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NeilS
25th October 2012, 12:57 PM
Belt grinders for sharpening, and in particular the Pro-Edge, is currently being covered in another thread (http://www.woodworkforums.com/f8/robert-sorby-pro-edge-sharpening-system-152167/).

The one aspect of belt grinding that hasn't had a lot of discussion more generally are the pros and cons of flat bevels for woodturning.

The following web page provide an argument in support of flat bevels for tool sharpening. Jon Siegel argues in favour of Flat Grind Versus Hollow Grind in his article, here (http://www.bigtreeturnings.com/articles/sharpening1.html).

Anyone have any experience of using flat bevel grinds and have an opinion of the pros and cons in comparison to concave grinds?

Paul39
25th October 2012, 02:36 PM
All my new accursed skews have come with flat grinds and I hone them on a diamond pad or 220 grit sandpaper on the lathe bed to maintain the flat. Some of the used, butchered accursed skews I have ground on the side of the wheel and then maintained with sandpaper on a flat surface or flat diamond pad.

Everything else I grind on an alox 8 inch 120 grit wheel. I do mostly bowls, so use bowl gouges and big heavy scrapers at the end before sanding.

I would think that a concave grind, especially from a 6 inch wheel, would need to be ground stubbier than a flat grind to get the same cutting angle out at the tip.

If ground the same length as the flat grind, it might be more aggressive in cutting, just like a long Ellsworth grind vs a 45 degree grind on a bowl gouge.

ADD:

After reading Jon Siegel, I more or less agree with him. I have been turning about 7 years and have never measured the angle of a turning tool. I some times think there is a bit too much measuring and figuring and trying to be precise that just turning something and paying attention to what takes off timber and gives a smooth surface would provide the answer.

If your tool grind angle and tool rest height are approximately right, and you start by rubbing the bevel and raise the handle to start cutting and then move up or down and twist the bowl gouge to make a long stream of curlies all the way across the bowl, that is what counts. After a while you don't even think about it, just present tool, up, down, twist, nice clean cut.

If a person spends 100 hours turning with decent tools and a grinder at hand, they will be a pretty good turner.

rsser
25th October 2012, 02:44 PM
Those two articles make good reading. Thanks Neil. (And finally I have the source for the proposition that a thou's wear at the tip = blunt :2tsup:).

I don't yet have experience of using flat bevelled tools but soon!

Tormek provide a figure for the degree of concavity in a grind using their 10" (250mm) wheel and it's very small.

Clearly that from a 6" (150mm) wheel will be much greater. And with a 6" wheel and an acute grind it's possible to end up with the included angle at the tip some degrees lower than a simple angle setter indicates. And so run into more of the problem with cutting edge life and control that Siegal mentions.

I would expect that in principle a flat grind will provide more support for the cutting edge.

One matter that all this raises for me is what exactly is meant by 'rubbing the bevel' with a cutting tool. Specifically, how much of the bevel? Clearly some of the bevel is necessarily riding the wood surface that the edge has just created, and that pressure has to be roughly matched by the downward pressure on the top bevel or flute from the emerging shaving in order to get an even and controllable depth of cut (Darlow writes about this). In practice the length of bevel rubbing can be small and in some interactions with wood have to be very small (eg. a drumstick shaped by a skew). In which event bevel concavity may mean relatively little.

But it did to Siegal. And I can see his reasoning when applied to planing a cylinder with a skew but cutting curves on a bowl with a gouge?

(PS, sorry Paul, we were writing at the same time).

Paul39
25th October 2012, 03:28 PM
One matter that all this raises for me is what exactly is meant by 'rubbing the bevel' with a cutting tool. Specifically, how much of the bevel? Clearly some of the bevel is necessarily riding the wood surface that the edge has just created, and that pressure has to be roughly matched by the downward pressure on the top bevel or flute from the emerging shaving in order to get an even and controllable depth of cut (Darlow writes about this). In practice the length of bevel rubbing can be small and in some interactions with wood have to be very small (eg. a drumstick shaped by a skew). In which event bevel concavity may mean relatively little.

But it did to Siegal. And I can see his reasoning when applied to planing a cylinder with a skew but cutting curves on a bowl with a gouge?

(PS, sorry Paul, we were writing at the same time).

As long as one is getting a nice clean cut, what does it matter how much is rubbing. I found the blunter sharpening angle less volatile than the fingernail grind. The first time I used my new-to-me Thompson with a long Tormek sharpened swept back grind, I nearly soiled myself.

It really removes the timber, and I learned to go by the book and have the tool right down on the rest and have a firm grip, because once it starts cutting, it is hang on and devil take the hindmost.

You have nothing to be sorry about, I am gratified to know my mind is running in the same ditch as that of a very competent and experienced turner.

petersemple
25th October 2012, 05:15 PM
I am not anywhere near an accomplished enough turner to really comment on this issue. I have read the Jon Siegal article, and he does make some interesting points. one comment that I do have though, is that he very vehemently makes some points in the article, where I have heard others state exactly the opposite opinion just as forcefully (some of the things about chisel shapes etc were what I noticed. He really doesn't like oval skews for example, where I have heard others state firmly that they are the best kind of skew to use).

stuffy
25th October 2012, 06:13 PM
I think there are too many variables to say one grind shape is better than another.
It can probably be proven in an isolated circumstance but that circumstance may be momentary.
The size and shape of the work piece is constantly changing so the tool presentation and edge support must change with it.

