Tool sharpness

[Reed Gray]

Just when you think you have things figured out, some one plants another idea in your head.

I was chatting with Mike Mahoney about shear cuts and shear scrapes, and I can see little difference, but that is another thread. We were talking about grinding tools, and I mentioned that it looked like he used a really coarse wheel. I had bought up the D Way tools CBN wheels, and he had tried them and preferred the 80 grit one, which is a bit coarse for my tastes. He said that he liked a more serrated edge for finish cuts. Hmmmm........... The 'to hone or not to hone' thread comes up about once a year, and we are on all sides of that one, but I never considered the more serrated edge idea. There are big differences in how green wood cuts from dry wood, and big differences in how kiln dried, air dried, vacuum kiln dried, and solar kiln dried wood cut. Standard KD wood, you rip a board on the table saw, you get dust. On air, vacuum, and solar kiln dried wood, you get shavings.

Could it really be that a more serrated edge cuts air dried bowls better than honed, or 120 grit, or 150 grit, or 180 grit, or honed edges do??????

My head hurts!!!!!! Now, I have to try it out. I think I might actually have some dried wood.

Exercise is like hot sauce. If it don't make you sweat, then it aint no good!

robo hippy

[Bill Bulloch]

My opion on sharpening is that you can only get a tool so sharp. You can grind it on a course grit wheel or a super smooth wheel, you can horn it with a diamond wheel, a wet wheel or a jewel tool, but as soon as it hits the wood that fine edge is lost. So, when it comes to sharpening, I think that "preference" referes to the way you like to sharpen. Myself, I don't spend too much time sharpening. I have a slow speed grinder with 80 and 120 grit wheels for my lathe tools and a grinder with paper wheels for knives. When the tool needs a fresh edge, be it for rough cutting or sheer cutting, I touch it up on the 80 grit wheel. Sheer cutting my require more tough up, but it only take a few seconds on the 80 grit wheel -- no horning for me.

[Tim Rinehart]

Interesting thread, I've also heard the debates. May get down to analogies of how long a cheap serrated blade in the kitchen lasts to continue cutting, vs the honed blade edge which dulls rather quickly. Interestingly, the steel used in the kitchen actually puts a microscopic serration on the blade's edge, as I understand.
I would suspect the preferred way to sharpen may vary somewhat with the nature of the cutting, i.e. roughing vs final cleanup.
Good thread, will be interesting to see where it goes.

[Greg Just]

I agree with Bill, although I do hone my skewe chisel. I have a variable speed grinder with the stock grinding wheels and have been using this with the Wolverine jig for 5 years. I have limited space and budget and would rather get other tools. Just my 2 cents

[John Keeton]

Reed, there does appear to be a uniqueness to the edge acquired using a CBN - at least to the naked eye. It does seem to have the appearance of a coarser edge, however, to the touch it feels much sharper and I find a very noticeable difference in the cut. Hard to explain without some microscopic inspection, I suspect. But, I just take it at face value and don't really need a better explanation!

I do think Bill is correct on a super sharp edge - it fades rapidly. I found interesting Stuart Batty's comment on his frequency of sharpening. As I have refined my turning skills (still a long way to go!) I find that I sharpen much more frequently. My touch is more controlled, and I seem to be able to sense the degradation of my tool edge much quicker.

I also think your supposition that different edges seem to work better in different conditions - dry wood, kiln dried, etc., and even perhaps between species.

So......I look forward to the results of your research!!

