but clear enough to see you sweaty face because this takes a bit of effort.
So, you've already set your bevel with the yukky grinder (cringe) so the next step is to refine the bevel surface. Some really great craftsmen can do this free hand but that's why they are really great craftsmen. I'm not that good so I use a guide. Not the really expensive ones that you can get from Lie Nielson or Veritas. Just the cheapo 15 buck one you get off eBay or someplace similar. They come with simple instructions and when they start to get sloppy I toss them. They should be good for a couple hundred sharpening's which for me is about a year. I have two that I use concurrently just in case I want to torture myself by doing two irons at a time. Now there are literally dozens of these guides on the market and some are really expensive and some are junk. Get one that matches your needs and your pocket book. If you are going to be sharpening your plane iron once a year why waste the money when a 15 dollar one works just as well?
So the instructions include a guide that tells you the angle of the bevel depending on the distance from the front edge of the honing guide to the leading edge of the iron. It's just the distance measured between the two. 25 degrees is or 30 degrees are stamped on the side of the guide in millimeters. I've just measured them once and drew lines on my workbench so I have only to put the blade in the guide, lay it against the side of the bench and move the blade till it meets the line on the bench. Simple enough.
Once you've established the bevel angle in the guide you are set. I like to run the bevel over my extra extra course diamond plate a couple times and adjust the set of the blade in the guide so it matches the 25 degree angle that's already established. It makes the job go faster doing it that way than trying to remove a bunch of hard steel. So now, run the guide with the attached plane iron over the diamond plate until the old grinder marks are all gone and the edge is nice and square with no little chips. Squareness (I like to call it "squarity) is also important when you are going through this process so keep a little bitty square handy and check the cutting edge to side edge a lot, adjusting finger pressure to the high side as needed. It doesn't have to be perfect because your lateral adjusting lever can make the minute changes you may need down the road. Now you just keep going over the progressively less course surfaces you used in the flattening stage until you get down to that beautiful mirror like surface you have on the flat side.
You are going to notice that there is a rough edge forming on the opposite side of your blade from the side you are working on. That's called a burr or wire. It will remove itself as you get that cutting edge finer and finer or you can roll it off with your finger if you dare. When you get to the 800 grit wet dry paper flip the iron over with the guide still attached and reflatten the flat side again. Maybe 20 or so strokes. That helps remove the burr as well. I like to alternate between doing the bevel side and the flat side a couple times until that edge is not quite sharp enough to shave the hair off the flea's leg...but almost.
If you want to go further, which I usually do, I will use the 4000/8000 grit Japanese water stone using basically the same process as before except I usually only draw the iron away from me in one direction, about 50 strokes on the 4000, then flatten the back like before, and then with about 50 strokes on the 8000. I finish it by raising the bevel edge about as little as I can while still making full contact with the stone just to concentrate a tiny bit of pressure on the very edge to loosen any residual molecules still hanging on to the bevel. I very gently do the same on the flat side too. If you did a good job you will be able to easily shave the hair off your leg or arm with very little pressure. This is not a highly recommended technique as you can inflict real serious damage if you did a really good job with your sharpening and then sneeze while you are testing it out on yourself. If you run out of hair on your leg or arm like I do on occasion, you can see if you can get consistent slices across a hanging newspaper with little effort. If the cutting edge hangs or pulls the paper you aint there yet so keep working. Now you should go look for a flea.
The best part about having the blade sharp and the bevel set is that you never really have to go through this whole process again so long as you maintain the bevel and flatness of the iron. All you'll have to do is refresh the flatness to remove any burr then refresh the bevel and once more on the flat side. Takes about 3 minutes.
So, it took me a long time to get my technique down and it still takes me about 30 minutes to get through the process. Don't expect perfection the first time or even the 100th time as perfection is a word left to the dictionary. (or to Chris Swartz, Ron Hock, or that guy that does the demos for Veritas and Wood River planes). If you want to see some real experts check out the video on the main page of the web site. Not the dork in the apron, but those fellows from Japan. Now they know how to make some kinda shavings.
Now that you've read my story here is your reward. A couple links to other guys pages so you can learn more about this stuff. Good luck and don't cut yourself