Back of Blades... Mirror Polish?

[Jim Foster]

Hi,

I'm getting to a point where I can get a reasonable edge on a blade with one shortcoming (I'm sure there are others, but... one thing at a time) I'm having challenges getting a mirror polish on the backs of plane and chisel blades. I've tried several things, waterstones 220, 800, 1200, 6000, also some diamond stones (the 8x2 ones that are not that flat) and sandpaper on granite. The small diamond stones set in plastic are not flat and I've decided not to use them. The waterstones take a long time and leave me with a clouded (pretty smooth surface) surface that takes a long time to improve, and the sandpaper also seems to take forever with incomplete results so far.

Once I get a good hollow grind on the blade, I seem to be getting the knack to honing on the waterstones, but getting a mirror polish on the backs is still illusive. Any and all advice will be appreciated.

[Sean Hughto]

I think the sharpening fetishization has gotten a tad out of hand. You don't need a mirror polish. If you want one, try an 8000 or 10000 stone.

[Jim Matthews]

Those planes can be infinitesimal in length, if that forms an edge.

I would be more interested in the edge balancing keenly between durable and sharp.
If you can slice cleanly across end grain, it's sharp enough.

I've taken to dabbing a little camellia oil on the backs, when the going gets rough.

You don't make money from sharpening - git er done.

[Sam Takeuchi]

Like Sean says, if you want mirror polish, go higher than 6000. Or you can polish it with green honing compound, too.

[David Weaver]

Your clouded surface is fine for woodworking, it's likely the limit of what your 6k stone will do.

If you want the iron or chisel to be sharper, you can work the ruler trick with a finer stone, and the iron will be just as sharp as it would be if you polished the entire back.

[Don Dorn]

I'm sure it's not completely copesetic, but I first flatten the back of a new blade on a granite plate using a strip of 220 sandpaper, then 400, then 600 wet, and I consider it polished enough. That takes about six or seven minutes and I don't need to ever do it again for the life of the blade.

Being flat is the key for me - and I agree with David on the ruler trick in that it allows the final polish you are wanting without the tedious work. I'm pretty lazy and refuse to spend a great deal of time sharpening - I use Cosmans method using two stones and so far, it's given me the results I need. It now takes more time to re-adjust the iron than to sharpen. I figure it's a pretty good method.

[Frank Drew]

I think the sharpening fetishization has gotten a tad out of hand.

I pretty much agree with Sean. Of course, the back of the blade should be honed to the same degree of fineness as the bevel since both planes contribute equally to the sharpness of the edge, but you don't have to hone/polish the entire length of the back.

[Chris Griggs]

Also more important than a perfect mirror, is doing an adequate job chasing off the burr - it's an easy thing to overlook and the first thing I check for if I have freshly sharpened blade that cuts a bit rough in end grain.

[Wilbur Pan]

The issue of whether shiny equals sharp comes up every so often. Although oftentimes the advice is given is to use whatever sharpening method you use to achieve a mirror finish, there are two problems with this piece of advice.

First, a sharp edge is achieved by the intersection of two flat surfaces, and flat is not necessarily the same as a mirror finish. If you don't believe this, look at any funhouse mirror, or the parabolic reflector in a flashlight. Those are certainly reflective surfaces that are not flat at all. A mirror finish is a characteristic of how even/repetitive the surface pattern is. You can certainly achieve a flat surface that is reflective, and you can use the reflection to see how flat your surface is by seeing if there is visible distortion in the reflected image in your tool. But the fact is that the flat and mirror finish are not equivalent.

Second, from an observational standpoint, tools sharpened with manmade Japanese waterstones will take on a very reflective surface, but those same tools sharpened with natural Japanese waterstones often can have a hazy or matte surface, even though either method can result in an extremely sharp edge. Here's an example of some chisels sharpened with natural Japanese waterstones, where you can see the matte finish that is left by the waterstone:

http://www.japan-tool.com/toishi/tennen/Nakayama_Asagi1/Nakayama_Asagi1_4.jpg

http://www.japan-tool.com/toishi/tennen/Nakayama_Asagi2/Nakayama_Asagi2_4.jpg

I've always felt that one explanation for this phenomenon is that the grit sizes in natural Japanese waterstones had more variation than what is seen in manmade waterstones. This leads to a more random scratch pattern in tools sharpened with natural Japanese waterstones, which diffuses light, which leads to the hazy surface. Manmade waterstones, on the other hand, often will leave a more regular scratch pattern, which leads to an increased reflectivity and that mirror finish.

Ron Hock has posted some electron micrographs (http://hocktools.wordpress.com/2010/02/15/matte-surface-mystery-part-2/) of tools sharpened with natural and manmade waterstones that support this theory. The tools sharpened with natural Japanese waterstones have a more random scratch pattern compared to the manmade waterstones. This may not be entirely due to grit size variation. It could also be that the natural Japanese waterstone develops more of a slurry, and that the sharpening particles are moving in a more random manner than the manmade waterstone, where it could be that the majority of sharpening particles are still embedded in the matrix. The shape of the abrasive particles also probably plays a role.