[Faust M. Ruggiero]

Wood carvers have had this often heated discussion as long as I remember. One sharpens by hand and buffs on leather strops while another hones with a buffing wheel or paper wheel and compound. In the end, it is just that, discussion. On a carving gouge, we make the inside of the tool as polished as the outside to remove the grinding marks left from the manufacturing process. Without doing that, a carving tool will leave lines in the work. Most wood turners, including me, don't do that to our turning tools. As long as the tiny grooves are left on the inside of the gouge, no amount of polishing on the outside bevel will make the edge anything but scalloped. But, for wood turners, that's OK. Years ago we used the wire edge to do most of the work. I personally think, we make sharpening a hobby by itself.
faust

[Doug Wolf]

I never used to hone, but I recently was trying to shear scrape the face of a 18" maple platter and got tried of grinding away my bowl gouge on the slow speed grinder to touch up the edge. So I pulled out the "Green" (Fine) diamond file and I couldn't belive that a couple of swipes would give me the edge I had been trying to get with the grinder. And now I'm honing 10 or 15 times before I go back to the grinder and I'm getting a better shear scrape cut.

[Reed Gray]

I have been playing around with different tools for finish cuts on dry wood to see what gives me the cleanest cut. I am using a piece of KD figured Myrtle.

Scrapers: grinder burr, burnished burr, honed burr, no burr. No negative rake burr though. The higher the shear angle, the better the cut, but no matter how steep the angle, always some very minor tear out left. I would give a very slight advantage to the burnished burr.

Bowl gouges: U, V, conventional square grind on the nose with very minimal sweep, swept back, HSS, Thompson, 40/40 degree bevel Stuart Batty grind, level handle, dropped handle, shear cut/non bevel rub. The bevel rubbing cuts got the best results. The broader, more rounded noses with the tool fluted rolled to 45 to 90 degrees away from the cut (I think this means open flutes, as opposed to closed flutes but never understood that one). It seems that the cleanest cut went to the 40/40 bevel. The conventional grind, rolled just slightly over was a very close second. The others were all pretty close. I would think that I could have started sanding most at 120.

Other: Spindle roughing gouges. I know, we are not supposed to use these on bowls. If you try to use a scraping cut with them, flutes straight up, that is suicidal for wood, tool, and turner (to see this, check out the You Tube video of the Laguna 18 inch lathe). However, if you rotate the flutes and do a shear cut, it actually does a very nice job. I actually got as clean of a surface as I did with any of the above gouges, and maybe even a bit cleaner. I used a standard SRG, and a continental style/broad sweep type as well. I tried the broad sweep (BS gouge???? oh, that is too much!!!!). It also cut very cleanly. I did find it cut better if I dropped the handle, as with the broad sweep, that kept the cutting edge balanced, or on the lower half of the tool, so no problem with it wanting to roll over in a nasty catch.

Fluteless gouge: This is Doug's tool, a tool that has been around for a while, similar tool is the bowl skew. This gave me the best cut of all. No contest. Shear angle when cutting with this one is around 70 degrees, and bevel rubbing.

Only conclusion thus far is that a high shear angle works best. That is easiest do do with a cutting tool that has a ) profile on the nose.

I repeated this on some old punky big leaf maple. Scrapers in any mode were impossible. The gouges were okay, but not good, the SRG and BS gouges were a little better, and again the fluteless gouge gave the best results. I have used a small scraper the same way, that is swept back on one side, and best description is it looks like half of a gouge. Bevel rubbing cut, high shear angle. I tried it with all burrs, and no burr, and like grinder burr best. I haven't noticed that 80 or 180 grit wheels made much or any difference.

The D Way CBN wheels seem to be breaking a little, they do not cut quite so aggressively as when new, but that 80 grit wheel flat out removes some steel, a very light touch is great.

I will try to get a You Tube video up in a week or so.

robo hippy

[Dan Hintz]

I found interesting Stuart Batty's comment on his frequency of sharpening.
John,

I'm assuming you're talking about my mention of Stuart only getting 15-20 seconds before needing to resharpen? Just so I'm clear, that was specifically mentioned about the burr on a shear scraper (well, his version of a shear scraper created from a standard chisel). While it shouldn't matter that his shear is different than most others, at least as far as the burr is concerned, I thought I should mention it, just in case. He truly is using the burr for all it's worth, and once it's gone, he wants it back immediately. I suppose this goes back to Bill's comment about burr longevity... whereas most of us would use the tool long past it's proper age (i.e., long after the burr is gone), Stuart is bucking the trend and using it properly :-/



Reed,

The difference between cut and scrapes is pretty clear, IMO... with the tool angled for a cut, the edge has a slicing motion in relation to the wood's plane, almost pulling up the grain as it goes. With it angled for a scrape, it's more of a burnishing, pushing the grain down.