Does a flat bevel provide better support for the cutting edge than a hollow grind? No. In order for the edge to cut there must be clearance behind the edge. It seems more likely that a hollow grind can give clearance and then support the edge closer to the cut.

Does a hollow grind change the effective edge angle? Yes. It will make a more acute angle but a smaller angle penetrates a little better with the down side that it wears more quickly. The grinding angle is easily adjusted to allow for this.

Does a curved cutting edge take a smaller cut than a straight edge? Not necessarily. In a concave cut a curved edge will have more contact than a straight edge.

I can see a benefit in a flat bevel on a skew for some cuts especially if you like to hone the edge. Honing a concave bevel, unless done on a wheel the same diameter as the grinding wheel, introduces a secondary bevel that can effect tool control.
A smooth bevel, sharp edge and support in line with the forces of the cut will give the best cut with the most control.

Best Wishes

Steve.
:)

Mobyturns
25th October 2012, 09:47 PM
To throw a cat amongst the pigeons, Israeli turner Eli Avisera has demonstrated a skew with a convex grind, one he developed for teaching his children how to use the skew. He says it is more forgiving for beginners. I firmly believe most skews are ground with far too sharp an angle (<25deg) and much prefer a blunt angle (around 45deg) myself for the work I do. The sharper bevel angle is fine for detail like deep vee cuts.

The flat & convex grinds on skews have one extra benefit, in that they don’t create as much bruising from the back edge of the bevel on concave cuts with the skew.

RETIRED
25th October 2012, 11:33 PM
To throw a cat amongst the pigeons, Israeli turner Eli Avisera has demonstrated a skew with a convex grind, one he developed for teaching his children how to use the skew. He says it is more forgiving for beginners. I firmly believe most skews are ground with far too sharp an angle (<25deg) and much prefer a blunt angle (around 45deg) myself for the work I do. The sharper bevel angle is fine for detail like deep vee cuts.

The flat & convex grinds on skews have one extra benefit, in that they don’t create as much bruising from the back edge of the bevel on concave cuts with the skew.You coming to Prossy?

robo hippy
26th October 2012, 04:54 AM
The only advantage I can see to a flat bevel would be on a skew chisel if you are making long straight pieces, or ones with very gentle arcs. Mostly the flat would work like the sole of a plane and help you keep on a straight/flat line. With the Eli Avesera convex grind, I found it great for more rounded pieces with more coves and arch, but more difficult to make long straight cuts like on a rolling pin. Other than that, the closer the bevel rub/kiss/very gently toughing the wood point is, the easier it is to control the cut. On the outside of a bowl or any convex piece, bevel angle makes almost no difference because the curve will have the cutting edge right where the cut is happening. On the inside of a bowl, you will be on the heel of the bevel, and most of us grind away most of the heel to prevent heel marks/bruising, and bring the rub point closer to the cutting edge.

robo hippy

dr4g0nfly
26th October 2012, 07:04 AM
I deliberately hollow grind my skews then hone across the hollow to give me my working edge, a narrow bevel for the 'rubbing' and a clearance.


I firmly believe most skews are ground with far too sharp an angle (<25deg) and much prefer a blunt angle (around 45deg) myself for the work I do. The sharper bevel angle is fine for detail like deep vee cuts.

I also have a sharper angle than 25 degrees, I've never n=measured it, but new skews get an immediate regrind to give a longer profile. As mI said previously in another thread, this works for me, but it does mean that I have to hone very regularly to maintain my [preferred] edge.

Mobyturns
26th October 2012, 08:13 AM
You coming to Prossy?

Yes, been following your woes. Nothing wrong with Barky, just not the place to be for a long time when you are used to greener pastures.

jimbur
26th October 2012, 10:09 AM
Moby, I was given a set of marples (small chisels) when I was starting and the skew was and still is concave. I sharpen it by running a ceramic stone following the curve. It is forgiving and is still brought out for awkward grain. It appears to be the original grind.
Cheers,
Jim

artme
26th October 2012, 05:42 PM
I keep having trouble with Windows Explorer making and keepin g contact withe forua.

I posted on this yesterday and it obviously fell ver the edge.:~


To me it stands to reason that a flat grind - at the correct angle of course - will be sturdier and longer lasting.
After all is has more metal supporting it.

powderpost
26th October 2012, 11:19 PM
I would normally let this topic "go through to the keeper". But I couldn't resist. The arguments about grinding and honing turning tools comes and goes. I have been turning in various capacities for a while now, and still find some of the points raised interesting. The following is my own personal views based on about 50 odd years turning, and subscribe to the concept, "This is how I do it. Try it and if it doesn't work, change it to work for you". I have never measured the angles used, and was never interested enough. When teaching, rather than quote numbers, in general state, "Make the length of the grind about twice the thickness of the steel in the tool at the grind point". The tool is then honed on a whet stone to get a sharp edge, with both the front and back of the bevel rubbing on the stone. The grinding angle was determined to a degree by the work it was to do. Softer timbers, I may make the bevel a little longer to produce a sharper edge to produce a finer surface. For hard timbers I would shorten the grind angle to produce a stronger cutting edge that may not be as sharp. This flies in the face of the need to replicate the angle every time. It is apparent then that I prefer a concave grind as produced by a 200mm diameter wheel. I agree with Paul, about arguments about this or that method and about "the correct" angle, is irrelevant, and not enough time spent observing the interaction between wood and tool. In my opinion far too much time is spent on arguing that this or that method produces a sharper tool. How sharp is sharp enough? The ultimate test is the quality of the surface left behind and to some extent to the quality of the shaving produced.

