flattening backs

Anyone have any tips for easier, quicker ways of flattening the backs of chisels,plane blades,etc.. I had gotten this slick from woodcraft a few years ago and finally gotten around to flattening its back. It came extremely rough and I normally use my 10 by 4 inch duosharp extra coarse(220 grit) for quick removal but it is testing my patience and my tendons.
I dont have any machines as I use these diamond stones for just about all sharpening except for final honing I do on 4000 8000 grit waterstones. Any tips would be helpful as I am sure this wont be the last scrappy tool I will want to work into good use. tb

I do the same - DMT (black) diamond stone(s) for rough, then waterstones for final. I tuned up a broad axe found at a flea market - and while I didn't have to 'flatten' like a slick - it took forever!!!! You could move to their 'coarse' silver stone - might take off material a bit quicker...

I took the slick I have now to a machinest. He flattened the back, and the front, on a liquid cooled surface grinder. In the future, I'll do it myself, as I don't like perfectly flat tools. I have a belt sander that I've clamped upside down to a sawhorse. Put your fingers on the back as you grind, and when you feel any heat, dip in water. It still takes awhile, but it's faster than the DMT stones. I've also used a flap wheel type disc on an angle grinder. Again, watch the heat.

I am with Dave on this one. I use a small cheap disc and belt sander combo to shape tools when in rough shape. Keep them cooled and take your time.

Tim

I know some of you have read me writing about this before...though I don't like removing a lot of material from the back, you have to remove some sometimes on an initial tuning. I have used a belt sander to rough it out. But it still has to be flattened after that, and most all of the stones are not coarse enough in my opinion to start. The belt sander is generally pretty coarse. I like to tune on plate glass with psa sandpaper, starting with 80 grit, 150, and 220. Then you can switch to the stones after that or work with finer grits on the glass. A piece of 3/8 or 1/2 inch plate glass is pretty cheap and so is the MDF Frame I make to hold it. My plate glass is about 30 inches long, by 5 or 6 inches wide. It works.

I use coarse emery cloth on glass, and a hammer and anvil. Often the part that needs to be flattened is near the edge, and why flatten the whole back for hours when you can flatten in minutes with a hammer?

Actually i've been advised against cold hammering on the old chisels in the past. Jim R., where do you stand on this? I've also found that you really only need first couple inches flat. You don't need to flatten all the way back to the socket.

When I first get a tool. I'll spend about an hour "flattening" the back. All I am looking for is a smooth surface and a sharp edge. What are you all looking for by flattening?

A curve in the back of a broad axe is a good thing, and I think that can also be said for a slick, although to much less of a degree. Your framing chisels, should be fairly flat, but I don't think one needs to be as anal as a cabinet maker.
The sandpaper on glass/granite works well. It has a cheap initial investment compared and one can make a larger sharpening or flattening surface then with stones.
When it comes to plane blades I am a fan of David Charlesworth's "ruler trick". You need a decent back to start out, but can save one a lot of time as it elevates the blade to a slight angle so one is only working the metal very close to the edge, basically creating a slight back-bevel. This does not hurt the performance of the plane because the blade is already pitched at a higher degree.

I've cracked a couple of blades using the hammer, but would not give it up. As I see it, the key is not to try to bend the blade with the hammer, but to spread out the material on top a bit, so when I'm striking the blade, the anvil is always directly below the hammer.
I've been told that hammering blades cold can actually make the steel harder. You never know what to beleive, just have to try stuff and use what works. The thing I am confident about is that you do have to sharpen the back just like the bevel, in other words, your finishing stone must be hitting the end of the edge full on.

I prefer to have my chisels and slicks flat on the back, and will often hollow grind the center of the back as well, like a japanese chisel.

Are these laminated chisels that you are flatteing with hammer on teh anvil? I would think the hardened layer on the back would not tolerate that kind of impact. CB.

