hollow grind debate on noisy side

Re: calculations re: hollow grinds (crosspost)

Dave Mount

>I did some math on the subject of hollow grinding. Some folks that don't venture off this board might find the data interesting.

Best,

Dave

*****************

I did some calculations that don't resolve this issue, but they put some real numbers into the mix. I calculated the actual reduction in angle at the sharpened arris for several bevels and wheel diameters. The wheel diameters were 4", 6", 8" and 10", the latter being what the Tormek wheel is if memory serves. I used bevel widths of 5/32", 1/4", and 1/2". If the nominal grind is 30 degrees, then the width of the bevel is basically 2x the thickness of the iron/chisel. The 5/32" bevel corresponds to the thickness of a stock Stanley plane iron. The 1/4" and 1/2" would be for 1/8" and 1/4" thick metal, respectively.

The data below show what I calculated. These are based on degrees *below* the nominal grind that will exist at the cutting edge.

I can't make the editor do a table properly, so I'll just list the values individually:

For a 10" wheel: 5/32" bevel = 0.9 deg, 1/4" = 1.4, 1/2" = 2.9

For an 8" wheel: 5/32" bevel = 1.1 deg, 1/4" = 1.8, 1/2" = 3.6

For a 6" wheel: 5/32" bevel = 1.5 deg, 1/4" = 2.4, 1/2" = 4.8

For a 4" wheel: 5/32" bevel = 2.2 deg, 1/4" = 3.6, 1/2" = 7.2

So if you are grinding a 1/4" bevel at a nominal 30 degrees on a 6 inch wheel, that means that right off the grinder, the actual arris is at 30-2.4 or 27.6 degrees. While I based this initially on a 30 degree grind, the numbers are relative to the bevel width and wheel diameter; therefore the table values can be applied to other grind angles, as long as the bevel width matches what's in the table. So, a 1/4" bevel ground at 20 degrees on a 6" wheel ends up at 20-2.4 or 17.6 degrees.

This does not tell the whole story of course, because the next step following hollow grinding is to hone a bevel which will actually be at the nominal grind angle. Therefore, the actual angle at the cutting edge is not affected by a hollow grind; the only thing that is affected is the arrangement of metal further back. When would this matter? It should matter most when the tool is being pushed into wood in angle that is not in line with long axis of the tool, such as in a bevel down plane (not I'm not saying it will make a *meaningful* difference necessarily, just that under these conditions is when it will have the greatest effect). When force is applied in line with the tool, such as in a paring chisel, this should have little effect. The effect should also be much smaller in low angle bevel up planes because they have better support for the iron.

So, I think the answer is, like most things, it depends. Bigger diameter wheels obviously reduce the effect, as to shorter bevels. As the secondary honing bevel increases in width, the effect is also reduced. Finally, how the edge is used will affect the impact a particular hollow grind will have.

I suspect everyone involved in this discussion will point to the data and be able to use it to support their viewpoint. Bill is right that for many situations the effect is very small. Denis is right that for thick irons with low bevel angles, and small wheels, the difference is more substantial.

Everyone will interpret these variables differently. I hollow grind on a Tormek and hone freehand on waterstones. I find the Tormek gives me very even and reproducible initial grinds, which I like, and the hollow, small as it may be, allows me to freehand hone with relatively little error, which is fast and easy.

Dave

Re: hollow grind debate on noisy side

Norman (Metcalfe, Ont.)

>I was reading that..

I'm glad to see may more folks are switching to freehand honing.

I use a Viel low-speed 1 inch. belt sander system for the primary grind on both plane irons and chisels. The bevel produced is very flat and accurate with the table mounted keyed system. I mention this because it is important to get a accurately ground flat bevel if you're going to use flat bevels as opposed to hollow-grinding.

The resulting flat bevel presents a nice, stable bearing surface to the honing stones afterwards. If one is to freehand grind a primary bevel however, I can see issues with a not flat bevel which can lead to rocking while honing. In this case hollow-grinding is a much better option for the reasons listed in the other thread.

In my opinion, the extra metal in the flat ground surface over a hollow-grind is very small and doesn't create much more effort in honing, if any at all.

Norman

A response

Bill Tindall, E.TN

>"n my opinion, the extra metal in the flat ground surface over a hollow-grind is very small and doesn't create much more effort in honing, if any at all."

I'm going to challenge this statement but first make some measurements. My guess before measuring is hollow wins by a factor of 10 less metal removed.

But Bill....

