Cutting Theory

[MichaelMouse]

Anyone else catch episode 2911 of The Woodwright's Shop with Roy yesterday? Brian Boggs gave some of the best information I've seen on working wood with an edged tool. His information on angles of attack applies to turning as well as shaving in a horse. You just have to make the mental leap to a moving piece and stationary tool.

 

[john lucas]

MM He came to the Craft Center for a demo and gave the same lecture. It is excellent. He certainly seems to know how an edge cuts although I think things might be slightly different at the speeds woodturning or a router bit are hit the wood. I would certainly like to read more.
A good example is many of the professional turners are going back down to 60 grit wheels because they feel it removes the wood better than 120 grit. This might be just on their particular style of turning but it tells you that sometimes a saw tooth edge is better than a smooth edge when the speed of turning is involved.

 

[Odie]

MM He came to the Craft Center for a demo and gave the same lecture. It is excellent. He certainly seems to know how an edge cuts although I think things might be slightly different at the speeds woodturning or a router bit are hit the wood. I would certainly like to read more.
A good example is many of the professional turners are going back down to 60 grit wheels because they feel it removes the wood better than 120 grit. This might be just on their particular style of turning but it tells you that sometimes a saw tooth edge is better than a smooth edge when the speed of turning is involved.

John......

60grit saw tooth grind.....!

Are we talking about gouges, scrapers, or both? I assume from what you're saying, the "professional turners" you speak of are taking the tool right from the 60grit wheel to the lathe......is that correct?

A good way to test this theory is to sharpen both ways on a single tool, and test it on a single chunk of wood.

I have done this in the past, and my findings for MY best method for getting the cleanest cut are as follows:

Both gouges and scrapers are sharpened on an 80gt Norton SG wheel. Scrapers go right to work using the fine burr created from the grinding wheel. All gouges go to a slow speed 200gt wet wheel.....and then either slip stone, or diamond hone.

I am able to re-hone gouges several times between grinding sessions, and scrapers are touched up frequently on the SG wheel.

I have come to my own way of doing things. I'm not saying what I do would be best for everyone, but after experimenting with other ways of sharpening, this is what works best for me. Although there seems to be a whole chorus of sharpening methods employed by woodturners, my method seems to be one of the more common ways to get a keen edge.

ooc

 

[MichaelMouse]

As you recall, John, the analogy I use is for the "tooth" effect of 60 vs 120 is that of the common pocket comb, where sighting along the teeth shows the same "sharpness" whether you look at the fine teeth or coarse. The name of the game is to present the tool to the work so the wood encounters the same view. As he explained, and as anyone who has ever whittled, let alone used a drawknife has discovered, drawing it across the piece while drawing it down takes the best (easiest) cut. With lathe work we have the rotation of the work to do this for us, we just have to present and feed the tool properly.

He also covered sharpness angle pretty clearly, though I'm not sure he used the Hoadley term.

 

[Rick M]

No link at the moment, but everyone can watch this page for an opportunity to see the episode online. I know **I'd** like to see it once the opportunity arises.

 

[Richard Baker]

Me too Rick. Hope someone will post if they notice it is available.

 

[Charlie Knighton]

Me too Rick. Hope someone will post if they notice it is available

Richard maybe they will bump it to the top also 😎

 

[john lucas]

Odie I might be wrong but I think they aren't necessarily looking for the cleanest cut. A good cut with an edge that lasts could be what they are talking about. I'll have to ask. I only know that I've heard it repeated by several of the top turners.

 

[Odie]

Odie I might be wrong but I think they aren't necessarily looking for the cleanest cut. A good cut with an edge that lasts could be what they are talking about. I'll have to ask. I only know that I've heard it repeated by several of the top turners.

Oh.....ok, John.

Yes, I guess I did misunderstand the purpose of the 60gt grind.

Thanks for the clarification......

ooc

 

[Joe Greiner]

I didn't know that Roy was back on the tube. I guess it's a local option with PBS stations.

I can appreciate that a saw-tooth edge would remove wood faster, same as a chain saw - probably more applicable to gouges than scrapers. Forstner bits work the same way. And the combination move with a drawknife is similar to a slicing, or paring cut with a hand chisel. For the finishing cut, the finer grind, and maybe honing too, should produce the best surface. Take another squint at Lacer and Wright's article in the Summer 2009 Journal.

 

[hockenbery]

60 grit wheels

Odie I might be wrong but I think they aren't necessarily looking for the cleanest cut. A good cut with an edge that lasts could be what they are talking about. I'll have to ask. I only know that I've heard it repeated by several of the top turners.