Brad:
Tom is here and I asked him about your question.
He says he uses a very coarse (240 grit) Japanese water stone to flatten the backs after the belt sander.

You only need to flatten the first few inches.

Also, he does not recommend cold hammering, especially on laminated chisels.

Jim Rogers

From the Japanese tool perspective (which use laminated steel), planes, chisels, and other laminated blades can be tapped out. This is done by very carefully tapping on the soft steel right above the lamination line. A much smaller hammer is used than what Mark's ball peen. This effectively bends the hard steel, but the force is dampened by the soft steel. The back of the blade is then lapped flat again. Cracked blades still happen.

I know a bit about the metal in Japanese tools, but really nothing on what was used in American or European laminated chisels. I mainly use Japanese chisels because I've yet to find a western chisel that holds an edge like my Tasai chisels. I like the weight and style of antique framing chisels, but I like the steel in the Japanese. It would be great if Barr could make a real framing chisel (as opposed to the firmer style he's got).

I started "tapping out" with japanese chisels, then started using the technique whenever I saw the back falling away just short of the edge, a common situation. Although the photo shows a big hammer, I don't swing it very hard.
I've probably tried the hammer on 20 or 30 different chisels and a couple of broadaxes, and only had a bad crack once, on an older laminated framing chisel... for me it's a fun technique, put on the ear protection and tap away for a bit. The real benefit for me is that it will produce a very flat back, which I like. It sounds as though there are not that many who like a flat back here, so the hammer is probably not going to apply.

TW, I agree. The quality of the Barr tools is awesome, both the steel and the workmanship. However, they just aren't shaped the way I like/am used to. How do your Japanese chisels hold up regarding chipping? It's always a trade-off. Japanese tools tend to run about 60-62 Rockwell, and American stuff around 58. I am always lapping the backs of my old chisels as I sharpen them. I figure a little at a time will keep the polished part advancing along as I use the tool. I don't think you use up much chisel, unless you're hitting a lot of hardware.

If I might offer something to this discussion...

It's not standard practice to tap out Japanese chisels, only the plane blades. The reason being that the Japanese plane blade is a compound-tapered form, and fitted precisely to the wood block, or dai, which carries it. Thus removing too much metal from the back flat of the blade to re-establish the hollow would result in a spoiling of the fit of the blade to the block. For that case, tapping out, ura-dashi, is necessary.

With a chisel, there is no fit issue to worry about, so when the bevel edge approaches the edge of the hollow on the back after repeated re-sharpenings, the normal process is to simply re-flatten the back to establish a good hollow again. This re-flattening is a sequential process up through the grits, concentrating most of the strokes on the stone to the last 1 cm of the blade (being careful not to create a step in the blade's back). You don't want to flatten the entire back evenly when re-establishing the hollow, as this prematurely thins out the cutting steel. The pressure while re-flattening needs to be concentrated at the tip of the blade as mentioned. The ideal is to carefully maintain the hollow so that the cutting steel lasts all the way to the shank of the chisel.

As for Japanese tools and 'chipping', that is a question that revolves around the bevel angle more than anything else. A lot of Japanese indigenous woodwork involves softwoods and the chisels you buy from the tool seller are often factory ground with that sort of material in mind - that is, with fairly acute cutting angles. If the chisel edge is prone to chipping, then steepen the bevel until the problem goes away. I have lots of chisels from many different makers and have never encountered significant problem with chipping, though I have received new chisels with a very acute bevel angle that needed re-configuring prior to use.

I recently worked a bunch of Wenge and found a couple of my chisel edges weren't standing up as well as normal (Wenge has a working quality akin to granite), so I steepened the bevels by a couple of degrees and the problem disappeared. If I work with a bunch of softer material next, I'll make the bevels on those same chisels a bit more acute again to obtain the cleanest cut.

