Thread: Tutorial on Shear scraping.

I could and probably should write a book on this subject. bowl turning DVD out in a year or two.

I have never understood why when you drop the handle on the gouge, and roll it far onto its side so you are cutting with the edge, and not rubbing the bevel it is called a shear scrape. You are cutting at a shear angle, but not scraping. A scraping cut is, to me, having the scraper flat on the tool rest, pointed slightly down hill, and plunging straight into the wood. This is a roughing cut. You can do the same cut with a gouge, tool level/parallel to the ground, flutes at 90 degrees to the wood rotation, and cutting without the bevel in contact with the wood. These are roughing cuts, and will remove a lot of wood in a hurry, and leave a fairly rough surface, as it pulls more at the wood fiber rather than slicing. Scrapers are my main tool for roughing out bowls.

Having the scraper at a 45 or so degree angle on the tool rest is a shear cut, and you generally don't rub the bevel, though you can. This is more of a pulling cut, and is an excellent finish cut. This is the same cut you are making with the gouge in the 'shear scrape' mode.

For sharpening scrapers, I have a 75 or so degree bevel, rather blunt. The bevel shown on those in the pictures seems to be more like 45 or so degrees. They do tend to be more grabby.

For most of my scraper cuts, I like the burr straight from the grinder. I have an 80 grit CBN (see thread on diamond grinding wheels) wheel which leaves a very smooth face on the tool. This raises a nice smooth even burr, which is very durable, and is fine enough to make good finish cuts, and strong enough for heavy roughing cuts. I do hone off the old burr before grinding a new one. You can hone the grinder burr off and use the scraper with no burr, and it works okay. You can raise a burr by first honing off the one from the grinder (both on the top of the tool and on the bevel) and then a light pass or two with a triangle burnisher (never could get a good burr with a round burnisher), or use the Veritas burnisher. This light burr is only good for very fine finish cuts and will dull/wear out quickly. It is totally unsuited for roughing work. A burr that is raised by honing is less durable than this.

You can burnish a heavy burr by applying more pressure. This burr is great for heavy roughing cuts, and finish cuts. It can be burnished down and raised again a few times, just like the burrs on a card scraper. The burnished burrs do give a slightly better cut than the grinder burrs for shear/finish cuts, but it depends more on the wood as to which gives the better finish cut. Some times the softer woods seem to finish better with one than the other, and some times it seems to be the other way around. Same with the harder woods. I never seem to get the same results every time. this could be me rather than the tool. I haven't found any noticeable difference in the durability of the grinder or burnished burr for roughing or shear cuts. I would expect that a finer grinder wheel would raise a more consistent and durable edge than a coarse wheel.

Generally, for my finish cuts, and touch up work on bowls, I prefer the scrapers for this job. Maybe it is because I can see where I am cutting rather than having the gouge covering the cut.

robo hippy

I think by definition it is called scraping because the cutting edge is not supported by the bevel as in a slicing cut.

Originally Posted by robo hippy

Generally, for my finish cuts, and touch up work on bowls, I prefer the scrapers for this job. Maybe it is because I can see where I am cutting rather than having the gouge covering the cut.

robo hippy

That's a good point. You can see what you are doing better. I was trying shear scraping with a gouge yesterday and it was working well. It seems to be self righting. If you do something slightly wrong sheer scraping with a scraper it whacks itself down on the tool rest. There is no where for a bowl gouge to go cos its already there.

Leaving aside definitions of what is a shear/scrape/cut (for now), my experience and understanding is much the same as Hippy's.

Some differences.

Some of my fine finishing 'scrapers' have angles as fine as 10<link rel="File-List" href="file:///C:/DOCUME%7E1/BRON%26N%7E1/LOCALS%7E1/Temp/msoclip1/01/clip_filelist.xml">° to 20<link rel="File-List" href="file:///C:/DOCUME%7E1/BRON%26N%7E1/LOCALS%7E1/Temp/msoclip1/01/clip_filelist.xml">° (like a knife), the others range through all of the angles mentioned so far.

