Thread: Cutting edge of hollow ground blades short lived?

Lappa, this was a post in an overseas forum I read when researching the flat v. hollow argument. There were no pics

While researching hollow v. flat grind, I read this post in Fine Woodworking. Unfortunately it makes no mention of whether hollow grind edges do not last long:
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The argument for a hollow 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

Read about the advances using the unicorn method on Wood Central, it was developed to overcome edge problems in lower quality blades initially and those who have used it are fairly enthusiastic about the results. David W or Derek C can be more forthcoming on the method.

As apprentices we used two sets of chisels. One set was hollow ground and the other flat ground. We also had two plane blades for each plane - One hollow the other flat ground. The reason for this was that we worked in some extremely hard timbers and also some very soft. The hollow ground chisels were prone to corner chipping in things like Ironbark, Gidgee etc. Particularly when chopping out mortices. The soft stuff, like Red Cedar, was much happier being worked with a hollow ground blade.

Originally Posted by Dengue

Lappa, this was a post in an overseas forum I read when researching the flat v. hollow argument. There were no pics

Sorry. Hit the button by mistake. Fingers like Mars Bars

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the unicorn method 


Wow, that is a real eye opener, Chris Parks. Just sharpened my set of old Narex chisels and spokeshave blades today, will dig out my buffing wheel and give it a go on these hollow ground bevels. Haven't used it for a couple of years

rustynail, thanks for this, makes sense as to why there is a place for both the flat and the hollow ground blades. Basically you are saying that the flat ground edge will last longer than the hollow ground edge, when used on the same timber