Thread: Tutorial on Shear scraping.

Originally Posted by dai sensei

Thanks for the tute


I would also like to argue that the bowl gauge cant catch when you roll too far, I can make anything catch

Neil, that's why I said "almost" impossible to have a catch.
There is always somebody with the extra skills needed to make a gouge catch.

Originally Posted by KenW

Photo 12: Vic showing how light a grip he has on the scraper, when used to do a normal scraping cut.

Attachment 130936

When I was shown this scrape with the bowl gouge , the position of the bottom hand as displayed by Vic on the photo was emphasized .
In fact I was told that there was no other way to hold it other than with the butt of the handle nestled in the palm of the hand .
It works well for me too .

Jock

Learned how to shear scrape with a bowl gouge at a workshop I visited, still can't get consistent results, so a lot more learning and practicing left. I have been reading that some of you flatten the top side of the scraper prior to using it, much like when one buys a new bench chisel or plane. After that is done you grind it forming a burr on the top of the scraper, hence a fresh cutting edge. I have also seen some running a hardened nail along the edge at a right angle to the top to roll the burr even more. Honing the top would fold the burr back to the front, correct? Need some clarification here. I really appreciate the pics and insight on the gouges, new way to think about when at the lathe tomorrow.

Scott

Yes, lap the top of the scraper. The finer the polishing job you do here the smoother the cutting edge, just as with bench tools.

Some use a lapped top as is, some like to turn a hook with a hard burnishing rod or even just a diamond hone after the top is lapped.

A burr created with a dry grinder is jagged and leaves a poorer finish.

Edit: ideally you wld hone the bevel too. A Tormek wheel will take it down to 1000 g (advertised), while the honing wheel charged with Tormek compound is said to get down to 1 micron.

Thanks to everyone for their expertise, time and efforts on this much needed tutorial.

I yepped my way through the instructions until I got to the following point from Ken...

Originally Posted by KenW

.....the angle formed between the top surface of the tool with respect to the face of the work).

...and Photo 10....

There is always one slow learner in every tutorial group...

I get the words with Photo 9 and 10, but the lines are confusing.

If I understand the concept correctly, the shear scraping angle is the same for Photo 9 and 10, but the tool has been swung out (like it's on a hinge fixed to the shear scrape angle) beyond 90deg to 'the face of the wood' in Photo 10. The superimposed lines don't help explain this.

The only way this can be clearly shown is if each photo is taken side on to the top surface of the scraper AND tangentially to the point at which the tool touches the wood. A precise point in three dimensional space that will clearly show the angle of the face of the scraper to 'the face of the wood'.

My rudimentary examples (using a blackened piece of wood to represent the scraper) are attached. First photo, angle less than 90deg. Second photo, more than 90deg. Both photos taken with the same shear scrape angle of about 30 deg (the line with dots) from the line of rotation, photo 3.

Hope the collected gurus don't mind me butting in on their tutorial...

.....

Thanks Ern,

I have been using the dry grinder set at the scraper bevel, then going straight back to work. So to clear up, after initial lapping/flatting, in the future just run a quick few passes with a diamond hone/card on the top, then raise the burr if desired? Sounds a whole lot easier than what I had been doing! It may take me a bit to understand everyone's wisdom here, but believe me, I am learning plenty! Thanks Scott

This is a bit OT but did mention using a sharp tool.

There are various ways.

Min: Grind the bevel at the angle you want. Flatten and polish the top.

Earlier posts suggest using the scraper as is. There is a case to be made however for another step and that is raising a burr with a hone or burnisher coming up from the bevel side. Maybe at 80* or so but I'd have to check. Look at the Lee Valley site for the Veritas turning tool burnisher eg.

Thanks for the bevel angle insight Ken.

Originally Posted by NeilS

Thanks to everyone for their expertise, time and efforts on this much needed tutorial.

I yepped my way through the instructions until I got to the following point from Ken...




...and Photo 10....

There is always one slow learner in every tutorial group...

I get the words with Photo 9 and 10, but the lines are confusing.

If I understand the concept correctly, the shear scraping angle is the same for Photo 9 and 10, but the tool has been swung out (like it's on a hinge fixed to the shear scrape angle) beyond 90deg to 'the face of the wood' in Photo 10. The superimposed lines don't help explain this.

The only way this can be clearly shown is if each photo is taken side on to the top surface of the scraper AND tangentially to the point at which the tool touches the wood. A precise point in three dimensional space that will clearly show the angle of the face of the scraper to 'the face of the wood'.

My rudimentary examples (using a blackened piece of wood to represent the scraper) are attached. First photo, angle less than 90deg. Second photo, more than 90deg. Both photos taken with the same shear scrape angle of about 30 deg (the line with dots) from the line of rotation, photo 3.

Hope the collected gurus don't mind me butting in on their tutorial...

.....

Neil, butt in all you like.
Your photos and description are spot on.
Thanks for the help.

I dont agree with the notion of a burr - a burr is not part of the cutting edge but a jagged overhang (yes a spark grinder is coarser than a tormek and a honing/lapping but a burr is a burr)

When i was a Beef slaughterman my knives were sharp enough to shave with and i can tell you a burr does not help a sharp edge but hinder it, A true sharp edge is perfectly flat & straight and will last for a long time - a burr is going to break/chip off and become a jagged edge very quickly. A butchers knife is sharpened/lapped on a stone and a "steel" is then used to stand the edge up straight - but it is not a burr it is the edge . If you get a burr when sharpening a knife you need to remove it and sharpen again.

I dont see that a turning tool is any different an edge is the intersection of 2 lines - a burr is a jagged edge with the interesecting lines at different angles to the edge you were grinding for, so if that is the angle/intersection you wanted then grind the tool to that angle in the first place.

Just my 1.5 cents worth. maybe 4.5 cents allowing for the experience here.

cheers

The discussions I recall on "using a burr on a turning scraper" all boil down to not too. the burr is too thin and just break of and embeds itself in the work. Rusting at some stage in the future. And also helping to blunt your scraper faster cos you are trying to cut more and more metal as the process continues. Sharp is necessary, but not with a burr.

There are jagged burrs (from a dry grinder) and a smooth burnished hook. See the parent thread.

Veritas make a burnishing tool claimed to produce a hook that cuts.

I've done this and put it under the 'scope and found a longer smoother edge than I got from a dry grinder, but it was still not a consistent hook. Maybe my poor technique.

The Lacer test referred to in the parent thread, on the cross grain of end grain, was not complimentary about the finish off a scraper without a hook. But his bevel was ground at 60 g on a dry grinder.

Originally Posted by rsser

There are jagged burrs (from a dry grinder) and a smooth burnished hook. See the parent thread.

Veritas make a burnishing tool claimed to produce a hook that cuts.

I've done this and put it under the 'scope and found a longer smoother edge than I got from a dry grinder, but it was still not a consistent hook. Maybe my poor technique.

The Lacer test referred to in the parent thread, on the cross grain of end grain, was not complimentary about the finish off a scraper without a hook. But his bevel was ground at 60 g on a dry grinder.

So like a hook on a cabinet scraper? I dunno. A lot of farting around for not much gain it seems to me. May as well have the scraper with no beval at all and burnish a burr. Prolly would end up with the same "effective angle" as the angle on a Ken W or Vic Wood scraper.

Thanks for this thread and discussion everybody
I think I'll ponder and ruminate on all this for a few months and then see if I can ask a sensible question