As for the argument, flat grind verses hollow grind, I prefer the hollow grind, it has stood the test of time. I am also very aware of "modern" methods and have replaced my carbon steel tools with the latest Thompson tools, I also use a Tormek, and use a lathe with a "V" belt and the latest electronic variable speed control. I also firmly believe that many of the "new" ideas, are not new and many of the "new" tools are gimmicks.

Jim

RETIRED
26th October 2012, 11:32 PM
Tongue is nearly missing.:wink:

Mobyturns
27th October 2012, 08:19 AM
Come in spinner, :U sorry Powderpost your words are spot on. I think I have a bevel measuring device there somewhere gathering dust. :rolleyes: Most of my skew work involves shearing end grain on some tough timbers (purpleheart, tamarind, kwilia etc). So for me I gave balanced the need for a stronger, longer wearing edge and tool control and find a blunt angle works best for me. I do use both long & short bevels on skews & love the original Sorby spindle master which is very fine but not long wearing.:2tsup:

jimbur
27th October 2012, 10:32 AM
Couldn't agree more with Powderpost, but then that's how I was taught and there's nothing better than having someone justify the methods you use.:D Honing with a stone means longer between grinds and to me that is a big plus. It's the same as the rationale for secondary bevels on plane irons - you grind when you find you're having to remove too much metal with the stone.
Cheers,
Jim

rsser
27th October 2012, 05:56 PM
Jim's post raises the question of 2ndary or micro-bevels. If memory serves doesn't Avisera use a 2ndary bevel at the tip of a gouge? Someone anyway who is worthy of a YouTube vid.

I've been touching up my hollow ground bevels with a diamond hone during a turning session. What that does is create two micro-bevels on the same plane, at the tip and the heel. Can't say that the diff. in handling has been obvious compared with a complete hollow grind off a 20cm wheel.

hughie
27th October 2012, 06:04 PM
Jim's post raises the question of 2ndary or micro-bevels. If memory serves doesn't Avisera use a 2ndary bevel at the tip of a gouge? Someone anyway who is worthy of a YouTube vid.


Yes thats the guy Stu in Tokyo has a few vids on the set up of the Avisera grind



I've been touching up my hollow ground bevels with a diamond hone during a turning session. What that does is create two micro-bevels on the same plane, at the tip and the heel. Can't say that the diff. in handling has been obvious compared with a complete hollow grind off a 20cm wheel.



I do the same I think we are just sharpening where as Avisrea secondary grind produces a second angle less than the first and its this that effect the finish, a slight burnishing effect.

rsser
27th October 2012, 06:14 PM
Yep Hughie; I'd call that a 2ndary bevel as Jim did.

Course there are turners who use a convex bevel on their gouges to aid in 'turning the corner' inside a bowl and reduce bruising. Never tried it. I just go for a smaller gouge where possible but that requires a curved rest to avoid edge chatter.

jimbur
27th October 2012, 06:53 PM
Ern and Hughie. Agree entirely. Heel and toe is the method I use. i used the secondary bevel mention as an illustration how we grind when that bevel becomes so long that it is quicker to regrind than hone with a stone.
Cheers,
Jim

Rod Gilbert
27th October 2012, 07:01 PM
Well it sound's to me like what work's for you is the right way to do it. I also have never measured an angle on a chisel all my grinding is done free hand and I rarely use a stone on them usually turn straight off the grinder, don't see the point of honing then losing that edge instantly you touch the timber, on rare occasion's I'll give them a rub for a specific job but not in general.
Regards Rod.

jimbur
27th October 2012, 07:09 PM
Rod, spot on. I'm not an evangelist for any particular method, I just continue the way I was first taught. The end result is what matters of course.
cheers,
Jim

NeilS
27th October 2012, 08:55 PM
Tongue is nearly missing.:wink:

Well, stop biting it and say whatever it is you were going to say...:D

Mobyturns
27th October 2012, 10:42 PM
don't see the point of honing then losing that edge instantly you touch the timber, Regards Rod.

Honing skews is very beneficial for fine / delicate spindle work. :2tsup: The honed surface produces a much more refined surface even when the honed edge wears. A keen edge only needs to be guided and not pushed creating fewer problems. :) Bit like those annoying TV ads with cutting tomatoes. I use a concave grind and hone creating the micro bevel, this eventually gets flatter and flatter. I only re-sharpen when honing will not restore the edge or the edge becomes nicked or damaged, but I’m not a production turner. I use a conventional grinder brought up to speed then turn off the power sharpening skews etc with a decelerating wheel. I also use the Tormek T7, the BG100 kit for the conventional grinder, with the Tormek WT kit and also a favourite Heligrind jig for fingernail grinds on spindle gouges.

Horses for courses, why hone if you are roughing spindle stock, or bowls where you run the risk of damage or high wear on the cutting edges with harder timbers etc. However a honed edge will give you a much better finish cut, but is also a complete waste of time if you then start with 120 sandpaper. :;

RETIRED
28th October 2012, 02:51 PM
Well, stop biting it and say whatever it is you were going to say...:DYou did ask!:D


This discussion reminds me of the man watching his wife prepare the leg of lamb for roasting. She always cut off the shank and roasted it seperately.

