Replies

1. 
   jeffs | Oct 13, 2011 04:01pm | #1

   hollow grinding

   I don't use a grinder to shape my chisel or plane blades so I can't really comment on hollow grind benefits. I have always sharpened my chisels and plane blades with water stones which means they are flat ground. I know this means I need to sharpen the whole face of the blade which means it takes longer but I find that for "re-sharpening", as opposed to a new blade, that is just not a big deal. It does not take that long to get a blade sharp using this method.

   Jeff

2. 
   LZCarpenter | Oct 13, 2011 08:17pm | #2

   Probably flat is best?

   I ran into alot of the same conflicting info on my searches of how to rehabilitate old-great-gramp's (etc.) tools and several that I bought.  General info seemed to say grinding wheel and hone enough to get the toothed (is that the right word?) surface off the edge and hone off the burr on the back.

   But you turn around and the 'best' tool people almost uniformly sharpen dead flat, and for those that have the finest equipment, to a mirror polish.

   I buy the physics on hollow ground, that is, that a concave bevel surface will "peel" wood off better (according to one tutorial I read), but on the other hand plane irons (traditionally) have the flat up.  I think, in my novice opinion, that even if a hollow ground surface is better in general, a mirror flat chisel or plane iron will be sharper than the best hollow-ground bevel you can muster by hand in a shop, and certainly better than a round grind.

   As a secondary note that may argue in favor of flat ground, LN always suggests that you put that second "micro-bevel" on the very edge for better edge durability.  I have found the second bevel on several well-honed old blades I've come across, everyone here probably will say that is the way to do it, and it does seem to work.  Assuming that the converse is true, that a thinner edge will wear worse, which is reasonable, then an "ideal" hollow grind might actually make blade performance worse.

   Again, that is based on what I've read and done with my tools so far, which isn't alot compared to the wisemen on here.

1. 
   joinerswork | Oct 14, 2011 08:48am | #3

   The argument for a holow grind on the bevel of a chisel or plane iron is not that it will somehow cut "better", or be stronger. It is simply an expedient means of removing excess metal from the end of the blade. Once the blade is honed, the hollow is gone from the blade's business end (the very edge). 

   The advantages of the hollow behind the edge are twofold: First, there is less metal to be removed when re-sharpenng a dull edge- only the very toe and heel of the bevel must be worn away to restore the edge.

   Secondly, and this only applies if one is sharpening freehand, not with a guide or jig to maintain the bevel angle, the hollow provides a more secure or positive reference bearing on the stone surface.  That is, it is easier to feel when you are rocking off of the bevel.

   Final note, when honing freehand, if one is in a hurry to resharpen and get back to the "real" work, it is all too easy to put more pressure on the toe of the bevel, to stone the very edge and not the whole bevel.  With a hollow grind, this has the effect of slightly increasing the bevel angle.  With a flat grind, this has the effect of rounding (making convex) the bevel- if this is severe enough, it can prevent even a very sharp plane from cutting- it is riding the bevel-or make it nigh impossible to pare with even a very sharp chisel.

   Ray 

1. 
   LZCarpenter | Oct 14, 2011 04:16pm | #4

   Ahhh, that is a much more self-consistent and technical explanation.  Thanks, JW.

2. 
   roc | Oct 14, 2011 11:19pm | #5

   Ray is Right. All the way.

   Hollow grind is only for sharpening without a jig or to help get the excess metal out of the way fast ( power grind verses endless time on the coarse stone ) so you can start in on the real sharpening which is all about the microscopic area at the very edge.

   Any hollow  beyond that is just not important to the cut.  At least in a hand plane or chisel used on wood.  There may be other arguments in other applications that I can't speak to such as heavy duty butchering or timber axes.  In those cases a good portion of the blade is buried in the material like a wedge with friction on both sides of the blade.  Woodworking there is not that situation except a little bit in mortising but still not a problem

3. 
   Metod | Oct 15, 2011 11:51am | #6

   Security

   Dave,

   This

   "hollow provides a more secure or positive reference bearing on the stone surface"

   is a quote from Ray's post. 

   If you get good with free-handing, you will be able to minimize the amount of metal removed. I treated hollow grind as a sort of training wheels - at one point of progress with free-handing you just do not need them anymore. 

   Hollow grind helped me, for the reason above,  to get 'good enough' with free-handing, and would reccommend that route to those starting out.

   Best wishes,

   Metod

   Metod

4. 
   Tony Z | Oct 15, 2011 02:38pm | #7

   I use hollow grinding because of the speed of going from dull to shaving sharp (bear in mind this is only for an edge beyond honing).  For normal work practices, I hone rather regularly (free hand, unless something extraordinary requires a jig, such as a very short blade).

   I don't make a science of sharpening--years ago I tried those methods and, to be frank, the edge I got was probably worse than I do now.  Maybe I just figured out how to hold my tongue????  I don't fret over angles either--I have a LN #4 with HA frog always ready to go when my normal planes don't cut it.  If the high angle doesn't work, then it's the scraper.

   But, again, I hollow grind whenever I got a nick to remove, or an angle to change.  

1. 
   EdHarrison | Oct 15, 2011 03:38pm | #8

   Another vote

   for hollow grinding. I usually use a hand grinder unless the edge is way out of square or something. To me it seems like if you use a power grinder the trick is to go slow, keep it cool, constantly check your progress. I picked up the tip from Ray to grind almost all the way to the cutting edge so as to not waste steel, and the tip from Larry to constantly dress the fine oilstones with a diamond plate to keep them flat. Also the idea from Larry that getting the back of the blade or chisel absolutely flat and and true is of crucial importance to developing the sharp cutting edge.

   No way I would see myself whaling away with a honing jig on something. Life is just too short to do that. 

1. 
   Recruiter | Oct 18, 2011 04:49pm | #9

   Thanks to all

   I think I need to "hone" my skills at sharpening the edge.  (I couldn't resist) 

   I had been hollow grinding my irons and chisels, then used a sharpening jig to set my final edge.  This way, I didn't need to worry if I caught the edge properly on the stone.  I would get the angle I needed each time, at the edge.  Kind of took the guesswork out of it, I suppose.

5. 
   derekcohen | Oct 22, 2011 09:25pm | #10

   Hi Dave

   There is no one "correct" way to sharpen. Thousands of different opinions abound.

   As Ray wrote, hollow grinding is expedient. What he needed to add was that it is essentially the grinding method preferred by woodworkers who freehand hone their blades. A hollow grind will self-jig the blade so that it is supported on the sharpening medium. A hollow grind automatically created a microbevel, which reduces the area to hone, making sharpening faster.

   Flat grinds are predominantly for those that (a) do not use a grinder at all, or (b) are intending to use a honing guide. Amongst those that do not use a grinder will be some who do not want any machines or prefer beltsanders, as the latter are cooler to grind and less likely to damage the metal. Also include those who use Japanese laminated blades. Using a honing guide focusses on creating a secondary bevel, so it matters not whether the grind is flat or hollowed.

   Regards from Perth

   Derek

6. 
   CaptainSkinnyBeard | Nov 08, 2011 08:42pm | #11

   This is an oversimplification,  but a tool edge made on the circumference of a grinding wheel is “hollow ground” and a tool edge made on a flat stone is “flat ground”.  Although there are implications for how a tool will be sharpened, flat or hollow grinding refers to how the edge of a tool is manufactured or how a damaged tool is reground.