chisel thoughts

[Ken S]

For many years I followed the traditional practice that the full length of the backs of bench chisels should be dead flat and brought to a mirror polish. I slaved away at this task with oilstones, waterstones, and the Tormek. My chisel backs looked fine, but my hands ached.

I have recently changed my thinking. I still agree with the theory, just not the necessity. A chisel with a hump in the back, generally called a belly, will not lay flat. Not being flat will cause the chisel not to cut properly when laid flat in a deep excavation. (If the chisel is concave, or negative belly, this is not a problem.) Either way, we purists preferred the chisel back to be dead flat and highly polished.

In the real world, critical, deep excavations are rare. Should I ever encounter such a situation, I have several nice vintage Buck crank neck chisels which lay flat. I also have some heavy mortise chisels.

For most work, including dovetails, working depth is generally less than an inch or 25mm. I no longer see the need to spend a lot of time preparing a lot of blade length for shallow cuts. Should that need ever arise, which I doubt, I can always flatten and polish more of the back of a particular chisel. I no longer see the need of spending hours making chisel backs look shiny in a tool chest.

Some chisels are manufactured with highly polished backs. The problem with these is that some non woodworking designer had a radius ground where the back meets the sides. While this looks and feels nice, it prevents the corners of the bevel from laying flat. Removing the steel the thickness of the radius is more labor than the chisel is worth. I do not know why tool sellers sell these poorly designed chisels. Do not buy a chisel unless the intersection of the back and sides is a sharp square. Thin sides work better for dovetails.

When grinding with the side of the Tormek wheel, placing the universal support close and resting your left hand on it will make side grinding much more controlled.

There is concern that using the Tormek leather honing wheel will "round over" the back. Two things will reduce this:

Pay attention to keep the chisel presented to the leather honing wheel flat. Care and experience help.
2)   Prepare the back fully before working on the bevel. Any rounding of the very edge will probably be ground away is sharpening the bevel.

There is nothing wrong with the full back flattening and polishing. I just do not feel it is the highest and best use of time.

Ken

[Hatchcanyon]

Ken

To polish the back sides on flat irons like chisels or planes I use the SJ stone. This is far less messy than using the leather wheel. I agree polishing must not necessarely be done over the full lenght.



Rolf

[Jan]

Rolf, polishing using a vertical grindstone results in hollow shape due to the radius of the stone. It is possible to get the chisel back almost flat near the cutting edge when the chisel meets the stone as a tangent. From your picture is clear that you aware of it. 

Jan

[Ken S]

Interesting post, Rolf. I had not thought of using the SJ wheel to polish chisel backs. Clever.

Jan, you make a good point about the radius of the wheel. This technique of using using round wheels to flatten chisels seems like something which requires some skill and care. The results look worth the effort.

I think of the back and the bevel as equal partners in creating a sharp edge. All too often, the back is relegated to second chair.

Has anyone tried using the side of the SJ to polish the back of a chisel?

Ken

[SharpenADullWitt]

From looking at Hatches picture, it looks like the side of the wheel has had something run on it (by the two main lines, about an inch and 1 1/2" for the darker line).
So I was wondering if the picture means he removes the burr on the backside (instead of the leather wheel) and polishes/flattens the back on the side of the wheel.


Although, personally I wish he wouldn't have posted that temptation to buy a SJ wheel.  (since the are on sale till the end of the month)

[RichColvin]

Ken,

I used the SJ wheel to polish the back of my planes. It worked quite well.  But, I don't try to get every scratch out of the surface. 

Kind regards,
Rich

[Hatchcanyon]

The marks on the side of the SJ stone are from another experiment.

Polishing backsides on the stone side didn't work very well for me.

I think hollow grinding ist not a very serious issue due tu the fact, that the SJ removes very little material and yes I too do not try to polish everything away.

Rolf

[Ken S]

Interesting comments. I think the SJ may be a more versatile tool than originally thought.

Ken

[Jan]

Rolf, you are correct, when you remove very little material the effect of the grindstone radius can be neglected.

Removing more material when the chisel does not touch the grindstone tangentially will cause one of the results shown in the attached sketches. 

Both examples are strongly exaggerated to show the risk of hollowing the flat back of a tool.

Jan

[Ken S]

Jan,

The second drawing, showing the very tip of the edge being rounded, would present a problem in that amount. I would be surprised if the SJ wheel, used with a light touch, would normally cause a problem. I have not tested this; I will try to test it next weekend. As far as hollowing further up onthe blade, that should not cause a problem. Japanese chisels are routinely made with a hammered hollow spot for easier back preparation.

Anyone advanced enough to be using the SJ to polish a back should be experienced enough to be careful with the grinding touch.

Ken

[RobinW]

I have tried flattening the backs of chisels and plane blades on the side of the wheel (SG) - but was not happy with the results. I found it difficult to hold them steady and flat and was not sure if I was introducing a slope across the back of the blade.

So I flatten them on a piece of 10mm thick float glass, (600mm long x 100mm wide, polished sides all round so no sharp edges for finger shredding, held in a wooden frame which clamps to the bench) on which I glue various abrasive papers.

When I have worked up through the grits I then finish polishing the backs of the blades on the honing wheel, so no problem with concave scalloping of the blade.

[Jan]

Ken,

both sketches show the situation when the tool does not touch the grindstone tangentially under 90° with respect to the radius. The first drawing shows the situation for 80° and second drawing for 100°.

I agree with you that an experienced sharpener who is aware of the hollowing risk can flatten the back side of the tool near the cutting edge.

Jan

[Ken S]

Robin,

I have shared your skepticism of flattening and polishing using the side of the wheel. One expert suggestion I received was to use a foot switch to turn the motor on and off and hold the chisel against the grinding wheel. This worked fine with my original T7. All newer Tormeks have the new and improved switch which will not return to on unless actually turned on again. I can appreciate this as a safety feature, however, it seems more fittedto a table saw than a Tormek.

Placing the universal support very  close and resting the chisel on it helps.

The Tormek works nicely for a prized chisel with a belly. I have a nice old Buck chisel I corrected this way. The Tormek saved wear and tear on my hands.

My latest chisels are the Irwin (formerly Marples, now made in China) Blue Chip that I use for sharpening practice. They are all slightly concave, so there is no need to flatten them, just polish.

I have several Lie-Nielsen odd size chisels. It seems you get what you pay  for. You can pay up front or often spend a long time flattening.

The glass plate and abrasive paper is still comfortable.

Jan, I agree with you. Experience and care help.

Ken

[Jan]

To minimise the risk of hollowing the chisel back side it is necessary to keep the tool tangentially to the grindstone.

Scissors jig support plate can be used as a platform, it is easy to align it properly to the grindstone. It provides guidance but preserves the freedom of freehand polishing.

Jan

[Ken S]

Excellent suggestion, Jan. Controlled grinding is where the Tormek excels, and your suggestion offers very good control of what can be an uncontrolled operation.

Ken