"Why do you cut the shank off and roast that separately?" he asks.

"My mother always did it that way," comes the reply.

A week later he is around at the Mother in Laws and asks the same question.

"Why do you cut the shank off and roast that separately?" he asks.

"My mother always did it that way," comes the reply.

A few weeks later they are round at Grandmas house and he asks the same question.

"Why do you cut the shank off and roast that separately?" he asks.

"Because it wouldn't fit in the roasting dish with it on!" comes the reply.

The point of this is to show that some things are done through habit to suit a purpose that is no longer applicable.

This is my take and reasoning on why things were done in the early days of sharpening tools on grinding wheels and why some habits persist to this day "because that is the way I was taught".

Early grinding wheels were hand operated and generally of stone that was quarried and then probably made round by stonemasons. In some cases they were probably a little coarse as well.

Water was not used to cool the tool but rather to wash the metal away to allow the stone to cut.

Because of this they were probably reasonably expensive and only big places could afford one. Workers would grind there own tools on the work one of a morning and hone the tools using their own stones (hand held) during the day to save time.

You should bear in mind that steel was softer then as well so honing was relatively quick and easy to do and their stones were probably finer than the grinding wheel.


When Franklin Norton and his cousin Frederick Hancock opened their pottery business in Worcester, Mass., in 1858, their fledgling company focused on redware and stoneware pottery and expanded eventually into the manufacture of diverse items such as jugs, beer bottles and spittoons. In 1873 an employee, Sven Pulson, invented a kiln-fired grinding wheel shaped from a mixture of emery powder, clay and water. Frank Norton patented the concept and began production of Pulson's grinding wheels.

Although Pulson's grinding wheels surpassed the quality of the industry standard wheels of the day, which were built of wood embedded with emery particles, company politics initially prevented success.

Read more: The History of the Grinding Wheel | eHow.com The History of the Grinding Wheel | eHow. (http://www.ehow.com/about_5117137_history-grinding-) wheel.html#ixzz2AYA0fHRn

So began the first manufactured grinding wheel as we know it. Probably still relatively expensive but the wheel was of consistent shape and grit and they were becoming powered not by hand but machine.

Great advances in the manufacture of wheels and steel have occurred since that first wheel was made.

Bonding agents, grit purity and regular size on wheels, harder and tougher steels and better manufacturing techniques have led to wheels and tools that most people can afford.

The choice is practically unlimited as far as power sharpening goes.

Today we have wheels that can leave a polished surface that is razor sharp without honing.

CBN wheels that hardly wear or need cleaning.

Sanding belts and discs are all used with success.

Wet grinders, slow speed grinders and all speeds between.

The speed of the grinder makes no difference but the feel and touch of the operator does make a huge difference whether freehand or jig sharpening.

I very rarely hone my tools as the edge off the wheel is sufficently sharp for most of the work we do and it makes no difference to the finish and very little difference to the longevity of cutting time. I will hone a skew occassionally on softer timbers for the final cut.

Concave versus flat versus convex bevels on spindle work.

I have tried all the different grinds to see if one is better that any other.

I prefer a concave grind because it seems to "fit" the timber better (particulary with gouges) and I find that bearing on 2 points (cutting edge and heel) is far easier to control than having a complete bevel to contend with. It is easier to "roll" the cutting edge into contact with the work. This may be because that is what I am used to.

One problem that I found with the flat bevel is that it is very easy to "dub" the cutting edge.

Other than those minor points a flat bevel cuts as well as a concave bevel.

Convex bevels like Eli Avistera uses are hard to control as there is virtually no support from the bevel at all and to do a planing cut with a skew shaped this way is hard work, to do a bead is very hard work. In Stus (Stu in Tokyo) video watch how many times he has to restart because you lose the cut.

To do "V" cuts and form square shoulders is nearly impossible.

Concave versus flat versus convex bevels on Bowl work.

I personally don't think that there would be much difference between a flat or concave bevel on the inside of a bowl as the curvature only allows 2 points of contact. A bevel that is too long is more of a problem because you can't maintain bevel contact at the transition. You either "lever" the cutting edge off the work with the bevel or you have no bevel support because you have lifted the bevel off to use the cutting edge.

On the outside of a bowl it is a different kettle of fish. I could see that the flat bevel being a dis advantage in that it would be a balancing act maintaining bevel support because of the curvature. I personally think that concave is an advantage no matter how small.

I have played around with convex bevels on the inside of a bowl and found that it depends on the size and curvature of the bowl as to whether it is an advantage or not. If the convexity is too great on bigger bowls you may as well use a pointed nail as there is no bevel support at all.

On the outside you get the same problem no matter what size the convexity is.

Bevel angles and sharpening.

No tool is sharp and ready to use as far as I am concerned from the factory. They all need tuning.

Sharp edges on blades need to be removed for ease of use and personal comfort. Flutes need to be polished as an edge is defined as the intersection of 2 planes, the bevel can be great but it is no good if the flute looks like a ploughed paddock. I have been advocating this for over 30 years and now people are just starting to catch on.

Some tools because of the way they are tempered are a little soft at the ends and you seem to be always sharpening them to get them right for a while. I find this an advantage as it gives you a little time to get them shaped right. Most of the m2 and powdered metal tools don't seem to have this problem.

I run most of my tools at 45 degrees bevel angle. I use other angles on some for special work.

The way that I arrived at this angle is that my grinder centre height was at the centre height of my lathe and when I sharpened freehand they naturally came into the same angle as the the way I worked.