John is right many professional turners have switched to coarser wheels for sharpening. Microscopically you get a serrated edge.
I've become a convert. Sharpening is a bit quicker. The edge seems to last a wee bit longer. I don't see a degradation in the quality of the surface.

The burr left on a scraper is a bit too course off a 60 grit so it is important to remove it and strike a new one with a slip stone or diamond burr.

for a skew I still use a finer wheel and hone it.

I'd expect to sand a skew surface with 320 and a most gouge surfaces with 220.
But the gouge doesn't cut any finer than 220 when sharped with a 100 grit wheel

my 2 cents
Al

 

[John Jordan]

The purpose of the 60 grit grind is that it works well, and it's easier to free hand. There's no payoff for a further refined edge in green wood turning. It doesn't last longer, or much less for that matter. Constant sharpening is the name of the game. If the tool is sharpened with something finer, it will work just fine. I'm a very good sharpener, and can easily get any sort of edge that I want, but prefer the 60 grit edge and the way it cuts. That fairly ragged edge (microscopically) cuts real good.😀

I would add that I doubt many of us have switched-it's what we've known for years. 🙂


John

 

[Rick M]

No link at the moment, but everyone can watch this page for an opportunity to see the episode online. . .

The link to the video is now up. Impatient folks may want to jump to roughly the 11 minute mark once that much has downloaded.

Interesting concept at work in those tools with the chip breaker functionality.

 

[Charlie Knighton]

help Rick, please post direct link 😱

 

[Richard Baker]

Charlie, Ya gotta select episode #2911 and play that. Took me a while to realize that and get the episode # from original post. Not sure I understood what was said about bevel angles and chip breakers.

 

[Rick M]

help Rick, please post direct link 😱

Sorry. As Texian responded, I just didn't remember to repeat the episode number from the OP. But once you know which episode to pick, the linked page above is probably the simplest way to view online since it disguises the direct link to the video itself by using JavaScript behind the Play button for each episode.

 

[Charlie Knighton]

thanks, i see what you mean about the chip breakers, i do not reconize the chip breaker on a turning tool, the tilt or uneven pull i reconize as the riding the bevel ????????

 

[MichaelMouse]

thanks, i see what you mean about the chip breakers, i do not reconize the chip breaker on a turning tool, the tilt or uneven pull i reconize as the riding the bevel ????????

It's the angle of the flute to the wood surface that breaks the chips. Steep angles, while harder to control and push, roll the potential shaving so rapidly that it breaks and folds rather than slips under and peels. Think of the bevel-up planes - no breaker there. A lot of people do something similar when they crank up the speed of the lathe. Since they can't feed the tool fast enough to compensate and get a smooth shaving, they make little couscous-style chips.

The flat folks will tell you there are two schools on planing wild grain. One is high pitch and crumbles for shavings, the other is low pitch, bevel up, and narrow throat with transparent shavings. I've got a LN low angle jack that will shine curly maple.

 

[Jerry Hall]

More food for thought

Over the years I have found it hard to beat the reasoning and test results on this sharpening issue as documented by Lyn J. Mangiameli in June 2004. His classic article is at:
http://www.morewoodturning.net/sharpen.pdf
and is well worth reading, even if you don't agree with the following excerpt:

"An edge formed off a
coarse wheel may well have the intersecting
angles be sharp, but the edge will
be uneven due to the uneven surface of
the stone, thus leaving an edge that looks,
at best, like this V VVV VV VV V. An
edge that is formed on a fine grit wheel
will have a surface more like this
vvvvvvvvvvvvvv. The tips of the V’s may
be equally pointed, but there is more side
support to the more closely and evenly
spaced tips. The widely spaced coarser
V’s are going to heat more quickly, and
will break down more quickly. This is in
part why a “sharper edge†(which might
be better called a finer edge) will actually
be longer lasting than a coarser edge."

 

[rsser]

Hmm, but what if the burr is like a ragged saw edge but thrown back as Farrance argued in an early test of dry ground spindle gouge performance?

 

[Odie]

Over the years I have found it hard to beat the reasoning and test results on this sharpening issue as documented by Lyn J. Mangiameli in June 2004. His classic article is at:
http://www.morewoodturning.net/sharpen.pdf
and is well worth reading, even if you don't agree with the following excerpt:

"An edge formed off a
coarse wheel may well have the intersecting
angles be sharp, but the edge will
be uneven due to the uneven surface of
the stone, thus leaving an edge that looks,
at best, like this V VVV VV VV V. An
edge that is formed on a fine grit wheel
will have a surface more like this
vvvvvvvvvvvvvv. The tips of the V’s may
be equally pointed, but there is more side
support to the more closely and evenly
spaced tips. The widely spaced coarser
V’s are going to heat more quickly, and
will break down more quickly. This is in
part why a “sharper edge†(which might
be better called a finer edge) will actually
be longer lasting than a coarser edge."

