Sharpness Epiphanies

[Warren Mickley]

It strikes me that for most this whole area is a non-issue.

I appreciate that professional workmen of Yesteryear attempted to preserve the expensive steel because it was a significant part of their overhead. Today, very few professional furnituremakers would use their handtools enough to wear them out, and they are cheap enough for this to be less of a concern (a friend if mine is a high end furnituremaker who is known as a specialist in handtools. I've watched him work many times, and only a small percentage of his work is done with handtools. His LN chisels still have the first hollow grind he put on them several years ago). It is more likely to be the jobsite carpenter who grinds a cheap chisel on a beltsander that will reduce blades to a stub more rapidly. The amateur who does use handtools may care more, but still is unlikely to use up the steel in their lifetime. There may be a few years of wastefulness until they dial it in.

Derek

A friend is a high end furniture maker, known as a specialist in handtools? And he hardly ever sharpens his chisels? You are straining credulity.

I have never seen a Tormek or a sharpening jig in a professional shop. I am sure there are some, but the idea that they are necessary is far fetched. The "workmen of Yesteryear" tended to use grindstones that were in the 20 inch diameter range, not much of a hollow grind. Try it sometime.

[Derek Cohen]

A friend is a high end furniture maker, known as a specialist in handtools? And he hardly ever sharpens his chisels? You are straining credulity.

Warren, I did not say that he hardly ever sharpens his chisels. I wrote that he has not re-ground them since the first grind.

Why do you persist in misinterpreting what I write?

The "workmen of Yesteryear" tended to use grindstones that were in the 20 inch diameter range, not much of a hollow grind. Try it sometime.

Why?

Regards from Perth

Derek

[Graham Haydon]

Stewie, mine is the Westons Scrumpy Cloudy Cider. One of my friends has a family that makes it "the old way". I only feature in the first photo http://www.foto8.com/live/the-cidermen/. It was a terrific bit of scrumpy!

I wish we still had our big grindstone, it made way for more machines and became a feature at my Grandparents house. Replaced by........a tormek! :-)

[Graham Haydon]

Derek, I think I may have got it.

Firstly this is your favorite method so it has to be based on your method. So in your example grinding means raising a burr before honing again. On the first hone after this "burr grind" you would indeed use little more length on the tool on the first hone only if you lifted for a secondary. After the first hone both hollow hone and secondary then remove the same amount of length as they have to overcome wear/damage

I think because I don't grind to the edge this had me confused. And for those not doing a "burr grind" my original point of all methods remove the same still stands. Do I have it or am I still missing it!

[Adam Stevens2]

I may have started something I didn't intend to, as I was more merely curious about the difference between flattening the entire bevel vs creating a microbevel. I didn't mean to imply that one procedure or another would have a significant impact on the wear of the tool. I'm just trying to figure out what is going to be the optimal way to hone without spending too much time on it.

I may have mentioned that I don't have a grinder and don't fancy myself using one at the moment, so hollow grinding is something of a moot point for me right now, though it is good to know that it is an option.

[Graham Haydon]

Adam, it's just a good natured discussion, truly it is . Most importantly you seem to be doing great and getting good results, keep doing it!

[Adam Stevens2]

My guess is a lot more metal is removed from the overall length of a chisel or plane iron by taking it to the grinder than removing a few ten thousandths of metal from the bevel on bench stones be they oil or water stones.

Most of the time my "quick polish" is raising a burr on a 4000 stone, cleaning off the burr and polishing the bevel with an 8000 stone and then a few strokes on a leather strop.

The slow shortening of the blade will likely take longer than the rest of my lifetime. A former work associate of mine nearly wasted away a blade by removing a lot of metal at the grinder. Surprisingly, he didn't over heat it.

jtk

Jim,

that process sounds reasonable and simple. I suppose it's the initial establishment of the primary bevel that's a little more time consuming, but once that's done it's just a matter of honing the bevel briefly as you describe. Maybe worth a try on the 1/2" chisel that hasn't seen a stone yet and see how that goes.

[Steve Voigt]

mine is the Westons Scrumpy Cloudy Cider. One of my friends has a family that makes it "the old way". I only feature in the first photo http://www.foto8.com/live/the-cidermen/. It was a terrific bit of scrumpy!

So I was outside splitting some sections of beech log that a neighbor brought by. I walk into the house (I am not making this up) and my wife hands me a glass of home-brewed hard cider…she's the brewer in the family. Then I sit down to read your posts, and it's all about cider. I think it was a providential sign that I should have a second glass.
Scrumpy is a great name! Enjoy!

[Steve Voigt]

Sorry Steve, but we are not on the same path this time. I think it may be terminology (some refer to a secondary as a micro, and vice versa - I do not).

Firstly, a coplanar grind/hone simply means "in a straight line", or "in the same plane". Therefore, when you hone directly on the surface, a 30 degree primary bevel produces a 30 degree cutting edge. There is no secondary bevel. Get the hollow close to the front of the blade, and you will have a coplanar micro (small) bevel.