I have never found raising a hook by burnishing worth the trouble (for woodturning, anyway), although I do raise a very fine burr on my knife edge scrapers with the power strop which is much closer to the burr produced by a burnisher than a grinding wheel, i.e. they are smoother and less fragile.

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Must admit that I do a lot of burr maintenance at the lathe with the fine diamond honing plate between visits to the grinder.

On the definitions, I'll leave the gurus to hammer that out between them. However, I do think it's important to do so. Agreed definitions avoid confusion, which is particularly important on an online forum like this. Having just said I will leave it to the gurus, I'll throw in the following thoughts.

Burrs are in effect micro bevels, which may in fact be rubbing even though the primary bevel is clear of the wood. See attached diagram. So, not wishing to put too fine a point on this (pun acknowledged), is a 'scraper' with a burr, that is rubbing, scraping?

Perhaps the angle at which the cutting face of the tool is presented to the face of the wood could be a better basis for a definition. Scrapers as used in general woodworking are inclined at 90° or less to the surface being planed. The wood removal action changes once you are at or below 90°, the fibres are grabbed and pulled, not severed first then parted from the board or blank. In which case, the first photo back in Post 21 would be shear scraping and the second photo a shear slicing cut (as long as it lasts).

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the first photo back in Post 21 would be shear scraping and the second photo a shear slicing cut (as long as it lasts).

That is my definition too.
In photo1 the bevel is well clear of the timber hence a scraping action.
In photo 2 the bevel is almost rubbing resulting in a cutting action.

It came up on another forum once about what types of cuts there are. One turner said there were two, one rubbing the bevel, and two not rubbing the bevel. My peculiar/particular definition is that that is part of it, but not all. Not rubbing the bevel doesn't make it a shear or scraping cut. I can make very clean cuts, and rough cuts without rubbing the bevel. 90 degrees to the rotation of the wood, like when the scraper is flat on the tool rest is a scraping cut, and when the tool is at a skewed angle like when the scraper is at 45 degrees, you have a shear cut. I can rub the bevel and get a shear cut, with both scraper and gouge, and I can do the same cuts with a scraper. I think I am confusing myself a bit here.

As to the scrapers maybe catching when doing shear cuts, I have never had a problem. Most of the time I use an inside (swept back to the left side) or round nose scraper, and don't work above the center line of the blade. Actually, most of the time I drop the handle, and work on the wing rather than on the nose as the nose gets dulled by heavy scraping cuts first. Basically the same as a shear cut with a gouge.

robo hippy

I won't buy into all the technical stuff, but "sheer cutting" can also be quite aggressive in removing wood - not just good for finishing cuts and removing tear-out.

IMHO, it is a mandatory technique to be shown to beginners and intermediates alike. Safe as houses - if you follow the rules of course - and the ripples (which cause some concern at first), just disappear with 240 grit paper.

And even then, if you do it right, there are very, very few ripples.

There endeth the lesson from the LG.

Stacks of 80-180 grit paper here going to waste.

Eagerly awaiting how the experts decipher this all in Plain English for we learners.

Happy typing.

Originally Posted by robo hippy

I have never understood why when you drop the handle on the gouge, and roll it far onto its side so you are cutting with the edge, and not rubbing the bevel it is called a shear scrape. You are cutting at a shear angle, but not scraping. A scraping cut is, to
me, having the scraper flat on the tool rest, pointed slightly down hill, and plunging straight into the wood.

Any time you are making a cut without bevel rub, you are scraping.


This is a roughing cut. You can do the same cut with a gouge, tool level/parallel to the ground, flutes at 90 degrees to the wood rotation, and cutting without the bevel in contact with the wood.

Again this is a scraping cut and very dangerous.

These are roughing cuts, and will remove a lot of wood in a hurry, and leave a fairly rough surface, as it pulls more at the wood fiber rather than slicing. Scrapers are my main tool for roughing out bowls.

