flattening chisel backs

[Ken S]

I understand the theory of wanting a dead flat, mirror polished chisel back. I do not understand the need for this degree of perfection for most chisel work.

Of course, we want both sides, bevel and back of a chisel to be highly polished. However, if the leading edge of the bevel is a micro bevel, why should we expect anything more from the back?

The notion of the completely flat back may go back to the days when a patternmaker or cabinetmaker might have chiseled out a long dado with a long crank neck chisel. Today we would probably this with an electric router or hand router plane. In fact, except for timber framing, using a chisel at a cutting depth of more than 3/4" (19mm) is rare. Even hand cut dovetailling is a relatively shallow operation.

All of this is leading up to questioning the importance of being able to use the side of a grinding wheel for flattening chisel backs.

Ken

[SharpenADullWitt]

You should look at some of the benches people still build.  The tops can be 2" or better and they still use dovetails.  The average woodworker may not use a chisel for more, but the more traditional hand tool woodworker does.
For a long time, I have heard the recommendation for 1" of the back to be flat, and as long as the rest had a valley, instead of a belly, it would be fine.  Just better to reference off a flat surface.

[Jan]

Ken, SADW, I agree with you that 1" flat chisel back should be more than sufficient. Nevertheless near the cutting edge the back of the chisel should have the same quality as the leading edge. 

In the past timber framing required a cutting depth of several inches. Heavy duty mortise chisels were used for this. Today carpenters on construction sites use chain mortisers while chisels are used to correct minor joint imperfections.

Jan

[SharpenADullWitt]

A lot of the mortise chisels were and still are used by hand tool workers, after your old bit and brace were used to hog out the majority of the wood.  Don't kid yourself, it has always been about speed, efficiency and least amount of work verses the benefit so you can continue to work on other stuff.  Wouldn't want to wear yourself out after a couple mortises for the day.
You might like Roy Underhill or Christopher Schwarz.

[Jan]

Yes, I like them. I see with pleasure that in some workshops are the hand-working skills restored. 

What I have mentioned is the situation on the majority of construction sites where the situation is for hand-tool woodworking less favourite. 

Jan

[Ken S]

I agree with both of you. I like a flat reference surface and the back should certainly equal the bevel for a keen edge. For deep dovetails and mortises, I would certainly want a dead flat and polished back.

My point is that these requirements are not typical for most chisel work.I would certainly flatten the back of mortising chisels and chisels used in deep dovetails. In fact, psychologically, looking at a chisel with a highly polished fully flat back is very satisfying. I just don't see where the extra effort provides any benefit for a chisel used to let in a door hinge. I would reserve the effort for the few chisels which really require it.

Ken

[Rob]

Morning Chaps and Happy New Year (it's been a while since I visited)

I've a quick question regarding back flattening as I've promised a friend of mine I'll do his chisels and plane irons tomorrow and I've not done any for ages.  Am I right in assuming it's possible/sensible to grade the side of the wheel with the stone grader to re-energise it? (for chisel back flattening).

This friend of mine has been slaving away on diamond stones by hand to flatten his blades and he's had enough.  I suggested we employ the "National Grid" with a Tormek plugged into one end of it to speed things up a bit.  The notion of speeding things up seems to me to be aided and abetted by having a dressed wheel side.

Hope you're all keeping well.

[Ken S]

Welcome home, Rob.

Dressing or grading the side of the wheel is one of those topics strangely not mentioned over the years by anyone associated with Sweden.

I would certainly give it a try. Keep your universal support close to help secure and steady the stone grader. I would use the SG wheel instead of the SB for chisels and plane blades. It is designed for carbon steel. I have also had better luck grading the SG.

For the plane blades, do not forget your countryman, David Charlesworth's ruler trick. If you are unfamiliar with it, the time spent googling it will be repaid a hundred fold.

If a chisel is way out of flat (throw it away!) I have started by just grinding the high area with the circumference of the grinding wheel until a straightedge tells you that you are close.

Sheffield's smartest heat treaters often heated blades in such a way that any warping of the backs was concave instead of bellied (convex). Especially for plane blades, that saved the end user much flattening work.

Do keep us posted.

best, always,

Ken

[Jan]

Rob, recently I was sharpening a 50 mm wide plane iron with 59-60 HRC and I needed almost 15 minutes to flatten its back on the side of the SG stone graded coarse. It was quite difficult task. I had to re-activate / de-clog the stone side several times during the flattening. I used the coarse side of the stone grader.

To avoid possible edge non squarness I align the edge of plane irons / wider chisels to a pencil line drawn on the stone when mounting it into the square edge jig. It is more precise than an alignment to the jig shoulder which works only for parallel tool sides. 

The initial edge should be square otherwise you replicate the skew! If the edge is not square make it square before mounting it into the jig.

The last issue is the shape of the edge. I was sharpening a straight edge not a camber shape. There is a general tendency ty overgrind (concave) the centre of the plane iron edge. To compensate for this tendency it is recommended to spend more time on the sides of the tool. 

Good luck! 
Jan

[Rob]

Thanks chaps.  I've just spent an hour or so reacquainting myself with flattening the backs on the side of the wheel.  It worked fine as long as you don't have too much chisel metal in play ie restrict the grinding to just the tip....then it goes quickly.  I didn't bother grading it but it's nice to know it can be done.  My experiment was with a block plane blade, so pretty much the same as your 2" Jan :-)

Once mounted it was quite slow going to redefine the primary bevel and I have the older square edge jig (is it the SE-76 not the 77??).  So one quick question:  Is the 77 any better for aligning the blade to give a grind that's 90 degrees to the sides?

I did find a bit of drift off the perpendicular as I ground and my personal trick has always been to mark a sharpie line on the back of the blade very close to the edge so you can easily compare your edge to it as a reference without having to slip the jig off the USB and use a square to assess the trueness of the grind.  My drift always seems to be to leave a high spot on the left hand wing as you're looking down at it in the jig.  I'm obviously pushing too hard on the right (I'm right handed) or spending too much grind time on that side.  But it's not difficult to over compensate on that high spot to remove it.  I think the most important thing is to have that reference so you can keep adjusting yourself back on course in little increments rather than waiting until the bevel is complete, checking the square and finding you're a mm out.  Then it's a pain to correct as the drift is so great.

So I ground a 30 degree 2ndry bevel and then honed it and loaded it up.  It simply blows my socks off every time I take the first few cuts.  I will NEVER tire of that simply exquisite feeling of the removal of a gossamer thin shaving with a uniform width and thickness.  I actually measured the shavings with a micrometer and they were 0.06mm ie a tad less than a tenth of a mm.  The resultant surface is close to shiny it's so fine and something you could never achieve with sandpaper because it's free from scratches, no matter how fine they are.

So now, not only do I have a very very sharp block plane, I also have a bald patch on my arm and a thumb nail with a little channel in it :-)

[Jan]

Congrats Rob, 0.06 mm (60 μm) thick shavings is really an outstanding result. It is less than the average diameter of human hair! 

I was sharpening a standard plane iron for a violin maker who told me that his shavings were some 0.10 mm (100 μm) thick. He considered this for a good result. 

We have a saying in this country: "Wood shavings of a Viennese cabinetmaker's should be as thin as a cigarette paper".

Jan

[Rob]

Viennese cabinetmaker - I like that :-)

[Ken S]

Nice saying, Jan. I agree. If the cabinetmaker's apprentice set his shavings that thin for preparing the board his his master, the cabinetmaker would have plenty of time to enjoy a nice coffee and pastry.

The thickness of the shaving should suit the work.

Ken