No one has mentioned which method requires more or less strokes. You introduced that. In this light, you suggested lifting the wear, which would create a secondary bevel. I did not suggest this. I am referring only to honing on the hollow (which creates a coplanar bevel face). As I noted before, this is essentially the same as honing on a flat bevel, but with a much reduced amount of steel to hone. Only in this regard do I mention speed, which is faster with the hollow vs the flat. I am not including the secondary hone here, which can be as fast or even faster to do, but not as easy to re-do.

Regards from Perth

Derek

Derek, I'm more than happy to drop this, but just a couple clarifications first.

I know what coplanar means…I used to teach math, you know. But you are missing my point. Your hollow grind (in your first diagram above) is an arc, and so by definition does not have a fixed angle. If it did, we'd have no use for calculus! Look at your diagram and draw a tangent line to the arc, right in the center of the arc. That line is parallel to to your "coplanar bevel," and so has the same angle. But if you draw the tangent line at the bottom of the arc, where the cutting edge actually is, that tangent line has a considerably shallower angle than your coplanar bevel. Conversely, at the top of the arc, the tangent line is steeper than your coplanar bevel. There is no such thing as "get the hollow close to the front"--the hollow is always in the center, it can't be any place else, unless you are not grinding away all of the old bevel. No matter how steep or shallow your hollow grind is, when you balance that hollow on your stone and hone, you will steepen the angle at the cutting edge, and reduce the angle at the heel of the bevel. That is why your coplanar bevel is in fact a secondary bevel.

Also, just to be clear, the reason I brought up lifting the back of the blade is that it was implied in your second diagram. I thought that was your intent, that the first diagram shows honing by balancing on the hollow, while your second diagram shows registering on a flat (could've been a hollow also) and then lifting the back of the blade.

This is making my head hurt. I'd have that beer now, but I already drank some of Graham's cider, er, scrumpy.

[Adam Stevens2]

Adam, it's just a good natured discussion, truly it is . Most importantly you seem to be doing great and getting good results, keep doing it!

Thanks Graham! I have a Hock kit plane that took me forever to finally get in working order, right up until yesterday (filing the mouth open was tedious!). Just now I decided to "let's see how this goes as a smoother", put a slight camber on the blade and it's cutting through red oak scrap like a hot knife through butter without leaving any track marks that I can see. So I'm very glad to feel like I'm "getting it" now.

[Graham Haydon]

Excellent Adam, life feel good when it comes together. What you can be sure of just when it feels like it's coming together along comes a curve ball!

[Derek Cohen]

I think I have figured it out. Steve, I'm sorry to say that I must disagree with your reasoning (more likely I do not understand your reasoning) - that this is more about geometry than calculus .. and the answer becomes apparent when a missing element is added in.

Firstly the bottom line: the hollow grind and the secondary bevel remove the same amount of metal. There is a provisor, however. I will come back to this part (keep you in suspense! ).

What was missing from our computations? Well, the hollow grind was on a bevel face of 30 degrees, and honing would take place on the hollow, with the hollow acting as a jig for the hone. The secondary bevel of 30 degrees would take place on a bevel face of 25 degrees. What was missing is that in both situations the honing is at 30 degrees. One imagines that the 30 degree secondary bevel is removing extra steel, but it is not - it is only removing the steel that would have been ground away if the primary bevel was 30 degrees ...



The orange section in the second figure represents the area of steel ground away from the 25 degree primary bevel that would be present if it were ground to 30 degrees.

The red lines represent the first hone. This should remove the same amount of steel from both blades as long as the 30 degree angle is maintained.

The blue lines represent the second hone. Again, this should remove the same amount of steel from both blades as long as the 30 degree angle is maintained.

Here is the provisor: freehand honing on the hollow grind essentially ensures that the bevel angle is maintained. However, this is not the case for the secondary bevel. Only a honing guide will ensure the angle is kept. When freehanding there is the tendency to increase the angle slightly. Eventually this will remove more steel this way, plus a later regrind to re-establish the angle will use up still more steel. By contrast, removing waste from the hollow does not alter the bevel angle, and ensures that the same amount of steel continues to be removed as always.

A hollow like this will last a long time ...




Regards from Perth

Derek

[Graham Haydon]

Thanks for the diagrams Derek. Diagram 2 shows the black line of the grind angle projecting beyond the red first hone. If when we grind we leave in a sliver of hone both methods changes the length by the same amount. I think these diagrams only work if you grind to a burr so to speak?

[Derek Cohen]

Hi Graham

Don't take the diagrams too literally - they are just rough drawings for illustration. Perhaps someone might redo them using SketchUp. That would be more accurate.

Still the answer is there, I believe. Time for a Scrumpy?

Regards from Perth

Derek

[Robert Engel]

Let me be the voice of reason:

Hard cider, axes and other thing related to sharp tools do not mix. LOL

Beyond the nuances and uber details, guys, I like hollow grinding because I usually touch up the edges freehand and I can rock the tool to find the "primary" bevel, then lift up slightly to hone the "secondary" bevel. This, to me, is the biggest advantage of hollow grinding.

Adam - trust me, you WILL want to get a grinder and try this technique before its over with.