hollow ground (wheel) vs. flat ground

[Greg]

I was just catching up on some posts and read a few discussions re: hollow grinding with a wheel vs. flat sharpening with a stone. I couldn't resist adding my two cents.

Someone said the old timer rolled their eyes about hollow grinding. This confuses me, since old timers are usually very pragmatic.

It may be a bit of a religious discussion with some folks, but in general keeping an edge on a hollow ground chisel takes alot less time. Just a few strokes on a high grit stone will get your micro bevel back to a razor sharp edge.

An obvious rebuttal is why in the world would anyone spend all the extra time and effort to remove all that material to flatten the entire bevel edge when the only edge that does the cutting in the front 1/32"

I think part of the answer, and partially some of the controversy, is what type of work are you doing with that chisel. Chisels either pare or chop. Paring of flat surfaces requires a flatter angle, which is usually found on slicks. Chopping or heavy work and/or prying requires a steeper angle, and a narrower width. (Personally when working on a given joint, I am constantly going back and forth between several different chisel types, a 1.5" general purpose Barr, a .5" mortising chisel, a 1" corner chisel and a 2" slick )

The conclusion, I have been told, is that your sharpening method should reflect the type of work the chisel is designed to do. Therefore, the exception to hollow grinding is to flat sharpen your heavier duty chopping chisels (mortise & corner), because it gives the edge more stength. The thinner micro bevel edge from a hollow ground is weaker and won't hold up as well to heavy chopping.

I of course, don't hold a monopoly of knowledge here.... just passing along the various theories I've experieced along the way.

Other thoughts?
Greg

[Zeke]

I think the biggest argument, in my mind, is the way the flat and hollow grinds are achieved. Typically a flat grind is achieved using sharpening stone. While a hollow grind is typically achieved through a dry high speed grinding process. Since our tools are not made of high speed steel, there is a great risk of overheating the tool with the high speed grinding. Once the tool is overheated the edge is ruined. Either the effected steel needs ground away or the tool needs to be re-heat treated.

I do use a hollow grind on my turning tools though. They are high speed steel and I prefer a hollow grind for most turning tools.

Zeke

[beetle]

I happen to use the hollow ground method mainly because it is quick to fine tune the edge, however, I have really only have worked Pine so there aint a whole lot of abuse to the edge. I have and use a very slow RPM wet wheel grinder to put the initial hollow grind on the tool, therefore, I dont cook the steel.

Works well for what I do.

[TN_man]

Greg,
I also find myself using the same chisels that you mentioned in your post. I really like a 2" slick over the bigger ones.

[Thehardway]

An excellent tutorial on microbevels and general sharpening of chisels/tools can be found at: http://www.antiquetools.com/sharp/sharpmicrobevel.html

[Doc]

Being a knifemaker and blacksmith (hobby on both) I would not suggest a hollow grind for any chisel that you will be tapping with a hammer or mallet. The blade geometry has no support behind the cutting edge to take the strain of being impacted with a mallet, and will ruin the edge. It should do very well on a slick as it was meant for shaving, not taking large chunks of anything. that is for a chisel grind.

The reason behind a flat grind is to leave the supporting material behind the cutting edge to keep the edge from chipping or rolling. It will take the impact of a mallet very well if the edge is hardened and tempered correctly, and should last for years with proper care and sharpening.

In the end, just like designing a frame, it is all about geometry and support structure. Hollow grinds are good for straight razors, paring knives,and in this case slicks. Chisel grinds are ground for heavy use.....this does not mean take a beetle or commander to it! You can't use a sledge on a chisel..... !!!!!!!

If you have a belt grinder, and the correct belts, you can put a hair popping edge on a chisel grind easily. You will need the flat platen attachment to achieve the correct grind, and the thicker the material behind the cutting edge the better the edge should work. Hollow grinds are for paper thin edges that can pop hair before they reach it (big exaggeration from the old timers....they say a proper hollow grind will scare the hair off your arm).

Doc

[iain]

Theres a semi permant bald patch behind my left wrist,
Linda only found out why, when she watched me sharpening one day
 said she alwas thought it was some defection in my genetic make up, but didnt like to say in case offended me

[beenthere]

iain
I know exactly what you mean. 

[Don P]

  , Mine's on the right arm.

I start hollow, tune it flat and field dress it till its about lost its hollow, then go back to the wheel. its easier for me to stay flat on 2 points, when the hollow is finally sharpened out I tend to rock on the stone and make a convex face...back to the wheel for me. I also change my mind on the best way about weekly 

[iain]

I find with hollow, that i can touch up quite a lot, by pulling back on a flat leather strop thats loaded with a bit of chrome polish, a good 5 or 6 sharps before i need to go back to the diamond,
 and after 5/6 tiimes on the diamond, i use the sharpening guide,  then start back with the strop, when i cant be bothered with the guide (length of time to get an edge) then its a regrind, i drop all i want at the saw sharpeners on monday morn 08:00, and pick them up on my way back from dropping the boys off at school 08:30, about $20 for 8 chisels and a big hand full of drills, or free if they need something dropped of on my way back to town.




  iain

[Doc]

I have a bald head.....try that for checking sharp! Seriously, I use a leg. I can hide it in pants, and get no questions. Looks liek my socks have worn the hair off in a spot or two.

Like I said above (I think I said this anyway), it really depends on the job the edge is expected to perform. It is all abotu geometry. The same geometry used to design and build frames. You have to build support for things the right way for the job they are going to perform....

Doc