Sharpening tools using a grinder.

[Weasel Howlett]

I have turned for a few years now and have used a grinder to sharpen my tools, as im sure the rest of you do also. But recently i have been chatting to various people (non turners) about woodturning and many have been astounded that i sharpen tools with a bench style grinder. They tell me that i am just obliterating my tools and should be using a stone.

Now i'm fairly sure sharpening a bowl gouge with a stone would be fairly hard but is there any reason we don't sharpen flat and round end scrapers, skews, and the like, with a whetstone, oilstone or something less abrasive than a bench grinder?

I know that a good turners grinder will be a slower speed version to limit the material taken away with each grind but i'm just interested to know what people think about this subject. (mainly so i have a good answer to give to the people who call me a madman for using a grinder).

Cheers

 

[woodpig]

I use a 50mm belt on my belt and disc sander to sharpen most of my tools for both metalworking and woodworking.

This is my modified Record BDS250:

 

[chipmunk]

Well I'd say it's down to convenience and the need to sharpen at least 10x more often than other woodworkers because most of the time we're removing more wood than they are.

Not many people would use a hand plane to go from a piece of 3x2 to a piece of 1x1 and if they did they might need to resharpen the plane a few times which would slow them down unless they had a short cut ;-)

Personally I use a cheap whetstone grinder (freehand) with plain old tap water for most of my turning tools as a first step and then I hone my skews and scrapers with a diamond hone. I keep it flat with a devil stone and for wider flat tools they get moved from side-to-side as I grind so that if the stone isn't flat it doesn't matter too much.

Don't tell anyone on the other groups but I do the same with my bench chisels too, and it works for me ;-)

I just eye-ball the angles on the grinder and then hone a secondary bevel with a diamond hone. These days I only use an oilstone for plane irons once they don't have a nick because my grinder is only 40mm wide.

HTH
Jon

 

[CHJ]

As far as I'm concerned there is no practical alternative to shaping and subsequent sharpening of lathe tools other than a grinder or belt sander.

Honing of skew to maximise sharpness of edge I do with a diamond on steel "stone" and keep the edge fresh with diamond cards during work on a piece.

The diamond cards are also used on my gouges during 'some' final cuts just to freshen the edge, but any major refresh of the tool is done with a quick swipe on the grinder.

As long as you develope the habit of only removing the minimum amount of material with light contact pressure on the grinder, material removal is hardly relevant, tools I've been sharpening since May 2005, including learning how, are no shorter now than the difference between brands of new ones.

 

[Paul Hannaby]

I use a bench grinder for sharpening and shaping of all my gouges and use them straight from the grind with no honing.

Most of my scrapers are shaped on the bench grinder but sharpened each time with a diamond hone. My skew chisels get the same treatment as the scrapers.

Most non turners don't appreciate just how often we need to sharpen tools. With some of the harder woods it can be every couple of minutes and I've even worked pieces of wood where I've had to sharpen every couple of cuts. I would suggest that using a bench grinder is the norm for woodturning for that reason.

I don't think a slow grinder would necessarily take away less metal, it just does it slower. i.e. an inexperienced user might still waste more metal even with a slow grinder. You need to take away enough metal to create a new, sharp edge and whether that's done with a fast or slow grinder, wet grinder, belt or stone is probably immaterial. The amount of metal removed will be a function of grinding speed, stone coarseness and operator influence so an experienced user would probably be able to create a sharp edge with less metal wasted.

 

[Richard Findley]

Just to add my thoughts, it also comes down to how sharp as well and non-turners often can't get their hads around that either!

To my mind there are 3/4 types of sharp:

Carving sharp: Tools need stoneing and stropping to razor sharpness with regular re-strops to maintain it

Fine furniture sharp: almost as sharp as carving but less need to strop, probably sharpened from a fine waterstone

Joinery sharp: Straight from a stone is fine, if you're old school you might use the back of your hand to remove the wire edge

Turning sharp: Straight from the grinder. No where near as sharp as the above but I've still cut myself with one!!