John in New Mexico

>You basically said the same thing on the other side (of course, you're using diamond, but the premise is the same). Don't get me wrong here, I sharpen the same way you do, just be careful you don't start arguing with yourself ;)

John

PS - I'll be back in Tucson in a couple weeks I hope, so if you email me your shipping address I'll send you that black powder.

what's the debate ;)

Moses Yoder in White Pigeon, MI

>I suppose I will go and read it. I think I deserve a little break, and the reading may be very humorous. I have never understood people who want a flat bevel. I think they come from a different planet. The problem is that on a flat bevel you are not polishing the very tip, which is where the metal meets the road so to speak. The only part where it is necessary for the metal to be flat (no grooves- the shinier the metal the smaller the grooves)is where the two planes of the iron meet. Theoretically this could be an edge that is one atom wide. In reality the edge crumbles slightly so I usually polish the edge about 1/16" wide. If it crumbles past 1/16", you are in desperate need of re-sharpening. Ever since reading Krenov back in the 80's or so I have sharpened all of my tools using the hollow grind. The problem I have with the flat grind is not so much the time it takes to polish the steel as the fact that the tendency to not polish all the way out to the edge overides any benefit from having the "extra steel" there. I would be very grateful for someone to prove me wrong on this.

Re: what's the debate ;)

Pam Niedermayer - Austin, TX

>Moses, an edge is defined as the intersection of two planes, so if you sharpen to a flat bevel it meets the back just as well as with a hollow grind.

Pam

Re: what's the debate ;)

MikeW

>It is more difficult for some people to know when the have rocked the edge tool off of its very edge with a flat bevel.

In other words, with a hollow grind, some people can feel the bevel's registration better.

For some people, neither flat nor hollow can be done freehand as they either rock the tool or do not maintain its registration across a stone.

Hollow, flat, jigged or not, doesn't matter...for myself, there are days the jig comes out because it speeds up honing on that day because I couldn't free hand hone to save my soul. Most days it's a piece of cake. Go figure. Glad I have options.

Take care, Mike

Re: what's the debate ;)

Pam Niedermayer - Austin, TX

>The thick Japanese blades obviate any sort of freehand problems I'd had, which in turn translated back to sharpening thinner blades quite nicely. I think it was a matter of getting the feel of holding a bevel flat.

Pam

Re: what's the debate ;)

Moses Yoder in White Pigeon, MI

>I have a great deal of respect for the eastern woodworking culture and think it is sad that western woodworkers tend to beleive they need more gadgets to do better work. If someone can actually hone a flat bevel in such a fashion that it is actually sharp I say hats off to them because they don't need a grinder, but am still in fact wondering how in the world they do it. My hand cranked grinder that I bought at my uncle's auction for $9 is the last thing in the shop I would give up. Even if I had no tools I could still play with the grinder. I guess I am still just a boy at heart.

Re: what's the debate ;)

Warren in Lancaster, PA

>Mose, I edged you out in a planing contest last year, but the differences in our shavings were insignificant. There was no telling whose edge was sharper. However, I used an iron that I had had since 1981, sharpened in excess of 10,000 times, and had never put to a grinder. I spent 2 minutes getting it ready for the contest. There is no need for "hats off", as you are a good workman with a wonderful pair of hands.

Re: what's the debate ;)

wilbur

>"For myself, there are days the jig comes out because it speeds up honing on that day because I couldn't free hand hone to save my soul."

Who knew sharpening was so much like putting? :@)

Re: hollow grind debate on noisy side

Dave Anderson Chester, NH

>My view is that(emphasis here) "any system will work well provided that it is used and practiced regularly." My pet peeve in this debate is not over what technique is used, but that folks expect that a handful of times sharpening with ANY single technique is going to produce good and consistent results. We seem to have this desire for instant gratification and an expectation that we should be able to produce results as good and consistent as those of a woodworker who has been shapening with the _______ method for 5-30 years. The purchase of the bestist, biggestist, super wonderful doodad seems to be todays substitute for spending the time and effort to become proficient. This is also manifest in the myriad of commercial jigs and fixtures available on the market today designed to perform almost any woodworking operation you can name. Forlornly, I would rather hope to see easily available basic tools of high quality at a reasonalbe price. Alas, this is unlikely to come to pass.

End of Rant

Oops, a disclosure in the interests of honesty

Dave Anderson Chester, NH

>Having ranted, I should in all honesty disclose that I own a LV MK II motorized sharpening system. My pathetic excuse is that I often have to sharpen 50 to 100 marking knife bevels at a single sitting and it cuts the time involved by far over 50%. At least that's my story and I'm not admitting otherwise. ;-)

data on metal removal

Bill Tindall, E.TN

>The bevel on my "go to" plane is 0.322" long. It is hollow ground. I measured the width of the honed portion of the bevel- 0.10 on top and 0.025 at the edge on the average. 0.035/.322 = about 10% of the bevel experienced abrasion during honing in this typical case. In contrast, had the bevel been flat 100% of the bevel would be abraded and comparatively more metal would be removed during honing. However, if a secondary bevel was honed on the flat bevel, then the cases of hollow vs flat are similar.