Further, some chisels end up with a slightly brittle edge after the tempering process is done as the heating of the blade and quenching have more intense effects down towards the bevel edge, unlike further up where there is more metal mass to absorb the heat. Here is where the blacksmiths skill really can make a difference. This over-heated edge problem tends to be phenomenon more associated to the less-expensive and more mass-produced products, however a chisel or plane blade that is at bit too hard and prone to chipping may only be like that for the first couple of mm of blade, and after that much better.

Conversely, a blade that does not chip at all may stand having its bevel angle pushed down a degree or two - there is a sweet spot for every blade and the material it is worked upon.

Those switching back and forth frequently between different woods of different working qualities will benefit from having dedicated chisel and plane sets, one for softer materials, and one for harder.

As for flattening the backs of large western chisels, um, been there done that and no thanks! Life is too short. It really is an advantage to have a hollowed back on an edge tool for the ease of flattening.

I had a bunch of Barr chisels and drawknives once, and though though it is nice to find a handmade black-smithed product in the West (and I very much wanted to support that) I didn't find the cutting edge as good as my Japanese tools, both in terms of ultimate sharpness and in respect to how well the tool held it's edge. So, I sold all my Barr stuff. I've had similar experiences with a few European planes as well - the cutting steel just doesn't quite, er, cut it.

I just like how easy the Barr tools sharpen, it's simple with little effort, yes I sharpen more often, I don't mind. I like a hollow grind on the bevel, though.

I also don't like the backs of my chisel to be "flat". I like them to be similar to my slick, a mini slick if you will.

Maybe could find a worn spot on my anvil to tap a sag into my chisels, maybe. I will just put that on the back burner for now.

Tim

Pretty much what Mark said. If there are areas that are higher on the back then the edge, then as you hone only these areas will be honed leaving that edge rough. Mo, this slick came extremely rough. All I need is to grind down the back enough so that the edge is honed smooth.Any other hollows I dont care about. Unfortunately this slick was pretty out of wack, as the middle of it was much higher than the ends( socket end and cutting edge)In order to get to the edge I have ground down this middle portion.
I thought about hollow grinding it down like Japanese chisels but I was already so far along. I dont use machines for sharpening as the stones usually do the job.
I have been meaning to get a piece of float glass and some silicon carbide papers. It seems like a good fix for some jobs. I always wondered if you were putting some elbow grease into the grinding, is the glass strong enough to not break? How thick should it be? float or plate glass? thanks all. tb

Which Japanese chisels are you referring to. Is there a specific make that you like and find available in the US ?
I am with you Mark. I like my chisels flat. I like to uses them as straight edges when cutting if I dont feel like picking up my square. tb

timber brained, if you were to put a straight edge on the back of the slick, parallel to the cutting edge and 1/2" away from the edge, it should be dead flat? Is this the hump you wanted to remove?

Tim

To be honest, I don't know if my glass is float or plate. I just went in and asked them to cut me a piece of 3/8 thick to my dimensions. I wonder if the difference would be significant in the distance over which we use it, and the way we use it? I do know that the glass I got works plenty good for my sharpening. I've put plenty of elbow grease into my glass when tuning a slick. No problem. I have the glass supported by an MDF frame/board, and this sets on my steel workbench. So long as your frame is on a reasonably flat surface, I think you'd be fine. Not you'd have this issue, but the glass does have a little flex to it before it would break, and I think the thicker you go, the stronger it will be. You could step up to 1/2 inch, but more than that is probably more than is necessary.

We have some plate glass piece here that we sell. I'd have to measure them to be sure of what the dimensions are before I comment on them.
If anyone is interested in a piece.

Glass is great, but the sandpaper needs to be glued well. I always stack another piece of glass on top of the paper I'm gluing and put some weight on it till dry. Also I use a straight edge to spread the glue as evenly as possible.
Even then, sand paper on glass is not like water stones, and I'll often see a bit of rounding at the edges of the surface I'm working on.

I use spray adhesive (3M Super 77). Afeter a few times, you need to scrape off the old glue with a razor blade. CB.