The main reason for this difference is a matter of longevity, if you treated a turning tool like a carving tool, the edge would last for seconds, by producing a "blunter" sharp edge, it lasts much longer and is more effective.

The other issue is that for turning a single clean bevel is best, the micro bevel produced when stone sharpening has no place on turning tools.

HTH

Richard

 

[Jonzjob]

Richard, sorry to be a bit thick.. Micro bevel when sharpened on a stone? I haven't heard that expression before?

The only turning tools I have that go on a stone are my skews and I was always under the impression that they needed to be the sharpest.

 

[CHJ]

Micro bevels are often used on flatworlders and carving tools to achieve the sharpest edge with maximum support or cutting angle in the case of planes.

On a turning tool they can easily be produced by a moments inattention when grinding or if you attempt to burnish them on a soft wheel such as leather or a poorly supported grinding belt.
This results in the equivalent of a 'round over' edge which means that the cutting edge when presented with main bevel support is in fact presenting the equivalent of a blunt edge.

Another cause is if you use a diamond 'stone' or card to refresh the edge, you must maintain the line of the main support and not round over the edge, although it will be razor sharp it will be presented a fraction above the intended cutting surface and appear blunt.

 

[Jonzjob]

Thanks Chas. That's clear now and I have never thought about it.

When I put my skews on the grinding wheel I then hone (?) it on my DMT diaond whet stone until there is no slight concave. With the slight concave I can rock the skew and feel the two points of the concave and then sharpen from there. When it's gone it's back on the grinder.. Otherwise there is a chance that I could get a convex face on the cutting edge..

 

[Richard Findley]

Hi John

Sorry, I'm a bit slow to answer and Chas beat me to it with a typically excellent answer (and a diagram too =D> =D> )

The only things to add to this is that "Micro bevel" might well be an Americanisation, I think we probably refer to it as a secondary bevel and it works well on woodworking chisels but isn't of any use in turning simply because the bevel is of such importance for controlling the cut.

Some turners hone their tools but I don't find the need, even the skew can be used straight from the grinder. Once you've mastered using the grinder you only take off half a gnats knacker each time, so I don't buy the argument "makes my tools last longer".

Cheers

Richard

 

[chipmunk]

Just to give another view on the secondary bevel/micro bevel dismissed by Chas and Richard ;-)

If memory serves, Les Thorne advocates a micro-bevel as a means to (temporarily) steepen the bevel rubbing angle on bowl gouges when hollowing out deep bowls and maintaining bevel contact.

So I think saying it has no place in woodturning may be stretching a point although I do agree that most of the time it isn't desirable.
Jon

 

[Jonzjob]

Jon, from what I have read here and Chas' diagramme they are in 2 different places. The micro bevel Richard's mentioning is right on the cutting edge whereas the secondary bevel for going deeper on a bowl gouge is on the trailing edge of the primary bevel. So they are completely different animals in that the first is accidental and the second deliberate.

Is that correct Chas/Richard and thank you both for the explanation :mrgreen:

 

[chipmunk]

Hi John,
With all respect take a look at this video...

http://www.youtube.com/watch?v=FKK4OXCLX-s

at about 4:05 minutes in for an explanation of the reason for the micro-bevel.

I think if it was on the back of the main bevel as you say the problems would be towards the outside of the bowl rather than the middle of the bowl.

I think that this is the old problem of maintaining bevel contact with bowl gouges across the bottom of the bowl and there are other solutions to the problem such as angling the tool upwards but again it suffers with catching the rim if the bowl's too deep.

Another approach is here...

http://www.peterchild.co.uk/tools/bowlg/anbg.htm

and the angled bowl gouge here...

http://www.robbcwa.info/hss_and_other_tooling.htm

Hope this helps
Jon

 

[jumps]

Hi John,
With all respect take a look at this video...

http://www.youtube.com/watch?v=FKK4OXCLX-s

at about 4:05 minutes in for an explanation of the reason for the micro-bevel.

I think if it was on the back of the main bevel as you say the problems would be towards the outside of the bowl rather than the middle of the bowl.

