Wasted Steel

[G S Haydon]

I'm opening myself up to look a twerp (nothing new there).

I've had a brief discussion with Derek about his thoughts on how his present honing method preserves the length of the chisel, plane iron etc more than any other.

Derek's thoughts
"For those with a Tormek or a CBN wheel, it is possible to grind to the edge of the blade. The aim is not to grind away the edge, but just to the edge. You can determine this by feeling for the wire edge. Stop grinding when you feel the finest of burrs. In my case I hone directly on the hollow, and the microbevel so created is coplanar with the primary bevel. In other words, no secondary bevel is formed.

The third method is to use a honing guide and add a secondary bevel. This could be done on a flat or hollow grind. The secondary bevel will shorten the blade more than the other two methods. "

My feeling is irrespective of sharpening method is that we all need to remove the same amount of wear to refresh the edge. I don't think any method reduces length more than any other apart from over zealous grinding. I can't imagine Japanese woodworkers are reducing their plane irons more quickly by not hollow grinding.

Or am I totally missing something (more than possible).

 

[MIGNAL]

At one time I used a similar method with a hand crank. If you were starting from scratch you would grind a primary bevel with 120G on the hand crank, the secondary bevel was formed with a 8,000G waterstone. That's it, nothing between the two grits. When the blade became dull you would continue to use the 8,000G stone. When the secondary bevel became too wide you would revert back to the 120G hand crank and creep up to the very tip of the blade, without going over it though. The only metal being removed from the edge is with the 8,000G or with stropping.
Now I use the same method but with a coarse Oil or coarse diamond stone. It's the relatively slow removal of material on the primary bevel that allows you to use this technique, it makes for easy control. It's also very easy to differentiate between the coarse grind marks and the polished bevel of the 8,000G stone.
I'll guess but the Sellers method probably removes more metal. The difference must be pretty slight though. Nothing to get worked up about.

 

[Cheshirechappie]

My feeling is irrespective of sharpening method is that we all need to remove the same amount of wear to refresh the edge. I don't think any method reduces length more than any other apart from over zealous grinding.

That's correct. A given amount of wear to the edge will require the same length of tool to be removed to refresh it, irrespective of the method used. Metal removal further up the (primary) bevel will not affect the edge sharpness one bit (it may affect edge strength, but that's a slightly different matter). Thus, using the Paul Sellers rounded bevel technique removes a greater volume of metal at each honing, but removes it from the whole bevel. Using the more common 'secondary bevel' removes much less volume of metal at initial honing after regrinding the primary, but bulk metal is removed when the primary is reground.

However, provided just enough work is done to restore a good edge each time, the overall rate of metal removal, averaged over a large number of honings, is the same for all methods; and the tool becomes the same amount shorter at each honing no matter what method is used to hone it.

That applies to flat (Japanese style)bevels, hollow ground bevels, convex bevels or any other bevel - the amount of metal removed, averaged over a large number of resharpenings, is the same for any method, provided just enough work is done to restore the worn edge to working sharpness each time.

 

[Trafalgar]

If you produce a burr at the wheel it will only get larger as you polish out the extraordinarily rough edge left by the grinder. This method uses up steel faster than producing the burr on one's finest or next to finest stone. It uses it up faster because the burr will grow when the edge is polished to rectify the rough edge left by the wheel.

One might like to preserve a favorite chisel or two but beyond that it's all disposable tooling - plane irons for sure.

I don't care to get on the upgrade path with respect to grinding wheels. The wheel's job 95% of the time is simply to restore the hollow, never grinding to the edge and producing a burr. The other 5% of the time if even that is carefully working out the relatively rare nicks and gouges. I can't imagine there is an advantage to regularly grinding all the way to the edge to produce a burr, the edge would be a very rough one indeed and need further treatment up through the grits right at the cutting edge with is the antithesis of being frugal with steel.

 

[G S Haydon]

All I hope is that I have not got the wrong end of the stick regarding Derek's point as it seems you all share my thoughts on this.

 

[Biliphuster]

I don't think it makes a difference, a 1mm nick will require the edge to move back 1mm to remove no matter how you do it. The same goes for folded steel, worn steel or any other sharpness malady, the new edge is somewhere in the body of the blade and anyway of removing the excess metal will be equivalent as long as you stop once a new edge is reached.

I do about 90% of my sharpening (full bevel) on my finest stone and I don't think I will ever get even half way down my most used chisel. I had always assumed the very short chisels you sometimes see had an owner who was over fond of the grinder.

 

[Trafalgar]

All I hope is that I have not got the wrong end of the stick regarding Derek's point as it seems you all share my thoughts on this.

I do agree. Grinding to a burr wastes steel. No doubt about it.

 

[G S Haydon]

I think so Charles, grinding to a burr is ok if you want but always best to leave a sliver of honed edge left.

 

[woodbrains]

I think so Charles, grinding to a burr is ok if you want but always best to leave a sliver of honed edge left.

Hello,

Absolutely, and this reduces the chances of drawing the temper if using a dry grinder.

The Tormek does not produce a very rough grind, though, so it is OK to grind right to the edge (but no further) and there will be no great loss of steel in the honing stage. There is no real danger of drawing temper, either. I suspect a CBN stone might create a coarser grind.

Mike.

 

[Cheshirechappie]

I do about 90% of my sharpening (full bevel) on my finest stone and I don't think I will ever get even half way down my most used chisel. I had always assumed the very short chisels you sometimes see had an owner who was over fond of the grinder.