That all sounds like sound reasoning to me, Jerry.....

I wonder if there is any additional possibilities we could suspect why some might want the coarse 60 grit grind.

I sure hate to make anyone's competence suspect, but just suppose there was a turner who never really could get a truly sharp edge. You don't suppose that person might mistakenly think the 60 grit grind might be just as good......but, in reality it's true that it's just as good as an edge that isn't as sharp as it could be.......?

ooc

 

[John Jordan]

Seems to work.🙂

John

 

[Odie]

Seems to work.🙂

John

There is a myth among woodturners surrounding fine shavings, and what they actually do indicate.

The problem is, fine shavings are not definitive as an absolute.

True, it's an indication of the level of fineness of cut, but not a standard which can be relied upon to separate it's performance from tools that are a little bit sharper.

A tool that is sharp to about 90% of it's potential, will produce fine shavings that resemble the shavings of the same tool (on the same piece of wood), which is sharpened to a higher degree of potential sharpness.

To grab a handful of fine shavings, and imply that this is proof that a better cut can't be had, is simply a false standard of measure.

The ONLY thing that is, or can be definitive......is how refined the cut is ON THE WOOD IN QUESTION.......when discussing sharpness in the upper levels of potential, there is nothing else that can be held as a standard of measure........nothing! (The only exception, is when discussing sharpness among those who haven't an enlightened sense of how to acquire it.)

ooc

 

[MichaelMouse]

There is a myth among woodturners surrounding fine shavings, and what they actually do indicate.

The problem is, fine shavings are not definitive as an absolute.

Well said! Whatever it was you said. 😕

The ability to take a continuous fine shaving requires a tool which is exerting so little lift and requires so little pressure to cut that even the crossgrain sections aren't broken.

A tool stropped to carving keenness, if presented at an improper angle, will chew its way through the wood. I think John just showed us that he knows that. As did Brian Boggs.

 

[Odie]

Well said! Whatever it was you said. 😕

The ability to take a continuous fine shaving requires a tool which is exerting so little lift and requires so little pressure to cut that even the crossgrain sections aren't broken.

A tool stropped to carving keenness, if presented at an improper angle, will chew its way through the wood. I think John just showed us that he knows that. As did Brian Boggs.

Whatever it was you said. 😕

Your confusion as to what I said is apparent, MM.....

Now, here's the point......plain and simple:

It's the quality of the cut on the wood that is the better indicator of......well.....the quality of the cut on the wood. 😉

The physical characteristics of the shaving can be the same, while the quality of the cut can vary between tools that can both be considered sharp.

While I'd have to agree that the shaving will vary considerably between tools that are sharp, tools that are not sharp, and sharp tools that are presented to the wood at a lesser cutting advantage than could be......this is not what I'm attempting to illuminate in my commentary......

ooc

 

[MichaelMouse]

I've always found that the smoothness of the shaving removed matches the smoothness of the surface left behind. Are you saying that's not so? Any particular type of edge you can think of that would make that so?

 

[Odie]

I've always found that the smoothness of the shaving removed matches the smoothness of the surface left behind. Are you saying that's not so? Any particular type of edge you can think of that would make that so?

No, that's not what I'm saying at all, MM.......

What I'm saying is you can make very fine ribbons of shavings, and tiny little fluff of shavings with tool edges that are identical in all aspects and both presented to the wood correctly and exactly the same manner.....except with the noted exception that one is sharper than the other.....mind you, both tools will be within the realm of what knowledgeable turners will consider to be sharp, but one will be sharp to a finer degree than the other.

The tool with the sharper edge will leave the finer quality of cut on the wood, but the shavings will have physical characteristics that appear identical. Now, on a small scale, you very well may be correct that the two shavings may have some differences when scrutinized microscopically, or elaborately. I'll have to admit that I haven't done that......nor, do I feel this is necessary, because the small intricacies of the shavings aren't my focal point......

.....this is because:

.......the surface quality of the cut is what concerns me.....not the shavings.

ooc

 

[steelguy]

sharpening theory

Suggest that a quick re-read of Lacer/Wright articles in AW from Summer 2009 and Winter 2008 would clarify some of these points