Grinding - Flat Or Hollow

In view of the new blade grinder developed by Derek it raises the issue of which is the best/prefered way of grinding plane and chisel blades.
As I see it the advantage of a hollow grind is it is easier to do the final sharpen.
A flat grind if done a couple of degrees less than the final hone will leave more meat at the business end and still be easy to do a final sharpen.
I have the machinery to do it either way, 40grit 8" white wheel on a grinder or slower speed white wheel on my horizontal blade grinder.
Which way do you prefer and why.

Termite,

I agree with you that hollow ground is probably the way to go but as I use waterstones, I grind mine flat.

I know there are different methods of producing a hollow grind and my memories from the past was using a grinder and ruining the edges by turning them blue even with the greatest of care.

I am more experienced now and perhaps better wheels etc cutting at slower rates would solve the problem but the waterstones will do me fine.

I am using my experimenting energy on my woodwork skills as I am reasonably satisfied with my sharpening and tool tuning and maintenance. I am not suggesting they are perfect.

Brother Wood, I use waterstones for my sharpening but I get the impression you do your initial grind on them too, is that correct? :confused:

I only use the grinder when a blade is nicked or would take too long on the 800 waterstone. Otherwise, it's all stones - flat bevel. They just look so nice and shiny :p

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Originally Posted by Termite

Brother Wood, I use waterstones for my sharpening but I get the impression you do your initial grind on them too, is that correct? :confused:

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Brother Mite,

The tools I buy nowadays are all pretty good so the blades only need a couple of minutes on the waterstones straight out of the box.

The older tools have been turned blue and ground at the wrong angles over the years but slowly and with a lot of sweat they are at the right angle and generally kept in sharpness ranging from sharp to very sharp.

If they are kept like this, a wipe every now and then on the mdf charged with the green Veritas honing compound is sufficient to keep the edges keen.

Every now and then when the honing compound is not bringing up the edge because it needs grinding, I give them a quick grind on the waterstones. My blades never go near a grinding wheel.

It works for me. I am no expert in sharpening and there are others who do it faster and sharper but I am reasonably happy with my results.

I always used to use a honing guide but Derek in one of his posts over 12 months ago encouraged me to do it free hand. That was my aim last year and my perseverance is producing good results. There is still room for improvement which I am working on. I only use my honing guide now every blue moon.

Thick plane blades (like my HNT Gordons) definitely require a hollow grind otherwise you'll spend all day sharpening a bevel thats about 12mm wide. If the blade happens to be the HSS option allow two days for a flat bevel. :D

I'm a hollow grinder (Tormek), with the grain, and topped with pure maple syrup.

There I think that covers everything. :D

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Originally Posted by outback

I'm a hollow grinder (Tormek), with the grain, and topped with pure maple syrup.

There I think that covers everything. :D

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Tall and tan and young and lovely, The girl from ........ You missed one....:D

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Originally Posted by Cliff Rogers

Tall and tan and young and lovely, The girl from ........ You missed one....:D

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No Cliff, the rest of us were over that days ago :D :D

Some useless info for you all.

When I was with QLD Forestry (many years ago) we were supplied with "Spear and Jackson" brush hooks that were "hollow ground" from the suppler. The idea with the hollow grind, was that the 'cut' would not bind.
Back then our "Ganger" would serverly chastise us if we filled off the hollow gring during routine mtc.

Looking back now, the hollow grind did stop the blade from binding in the cut.
Today a brush hook is like a 'black snake' and why would you want to pick one up?

I may be slow on the uptake, but to me, having a hollow grind on you tools only places less metal between the tool and the work!

I must admit that on my turning tools there is a hollow grind, that's because I use a 8inch grinder to sharpen the tools. I have not used a 'flat grind' on these to ascertain if there is any difference to the performance.

Anyway we were talking about planes and chisels weren't we?
:)

For some time now I have been seeking the fastest way to the sharpest edge for the job. Now this is not necessarily the same thing as seeking the sharpest edge. It is really about speed and recognising what is relevant.

It is quicker to hone an already sharp edge (ala Wood Borer).

It is quicker to sharpen freehand than set up a guide.

It is easier to sharpen freehand on a broad, flat edge.

It is quicker to sharpen a microbevel than regrind and sharpen a full bevel.

A flat grind produces a stronger edge than a hollow grind.

A microbevel produces a stronger edge than a flat grind.

A smoothing plane's blade needs to be smooth (!) as well as razor sharp. By contrast, a scrub plane needs to be razor sharp but not necessarily as smooth.

Chisels also need to be razor sharp and smooth but not necessarily as smooth as a smoothing plane.

Note: smooth cuts, anything less just tears the wood fibres.

My current sharpening strategy is:

When freshly flat ground on the belt sander to 600 grit, plane blade bevels are sharpened freehand on waterstones to 6000 grit and honed with Veritas green rouge. This leaves a razor sharp and very smooth edge. When it comes time to resharpen them, I plan to add a 2 degree microbevel using the Veritas guide on 1200 and 6000 waterstones (I do have a natural waterstone as well, supposedly better than the King 6000 I have referred to, but I am still coming to terms with how to use it).

My chisels are sharpened in the same way, stopping short of the waterstones (i.e. only sharpened on the belt sander). They are sharp (+++) but not as smooth. For dovetails, mortices, and trimming they are just fine.

It is worthwhile getting a copy of the David Charlesworth video on sharpening. He focuses on the use of microbevels.

Regards from Perth

Derek

Hi Termite,

I have, like many of us I'm sure, tried various means and methods of sharpening, often governed by the hip pocket and the desire to get the job done quickly. I am certainly guilty of both.

So to answer your question, flat or hollow?

I am a definite flat bevel bloke, never, never hollow grind.
Why?? Prefer more meat in the blade at the business end. Hate the look of hollow ground bevels and they are not consistant. And maybe because my father always flat ground his chisels, heavy firmers mostly, so that is how I got learned proper like.

For 'in shape' blades I tend to use either scary sharp or oil stones, (again, my father's legacy). For 'out of shape' blades I use the 6" bench grinder to sort of surface grind the bevel into shape, (freehand and very slowly to reduce heat) and then do a gentle flattening using the wheel side, (yes I know, bad, very bad, but the old bloke is not about to belt me for it). Or I flatten the bevel on the belt sander, and then go scary sharp etc., etc.

For these 'out of shape' blades, (for I have several from garage sales etc.) I have been thinking, for some years now, to build a surface grinding jig for the bench grinder, to get a flat, square bevel. Takes a little longer to grind but minimises the heat build up significantly. It would be a double sliding table with screw travel on one axis. One day,... one day, and another thread.

So flat bevels for me Termite. Hope I have not offended any of the hollow grinders.

P.S. Derek's method above is what I will be using for the "in shape' blades in the future including the micro bevel, (have to buy a 6000 waterstone). Am glad I did not buy the Tormek some years ago. And I certainly agree with Derek's philosophy too, fastest and sharpest, (but no hollow grinding) and fit for purpose.

Cheers,
Pops

I'm with Wood Borer on this one, use a waterstone and grind 'em flat.