Thread: Experimental application of David Weaver's 'Unicorn' sharpening method to scrapers

Hi, Neils - this is the conclusion I would expect. The unicorn method can't make something more abrasion resistant, rather it's intended to address early failure due to impact. As you mentioned, the one offshoot with the buffer even if it doesn't improve wear resistance is that it does greatly improve edge fineness and uniformity without much effort. if there's a little bit of rounding, sometimes this has to be offset by adjusting the angle before using it.

As far as skews go, if a skew is used at an apex angle where it fails ultimately by wear and not by impact, then this method will again just provide a high level of polish (Which someone may like finishing off of the skew) without having to do much hand work. You can more or less go from any medium stone to the buffer and get a scratch pattern on an edge as fine or finer than any synthetic stone.

In terms of rounding, if it's going to be applied to both sides of the bevel, the angle into the buff and the level of pressure should both be reduced a little bit to avoid an apex being too rounded (or just less buffing - whatever it takes to make for a little bit less total rounding since the rounding is being done twice instead of once).

I buff my HSS skew off of a diamond hone. The surface finish is sublime, but I have no idea if it actually lasts any longer than honing the edge by hand did - it's just quick and lazy and good at completing the job. I'm not much of a turner ,but would guess some people like a flat bevel on a skew and some like one more rounded. It'll take a little bit of experimentation for everyone to find out if they need to back off on bevel angles before buffing to avoid having a skew that doesn't initiate in a cut about the same as they're used to feeling with a grind or hand hone.

When this topic first came up, I avoided suggesting anyone use it for planes - because planes fail by abrasive wear (except in dirty, interrupted and very hard, silica laden wood...). It took some finagling to come up with a method to use the buffer to finish an edge and get the same longevity as really fine hand honing to a crisp apex, but it's doable. What I did find is that wood that has silica in it on a hand plane blade suddenly doesn't nick or notch the edge, but the trade off is about 20% of edge life in clean wood. If the comparison is done in abusive or dirty wood, the unicorned blade lasts much longer - silica laden khaya, mahogany or cocobolo will make an edge fail fast, but the bolstered apex of the unicorn method makes planing seem like it's occurring in normal wood as the deformed apex is what stops entering the cut when planing wood like that rather than rounding wear being the issue. When an edge is nicked or dented, it doesn't just get pushed back, but bent back and forth on both sides.

while doing a plane wear test unrelated to the unicorn in june/july 2019, I ran into an inclusion in maple that looked like silica. This is the result:
https://i.imgur.com/vuyz0Ho.jpg

Every type of iron that I was testing for wear (various alloys and different hardnesses) failed at this spot - the apex got bent and then the damage went further into the edge. Not on the first stroke, but over several strokes. You can just make out in looking at the voids (which are around a few thousandths of an inch each, but covered about a quarter to a third of the blade) that the metal is partially nicked out, and partially bent. the scope only sees well what reflects directly back at it, so bent metal's light level falls off pretty easily.

I took one of the irons like this (in this condition, it will not start a cut) and bent the edge back on cast iron. It wasn't damage free, but it planed fine again with the voids bent back.

A unicorned plane blade will sustain much less damage or none in a situation like this (but it's also probably not common for people to plane through this kind of stuff)

Back to turning tools - if someone has a skew that shows marked nicks in it once it's worn rather than a reflective even line of no-damage wear, they'll probably see increased edge life off of the skew. Almost everyone will find the buffed edge finish off of the skew several times brighter than they've seen before (the same is true of planing -the rounded bevel side either burnishes the wood or the uniformity of the edge/polish is just better because the planed surface is like a mirror)

This is a picture of the reflectivity on the surface of a piece of cherry after buffing (with 5 micron compound, though the buffer probably leaves a surface more like 1 micron something else and it completes the job well). You can see the individual LEDs on the surface. The iron that I used to make this is one that home depot sold for $2.99 here. It's a good candidate for buffing because it's just a little soft and not very good if a crisp apex is left on it. If the apex is buffed, it holds up extremely well (I'm still using it in my smoother - it's quick to sharpen and its longevity issue went away once the edge was strengthened).

https://i.imgur.com/ivsb5X8.jpg

Unfortunately for us in the states, the irons also went away (home depot discontinued them).

separate comment 2 - it just occurred to me that some turners will finish the edges of cylinders, etc, with a block plane. The unicorn method is super for this (you can use old vintage block plane irons that are soft as cheese on the hardest of woods and they work well and leave a very bright finish).