Most of my skews are 1.5 times the thickness of the blade. I find this a good compromise angle for the variety of work we do and they are easier to control at this angle for beginners. i also have some sharpened at 2 and 2.5 the thickness for special work.

Angles really don't matter as long as the tool is sharp and you have the abilty to change to suit the angle.

So after all that: Are we doing things out of habit when there could be better options that have not been explored?

jimbur
28th October 2012, 03:30 PM
, reminds me of the story where there seems to be one too many men working a gun in the artillery. They had to find an old bloke to tell them what he was meant to be doing - holding the horses.
Cheers,
Jim

rsser
28th October 2012, 03:58 PM
LOL.

This thread has covered a lot of ground. Seems all up that folk can get good or good-enough results with a variety of tool treatments.

And yeah, learning turning is at best a kind of apprenticeship for many, with all the strengths and weaknesses of that system.

But there's an evidence basis for refining the tool edge on two criteria.

powderpost
28th October 2012, 04:45 PM
Geez , I hope those parts come tomorrow, the stress cracks are starting to show.... :D:spyme:
Jim

RETIRED
28th October 2012, 06:01 PM
Geez , I hope those parts come tomorrow, the stress cracks are starting to show.... :D:spyme:
JimYeah, I know.:D

jimbur
28th October 2012, 06:10 PM
LOL.

This thread has covered a lot of ground. Seems all up that folk can get good or good-enough results with a variety of tool treatments.

And yeah, learning turning is at best a kind of apprenticeship for many, with all the strengths and weaknesses of that system.

But there's an evidence basis for refining the tool edge on two criteria.
Fair summary Ern, and there's no evidence of rising blood pressure unlike some sharpening topics.
Cheers,
Jim

rsser
28th October 2012, 06:10 PM
Jim posted: Geez , I hope those parts come tomorrow, the stress cracks are starting to show...

Can only be microfractures.

Macrofractures = a rant and is too much the gent for that.

NeilS
28th October 2012, 07:20 PM
Good wrap , thanks.

Tim the Timber Turner
28th October 2012, 07:37 PM
There is a group that debate, argue and discuss the process.

And then there is another group that actually do it.

Which group you belongem?

Cheers

Tim:)

NeilS
28th October 2012, 08:46 PM
Which group you belongem?



I do, when I can.

When I can't, I ask.

And, if I'm asked, I say what I can do.

But, don't mind a discussion when I'm not doing...:p

Paul39
30th October 2012, 10:09 AM
I keep having trouble with Windows Explorer making and keepin g contact withe forua.

I posted on this yesterday and it obviously fell ver the edge.:~


To me it stands to reason that a flat grind - at the correct angle of course - will be sturdier and longer lasting.
After all is has more metal supporting it.

It may be your Internet Service Provider. Mine is ATT and at noon or quitting time I cant get on or it drops out.



Mozilla Firefox is a better browser. Mozilla Firefox Web Browser (http://www.mozilla.org/en-US/firefox/fx/)

A few things must have Explorer to work.

rsser
31st October 2012, 03:27 PM
I do, when I can.

When I can't, I ask.

And, if I'm asked, I say what I can do.

But, don't mind a discussion when I'm not doing...:p

LOL. So to bookend your thread Neil (you can't get off so easily despite the wisdom and wit!) what's your take on the issue you raised?

NeilS
31st October 2012, 10:44 PM
So to bookend your thread Neil ... what's your take on the issue you raised?

1. With only a few exceptions, most of us have not actually used a flat grind on which to base our comments, me included.

2. Some hand hone the tip and heel flat on their concave grind and offered comments based on that being a short flat bevel. However, at that length the difference between a flat and concave grind would be infinitesimal.

3. There was mixed views on flat vs concave bevels on skews. Our most experienced spindle turners prefer a concave grind.

4. Most saw a concave grind for turning the outside of bowls an advantage.

5. Most saw single grinds (concave or flat) as a problem on the inside of bowls. Some resort to grinding off the heel while others just use a smaller gouge for 'turning the corner'.

6. There was discussion on grind angles, the most significant point (IMO) was that a flat grind will change the bevel angle (slightly more obtuse) which should be taken into account. 's comment, "angles really don't matter as long as the tool is sharp and you have the ability to change to suit the angle", summarises my own take on this.

7. Discussion on honing to create a sharper edge and saving trips to the grinder, although of interest, was off-topic. It is understandable that it came up as it was raised by the Jon Siegel article.

8. There were other points that were raised which were also off-topic, many of them valuable in themselves, but again didn't throw any light on the primary topic.

9. My conclusion from the discussion is that there are some advantages to the concave grind, but that they are not so significant to make it indisputably better. An experienced turner should be able to adapt to a flat grind.

Thank you everyone for their contributions.

rsser
18th November 2012, 05:46 PM
By oversight I've ended up with 2 of 3/8" beading and parting tools, both with fairly long bevels. One was done on the Sorby ProEdge and had a flat bevel, the other was hollow ground with an 8" grind wheel.

So for a test both got a lick or two on each bevel with a very fine diamond hone to take off any burrs. I do this with any tool that's got to cut Radiata Pine or other softwoods cleanly.

I cut flats on a spindle piece of that Pine with light fine peeling cuts.

My immediate impression was that the flat bevel was easier to control.

Then I alternated between the two and found no difference.