[Reed Gray]

When Stuart scrapes, he uses a negative rake scraper, and it is a grinder burr. Because of the double bevel, that burr is very fragile, and is gone in seconds, just like a honed burr. A burnished burr is very strong, and will keep a good cutting edge as long as any gouge. A burr from my CBN wheels is almost as strong as the one from burnishing. A burr from more standard aluminum oxide wheels is not as sturdy as the the others, but more long lasting than the negative rake scraper burr.

I agree that the fresh off the grinder edge is gone in a few seconds, and the harder steels will keep a working edge longer than HSS, but not the 'fresh' edge.

The difference between cuts and scrapes is pretty clear. Scraping cut with a scraper: tool flat on the tool rest, angles slightly down. Excellent cut for roughing, and cutting edge is 90 degrees to the wood rotation. You can do the same cut with a gouge, with the flutes rotated 90 degrees to the side. The 'shear scrape' is mostly defined as the cutting edge being at a 45 or so degree angle to the wood rotation, and the bevel is not rubbing, and this can be done with either scrapers of gouges. Thing is I can get the same surface results on wood with a shear angled cut with either tool, the shavings look the same, and it doesn't seem to matter if the bevel rubbing or not. Only difference that I can see or feel is that the bevel rubbing leaves the wood slightly burnished/shiny, while the non bevel rubbing cut does not. I have never gotten a burnished wood surface from a scraping cut. It does cut and lift the fiber, more by pulling, with a coarse slicing action, which is why it is called a scrape. You can get a good clean surface if you are cutting end grain, but not if you are cutting side grain. Mike mentioned to me that the difference is what you get from finish cuts on green wood compared to finish cuts on dry wood. Not all of the same cuts I use for finish cuts on green wood will work as well on dry wood, and dry wood will take different methods to get a better surface.

The best analogy I have been able to come up with for explaining the difference between scraping and shear cuts is speed bumps in the parking lot. If you hit them head on, that is more of a scraping cut. If you angle over them, that is more like a shear cut, as the bump is still the same height, but it is a lot smoother.

I guess you could say that a gouge can shear and scrape cut because the wing can be scraping while the nose, which is rounded up will be at a shear angle.

I can't ever seem to be content with knowing that some thing works, I have to also know how and why.

robo hippy

[Jim Burr]

I was thrilled to go from a 80g highspeed wheel to a Tormek...Like being in a coma then waking up! How sharp is a matter of taste to a point. Go back to the old knife sharpening guides from the 40's and 50's, maybe farther back. A lower angle...thinner blade...is sharper, but only for a short time. A fatter angle...fatter angle and less cutting surface but lasts longer...more durable. I'd challange anyone to turn a pen at 3000 rpm with a Swiss Army Knife!!!! I sharpen when it feels right, a science to be sure, a skill as well, so the best affordable system with the best results would be reasonable. I'm thinking that angle of surface and the durability of that angle would play a part in how often one hits the grinder.

[Bob Bergstrom]

I wonder if honing and super sharp edges are more of a concern to novice and more part time turners. I sharpen with no jigs and put an edge I feel will best suit what I'm doing. Roughing out a bowl is fast and quick at the sharpener. Finish cuts and thin turning get a little more attention. I used to sharpen on a 3x sixty grit wheel. I like the saw tooth edge but the wheel disappeared too quickly. I went to an eighty grit 3x and really see little difference in what I do. I've turned a lot of spindles and use the skew right of the grinder also. It cuts what I want and does it well enough that I need little sanding. As has been said, we all can do things differently, but the finished result is a good looking piece.