I think that this is the old problem of maintaining bevel contact with bowl gouges across the bottom of the bowl and there are other solutions to the problem such as angling the tool upwards but again it suffers with catching the rim if the bowl's too deep.

Another approach is here...

http://www.peterchild.co.uk/tools/bowlg/anbg.htm

Hope this helps
Jon

I think this 'drift' is a good example of how terminology can become confusing.

If you take the superflute, as in Peter's link you provide, he is clearly illustrating the reduction of the main rubbing bevel (A) by, effectively, removing the majority of the bevel/back of the bevel as referred to by John.

Les is, I believe, referring to a similar grind when he talks about switching to a micro bevel tool ie the rubbing bevel is kept to a minimum but it is still the working bevel.

In both cases the (any) secondary bevel is non-functional and the practical benefit comes from material not being there, rather than being there ie it's clearance.

None of this has the slightest relevance to the points made, and illustrated, by Richard and Chas; other than to reinforce the concept of the working bevel angle and area in a turning tool.

 

[CHJ]

Just to give another view on the secondary bevel/micro bevel dismissed by Chas and Richard ;-)

If memory serves, Les Thorne advocates a micro-bevel as a means to (temporarily) steepen the bevel rubbing angle on bowl gouges when hollowing out deep bowls and maintaining bevel contact.

So I think saying it has no place in woodturning may be stretching a point although I do agree that most of the time it isn't desirable.
Jon

I think you are confusing Micro Bevel with what I would call a Mini Bevel.
In the case of the Mini Bevel it is used as the support facet, if you try this with a Micro bevel it will just dive into the wood through lack of blade support.

Personally I have two Bowl gouges that are my 'inners' of choice.
My do everything grind and one with a front face bevel somewhere in the order of 50 deg, the latter allows a more straight in approach to the inner bottom of a deeper bowl without the shaft fouling the sides and never find the need to mess around with the basic profile for individual pieces..

 

[chipmunk]

Chas,
Agreed. You and Les can argue about the name ;-)
Jon

 

[Richard Findley]

Hi Jon

As Chas says, we're discussing 2 entirely different things with the same name. My bowl gouge also has 2 bevels although I do it by grinding the heel away rather than at the cutting edge.

The secondary bevel on a woodworking chisel is there to add to the tool's cutting ability rather than to assist smooth cutting like that of a bowl gouge.

Hope this is clear

Richard

 

[robo hippy]

I go with the secondary bevel definition. On the outside of the bowl, with a convex shape, any gouge angle will work. You are always rubbing the bevel close to the cutting edge. When you get inside the bowl, with a concave surface/profile, you run into problems. A 45 degree bevel is good for the sides, but can't go through the transition area and across the bottom. Also, when rubbing the bevel, the heel tends to be sharp, and will leave bruise marks in the wood. It also contributes to getting concentric rings on the inside of your bowl. I relieve the heel of the bevel by grinding away about half of it. This takes care of the sharp edge, but still does not get you through the transition and across the bottom. On more open forms, a 60 degree bevel angle will do this, allowing you to make the cut and keep the bevel in contact with the wood, but not having the handle of your gouge run into the rim of the bowl, or your tool rest. Again, relieve the heel of the bevel. I have a couple of gouges that have a 75 degree bevel (same as my scrapers). This is my main transition and across the bottom gouge.

I guess I would say there is a primary bevel angle which is the part that you rub when you cut. The secondary bevel is not in contact with the wood when you cut, mostly you are getting steel out of the way so you can rub nearer the cutting edge on a convex surface, and relieving the sharp edge which can mark the wood.

robo hippy

 

[vomog]

Hi Woodpig. Can you explain to me your beltsander setup!! What is that flat vertical bevelled bar on the belt bed??

 

[jumps]

Hi Woodpig. Can you explain to me your beltsander setup!! What is that flat vertical bevelled bar on the belt bed??

my guess is that this is the support bed for his 50mm belt, with the bevel simply being the transition between roller and bed - but no doubt Woodpig will be back to confirm!

it's always great to see such lovingly constructed shop gear - the extreme opposite to some of my heath robinson bits =D>