Maybe the initial impression was a Hawthorne effect. Maybe I'd unconsciously compensated for the hollow grind when alternating.

Inconclusive but interesting.

Is life too short to get worked up about the potential differences? Definitely.

Mobyturns
18th November 2012, 06:10 PM
Is life too short to get worked up about the potential differences? Definitely.

Some get rather passionate - like Holden vs Ford! :wink:

NeilS
19th November 2012, 07:06 AM
Is life too short to get worked up about the potential differences? Definitely.



Agreed.

Thank you for sharing your test run observations, Ern.

Bushmiller
9th December 2012, 01:44 PM
You did ask!:D


My mind is boggled. (response to 's epic post. Shortened version as my Irish computer only has a single page on screen). :- .

Your comment conjured up two recollections from the past. The second I have to research so I'll give you the first.

Robert Mitchum was interviewed by a journalist, who was quick to point out that it normally took two people to interview him as he had a reputation for being unpredictable and the forerunner of WPHS required backup.

For one page of the publication (I think it was "Private Eye," but not certain) RM was clearly disinterested and monosylabically replied "Yep" or "Nope" to an array of questions.

Then the journo asked him what was the strongest alocohol he ever drank. Mitchum spoke for two pages without stopping. You just had to get him on his subject. :D

Digression over. Back to the sharp end. I enjoy these discussions.

Regards
Paul

Bushmiller
9th December 2012, 02:08 PM
You did ask!:D


This discussion reminds me of the man watching his wife prepare the leg of lamb for roasting. She always cut off the shank and roasted it seperately.

"Why do you cut the shank off and roast that separately?" he asks.

"My mother always did it that way," comes the reply.

A week later he is around at the Mother in Laws and asks the same question.

"Why do you cut the shank off and roast that separately?" he asks.

"My mother always did it that way," comes the reply.

A few weeks later they are round at Grandmas house and he asks the same question.

"Why do you cut the shank off and roast that separately?" he asks.

"Because it wouldn't fit in the roasting dish with it on!" comes the reply.

The point of this is to show that some things are done through habit to suit a purpose that is no longer applicable.



Another exert from 's epic. I recalled my second recollection.

An experiment was conducted with five monkeys in a cage. Bananas were placed at the top of the ladder but anytime one tried to climb the ladder and grab the babanas all the monkeys were doused with freezing cold water. Soon the monkeys grabbed any simian rash enough to climb the ladder and hauled him back down.

Then the water was disconnected but the monkeys continued to self-police. Even when monkeys were replaced the newcomer was prevented from getting the bananas by the others.

Eventually none of the original monkeys remained but still any newcomer was restrained from going up the ladder. If asked why, the monkeys said,

"This is how we've always done it."

The analogy of course is the resistence to change. I guess we all need to keep an open mind and in the case of sharpening techniques and systems there may be no right answer for all situations. Sharpening like most things in life is a compromise.

Regards
Paul

(PS. (I'm out of white out) I like 's analogy, in no small part because I really like lamb shanks :D.)

artme
9th December 2012, 04:30 PM
Don't get me started Paul. Change theory and practice is a very interesting subject
and one subject to heated debate.

Bushmiller
9th December 2012, 07:31 PM
Don't get me started Paul. Change theory and practice is a very interesting subject
and one subject to heated debate.

Arthur

I agree entirely, but it wasn't my intention to hijack the thread. It was just a couple of tiny digressions inspired purely by 's epic reply.

I am hoping I am allowed tiny digressions. If not, my backup plan is a tendency to absentmindedness, which, unlike wine, is not improving with age.

If none of that is acceptable, I plead temporary, total insanity :p .

Regards
Paul

RETIRED
9th December 2012, 08:10 PM
If none of that is acceptable, I plead temporary, total insanityThat excuse I can believe!:wink:

Bushmiller
9th December 2012, 08:18 PM
Never fails. LA La la la; LA La la la :D.

Regards
Paul

rsser
9th December 2012, 09:19 PM
Clearly, anyone who has bought a common Sorby tool got a flat grind. With the first grind on a wheel they turned it into a hollow grind and didn't notice the diff.

I'm waiting for replies to questions re the factory grind from other makers - HT and Thompson. HT owns Hamlet so maybe those got the same treatment as HTs.

Will report back.

RETIRED
9th December 2012, 09:34 PM
Clearly, anyone who has bought a common Sorby tool got a flat grind. With the first grind on a wheel they turned it into a hollow grind and didn't notice the diff.

I'm waiting for replies to questions re the factory grind from other makers - HT and Thompson. HT owns Hamlet so maybe those got the same treatment as HTs.

Will report back.You piqued my curiosity with the highlighted statement.

I have 2 brand new in the packet Henry Taylor HS 32 gouges that we use for roughing gouges and was curious as to whether they were hollow ground or not.

Both are definitely done on a wheel. I would hazard a guess and say about 12" Diameter as there is not a great deal of difference as the ones sharpened on the 8" wheel.

rsser
9th December 2012, 10:05 PM
Good to have some data . Thanks.

On my big HT skew that was reground on a Tormek 10" wheel, the hollow looks to be a mm or less - that's with a bevel of a cm.

Tormek's manual says that with a 2 mm thick tool and a grind angle of 20 degrees the hollow is 0.03 mm.

To state the obvious, hollows vary. All my other tools have bevels shorter than a cm and so the concavity produced by a 20 cm wheel will clearly be less than on the HT skew. *

Distinctions without practical differences perhaps.