[Jeff Nicol]

Reed, The way I see it is that when you take an edge that is fresh off the wheel with the bur for scraping and shear scraping, it is like a bunch of little razors all hooked together that kind of cut independently from each other. This creates less of a surface area like a nicely honed edge, allowing less friction and the ablility to not worry so much about a perfect angle for the scrape or shear scrape. With honed edge if you are off just a little it can catch or not cut at all, with a burnished bur on a true scraper the tool is held above center with the edge tipped down to center to use just the bur for the scraping action. If I use a freshly sharpened half round or round scraper I use it the same way, but like you said a burnished bur lasts a bit longer, but I like the ground bur better for the reason I stated above, lots of little razors.

Now for "Shear scraping" this can be done with a regular flat scraper tipped up so the edge is addressing the wood at the steeper angle thus giving you more of a shearing action but with a scraping type cut. With all other tools the shear scrape can be achieved the same way by addressing the wood at the steep angle with the edge of whichever tool you are using. The same thing works here with the ground bur and the honed bur, I like the grond bur with it's many little cutting edges better for larger surfaces and I will sometimes hone the edge for working around beads on the outside of a bowl or when I am near the foot or other embellishments. I can get in and make very steep angled shearing cuts that produce very fine "Angel Hair" curls for a very clean cut.

So It is true we all have our favorite way of doing each cut, but the scraping cuts can be related to this: What kind of knife cuts through a warm loaf of bread best? Serrated or razor sharp, the sharp knife will do the job, but the serrated one will not squash the bread and you will end up with a slice not a blob!

My 2 cents worth of turning knowledge,

Jeff

[Larry Marley]

my experience is sharp tools are better. I was at a trade show without a jig for the bowl gouge and Craft supply offered to sharpen my gouge any time I needed
it. so on the first day they sharpened it 3 times in 6 hours. They used an 80 grit stone. then Jeff from Tormek took all bowl gouges and said "You will see
these in the morning after my first demo." The next day he handed me two gouges that were polished like a mirror. People actually stopped to ask me how I got
them so perfectly polished like that and I sent them to Jeff. the result? two days of turning 9 hours on Saturday and 5 on Sunday and I never needed to
sharpen them.

[Joshua Dinerstein]

I found interesting Stuart Batty's comment on his frequency of sharpening.

John, Do you have a reference for this comment? I would like to read what he had to say.

Thanks,
Joshua

[Reed Gray]

I will admit that I have never tried a tool sharpened on a Tormek. Might have to give that one a try. Probably should ask Mike about that one too.

robo hippy

[John Keeton]

John, Do you have a reference for this comment? I would like to read what he had to say.

Thanks,
JoshuaJoshua, I apologize - I should have quoted the reference to this thread (http://www.sawmillcreek.org/showthread.php?171177-Woodturning-Workshop-feat.-Stuart-Batty&highlight=) started by Dan Hintz, in which he made this comment about Batty - "His use of a standard chisel (reground, of course) as a scraper was interesting, and I was surprised to hear him say he only got 15-20 seconds worth of turning before needing to put a new edge on the tool."

I will say that Stuart went to his sharpening station frequently during his demos at AAW, though there was a lot of speaking, etc. going on, and I did not notice the times being that short. Of course, Dan was also just referencing the use of the scraping function, too. But, I suspect Stuart also sharpens his gouge with much more frequency than most given what I observed.

It could also be that he was marketing his hi-tech sharpening station, too!!

[Reed Gray]

Well, went out to the shop, brushed a couple of years worth of dust off my Tormek, put on a fresh black Japanese stone that I have had for a couple of years, and sharpened one of my gouges on it. It was sharp, maybe as good as my CBN wheels, but not any better. It didn't cut any better either. I did use the hone wheel on it, but it could use some fresh compound on it, but it did polish up, and still, no better than my CBN wheels. I did put in a PM to Tormek to see if they can put me in touch with an expert. I did touch one of my fluteless gouges, and got the same results. Honed or not, still the cleanest cut.

robo hippy

robo hippy