Again, this is not to say that you should aim for either a matte or mirror finish when sharpening. The point is that how reflective the tool surface is not necessarily the same as a flat surface, and flatness is really the goal when sharpening a tool. In your case, this may just be the interaction with your particular waterstones and the tools that you have. At the end of the day, if your tools are sharp, it doesn't really matter how shiny it is.

[Mike Siemsen]

A poor grade of chisel will never polish up. The steel must to be hard to take a polish. You can see this in Wilbur's photos of a laminated chisel where the mild steel of the chisel front is much duller than the hardened steel of the edge and back. The advice to polish/hone both the bevel and the back the same is sound. You will need a finer grit to get a mirror polish. I use the ruler trick on plane irons but I don't see how you can keep a chisel back flat using it. It sounds like it works for you guys.

[Jim Koepke]

As long as the backs of my blades are reasonably flat, seeing my reflection is not important. Some of my blade backs are mirror like. Many have scratches left from coarse stones. They get a few rubs on the fine stone each time they are honed.

Why worry about a pit that is a quarter inch up the back? It will not effect the blade's performance until the sharpening reaches that point. Until then, it is nothing to be concerned about.

jtk

[Jim Foster]

Guys,

Thanks for all the advice. My thoughts were that once the back is flat and has a mirror finish, I don't have to worry that it can be improved, however, I'm going to stop where I am with the level of matte finish I'm getting for now and focus on making sure my skills at honing the hollow grind keep improving.

[Jessica Pierce-LaRose]

I agree with what others say about not needing the mirror polish, but I will say, I find it nice to have at least one chisel with a mirror polish on the back hanging around - it makes using the chisel to cut some binding and inlay pieces to the right angle easier for me to sight it along the back of the chisel when I'm trying to match up an butt joint at an angle that's difficult to measure.

[Zander Kale]

A poor grade of chisel will never polish up. The steel must to be hard to take a polish.
Not true - I can get a mirror polish on mild steel; I have a hammer head I made with O-1 welded to mild steel with stainless filler and after polishing, I can not see the transitions between the different steels but I can see my reflection.

[Peter Hawser]

I used to get a mirror polish on the back of my chisels, but it kept interfering with my shop productivity. When using my chisels, I would often stop, look at the back of the chisels and then think about just how gosh darn handsome I am.

[James Taglienti]

I used to get a mirror polish on the back of my chisels, but it kept interfering with my shop productivity. When using my chisels, I would often stop, look at the back of the chisels and then think about just how gosh darn handsome I am. Now thats funny

[Harlan Barnhart]

Not true - I can get a mirror polish on mild steel; I have a hammer head I made with O-1 welded to mild steel with stainless filler and after polishing, I can not see the transitions between the different steels but I can see my reflection.

Off topic here but I would like to see a picture of that hammer. I'm a sucker for shop made tools...

[Sam Joyce]

I used to get a mirror polish on the back of my chisels, but it kept interfering with my shop productivity. When using my chisels, I would often stop, look at the back of the chisels and then think about just how gosh darn handsome I am.

This has consistently been a problem with me as well.

[george wilson]

Wrought iron will take a mirror polish,so will copper and brass. They are a TAD BIT softer than hardened steel:):):)

[Jim Neeley]

Modesty may not be my *greatest* asset.....

..but *look* at what it has to *compete* with!!! :cool:

[Ray Gardiner]

Your clouded surface is fine for woodworking, it's likely the limit of what your 6k stone will do.

If you want the iron or chisel to be sharper, you can work the ruler trick with a finer stone, and the iron will be just as sharp as it would be if you polished the entire back.

Hi David,

Really, do you use the ruler trick on chisels... ?

Regards
Ray

[Bob Smalser]

I think many of y'all waste amazing amounts of time and effort. Get serious about stropping, and you can sharpen your tools on a cinder block, and have your mirror polish to boot.

http://pic20.picturetrail.com/VOL12/1104763/2594266/398030055.jpg

[David Weaver]

Hi David,

Really, do you use the ruler trick on chisels... ?

Regards
Ray

No, sorry to imply that I (or anyone) would or should.

I do usually mirror polish the backs of my chisels for a small way (inch?), but they are not the same animal as plane blades because of the way they wear, and generally they are a lot easier to mirror polish because they are narrower, and easier to keep in good shape because they don't develop a big wear bevel up the back.

[David Weaver]

I think many of y'all waste amazing amounts of time and effort.

Some may, but probably a lot more of us aren't using any of those big slicks. And for the cabinet size stuff, running a hollow grind across two shaptons, including lapping the back, takes less than 30 seconds - unless the user is a serious tool abuser.

[george wilson]

I never,ever buff an edge.

[john brenton]

That, and the stones aren't what make people waste time. It's the poor selection in the "coarse, medium and fine" spectrum that wastes time.


Some may, but probably a lot more of us aren't using any of those big slicks. And for the cabinet size stuff, running a hollow grind across two shaptons, including lapping the back, takes less than 30 seconds - unless the user is a serious tool abuser.