*Added: too late at night! That's not right; can only say the shorter the bevel for a given wheel the less the concavity.

jimbur
10th December 2012, 03:39 PM
can only say the shorter the bevel for a given wheel the less the concavity.
That strikes a chord Ern:D

rsser
10th December 2012, 04:40 PM
Nice pun Jim!

Bushmiller
11th December 2012, 01:35 AM
While this thread has been primarily a comparrison of the benefits of a flat grind versus a hollow grind what is the optimum wheel size for a hollow grind? 150mm, 200mm, 250mm, bigger?

Is the optimum modified by the size of the tool and is it more critical with turning tools where there may be considerable loading on the cutting edge (compared to a bench chisel or a plane blade for example)?

My understanding was the only benefit of a hollow grind was in reduced effort in final honing. The advantage of a flat grind is increased strength of the cutting edge, although there is clearly a technique used with turning tools of using the heal for control.

Regards
Paul

NeilS
11th December 2012, 08:15 AM
...what is the optimum wheel size for a hollow grind? 150mm, 200mm, 250mm, bigger?




In brief, you will quickly adapt to whichever you adopt.



244299

Mobyturns
11th December 2012, 08:22 AM
This discussion could go on forever! :D

Very few turners have tool skills advanced enough to be able to detect the benefits of wet vs dry; flat vs hollow & then the benefits of a hollow grind from a 150mm thru to a 250mm dia wheel. Those few gifted turners that do have very high level tool skills still have very polarised views on which system is best. :wink:

A sweet single curve shape (i.e. not multi faceted :no: ) with a consistently reproduced profile that is sharp is what most turners desire and struggle to acheive. Finding a system that they can afford, then learning how to use it correctly so that it works for them is more important than size of wheel etc. Time and many turners of all skill levels have proved that acceptable results can be obtained with almost any shape & style of cutting edge acheived from almost any sharpening system that has ever been devised. Just some are simpler & more efficient to use than others.

Having said that my preference is for a 200mm wheel on my "spark grinder" with a Tormek BG100 for bulk shaping then the Tormek T7 with accessories for sharpening. However I went quite nicely for years with the clubs "spark grinder" and all manner of jigs because I was lucky enough to find a mentor who had the skills & knew how to get the best from what we had. :U His knowledge & experience & mine both gained from learning the traditional skills of saw, plane & chisel sharpening certainly helped heaps.

RETIRED
11th December 2012, 08:44 AM
This discussion could go on forever! :D

Very few turners have tool skills advanced enough to be able to detect the benefits of wet vs dry; flat vs hollow & then the benefits of a hollow grind from a 150mm thru to a 250mm dia wheel. Those few gifted turners that do have very high level tool skills still have very polarised views on which system is best. :wink:

A sweet single curve shape (i.e. not multi faceted :no: ) with a consistently reproduced profile that is sharp is what most turners desire and struggle to acheive. Finding a system that they can afford, then learning how to use it correctly so that it works for them is more important than size of wheel etc. Time and many turners of all skill levels have proved that acceptable results can be obtained with almost any shape & style of cutting edge acheived from almost any sharpening system that has ever been devised. Just some are simpler & more efficient to use than others.

Having said that my preference is for a 200mm wheel on my "spark grinder" with a Tormek BG100 for bulk shaping then the Tormek T7 with accessories for sharpening. However I went quite nicely for years with the clubs "spark grinder" and all manner of jigs because I was lucky enough to find a mentor who had the skills & knew how to get the best from what we had. :U His knowledge & experience & mine both gained from learning the traditional skills of saw, plane & chisel sharpening certainly helped heaps.Perzactly.

Sawdust Maker
11th December 2012, 09:29 AM
Clearly, anyone who has bought a common Sorby tool got a flat grind. With the first grind on a wheel they turned it into a hollow grind and didn't notice the diff.

I'm waiting for replies to questions re the factory grind from other makers - HT and Thompson. HT owns Hamlet so maybe those got the same treatment as HTs.

Will report back.

My recollection of the Thompson was that it was hollow ground (probably on an 8" wheel)

Bruce White
11th December 2012, 10:08 AM
Too hard for me to worry about grinds. I just sharpen a lot - every few minutes.

Paul39
11th December 2012, 11:22 AM
Too hard for me to worry about grinds. I just sharpen a lot - every few minutes.

I believe that is the secret. A razor sharp tool is easier to control as you don't have to use so much force, and will make a cleaner cut.

I pulled a piece of close grained hemlock 2 X 4 out of my burn pile today and made a tool handle. After roughing it to two round sides and two flat sides, I grabbed the accursed skew that was on top of the pile of tools on the bench.

It was a cheap Chinese 3/4 inch of mystery metal. As this thread has been on my mind, I looked at the bevel, it was convex as I had been using it for making spigots on bowls and sharpening a lot on clogged sand paper on the lathe bed.

I gave it a few strokes on some 220 grit on the lathe bed and had a go. It cut no better or worse than my Craftsman Professional high speed steel accursed skew, on which I have kept meticulously flat bevels on a 600 grit diamond hone.

It did not stay sharp as long as the Craftsman, but I gave it a few strokes after a couple of passes across the tool handle. For the last finishing cuts I honed it on a 400 grit diamond hone. That did make for easier cutting.

Bushmiller
11th December 2012, 02:16 PM
This discussion could go on forever! :D



And there MobyT, you have summed up the essence of the Forum. Without it, the Forum would be one Nth the size it is.