The buffing has to be done to the bevel side only in that case (for obvious clearance-related reasons).

For people who turn and wouldn't have read this, the method is just to completely refresh the bevel (removing any buffed edge) each time you sharpen using a medium stone and then buff just the tip. if the buffed bevel isn't removed, then the result is predictable - the apex rounding continues to get steeper until starting is difficult. This is easy to avoid just by honing the whole thing off each time.

Originally Posted by D.W.

Hi, Neils - this is the conclusion I would expect. The unicorn method can't make something more abrasion resistant, rather it's intended to address early failure due to impact. As you mentioned, the one offshoot with the buffer even if it doesn't improve wear resistance is that it does greatly improve edge fineness and uniformity without much effort. if there's a little bit of rounding, sometimes this has to be offset by adjusting the angle before using it.

As far as skews go, if a skew is used at an apex angle where it fails ultimately by wear and not by impact, then this method will again just provide a high level of polish (Which someone may like finishing off of the skew) without having to do much hand work. You can more or less go from any medium stone to the buffer and get a scratch pattern on an edge as fine or finer than any synthetic stone.

In terms of rounding, if it's going to be applied to both sides of the bevel, the angle into the buff and the level of pressure should both be reduced a little bit to avoid an apex being too rounded (or just less buffing - whatever it takes to make for a little bit less total rounding since the rounding is being done twice instead of once).

I buff my HSS skew off of a diamond hone. The surface finish is sublime, but I have no idea if it actually lasts any longer than honing the edge by hand did - it's just quick and lazy and good at completing the job. I'm not much of a turner ,but would guess some people like a flat bevel on a skew and some like one more rounded. It'll take a little bit of experimentation for everyone to find out if they need to back off on bevel angles before buffing to avoid having a skew that doesn't initiate in a cut about the same as they're used to feeling with a grind or hand hone.

Thank you David for your expert analysis.

The point you make about skews prepared in this way not initiating a cut in the way they normally would is, I anticipate, one of the potential downsides of its use on skews. Infrequent users of the skew faff away trying to get it right and a slightly higher entry angle will be inconsequential to their efforts, whereas for the skilled skew users the best angles of approach have become almost built into their muscle memories and they may balk at any small changes to the geometry of the tool. That is why I have left it to the skew officianardos to give us their verdict.

~.~

I've recently experimented further using this method for the maintenance of bowl gouge flutes, not the bevels. I experimented with the method on the bevels and found no discernible benefit, but many of our bowl gouge brands come with hectic milling/grinding tracks in their flutes that require considerable effort to remove them sufficiently to give a good cutting edge... as we know, both surfaces are important in forming that good cutting edge.

Given the tricky curvature in the flutes and the amount of work required to grind out and polish away those milling tracks, most of us turners only fully tame a few millimeters or so on the tip of the flute with the intention of doing more work on them if and when required. A narrow cotton buffing wheel loaded with fast cutting compound gets into the flute and speeds up the final polishing after doing the initial grinding out of the milling tracks near the tip end.

What I have been doing lately is also using the buffer on the flute every three or four sharpenings and this is gradually extending the fully polished zone while also cleaning out any build up of crud there. I do that before sharpening the bevel, not after. It is very quick to do with the contact time on the buffer taking only 4-5 seconds each time.

Theoretically buffing the flute after sharpening the bevel would remove any residual "flaky bits of steel" left on the edge, which may improve its performance, but I haven't found a noticeable benefit from doing so the way I did with scrapers. Unlike the scrapers that are used for light finishing cuts, turning gouge are used for heavy cuts and their sharp edges lasts so briefly that small tweaks like buffing the flute after each sharpening is unlikely to make a noticeable difference.

Although related, using the buffer to maintain the polished area of the flute near the tip does not serve quite the same purpose as flat work users of the method on their hand planes, however, over time it will reduce the included angle at the very edge by a few degrees, which may or may not be significant for you, which you may need to make adjustments for.

I've been using a fine green buffing compound, as that is what I had, but a coarser grit might be quicker.

I expect that spindle gouges would also benefit from having the same treatment, although their flutes are much easier to deal with than bowl gouges.

I think as DW says, I'd want to get an idea for how the edges are failing. The unicorn works magic when the fine bevel edge chips or rolls or wire edges hang on. These failures tend to work their way up the bevel with extended use.

Things it doesn't fix:
Gross failure behind the bevel from the steel being too thin for the work being done.
Pure wear dulling....