A scraper shoud never be used as roughing tool. A scraper can be very dangerous when used for roughing and leaves a very poor finish.

Having the scraper at a 45 or so degree angle on the tool rest is a shear cut, Shear Scrape.
and you generally don't rub the bevel, though you can. This is more of a pulling cut, and is an excellent finish cut. This is the same cut you are making with the gouge in the 'shear scrape' mode.

For sharpening scrapers, I have a 75 or so degree bevel, rather blunt. The bevel shown on those in the pictures seems to be more like 45 or so degrees. They do tend to be more grabby.

I did mention that you needed to use a scraper with a bevel angle of 45 degrees with care. It will however leave a better finish than a scraper with a blunter angle and stay sharper longer.

For most of my scraper cuts, I like the burr straight from the grinder.

IMHO puting a burr on a tool with a grinder is not a good idea. The resulting burr is a mixture of molten steel and some of the grinding wheel (called sintered metal). The burr is not very strong and wears away fairly quickly. Some of the burr is left imbeded in your turning which helps blunt your scraper on the next pass, leaving even more metal in your work.
To prove this, I have scraped a light coloured bowl with a scraper that had a burr from a dry grinder, then put it outside in the rain. The bowl went rusty in small spots.

robo hippy

I thought this thread was surposed to be about shear scraping.

Originally Posted by jefferson

I won't buy into all the technical stuff, but "sheer cutting" can also be quite aggressive in removing wood - not just good for finishing cuts and removing tear-out.

.

Agree with you LG about the value of the shear cut. However, I'm surprised that you find it can be quite aggressive. By laying the tool over (with scrapers) or dropping the handle and rotating (with gouges) you are in effect decreasing the cutting angle allowing for a more controlled shallow cut or scrape. That's why we finish with these.

If we are both talking about the same thing, a shear cut should produce a thin narrow shaving that isn't removing much wood at all. If the bevel is rubbing it should be very difficult to get aggressive with this cut, I would have thought. Or, am I misunderstanding something, LG?

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Originally Posted by KenW

I thought this thread was surposed to be about shear scraping.

It is, but I would have thought that making the distinction between shear scraping and shear cutting helps us better understand what is scraping.

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(Boldly striding out into hot water. ) I don't think Sheer cutting exists. At least not for long cos it will catch very easily and put a huge hole in the side of your bowl. DAMHIK!

Originally Posted by NeilS

It is, but I would have thought that making the distinction between shear scraping and shear cutting helps us better understand what is scraping.

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Neil, I haven't noticed anybody correctly describing shear cutting so far in this thread.
I have kept away from describing shear cutting, as I find the description hard to put into words. If not done correctly shear cutting can be very dangerous.

Shear scraping with a bowl gouge can remove large amounts of wood, you just need to press the tool into the wood a lot harder.

I reckon we'd all be better off calling it something else other than 'shear scraping' cos all that does is lead everyone into arguments over definitions. The "action" Ken and Vic demonstrated in the photo's works beautifully once practiced and that's all that matters. Maybe leave 'cut', 'slice', 'dice' etc out of it - how about 'microdefragulation'. Nah??! Open to suggestions then

Originally Posted by NeilS

If we are both talking about the same thing, a shear cut should produce a thin narrow shaving that isn't removing much wood at all. If the bevel is rubbing it should be very difficult to get aggressive with this cut, I would have thought. Or, am I misunderstanding something, LG?

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No, Neil, the bevel isn't rubbing, I am still sheer scraping. But I am now taking a largish narrow shaving with my HT Ellsworth grind on the outside of the bowl in the manner described. When I was first shown the method by Ken W, I was barely taking anything. A little too cautious.

All I am saying is that the more confident I am with the cut, the more of the curlies that I can see without 2x glasses. And I am probably presently the tool closer to 45 degrees than before, so the shaving have got to be fatter (I think).

Still trying to work out how to sheer scape the INSIDE of a bowl yet.....