Chisle Bezel & Performance

Re: Chisle Bezel & Performance

joel

>I term a microbevel a secondary bevel about 1/64" wide or under. It most certainly helps edge retention while at the same time allowing the tool to act as if it has an overall lower angle. So yes it does improve the performance of the tool drastically. I can keep my paring chisels at 20 degrees but with with a 5 degree microbevel they still behave as if they were ground at 20. and bench chisels I get the performance of a 25 degree chisel with the edge retention of a 30 degree chisel.

For a time I stopped using microbevels - then I started up again - I don't why I stopped using them.

But if the microbevel is allowed to grow wider then entire performance of the chisels changes for the worse.

Re: Chisle Bezel & Performance

Bob Hackett

>It`s my understanding that while it makes it somwhat easier to sharpen,the real reason a micro-bevel is used is to strengthen the edge and help prevent things such as edge crumbling during use.If the chisel works well and holds up well at the lower angle then a micro-bevel would be just an added step that really isn`t needed till you encounter tougher material or processes such as chopping mortices.

I`m sure others will have somthing to add,maybe Adam will respond and explain his non-chopping approach to morticing yet again.I`m looking forward to trying his process as soon as I recover from my shoulder surgery.

Mainely,Bob

Re: Chisle Bezel & Performance

Lyn J. Mangiameli

>"Is the process of adding a "micro-bevel" (grind + hone + secondary bevel) soley to improve the sharpening process; or does it actually improve the performance of the tool (sharpness being equal)?"

Think of it this way. The cutting characteristics of a blade through wood are primarily controlled by the geometry of the blade edge itself and its orientation to the wood (bedding angle with a plane, holding angle with a chisel, skew angle with both) as it cleaves the wood fibers (yes there are some secondary things like vibration,etc., but they are of much smaller effect). The sharpness and refinement of the edge really are only another aspect of how well the determined geometry is manifested (ie, do the two sides of the angle intersect along precise planes).

This area of cleavage occurs within the smallest fraction of an inch entry into the wood. So only the tiniest microbevel is actually quite sufficient to establish the cutting characterisitics, which will be whatever is consistent with the overall bevel angle and the bevel's approach to the wood (again, the, bedding, holding, skew angles).

Thus, in a bevel up application (low angle plane, or chisel held with its back to the wood surface) a 20 degree primary bevel that has had a microbevel applied that gives an overall 25 degee geometry will behave precisely the same as a blade with a single (primary) bevel of 25 degrees. It won't behave any better or worse, as at the fracture area of the wood, there is no difference. Same thing goes for 30 and 40 degree angles, whether primary alone or combined primary and secondary (microbevel).

The advantage of the microbevel in these applications (I will skip back bevels here for simplicity) is solely ease of sharpening. Nothing more or less.

Yes a microbevel often offers an increase in edge retention, because of greater buttressing to the edge, but that increase is consistent with the angle of the presenting bevel, whether it be primary or secondary. That is, a 25 degree geometry will have somewhat greater edge retention than a 20 degree angle in most common woodworking tool steels, irrespective of whether that edge retention is achieved solely from a primary bevel, or through the combination of a primary and secondary microbevel. Again, the area involved in the cleavage of the wood is the determinant, and both primary or combined primary and secondary angles of the same overall geometry will perform identically, again, neither better nor worse than their counterpart of the same edge geometry.

This discussion can easily be drawn out to chapter length to take in various applications, and indeed both Bruce Hoately and Leonard Lee have done so in their books, but I hope this short essay will give you the conceptual basics.

Great Answer! Thanks

Fritz In Michigan

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Re: Chisle Bezel & Performance

joel

>"Thus, in a bevel up application (low angle plane, or chisel held with its back to the wood surface) a 20 degree primary bevel that has had a microbevel applied that gives an overall 25 degee geometry will behave precisely the same as a blade with a single (primary) bevel of 25 degrees."

This goes against what I was trained to do and my practical experiece. If the microbevel is small enough and a shaving thick enough (does not apply as much to planes where we plane really thin but applies to chisels). The higher angle strengthens the edge but the overall angle which is lower means that the chip will be less prone to breakout and split. But again This only works for very very small microbevels - otherwise I would agree with you.

I create a microbevel with about 5 stokes on my finest stone I am using, and then chase it. I remove it with every sharpening so it does not grow.

Re: Chisle Bezel & Performance

Alan Hamilton

>Fritz,

I use micro-bevels because I'm lazy.

On my edge tools I grind the bevel a degree or two or three less than the ideal angle. When stropping no longer restores enough sharpness, I get out my finest stone and put on a micro-bevel that's probably a degree or two or three greater than ideal. Only when the micro-bevel gets embarrassingly wide do I dig out my coarser stones and re-shape the bevel.

So I use micro-bevels as a time saver. (I told you I'm lazy!) When an edge gets too dull I don't always have to re-grind the entire bevel. I will let others debate the technical whys, whats, hows, and whens--not wholly because I know next to nothing about all the scientific stuff--but mainly because I'm too lazy to write any more. (Man, are my fingers tired. I think I should go lie down.)

Alan