Indeed - or possibly a chisel that has served two or three generations of craftsmen. I doubt many people would wear out a full-length chisel in a lifetime. Plane irons are a different matter, though - a well-used bench plane might consume two or three irons in a craftsman's lifetime.

 

[Derek Cohen (Perth Oz)]

Tormek and CBN wheels grind very cool and there is no burning of the steel when you grind to the edge. Further, this does not weaken the steel. I have never experienced a failure as a result of a hollow ground edge.

Now what Graham has not explained is that I am not advocating grinding over the edge, but to the edge. This becomes apparent when you create the very finest of wire edges - indeed the type of wire edge from 1 or 2 strokes on a 1000 grit waterstone (that is all I need).

What I wrote: "For most, hollow grinding a blade removes waste from the centre of the hollow. The subsequent honing removes the same amount of steel as honing on a flat bevel. All a hollow does is remove the unimportant steel from the equation when honing. Honing here removes the same amount of steel as the next method, but takes longer.

For those with a Tormek or a CBN wheel, it is possible to grind to the edge of the blade. The aim is not to grind away the edge, but just to the edge. You can determine this by feeling for the wire edge. Stop grinding when you feel the finest of burrs. In my case I hone directly on the hollow, and the microbevel so created is coplanar with the primary bevel. In other words, no secondary bevel is formed.

The third method is to use a honing guide and add a secondary bevel. This could be done on a flat or hollow grind. The secondary bevel will shorten the blade more than the other two methods. "

The question that started the whole debate on SMC was whether a secondary bevel (on either a straight or hollow grind) shortens the blade more than honing a coplanar bevel on a hollow grind. My position was that the secondary bevel (a bevel with a higher angle to the primary bevel) shortens the steel fastest.

Why do I hone as close to the edge as possible? Simply because it takes less time and effort to hone, and there is less need for grinding thereafter. Ironically, to grind this close - and end up grinding less - one needs a more expensive set up.

Regards from Perth

Derek

 

[G S Haydon]

Removing the style of honing we may prefer the only aim of honing is to remove wear or damage. That is a fixed distance that any method must travel. And I've not been on the scrumpy Derek, not yet anyway :lol:

Raising any kind of burr on a grind is waste. I'll freely admit it's not worth worrying about in the slightest but if preserving tool length is important then just leave a sliver in?

 

[Trafalgar]

The hollow only needs to be restored to the extent it will function as a jig for freehand honing. If one hones on the grind then the angle does not grow so there is not need to grind to, or just behind the edge to the extent there is danger of going over. Just put the hollow back in so you can 'click' the unit to the stone and hone. No real need to get exceedingly close if you hone on the grind.

Secondary bevels do use up steel the fastest as Derek points out.

I've yet to wear a chisel completely down, though I'm pretty close on a quarter inch chisel.

 

[MIGNAL]

Why do secondary bevels use up more steel? Why can't you continue to use a secondary bevel and remove just the wear ? which is exactly what you are doing if you use a single bevel.
Surely honing coplanar on a hollow grind is effectively a secondary bevel, No?

 

[G S Haydon]

I'm with you here MIGNAL. This has to be a truly original sharpening debate, I don't recall one like it before!

Charles, would you say they shorten the tool faster? For instance bearing in mind all we have to do in the race is remove the red portion of the image and stop how will any method of honing remove more?

 

[G S 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!

 

[Trafalgar]

On chisels ground and honed higher the wear becomes more rounded and thicker. One usually keeps honing higher and higher at each session in order to produce a burr quickly until the unit finally has to be ground back to work again - the wear is figuratively as thick as your thumb at that point. You have to get all the way back behind the rounded wear that goes too far up the face of the chisel -- you have to take out thickness AND length to get behind it.

More steel behind the edge means more has to come off to get behind the wear.

 

[MIGNAL]

But you don't have more steel behind the edge on coplanar and a hollow grind. Nor do you have to hone at a higher and higher angle on a secondary bevel.
Let's forget trying to get a burr. My newly bought chisel comes to me with a single bevel ground at 25 degrees. Let's say I hone a secondary bevel a few degrees higher using an 8,000 fine stone. I get a polished glint across the entire width of the chisel that has a depth of 0.3 mm's. I use it, it becomes a little blunt. I then take it back to the very fine stone and work on the secondary bevel only until the chisel is sharp. Let's assume that the glint now is at 0.6 mm's depth. I do the same again but this time the glint has grown to 0.9mm's.
After this I deem that it now takes too long with the very fine stone. I go back to the primary bevel and grind back using a very coarse stone. I take that primary grind to 0.3 mm's (or thereabouts) of the blades edge. I do not take it past the tip. I continue to hone with the very fine stone.
This is essentially the method that I use. It's really no different to the method that I used before, which was a hollow grind using a hand crank and coplanar hone with an 8,000G waterstone. When the glint became too wide I would take it back to the hand crank and grind near to the tip.
I honestly cannot see the difference. One is a secondary bevel and the other, the coplanar hollow grind is also a secondary bevel but the steel behind the edge on that is a touch thinner.

 

[bridger]

For the tools I use and sharpen, the wear bevel on the flat side is usually the thing that determines how much steel needs to be removed. The angle and condition of the final bevel, the one that actually makes the cutting edge, has the most to do with how the tool performs. Everything behind that, whether it is flat grind, hollow grind, convex grind or some multiple of flat bevels is irrelevant. Do the bevel shaping by the method of your choice, using the tools you have, and don't waste good steel, or time spent sharpening.

 

[Derek Cohen (Perth Oz)]

I think I have figured it out - this is more about geometry .. 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