Sharpening marking knife bevels

Paul M. in San Diego

>Hi Dave,

I've made quite a mess of my marking knife bevels using my LV MkII sharpener. I would be interested in how you do this. I'm guessing that you are sharpening these on the MkII before you install the blades in the handles, which means that you could use some sort of jig to help keep the bevels stable on the surface. My marking knife is already handled, so the wooden body of the handle seems to prevent my getting jiggy with it.

I attempted to freehand the angled bevels on the spinning wheel with much less than satisfactory results. I would love to hear how the master does this!

Crutches, Training Wheels; results count for somet

Bill Tindall, E.TN

>Fact: nearly all woodworking classes attempt to produce a product from the class.

Assumption: People teaching the classes understand the marketing of their product.

Conclusion: Most woodworkers do woodworking to make stuff.

Corollary: If most woodworkers were not successful making stuff they would do something else with their time.

If clunky, time consuming, expensive (and other adjectives of choice) gadgets enable beginning or time constrained woodworkers to accomplish (filll in the task) some task in the time they have to spend on the task, be it sharpening or making a desk, I support their efforts. If they keep at it a weaning process will occur for the tasks that are done often. For those tasks that aren't done often enough to establish proficiency, if a gadget enables the woodworker to proceed to a product then it should not be discouraged.

Bottom line is that I think we should spend more effort critiquing someone's results than the process they took to get there. A well designed tea table made with a jig sharpened chisel is a whole lot better than the tea table that never got made.

Re: Sharpening marking knife bevels

Dave Anderson Chester, NH

>Yes Paul, I do all of the sharpening before the knives are adssembled. Believe it or not, I don't use a jig. After the first few hundred you develop a feel and some muscle memory which makes it pretty easy. That's not to say I haven't slipped and butchered a few on occasion. Sorry that it's not the answer that you want. Sharpening after assembly is done by hand.

Re: Sharpening marking knife bevels

Pam Niedermayer - Austin, TX

>Have you tried to make a jig with which you could sharpen multiple blades at once?

Pam

Re: Sharpening marking knife bevels *LINK*

Derek Cohen (in Perth, Australia)

>Pam and Paul

I did post the jig I use here a while back. Link below.

Regards from Perth

Derek


Jig for grinding/honing marking knife blades

Re: hollow grind debate on noisy side

ThomD

>"The problem I have with the flat grind is not so much the time it takes to polish the steel as the fact that the tendency to not polish all the way out to the edge overides any benefit from having the "extra steel" there. I would be very grateful for someone to prove me wrong on this."

You may not be able to prove yourself wrong, but if you ran into a skilled sharpener they might prove you wrong. There are various trades that consist largely of sharpening, even if at time ours feels as though it does. Those people may wonder why we bother with dovetails when nails work so well for them, but actually sharpening with incredible accuracy is not their problem.

"If clunky, time consuming, expensive (and other adjectives of choice) gadgets enable beginning or time constrained woodworkers to accomplish (filll in the task) some task in the time they have to spend on the task, be it sharpening or making a desk, I support their efforts."

Me too, so long as the task that interests them is not personal skills improvement, then they should probably try to learn how to do something. At the end of the day even a baby notices the advantages of biking without training wheels.

There does seem to be a lot of talk about hollow grinds vs flat grinds as though convex grinds didn't exist. There are many useful instances in woodworking and elsewhere, such as axes and drawknives. Sharpening these by hand is very difficultish. I don't know of any commercial woodworking jigs, there are some home shop ones, and power tools for it. I think it is fairly pointless to argue for an all convex world, it doesn't really survive a contact with reality.

"It is more difficult for some people to know when the have rocked the edge tool off of its very edge with a flat bevel."

I don't find that, the trick is to watch for the squirt of oil/water. The other trick is to try to abrace the middle third of the bevel pay no attention to the edge or heel.

"The thick Japanese blades obviate any sort of freehand problems I'd had,"

You, however are skilled. The biggest problem with the Jap. blades is that they are not equally hard across the bevel and the soft zone is the one with the extra weight in most cases. Not a biggie but one can certainly get in a bad place with them also.

jig

Pam Niedermayer - Austin, TX

>Looks good, Derek, but I'd have thought that if one were making tens or hundreds of marking knives routinely, it would be a lot easier if one invented a jig that could handle five or ten blades at once.

Pam