Thank you for your well-considered reply. Simplicity and economy are clearly the high priorities for the majority of us.

Regards
Paul

Bushmiller
11th December 2012, 02:22 PM
In brief, you will quickly adapt to whichever you adopt.



244299



Neil

I take your point. (he'll be sorry if those wiskers ever catch on the grinding wheel, but not as sorry as he will be if the guard should suddenly wear through :wink: .)

Regards
Paul

rsser
11th December 2012, 03:21 PM
Compared with flatware workers, turners tend to use higher grind angles. This is about edge durability.

One wrinkle with low nominal grind angles is that the smaller the wheel the lower the actual angle is near the tool tip - cos of the greater hollowing effect. This can make a diff. down at the 25 degree mark; less so at higher angle all other things equal. That is something to consider with bench chisels and plane blades where you're aiming for the lowest grind angle consistent with edge retention.

One thing that we share with flatware workers is that when we skew bevel-rubbed edge, typically a skew chisel, the cutting angle is effectively lowered for a given grind angle.

As for hollow v flat bevels, it seems this debate has been around for a while, and there are some turners whose views I respect who are convinced that flat is the way to go.

When the Xmas madness is over I'll do some more tests. I'm not expecting to find much difference but remain open; and say that cos in a lot of my turning I'm making unconscious adjustments to the variables in play. It would be interesting to have some testing done by a newbie.

Bushmiller
11th December 2012, 06:46 PM
Compared with flatware workers, turners tend to use higher grind angles. This is about edge durability.

One wrinkle with low nominal grind angles is that the smaller the wheel the lower the actual angle is near the tool tip - cos of the greater hollowing effect. This can make a diff. down at the 25 degree mark; less so at higher angle all other things equal. That is something to consider with bench chisels and plane blades where you're aiming for the lowest grind angle consistent with edge retention.

One thing that we share with flatware workers is that when we skew bevel-rubbed edge, typically a skew chisel, the cutting angle is effectively lowered for a given grind angle.

As for hollow v flat bevels, it seems this debate has been around for a while, and there are some turners whose views I respect who are convinced that flat is the way to go.

When the Xmas madness is over I'll do some more tests. I'm not expecting to find much difference but remain open; and say that cos in a lot of my turning I'm making unconscious adjustments to the variables in play. It would be interesting to have some testing done by a newbie.

Ern

Thanks for that.

It was what I was expecting, but because I do minimal turning (tools handles are 99% of it and no bowls at all) and about half my tools are home made from spring steel I don't really have a good basis to make judgements.

Regards
Paul

NeilS
11th December 2012, 07:28 PM
... but not as sorry as he will be if the guard should suddenly wear through :wink: .)

l


....... :rotfl:

Paul39
12th December 2012, 05:43 AM
This by rsser:

When the Xmas madness is over I'll do some more tests. I'm not expecting to find much difference but remain open; and say that cos in a lot of my turning I'm making unconscious adjustments to the variables in play. It would be interesting to have some testing done by a newbie.

And the reference to Richard Raffan's multifaceted bowl gouge leads me to say:

I think that when a person starts turning and have had no hands on training, but have done a lot of reading they will have a tendency to sharpen the perfect, endorsed by Famous Turner tool at a given number of degrees of angle, on the perfect grinding system, and present the tool to the rotating timber at the prescribed angle, and wonder why it doesn't make those bushels of streaming curlys like the guy doing the demo.

After a person has spent hundreds, or thousands of hours, at the lathe they can grab most any tool, give it a few swipes on a reasonable grinder, present it to a rotating piece of timber and make a stream of curlys.

After a person has spent enough time turning they do not think about angles, but present the tool and adjust up or down, twist left or right, and it cuts.

It becomes unconscious, automatic, and one does not even have to look at what is going on. It can be felt.

Maybe in 100 years that will come to me with the accursed skew. I make 25 bowls for each spindle. The only spindles I make are tool handles for myself.

RETIRED
12th December 2012, 07:51 AM
Wolverine Grinding Jig & Accessories (http://www.oneway.ca/sharpening/index.htm)

An oft quoted line used by me at the start.

TTIT
12th December 2012, 10:03 AM
....An oft quoted line used by me at the start.You must mean this bit.... "Professional turners don't behave in a predictable fashion" . . . . . or maybe my speed reading missed something! :;

powderpost
12th December 2012, 09:09 PM
After a person has spent enough time turning they do not think about angles, but present the tool and adjust up or down, twist left or right, and it cuts.

It becomes unconscious, automatic, and one does not even have to look at what is going on. It can be felt.

There in lies the answer to this whole discussion.
Jim

rsser
12th December 2012, 10:06 PM
Not having read back through all the posts, is it the case that only one post reports a side-by-side comparison?

See also post #53 here: http://www.woodworkforums.com/f8/robert-sorby-pro-edge-sharpening-system-152167/index4.html#post1585407

rsser
14th December 2012, 09:58 PM
With a couple of skews now with bevels ground flat (in the interlude between Xmas shopping and cooking) I'd offer some more observations.

Note, these are 'end-on' tests, not side by side. The skews were 1/2" and 1.25" with a straight cutting edge.

Planing cuts were easier to control.

Shallow curves were distinctly easier to form.

Found no diff. with shallow V cuts.

Beads: hard to tell. With me rolling beads is mostly about confidence and that varies day by day.