Actually, what the method does is sort out premature edge failures and get you back to "Conventional wear." At that point, the edge that falls off after an unacceptably short amount of work holds up "like it should" for the steel and heat treatment.

If it's lasting "As expected," then you probably won't get any benefit. So for example, for the giant heat and cutting forces generated in stock removal turning, I would guess the larger benefit would come from moving up to progressively higher carbide volumes of stuff like CPM10V... Of course the downside is that sharpening the stuff is hateful, but given the right grinder wheels, probably not that bad.

Originally Posted by truckjohn

If it's lasting "As expected," then you probably won't get any benefit. So for example, for the giant heat and cutting forces generated in stock removal turning, I would guess the larger benefit would come from moving up to progressively higher carbide volumes of stuff like CPM10V... Of course the downside is that sharpening the stuff is hateful, but given the right grinder wheels, probably not that bad.

Many of us turners have more recently gone over to CBN grinding wheels and they makes short work of any of the HSSs that we poke at them, including CPM10v, CPM15v, M42 and standard M2 that has been cryogenically triple treated.

Although the manufacturers claim otherwise, IME there isn't a big difference between any of those HSS used for turning tools. They are all good for our purposes. If I was to make any distinctions between any of them I would say that the edge on CPM15v does outlast the others by a bit, but then doesn't take such a keen edge. I put that down to the larger carbides size in that steel. And, M42 does give one of the finest edges, which is nice for finishing cuts.

With any of those HSSs the effective cutting edge on a bowl gouge that is hogging down a blank lasts so briefly that small nuances in edge failure are insignificant in terms of the grind, turn, grind, turn... work rhythm... so much so with some of the harder and abrasives woods we use down here that we leave our grinders running when we are turning them...

Hmmm...

My takeaway from this - if I've read it correctly - is that in terms of productivity the only time it makes a difference is in the finishing cuts.

For a turner who automatically reaches for 240grit or lower as part of their SOP for finishing then this method is fairly pointless.

Me, I love turning... but where I fall down big time is in the finishing process. I have no patience for it once I've got the bulk of an idea out of my head and onto the lathe. My 'ideal' for a finishing process is to be able to apply a wipe-on finish to a surface straight off the tool, so I can get back to turning and trying to get the next idea out of my head.

But, sadly, ideals are rarely reached.


Anywho, my point is that as such for finishing cuts I always use a freshly sharpened tool and keep it sharp for the duration. (Unlike when roughing. I know I should keep the roughing/shaping tools as sharp, but still... )

FWIW, I rarely raise a burr on my finishing scrapers as I generally don't find the benefit worth it, unless it's a situation with cantankerous wood that absolutely demands it. For similar reasons I rarely buff the bevels.

So I pretty much regrind every trip to the station, which means my favourite tools rarely have a generous lifespan..

I'm going to give this method a trial period, mainly because I like the idea of spending less time to keep the edge usable than a full bevel grind. Any significant life extension to the tool due to less grinds required would be icing on the cake.


Thanks Neil, for putting in the legwork and pointing out the possible application...

Andy, I will be interested to read what you think after giving it a go.

One of the best compilations of articles on sharpening turning tools was done by the American Association of Woodturners back in 2014. The article written by Alan Lacer and Jerry Wright titled, Does Honing Payoff?, on Pg58 is directly relevant to the topic of this thread, as is also the contribution by David Ellsworth, on Pg 17, that gives another opinion on honing/buffing when it comes to Bowl gouges...

https://www.mnwoodturners.com/cms-fi...oolsbookdo.pdf

There are many other very good articles in the above compilation that are very worth reading, if you haven't done so already.

PS - The article by Alan Lacer on tool steels, starting on Pg 18, is a bit out of date and doesn't include the now more frequently used CPMV10 or M42 steels.

Before I embarrass myself, like I did some months back, in 200 words or less... What is the unicorn sharpening method.

Originally Posted by The Spin Doctor

... What is the unicorn sharpening method.

As applied to flatware working tools, just read the initial post by Derek Cohen in this thread started by him...

The Unicorn method

That first post by Derek is more than enough to explain the method.

Originally Posted by Skew ChiDAMN!!

Hmmm...

My takeaway from this - if I've read it correctly - is that in terms of productivity the only time it makes a difference is in the finishing cuts.

