Thread: Flat Grind Versus Hollow Grind

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. 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

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.

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.

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.

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

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.

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

Originally Posted by

Tongue is nearly missing.

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

Originally Posted by Rod Gilbert

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. 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.

Originally Posted by NeilS

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

You did ask!


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. 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?

, 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

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.

Geez , I hope those parts come tomorrow, the stress cracks are starting to show....
Jim

Originally Posted by powderpost

Geez , I hope those parts come tomorrow, the stress cracks are starting to show....
Jim

Yeah, I know.