Thread: Flat Grind Versus Hollow Grind

Never fails. LA La la la; LA La la la .

Regards
Paul

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.

Originally Posted by rsser

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.

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.

Originally Posted by rsser

can only say the shorter the bevel for a given wheel the less the concavity.

That strikes a chord Ern

Nice pun Jim!

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

Originally Posted by Bushmiller

...what is the optimum wheel size for a hollow grind? 150mm, 200mm, 250mm, bigger?

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

Knife sharpening on waterstone wheel.jpg

This discussion could go on forever!

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.

A sweet single curve shape (i.e. not multi faceted ) 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. His knowledge & experience & mine both gained from learning the traditional skills of saw, plane & chisel sharpening certainly helped heaps.

Originally Posted by Mobyturns

This discussion could go on forever!

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.

A sweet single curve shape (i.e. not multi faceted ) 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. His knowledge & experience & mine both gained from learning the traditional skills of saw, plane & chisel sharpening certainly helped heaps.

Perzactly.

Originally Posted by rsser

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)

Too hard for me to worry about grinds. I just sharpen a lot - every few minutes.

Originally Posted by Bruce White

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.

Originally Posted by Mobyturns

This discussion could go on forever!

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