SNIP

Depends on what you're doing and the wood. I used to be a production turner. Turned, table legs, urns, and fence post caps 7.5 hours a day, 5 days a week - by hand. In the late eighties and early nineties, I was making about 100/hour turning on a Oneway 2436. But damn was it hard on the hands and elbows (which was a motivation to reduce the stress from dull tools on the hands and elbows). Other than the urns the post caps and table legs were made from pine or fir, so lots of knots were to be expected (which is key to my advocating buffing). In a days work I could turn between 60 and 150 post caps, depending on complexity or between 45 and 60 legs, depending on whether they were coffee table legs or not and complexity. Primary turning tools were 1 ¼” square chisel, ½” bowl gouge, 1” roughing gouge and ¼” parting tool. As I was saying, the pine and fir have knots, sometimes lots, so I could expect my bowl gouge, which was the work horse, to smash through between 60 and 200 knots in a day. I think it was Neil who said you leave the grinder running... Yup, one step to the left from the head stock, left on all day. That was before I started, first honing, and then evolved to buffing. And then the grinder/buffer was left on all day... As anyone that has turned knotty wood, a hard knot can significantly dull a tool in two revolutions or less, so that makes for a lot of grinding to avoid hand and elbow stress... And all this was happening at 2000rpm so they can dulled real quick.

Honing worked pretty good but was time consuming and therefore not worth it. Buffing, at first thought, posed too many problems in that you don't want a rounded edge on turning tools... So I played with really heavily buffing the flute of the roughing gouge and bowl gouge, and then light touch to the bevel side just to clean off any remnant of a wire edge... For the chisel I marked one side so I only buffed that side and kept the other bevel really crisp with just a light touch...

The conclusion was that the bowl gouge could smash through at least 3 times as many knots than if it were only ground, thus reducing sharpening time a lot. And my ratio of grinding to buffing was about 1 to 4, which reduced time on the grinder a lot also as buffing took a few seconds. And for me the effort to push a razor sharp gouge or chisel through the wood was so much less taxing than before when just using a ground edge. So I'd clean up the bevel a few times a day on the grinder and then buff the flute to resharpen the edge the rest of the time. I also used a grey compound that is quite aggressive. I wouldn't use it on my bench or carving chisels. I even found buffing the roughing gouge to be a significant benefit. Overall with all the tools there is simply far less effort and stress on the fingers and elbows to use them when they cut through the wood so much easier.

My suspicion is that creating a rounded bevel on the back while also increasing their relative sharpness increased their durability. And or a finer edge will penetrate far more efficiently the wood than a relatively dull edge reducing edge failure, especially when that edge has to go through soft then super hard 50 times in less than 10 seconds (even though the user may think it's sharp)

I doubt woodworkforums keeps conversations going back to 2005 but I made mention of it back then when I was logging in as toolin around

Spin Doctor

I take my hat off to anyone who can turn for 7¹/₂ hrs a day, 5 days a week!!!

Nowadays I'm doing well if I can put in 2hrs straight....

Anyway, if you found with your extensive experience that buffing made that amount of difference under the conditions you outlined then it's case closed on the buffing question for me.

A couple of questions comes to mind:

Did you reduce the included angle on either of your gouges to compensate for the increased angle at the cutting edge from buffing it?

What grit size did you have on your grinding wheel?

Originally Posted by NeilS

Spin Doctor

I take my hat off to anyone who can turn for 7¹/₂ hrs a day, 5 days a week!!!

Nowadays I'm doing well if I can put in 2hrs straight....

Anyway, if you found with your extensive experience that buffing made that amount of difference under the conditions you outlined then it's case closed on the buffing question for me.

A couple of questions comes to mind:

Did you reduce the included angle on either of your gouges to compensate for the increased angle at the cutting edge from buffing it?

What grit size did you have on your grinding wheel?

No need to take your hat off... I stopped production turning in about 2004. It took another 10 years for me to get my neck sorted, lathes are about 4" too low for such work... My tennis elbow still isn't sorted.

No compensation on the bevel angle. Though!! My bowl gouge has a variable bevel angle. The tip is about 45 degrees and decreases as it extends to the wings to about 20. The roughing gouge is at about 40 degrees and the square end chisel is at about 25 to 30 combined (bevel on both sides). And the grinding wheel is an off the shelf grey wheel at probably 80 grit. I grind at 300rpm or lower so grit is not nearly as important as those that grind at 1700 or 3000.

Originally Posted by The Spin Doctor

Depends on what you're doing and the wood. I used to be a production turner. Turned, table legs, urns, and fence post caps 7.5 hours a day, 5 days a week - by hand. In the late eighties and early nineties, I was making about 100/hour turning on a Oneway 2436. But damn was it hard on the hands and elbows (which was a motivation to reduce the stress from dull tools on the hands and elbows). Other than the urns the post caps and table legs were made from pine or fir, so lots of knots were to be expected (which is key to my advocating buffing). In a days work I could turn between 60 and 150 post caps, depending on complexity or between 45 and 60 legs, depending on whether they were coffee table legs or not and complexity. Primary turning tools were 1 ¼” square chisel, ½” bowl gouge, 1” roughing gouge and ¼” parting tool. As I was saying, the pine and fir have knots, sometimes lots, so I could expect my bowl gouge, which was the work horse, to smash through between 60 and 200 knots in a day. I think it was Neil who said you leave the grinder running... Yup, one step to the left from the head stock, left on all day. That was before I started, first honing, and then evolved to buffing. And then the grinder/buffer was left on all day... As anyone that has turned knotty wood, a hard knot can significantly dull a tool in two revolutions or less, so that makes for a lot of grinding to avoid hand and elbow stress... And all this was happening at 2000rpm so they can dulled real quick.

Honing worked pretty good but was time consuming and therefore not worth it. Buffing, at first thought, posed too many problems in that you don't want a rounded edge on turning tools... So I played with really heavily buffing the flute of the roughing gouge and bowl gouge, and then light touch to the bevel side just to clean off any remnant of a wire edge... For the chisel I marked one side so I only buffed that side and kept the other bevel really crisp with just a light touch...

The conclusion was that the bowl gouge could smash through at least 3 times as many knots than if it were only ground, thus reducing sharpening time a lot. And my ratio of grinding to buffing was about 1 to 4, which reduced time on the grinder a lot also as buffing took a few seconds. And for me the effort to push a razor sharp gouge or chisel through the wood was so much less taxing than before when just using a ground edge. So I'd clean up the bevel a few times a day on the grinder and then buff the flute to resharpen the edge the rest of the time. I also used a grey compound that is quite aggressive. I wouldn't use it on my bench or carving chisels. I even found buffing the roughing gouge to be a significant benefit. Overall with all the tools there is simply far less effort and stress on the fingers and elbows to use them when they cut through the wood so much easier.

My suspicion is that creating a rounded bevel on the back while also increasing their relative sharpness increased their durability. And or a finer edge will penetrate far more efficiently the wood than a relatively dull edge reducing edge failure, especially when that edge has to go through soft then super hard 50 times in less than 10 seconds (even though the user may think it's sharp)

I doubt woodworkforums keeps conversations going back to 2005 but I made mention of it back then when I was logging in as toolin around

This is such an excellent post because the information is credible and it comes out of something where you had a whole lot of time to discern and observe things and incrementally improve.

Most of the cutting tests and cutting test data can't really compare because they will test one thing against another in an ideal situation - like knife angle information. The thinner the bevel generally, the longer the edge lasts, but the machine that does the tests is cutting through note cards with silica in them. It wouldn't even threaten untempered steel in most cases, so a brittle steel right out of a liquid nitrogen quench finish would test best.

what I found when I was testing edges, including duration planing, which is similar to running a turning tool on wood, is that the absolute crispest edge would plane the longest. But the results of the test fell apart as soon as you get away from it and have to plane something that will damage an edge, and I got a look under the edges that stopped cutting due to damage under the scope. The amount of damage needed to prevent an otherwise new edge from entering a cut is fairly small. Buffing the edge of a tool supports the steel around the blunted apex better, and there is no very tip of the apex to start failure or get dented.

Once failure is controlled, then suddenly all of the discussions about this or that plane alloy or hardness is less significant.

Planing knots is usually easier on an edge than cutting through them with turning tools at high speed, but planing silica is pretty torturous to edges. If the tip of a plane iron is buffed enough to deal with silica, it feels less sharp for the first couple of strokes but after that, the unbuffed edge gets damaged so quickly that it's forgotten. There is no alloy or hardness of plane iron that will plane through silica with a "two flat planes meeting in a line" edge. But the cheapest of plane irons with the apex buffed off a little but not enough to make it too blunt to cut will plane the hardest of woods without issue, including when they have silica in them.

Turning for 7.5 hours a day sounds like tough work.

Gray compound on HSS is a good idea, too. I think the shape of the buffed tip is a little bit more favorable when the abrasive has the enough cutting speed- and I don't think the ultra fine buffing sticks have enough cutting speed on hard steels with a large carbide volume.